/* Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2017, The Tor Project, Inc. */
/* See LICENSE for licensing information */

#define DIRECTORY_PRIVATE

#include "or.h"
#include "backtrace.h"
#include "bridges.h"
#include "buffers.h"
#include "circuitbuild.h"
#include "config.h"
#include "connection.h"
#include "connection_edge.h"
#include "conscache.h"
#include "consdiff.h"
#include "consdiffmgr.h"
#include "control.h"
#include "compat.h"
#define DIRECTORY_PRIVATE
#include "directory.h"
#include "dirserv.h"
#include "dirvote.h"
#include "entrynodes.h"
#include "geoip.h"
#include "hs_cache.h"
#include "hs_common.h"
#include "main.h"
#include "microdesc.h"
#include "networkstatus.h"
#include "nodelist.h"
#include "policies.h"
#include "relay.h"
#include "rendclient.h"
#include "rendcommon.h"
#include "rendservice.h"
#include "rephist.h"
#include "router.h"
#include "routerlist.h"
#include "routerparse.h"
#include "routerset.h"
#include "shared_random.h"

#if defined(EXPORTMALLINFO) && defined(HAVE_MALLOC_H) && defined(HAVE_MALLINFO)
#if !defined(OpenBSD)
#include <malloc.h>
#endif
#endif

/**
 * \file directory.c
 * \brief Code to send and fetch information from directory authorities and
 * caches via HTTP.
 *
 * Directory caches and authorities use dirserv.c to generate the results of a
 * query and stream them to the connection; clients use routerparse.c to parse
 * them.
 *
 * Every directory request has a dir_connection_t on the client side and on
 * the server side.  In most cases, the dir_connection_t object is a linked
 * connection, tunneled through an edge_connection_t so that it can be a
 * stream on the Tor network.  The only non-tunneled connections are those
 * that are used to upload material (descriptors and votes) to authorities.
 * Among tunneled connections, some use one-hop circuits, and others use
 * multi-hop circuits for anonymity.
 *
 * Directory requests are launched by calling
 * directory_initiate_request(). This
 * launch the connection, will construct an HTTP request with
 * directory_send_command(), send the and wait for a response.  The client
 * later handles the response with connection_dir_client_reached_eof(),
 * which passes the information received to another part of Tor.
 *
 * On the server side, requests are read in directory_handle_command(),
 * which dispatches first on the request type (GET or POST), and then on
 * the URL requested. GET requests are processed with a table-based
 * dispatcher in url_table[].  The process of handling larger GET requests
 * is complicated because we need to avoid allocating a copy of all the
 * data to be sent to the client in one huge buffer.  Instead, we spool the
 * data into the buffer using logic in connection_dirserv_flushed_some() in
 * dirserv.c.  (TODO: If we extended buf.c to have a zero-copy
 * reference-based buffer type, we could remove most of that code, at the
 * cost of a bit more reference counting.)
 **/

/* In-points to directory.c:
 *
 * - directory_post_to_dirservers(), called from
 *   router_upload_dir_desc_to_dirservers() in router.c
 *   upload_service_descriptor() in rendservice.c
 * - directory_get_from_dirserver(), called from
 *   rend_client_refetch_renddesc() in rendclient.c
 *   run_scheduled_events() in main.c
 *   do_hup() in main.c
 * - connection_dir_process_inbuf(), called from
 *   connection_process_inbuf() in connection.c
 * - connection_dir_finished_flushing(), called from
 *   connection_finished_flushing() in connection.c
 * - connection_dir_finished_connecting(), called from
 *   connection_finished_connecting() in connection.c
 */
static void directory_send_command(dir_connection_t *conn,
                                   int direct,
                                   const directory_request_t *request);
static int body_is_plausible(const char *body, size_t body_len, int purpose);
static char *http_get_header(const char *headers, const char *which);
static void http_set_address_origin(const char *headers, connection_t *conn);
static void connection_dir_download_routerdesc_failed(dir_connection_t *conn);
static void connection_dir_bridge_routerdesc_failed(dir_connection_t *conn);
static void connection_dir_download_cert_failed(
                               dir_connection_t *conn, int status_code);
static void connection_dir_retry_bridges(smartlist_t *descs);
static void dir_routerdesc_download_failed(smartlist_t *failed,
                                           int status_code,
                                           int router_purpose,
                                           int was_extrainfo,
                                           int was_descriptor_digests);
static void dir_microdesc_download_failed(smartlist_t *failed,
                                          int status_code);
static int client_likes_consensus(const struct consensus_cache_entry_t *ent,
                                  const char *want_url);

static void connection_dir_close_consensus_fetches(
                   dir_connection_t *except_this_one, const char *resource);

/********* START VARIABLES **********/

/** How far in the future do we allow a directory server to tell us it is
 * before deciding that one of us has the wrong time? */
#define ALLOW_DIRECTORY_TIME_SKEW (30*60)

#define X_ADDRESS_HEADER "X-Your-Address-Is: "
#define X_OR_DIFF_FROM_CONSENSUS_HEADER "X-Or-Diff-From-Consensus: "

/** HTTP cache control: how long do we tell proxies they can cache each
 * kind of document we serve? */
#define FULL_DIR_CACHE_LIFETIME (60*60)
#define RUNNINGROUTERS_CACHE_LIFETIME (20*60)
#define DIRPORTFRONTPAGE_CACHE_LIFETIME (20*60)
#define NETWORKSTATUS_CACHE_LIFETIME (5*60)
#define ROUTERDESC_CACHE_LIFETIME (30*60)
#define ROUTERDESC_BY_DIGEST_CACHE_LIFETIME (48*60*60)
#define ROBOTS_CACHE_LIFETIME (24*60*60)
#define MICRODESC_CACHE_LIFETIME (48*60*60)

/********* END VARIABLES ************/

/** Return false if the directory purpose <b>dir_purpose</b>
 * does not require an anonymous (three-hop) connection.
 *
 * Return true 1) by default, 2) if all directory actions have
 * specifically been configured to be over an anonymous connection,
 * or 3) if the router is a bridge */
int
purpose_needs_anonymity(uint8_t dir_purpose, uint8_t router_purpose,
                        const char *resource)
{
  if (get_options()->AllDirActionsPrivate)
    return 1;

  if (router_purpose == ROUTER_PURPOSE_BRIDGE) {
    if (dir_purpose == DIR_PURPOSE_FETCH_SERVERDESC
        && resource && !strcmp(resource, "authority.z")) {
      /* We are asking a bridge for its own descriptor. That doesn't need
         anonymity. */
      return 0;
    }
    /* Assume all other bridge stuff needs anonymity. */
    return 1; /* if no circuits yet, this might break bootstrapping, but it's
               * needed to be safe. */
  }

  switch (dir_purpose)
  {
    case DIR_PURPOSE_UPLOAD_DIR:
    case DIR_PURPOSE_UPLOAD_VOTE:
    case DIR_PURPOSE_UPLOAD_SIGNATURES:
    case DIR_PURPOSE_FETCH_STATUS_VOTE:
    case DIR_PURPOSE_FETCH_DETACHED_SIGNATURES:
    case DIR_PURPOSE_FETCH_CONSENSUS:
    case DIR_PURPOSE_FETCH_CERTIFICATE:
    case DIR_PURPOSE_FETCH_SERVERDESC:
    case DIR_PURPOSE_FETCH_EXTRAINFO:
    case DIR_PURPOSE_FETCH_MICRODESC:
      return 0;
    case DIR_PURPOSE_HAS_FETCHED_RENDDESC_V2:
    case DIR_PURPOSE_UPLOAD_RENDDESC_V2:
    case DIR_PURPOSE_FETCH_RENDDESC_V2:
      return 1;
    case DIR_PURPOSE_SERVER:
    default:
      log_warn(LD_BUG, "Called with dir_purpose=%d, router_purpose=%d",
               dir_purpose, router_purpose);
      tor_assert_nonfatal_unreached();
      return 1; /* Assume it needs anonymity; better safe than sorry. */
  }
}

/** Return a newly allocated string describing <b>auth</b>. Only describes
 * authority features. */
STATIC char *
authdir_type_to_string(dirinfo_type_t auth)
{
  char *result;
  smartlist_t *lst = smartlist_new();
  if (auth & V3_DIRINFO)
    smartlist_add(lst, (void*)"V3");
  if (auth & BRIDGE_DIRINFO)
    smartlist_add(lst, (void*)"Bridge");
  if (smartlist_len(lst)) {
    result = smartlist_join_strings(lst, ", ", 0, NULL);
  } else {
    result = tor_strdup("[Not an authority]");
  }
  smartlist_free(lst);
  return result;
}

/** Return a string describing a given directory connection purpose. */
STATIC const char *
dir_conn_purpose_to_string(int purpose)
{
  switch (purpose)
    {
    case DIR_PURPOSE_UPLOAD_DIR:
      return "server descriptor upload";
    case DIR_PURPOSE_UPLOAD_VOTE:
      return "server vote upload";
    case DIR_PURPOSE_UPLOAD_SIGNATURES:
      return "consensus signature upload";
    case DIR_PURPOSE_FETCH_SERVERDESC:
      return "server descriptor fetch";
    case DIR_PURPOSE_FETCH_EXTRAINFO:
      return "extra-info fetch";
    case DIR_PURPOSE_FETCH_CONSENSUS:
      return "consensus network-status fetch";
    case DIR_PURPOSE_FETCH_CERTIFICATE:
      return "authority cert fetch";
    case DIR_PURPOSE_FETCH_STATUS_VOTE:
      return "status vote fetch";
    case DIR_PURPOSE_FETCH_DETACHED_SIGNATURES:
      return "consensus signature fetch";
    case DIR_PURPOSE_FETCH_RENDDESC_V2:
      return "hidden-service v2 descriptor fetch";
    case DIR_PURPOSE_UPLOAD_RENDDESC_V2:
      return "hidden-service v2 descriptor upload";
    case DIR_PURPOSE_FETCH_MICRODESC:
      return "microdescriptor fetch";
    }

  log_warn(LD_BUG, "Called with unknown purpose %d", purpose);
  return "(unknown)";
}

/** Return the requisite directory information types. */
STATIC dirinfo_type_t
dir_fetch_type(int dir_purpose, int router_purpose, const char *resource)
{
  dirinfo_type_t type;
  switch (dir_purpose) {
    case DIR_PURPOSE_FETCH_EXTRAINFO:
      type = EXTRAINFO_DIRINFO;
      if (router_purpose == ROUTER_PURPOSE_BRIDGE)
        type |= BRIDGE_DIRINFO;
      else
        type |= V3_DIRINFO;
      break;
    case DIR_PURPOSE_FETCH_SERVERDESC:
      if (router_purpose == ROUTER_PURPOSE_BRIDGE)
        type = BRIDGE_DIRINFO;
      else
        type = V3_DIRINFO;
      break;
    case DIR_PURPOSE_FETCH_STATUS_VOTE:
    case DIR_PURPOSE_FETCH_DETACHED_SIGNATURES:
    case DIR_PURPOSE_FETCH_CERTIFICATE:
      type = V3_DIRINFO;
      break;
    case DIR_PURPOSE_FETCH_CONSENSUS:
      type = V3_DIRINFO;
      if (resource && !strcmp(resource, "microdesc"))
        type |= MICRODESC_DIRINFO;
      break;
    case DIR_PURPOSE_FETCH_MICRODESC:
      type = MICRODESC_DIRINFO;
      break;
    default:
      log_warn(LD_BUG, "Unexpected purpose %d", (int)dir_purpose);
      type = NO_DIRINFO;
      break;
  }
  return type;
}

/** Return true iff <b>identity_digest</b> is the digest of a router which
 * says that it caches extrainfos.  (If <b>is_authority</b> we always
 * believe that to be true.) */
int
router_supports_extrainfo(const char *identity_digest, int is_authority)
{
  const node_t *node = node_get_by_id(identity_digest);

  if (node && node->ri) {
    if (node->ri->caches_extra_info)
      return 1;
  }
  if (is_authority) {
    return 1;
  }
  return 0;
}

/** Return true iff any trusted directory authority has accepted our
 * server descriptor.
 *
 * We consider any authority sufficient because waiting for all of
 * them means it never happens while any authority is down; we don't
 * go for something more complex in the middle (like \>1/3 or \>1/2 or
 * \>=1/2) because that doesn't seem necessary yet.
 */
int
directories_have_accepted_server_descriptor(void)
{
  const smartlist_t *servers = router_get_trusted_dir_servers();
  const or_options_t *options = get_options();
  SMARTLIST_FOREACH(servers, dir_server_t *, d, {
    if ((d->type & options->PublishServerDescriptor_) &&
        d->has_accepted_serverdesc) {
      return 1;
    }
  });
  return 0;
}

/** Start a connection to every suitable directory authority, using
 * connection purpose <b>dir_purpose</b> and uploading <b>payload</b>
 * (of length <b>payload_len</b>). The dir_purpose should be one of
 * 'DIR_PURPOSE_UPLOAD_{DIR|VOTE|SIGNATURES}'.
 *
 * <b>router_purpose</b> describes the type of descriptor we're
 * publishing, if we're publishing a descriptor -- e.g. general or bridge.
 *
 * <b>type</b> specifies what sort of dir authorities (V3,
 * BRIDGE, etc) we should upload to.
 *
 * If <b>extrainfo_len</b> is nonzero, the first <b>payload_len</b> bytes of
 * <b>payload</b> hold a router descriptor, and the next <b>extrainfo_len</b>
 * bytes of <b>payload</b> hold an extra-info document.  Upload the descriptor
 * to all authorities, and the extra-info document to all authorities that
 * support it.
 */
void
directory_post_to_dirservers(uint8_t dir_purpose, uint8_t router_purpose,
                             dirinfo_type_t type,
                             const char *payload,
                             size_t payload_len, size_t extrainfo_len)
{
  const or_options_t *options = get_options();
  dir_indirection_t indirection;
  const smartlist_t *dirservers = router_get_trusted_dir_servers();
  int found = 0;
  const int exclude_self = (dir_purpose == DIR_PURPOSE_UPLOAD_VOTE ||
                            dir_purpose == DIR_PURPOSE_UPLOAD_SIGNATURES);
  tor_assert(dirservers);
  /* This tries dirservers which we believe to be down, but ultimately, that's
   * harmless, and we may as well err on the side of getting things uploaded.
   */
  SMARTLIST_FOREACH_BEGIN(dirservers, dir_server_t *, ds) {
      routerstatus_t *rs = &(ds->fake_status);
      size_t upload_len = payload_len;

      if ((type & ds->type) == 0)
        continue;

      if (exclude_self && router_digest_is_me(ds->digest)) {
        /* we don't upload to ourselves, but at least there's now at least
         * one authority of this type that has what we wanted to upload. */
        found = 1;
        continue;
      }

      if (options->StrictNodes &&
          routerset_contains_routerstatus(options->ExcludeNodes, rs, -1)) {
        log_warn(LD_DIR, "Wanted to contact authority '%s' for %s, but "
                 "it's in our ExcludedNodes list and StrictNodes is set. "
                 "Skipping.",
                 ds->nickname,
                 dir_conn_purpose_to_string(dir_purpose));
        continue;
      }

      found = 1; /* at least one authority of this type was listed */
      if (dir_purpose == DIR_PURPOSE_UPLOAD_DIR)
        ds->has_accepted_serverdesc = 0;

      if (extrainfo_len && router_supports_extrainfo(ds->digest, 1)) {
        upload_len += extrainfo_len;
        log_info(LD_DIR, "Uploading an extrainfo too (length %d)",
                 (int) extrainfo_len);
      }
      if (purpose_needs_anonymity(dir_purpose, router_purpose, NULL)) {
        indirection = DIRIND_ANONYMOUS;
      } else if (!fascist_firewall_allows_dir_server(ds,
                                                     FIREWALL_DIR_CONNECTION,
                                                     0)) {
        if (fascist_firewall_allows_dir_server(ds, FIREWALL_OR_CONNECTION, 0))
          indirection = DIRIND_ONEHOP;
        else
          indirection = DIRIND_ANONYMOUS;
      } else {
        indirection = DIRIND_DIRECT_CONN;
      }

      directory_request_t *req = directory_request_new(dir_purpose);
      directory_request_set_routerstatus(req, rs);
      directory_request_set_router_purpose(req, router_purpose);
      directory_request_set_indirection(req, indirection);
      directory_request_set_payload(req, payload, upload_len);
      directory_initiate_request(req);
      directory_request_free(req);
  } SMARTLIST_FOREACH_END(ds);
  if (!found) {
    char *s = authdir_type_to_string(type);
    log_warn(LD_DIR, "Publishing server descriptor to directory authorities "
             "of type '%s', but no authorities of that type listed!", s);
    tor_free(s);
  }
}

/** Return true iff, according to the values in <b>options</b>, we should be
 * using directory guards for direct downloads of directory information. */
STATIC int
should_use_directory_guards(const or_options_t *options)
{
  /* Public (non-bridge) servers never use directory guards. */
  if (public_server_mode(options))
    return 0;
  /* If guards are disabled, we can't use directory guards.
   */
  if (!options->UseEntryGuards)
    return 0;
  /* If we're configured to fetch directory info aggressively or of a
   * nonstandard type, don't use directory guards. */
  if (options->DownloadExtraInfo || options->FetchDirInfoEarly ||
      options->FetchDirInfoExtraEarly || options->FetchUselessDescriptors)
    return 0;
  return 1;
}

/** Pick an unconstrained directory server from among our guards, the latest
 * networkstatus, or the fallback dirservers, for use in downloading
 * information of type <b>type</b>, and return its routerstatus. */
static const routerstatus_t *
directory_pick_generic_dirserver(dirinfo_type_t type, int pds_flags,
                                 uint8_t dir_purpose,
                                 circuit_guard_state_t **guard_state_out)
{
  const routerstatus_t *rs = NULL;
  const or_options_t *options = get_options();

  if (options->UseBridges)
    log_warn(LD_BUG, "Called when we have UseBridges set.");

  if (should_use_directory_guards(options)) {
    const node_t *node = guards_choose_dirguard(guard_state_out);
    if (node)
      rs = node->rs;
  } else {
    /* anybody with a non-zero dirport will do */
    rs = router_pick_directory_server(type, pds_flags);
  }
  if (!rs) {
    log_info(LD_DIR, "No router found for %s; falling back to "
             "dirserver list.", dir_conn_purpose_to_string(dir_purpose));
    rs = router_pick_fallback_dirserver(type, pds_flags);
  }

  return rs;
}

/**
 * Set the extra fields in <b>req</b> that are used when requesting a
 * consensus of type <b>resource</b>.
 *
 * Right now, these fields are if-modified-since and x-or-diff-from-consensus.
 */
static void
dir_consensus_request_set_additional_headers(directory_request_t *req,
                                             const char *resource)
{
  time_t if_modified_since = 0;
  uint8_t or_diff_from[DIGEST256_LEN];
  int or_diff_from_is_set = 0;

  /* DEFAULT_IF_MODIFIED_SINCE_DELAY is 1/20 of the default consensus
   * period of 1 hour.
   */
  const int DEFAULT_IF_MODIFIED_SINCE_DELAY = 180;
  const int32_t DEFAULT_TRY_DIFF_FOR_CONSENSUS_NEWER = 72;
  const int32_t MIN_TRY_DIFF_FOR_CONSENSUS_NEWER = 0;
  const int32_t MAX_TRY_DIFF_FOR_CONSENSUS_NEWER = 8192;
  const char TRY_DIFF_FOR_CONSENSUS_NEWER_NAME[] =
    "try-diff-for-consensus-newer-than";

  int flav = FLAV_NS;
  if (resource)
    flav = networkstatus_parse_flavor_name(resource);

  int32_t max_age_for_diff = 3600 *
    networkstatus_get_param(NULL,
                            TRY_DIFF_FOR_CONSENSUS_NEWER_NAME,
                            DEFAULT_TRY_DIFF_FOR_CONSENSUS_NEWER,
                            MIN_TRY_DIFF_FOR_CONSENSUS_NEWER,
                            MAX_TRY_DIFF_FOR_CONSENSUS_NEWER);

  if (flav != -1) {
    /* IF we have a parsed consensus of this type, we can do an
     * if-modified-time based on it. */
    networkstatus_t *v;
    v = networkstatus_get_latest_consensus_by_flavor(flav);
    if (v) {
      /* In networks with particularly short V3AuthVotingIntervals,
       * ask for the consensus if it's been modified since half the
       * V3AuthVotingInterval of the most recent consensus. */
      time_t ims_delay = DEFAULT_IF_MODIFIED_SINCE_DELAY;
      if (v->fresh_until > v->valid_after
          && ims_delay > (v->fresh_until - v->valid_after)/2) {
        ims_delay = (v->fresh_until - v->valid_after)/2;
      }
      if_modified_since = v->valid_after + ims_delay;
      if (v->valid_after >= approx_time() - max_age_for_diff) {
        memcpy(or_diff_from, v->digest_sha3_as_signed, DIGEST256_LEN);
        or_diff_from_is_set = 1;
      }
    }
  } else {
    /* Otherwise it might be a consensus we don't parse, but which we
     * do cache.  Look at the cached copy, perhaps. */
    cached_dir_t *cd = dirserv_get_consensus(resource);
    /* We have no method of determining the voting interval from an
     * unparsed consensus, so we use the default. */
    if (cd) {
      if_modified_since = cd->published + DEFAULT_IF_MODIFIED_SINCE_DELAY;
      if (cd->published >= approx_time() - max_age_for_diff) {
        memcpy(or_diff_from, cd->digest_sha3_as_signed, DIGEST256_LEN);
        or_diff_from_is_set = 1;
      }
    }
  }

  if (if_modified_since > 0)
    directory_request_set_if_modified_since(req, if_modified_since);
  if (or_diff_from_is_set) {
    char hex[HEX_DIGEST256_LEN + 1];
    base16_encode(hex, sizeof(hex),
                  (const char*)or_diff_from, sizeof(or_diff_from));
    directory_request_add_header(req, X_OR_DIFF_FROM_CONSENSUS_HEADER, hex);
  }
}

/** Start a connection to a random running directory server, using
 * connection purpose <b>dir_purpose</b>, intending to fetch descriptors
 * of purpose <b>router_purpose</b>, and requesting <b>resource</b>.
 * Use <b>pds_flags</b> as arguments to router_pick_directory_server()
 * or router_pick_trusteddirserver().
 */
MOCK_IMPL(void, directory_get_from_dirserver, (
                            uint8_t dir_purpose,
                            uint8_t router_purpose,
                            const char *resource,
                            int pds_flags,
                            download_want_authority_t want_authority))
{
  const routerstatus_t *rs = NULL;
  const or_options_t *options = get_options();
  int prefer_authority = (directory_fetches_from_authorities(options)
                          || want_authority == DL_WANT_AUTHORITY);
  int require_authority = 0;
  int get_via_tor = purpose_needs_anonymity(dir_purpose, router_purpose,
                                            resource);
  dirinfo_type_t type = dir_fetch_type(dir_purpose, router_purpose, resource);

  if (type == NO_DIRINFO)
    return;

  if (!options->FetchServerDescriptors)
    return;

  circuit_guard_state_t *guard_state = NULL;
  if (!get_via_tor) {
    if (options->UseBridges && !(type & BRIDGE_DIRINFO)) {
      /* We want to ask a running bridge for which we have a descriptor.
       *
       * When we ask choose_random_entry() for a bridge, we specify what
       * sort of dir fetch we'll be doing, so it won't return a bridge
       * that can't answer our question.
       */
      const node_t *node = guards_choose_dirguard(&guard_state);
      if (node && node->ri) {
        /* every bridge has a routerinfo. */
        routerinfo_t *ri = node->ri;
        /* clients always make OR connections to bridges */
        tor_addr_port_t or_ap;
        directory_request_t *req = directory_request_new(dir_purpose);
        /* we are willing to use a non-preferred address if we need to */
        fascist_firewall_choose_address_node(node, FIREWALL_OR_CONNECTION, 0,
                                             &or_ap);
        directory_request_set_or_addr_port(req, &or_ap);
        directory_request_set_directory_id_digest(req,
                                            ri->cache_info.identity_digest);
        directory_request_set_router_purpose(req, router_purpose);
        directory_request_set_resource(req, resource);
        if (dir_purpose == DIR_PURPOSE_FETCH_CONSENSUS)
          dir_consensus_request_set_additional_headers(req, resource);
        directory_request_set_guard_state(req, guard_state);
        directory_initiate_request(req);
        directory_request_free(req);
      } else {
        if (guard_state) {
          entry_guard_cancel(&guard_state);
        }
        log_notice(LD_DIR, "Ignoring directory request, since no bridge "
                           "nodes are available yet.");
      }

      return;
    } else {
      if (prefer_authority || (type & BRIDGE_DIRINFO)) {
        /* only ask authdirservers, and don't ask myself */
        rs = router_pick_trusteddirserver(type, pds_flags);
        if (rs == NULL && (pds_flags & (PDS_NO_EXISTING_SERVERDESC_FETCH|
                                        PDS_NO_EXISTING_MICRODESC_FETCH))) {
          /* We don't want to fetch from any authorities that we're currently
           * fetching server descriptors from, and we got no match.  Did we
           * get no match because all the authorities have connections
           * fetching server descriptors (in which case we should just
           * return,) or because all the authorities are down or on fire or
           * unreachable or something (in which case we should go on with
           * our fallback code)? */
          pds_flags &= ~(PDS_NO_EXISTING_SERVERDESC_FETCH|
                         PDS_NO_EXISTING_MICRODESC_FETCH);
          rs = router_pick_trusteddirserver(type, pds_flags);
          if (rs) {
            log_debug(LD_DIR, "Deferring serverdesc fetch: all authorities "
                      "are in use.");
            return;
          }
        }
        if (rs == NULL && require_authority) {
          log_info(LD_DIR, "No authorities were available for %s: will try "
                   "later.", dir_conn_purpose_to_string(dir_purpose));
          return;
        }
      }
      if (!rs && !(type & BRIDGE_DIRINFO)) {
        rs = directory_pick_generic_dirserver(type, pds_flags,
                                              dir_purpose,
                                              &guard_state);
        if (!rs)
          get_via_tor = 1; /* last resort: try routing it via Tor */
      }
    }
  }

  if (get_via_tor) {
    /* Never use fascistfirewall; we're going via Tor. */
    pds_flags |= PDS_IGNORE_FASCISTFIREWALL;
    rs = router_pick_directory_server(type, pds_flags);
  }

  /* If we have any hope of building an indirect conn, we know some router
   * descriptors.  If (rs==NULL), we can't build circuits anyway, so
   * there's no point in falling back to the authorities in this case. */
  if (rs) {
    const dir_indirection_t indirection =
      get_via_tor ? DIRIND_ANONYMOUS : DIRIND_ONEHOP;
    directory_request_t *req = directory_request_new(dir_purpose);
    directory_request_set_routerstatus(req, rs);
    directory_request_set_router_purpose(req, router_purpose);
    directory_request_set_indirection(req, indirection);
    directory_request_set_resource(req, resource);
    if (dir_purpose == DIR_PURPOSE_FETCH_CONSENSUS)
      dir_consensus_request_set_additional_headers(req, resource);
    if (guard_state)
      directory_request_set_guard_state(req, guard_state);
    directory_initiate_request(req);
    directory_request_free(req);
  } else {
    log_notice(LD_DIR,
               "While fetching directory info, "
               "no running dirservers known. Will try again later. "
               "(purpose %d)", dir_purpose);
    if (!purpose_needs_anonymity(dir_purpose, router_purpose, resource)) {
      /* remember we tried them all and failed. */
      directory_all_unreachable(time(NULL));
    }
  }
}

/** As directory_get_from_dirserver, but initiates a request to <i>every</i>
 * directory authority other than ourself.  Only for use by authorities when
 * searching for missing information while voting. */
void
directory_get_from_all_authorities(uint8_t dir_purpose,
                                   uint8_t router_purpose,
                                   const char *resource)
{
  tor_assert(dir_purpose == DIR_PURPOSE_FETCH_STATUS_VOTE ||
             dir_purpose == DIR_PURPOSE_FETCH_DETACHED_SIGNATURES);

  SMARTLIST_FOREACH_BEGIN(router_get_trusted_dir_servers(),
                          dir_server_t *, ds) {
      if (router_digest_is_me(ds->digest))
        continue;
      if (!(ds->type & V3_DIRINFO))
        continue;
      const routerstatus_t *rs = &ds->fake_status;
      directory_request_t *req = directory_request_new(dir_purpose);
      directory_request_set_routerstatus(req, rs);
      directory_request_set_router_purpose(req, router_purpose);
      directory_request_set_resource(req, resource);
      directory_initiate_request(req);
      directory_request_free(req);
  } SMARTLIST_FOREACH_END(ds);
}

/** Return true iff <b>ind</b> requires a multihop circuit. */
static int
dirind_is_anon(dir_indirection_t ind)
{
  return ind == DIRIND_ANON_DIRPORT || ind == DIRIND_ANONYMOUS;
}

/* Choose reachable OR and Dir addresses and ports from status, copying them
 * into use_or_ap and use_dir_ap. If indirection is anonymous, then we're
 * connecting via another relay, so choose the primary IPv4 address and ports.
 *
 * status should have at least one reachable address, if we can't choose a
 * reachable address, warn and return -1. Otherwise, return 0.
 */
static int
directory_choose_address_routerstatus(const routerstatus_t *status,
                                      dir_indirection_t indirection,
                                      tor_addr_port_t *use_or_ap,
                                      tor_addr_port_t *use_dir_ap)
{
  tor_assert(status != NULL);
  tor_assert(use_or_ap != NULL);
  tor_assert(use_dir_ap != NULL);

  const or_options_t *options = get_options();
  int have_or = 0, have_dir = 0;

  /* We expect status to have at least one reachable address if we're
   * connecting to it directly.
   *
   * Therefore, we can simply use the other address if the one we want isn't
   * allowed by the firewall.
   *
   * (When Tor uploads and downloads a hidden service descriptor, it uses
   * DIRIND_ANONYMOUS, except for Tor2Web, which uses DIRIND_ONEHOP.
   * So this code will only modify the address for Tor2Web's HS descriptor
   * fetches. Even Single Onion Servers (NYI) use DIRIND_ANONYMOUS, to avoid
   * HSDirs denying service by rejecting descriptors.)
   */

  /* Initialise the OR / Dir addresses */
  tor_addr_make_null(&use_or_ap->addr, AF_UNSPEC);
  use_or_ap->port = 0;
  tor_addr_make_null(&use_dir_ap->addr, AF_UNSPEC);
  use_dir_ap->port = 0;

  /* ORPort connections */
  if (indirection == DIRIND_ANONYMOUS) {
    if (status->addr) {
      /* Since we're going to build a 3-hop circuit and ask the 2nd relay
       * to extend to this address, always use the primary (IPv4) OR address */
      tor_addr_from_ipv4h(&use_or_ap->addr, status->addr);
      use_or_ap->port = status->or_port;
      have_or = 1;
    }
  } else if (indirection == DIRIND_ONEHOP) {
    /* We use an IPv6 address if we have one and we prefer it.
     * Use the preferred address and port if they are reachable, otherwise,
     * use the alternate address and port (if any).
     */
    have_or = fascist_firewall_choose_address_rs(status,
                                                 FIREWALL_OR_CONNECTION, 0,
                                                 use_or_ap);
  }

  /* DirPort connections
   * DIRIND_ONEHOP uses ORPort, but may fall back to the DirPort on relays */
  if (indirection == DIRIND_DIRECT_CONN ||
      indirection == DIRIND_ANON_DIRPORT ||
      (indirection == DIRIND_ONEHOP
       && !directory_must_use_begindir(options))) {
    have_dir = fascist_firewall_choose_address_rs(status,
                                                  FIREWALL_DIR_CONNECTION, 0,
                                                  use_dir_ap);
  }

  /* We rejected all addresses in the relay's status. This means we can't
   * connect to it. */
  if (!have_or && !have_dir) {
    static int logged_backtrace = 0;
    log_info(LD_BUG, "Rejected all OR and Dir addresses from %s when "
             "launching an outgoing directory connection to: IPv4 %s OR %d "
             "Dir %d IPv6 %s OR %d Dir %d", routerstatus_describe(status),
             fmt_addr32(status->addr), status->or_port,
             status->dir_port, fmt_addr(&status->ipv6_addr),
             status->ipv6_orport, status->dir_port);
    if (!logged_backtrace) {
      log_backtrace(LOG_INFO, LD_BUG, "Addresses came from");
      logged_backtrace = 1;
    }
    return -1;
  }

  return 0;
}

/** Return true iff <b>conn</b> is the client side of a directory connection
 * we launched to ourself in order to determine the reachability of our
 * dir_port. */
static int
directory_conn_is_self_reachability_test(dir_connection_t *conn)
{
  if (conn->requested_resource &&
      !strcmpstart(conn->requested_resource,"authority")) {
    const routerinfo_t *me = router_get_my_routerinfo();
    if (me &&
        router_digest_is_me(conn->identity_digest) &&
        tor_addr_eq_ipv4h(&conn->base_.addr, me->addr) && /*XXXX prop 118*/
        me->dir_port == conn->base_.port)
      return 1;
  }
  return 0;
}

/** Called when we are unable to complete the client's request to a directory
 * server due to a network error: Mark the router as down and try again if
 * possible.
 */
static void
connection_dir_request_failed(dir_connection_t *conn)
{
  if (conn->guard_state) {
    /* We haven't seen a success on this guard state, so consider it to have
     * failed. */
    entry_guard_failed(&conn->guard_state);
  }
  if (directory_conn_is_self_reachability_test(conn)) {
    return; /* this was a test fetch. don't retry. */
  }
  if (!entry_list_is_constrained(get_options()))
    router_set_status(conn->identity_digest, 0); /* don't try this one again */
  if (conn->base_.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
             conn->base_.purpose == DIR_PURPOSE_FETCH_EXTRAINFO) {
    log_info(LD_DIR, "Giving up on serverdesc/extrainfo fetch from "
             "directory server at '%s'; retrying",
             conn->base_.address);
    if (conn->router_purpose == ROUTER_PURPOSE_BRIDGE)
      connection_dir_bridge_routerdesc_failed(conn);
    connection_dir_download_routerdesc_failed(conn);
  } else if (conn->base_.purpose == DIR_PURPOSE_FETCH_CONSENSUS) {
    if (conn->requested_resource)
      networkstatus_consensus_download_failed(0, conn->requested_resource);
  } else if (conn->base_.purpose == DIR_PURPOSE_FETCH_CERTIFICATE) {
    log_info(LD_DIR, "Giving up on certificate fetch from directory server "
             "at '%s'; retrying",
             conn->base_.address);
    connection_dir_download_cert_failed(conn, 0);
  } else if (conn->base_.purpose == DIR_PURPOSE_FETCH_DETACHED_SIGNATURES) {
    log_info(LD_DIR, "Giving up downloading detached signatures from '%s'",
             conn->base_.address);
  } else if (conn->base_.purpose == DIR_PURPOSE_FETCH_STATUS_VOTE) {
    log_info(LD_DIR, "Giving up downloading votes from '%s'",
             conn->base_.address);
  } else if (conn->base_.purpose == DIR_PURPOSE_FETCH_MICRODESC) {
    log_info(LD_DIR, "Giving up on downloading microdescriptors from "
             "directory server at '%s'; will retry", conn->base_.address);
    connection_dir_download_routerdesc_failed(conn);
  }
}

/** Helper: Attempt to fetch directly the descriptors of each bridge
 * listed in <b>failed</b>.
 */
static void
connection_dir_retry_bridges(smartlist_t *descs)
{
  char digest[DIGEST_LEN];
  SMARTLIST_FOREACH(descs, const char *, cp,
  {
    if (base16_decode(digest, DIGEST_LEN, cp, strlen(cp)) != DIGEST_LEN) {
      log_warn(LD_BUG, "Malformed fingerprint in list: %s",
              escaped(cp));
      continue;
    }
    retry_bridge_descriptor_fetch_directly(digest);
  });
}

/** Called when an attempt to download one or more router descriptors
 * or extra-info documents on connection <b>conn</b> failed.
 */
static void
connection_dir_download_routerdesc_failed(dir_connection_t *conn)
{
  /* No need to increment the failure count for routerdescs, since
   * it's not their fault. */

  /* No need to relaunch descriptor downloads here: we already do it
   * every 10 or 60 seconds (FOO_DESCRIPTOR_RETRY_INTERVAL) in main.c. */
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
             conn->base_.purpose == DIR_PURPOSE_FETCH_EXTRAINFO ||
             conn->base_.purpose == DIR_PURPOSE_FETCH_MICRODESC);

  (void) conn;
}

/** Called when an attempt to download a bridge's routerdesc from
 * one of the authorities failed due to a network error. If
 * possible attempt to download descriptors from the bridge directly.
 */
static void
connection_dir_bridge_routerdesc_failed(dir_connection_t *conn)
{
  smartlist_t *which = NULL;

  /* Requests for bridge descriptors are in the form 'fp/', so ignore
     anything else. */
  if (!conn->requested_resource || strcmpstart(conn->requested_resource,"fp/"))
    return;

  which = smartlist_new();
  dir_split_resource_into_fingerprints(conn->requested_resource
                                        + strlen("fp/"),
                                       which, NULL, 0);

  tor_assert(conn->base_.purpose != DIR_PURPOSE_FETCH_EXTRAINFO);
  if (smartlist_len(which)) {
    connection_dir_retry_bridges(which);
    SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
  }
  smartlist_free(which);
}

/** Called when an attempt to fetch a certificate fails. */
static void
connection_dir_download_cert_failed(dir_connection_t *conn, int status)
{
  const char *fp_pfx = "fp/";
  const char *fpsk_pfx = "fp-sk/";
  smartlist_t *failed;
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_CERTIFICATE);

  if (!conn->requested_resource)
    return;
  failed = smartlist_new();
  /*
   * We have two cases download by fingerprint (resource starts
   * with "fp/") or download by fingerprint/signing key pair
   * (resource starts with "fp-sk/").
   */
  if (!strcmpstart(conn->requested_resource, fp_pfx)) {
    /* Download by fingerprint case */
    dir_split_resource_into_fingerprints(conn->requested_resource +
                                         strlen(fp_pfx),
                                         failed, NULL, DSR_HEX);
    SMARTLIST_FOREACH_BEGIN(failed, char *, cp) {
      /* Null signing key digest indicates download by fp only */
      authority_cert_dl_failed(cp, NULL, status);
      tor_free(cp);
    } SMARTLIST_FOREACH_END(cp);
  } else if (!strcmpstart(conn->requested_resource, fpsk_pfx)) {
    /* Download by (fp,sk) pairs */
    dir_split_resource_into_fingerprint_pairs(conn->requested_resource +
                                              strlen(fpsk_pfx), failed);
    SMARTLIST_FOREACH_BEGIN(failed, fp_pair_t *, cp) {
      authority_cert_dl_failed(cp->first, cp->second, status);
      tor_free(cp);
    } SMARTLIST_FOREACH_END(cp);
  } else {
    log_warn(LD_DIR,
             "Don't know what to do with failure for cert fetch %s",
             conn->requested_resource);
  }

  smartlist_free(failed);

  update_certificate_downloads(time(NULL));
}

/* Should this tor instance only use begindir for all its directory requests?
 */
int
directory_must_use_begindir(const or_options_t *options)
{
  /* Clients, onion services, and bridges must use begindir,
   * relays and authorities do not have to */
  return !public_server_mode(options);
}

struct directory_request_t {
  /**
   * These fields specify which directory we're contacting.  Routerstatus,
   * if present, overrides the other fields.
   *
   * @{ */
  tor_addr_port_t or_addr_port;
  tor_addr_port_t dir_addr_port;
  char digest[DIGEST_LEN];

  const routerstatus_t *routerstatus;
  /** @} */
  /** One of DIR_PURPOSE_* other than DIR_PURPOSE_SERVER. Describes what
   * kind of operation we'll be doing (upload/download), and of what kind
   * of document. */
  uint8_t dir_purpose;
  /** One of ROUTER_PURPOSE_*; used for uploads and downloads of routerinfo
   * and extrainfo docs.  */
  uint8_t router_purpose;
  /** Enum: determines whether to anonymize, and whether to use dirport or
   * orport. */
  dir_indirection_t indirection;
  /** Alias to the variable part of the URL for this request */
  const char *resource;
  /** Alias to the payload to upload (if any) */
  const char *payload;
  /** Number of bytes to upload from payload</b> */
  size_t payload_len;
  /** Value to send in an if-modified-since header, or 0 for none. */
  time_t if_modified_since;
  /** Hidden-service-specific information */
  const rend_data_t *rend_query;
  /** Extra headers to append to the request */
  config_line_t *additional_headers;
  /** */
  /** Used internally to directory.c: gets informed when the attempt to
   * connect to the directory succeeds or fails, if that attempt bears on the
   * directory's usability as a directory guard. */
  circuit_guard_state_t *guard_state;
};

/** Evaluate the situation and decide if we should use an encrypted
 * "begindir-style" connection for this directory request.
 * 0) If there is no DirPort, yes.
 * 1) If or_port is 0, or it's a direct conn and or_port is firewalled
 *    or we're a dir mirror, no.
 * 2) If we prefer to avoid begindir conns, and we're not fetching or
 *    publishing a bridge relay descriptor, no.
 * 3) Else yes.
 * If returning 0, return in *reason why we can't use begindir.
 * reason must not be NULL.
 */
static int
directory_command_should_use_begindir(const or_options_t *options,
                                      const directory_request_t *req,
                                      const char **reason)
{
  const tor_addr_t *or_addr = &req->or_addr_port.addr;
  //const tor_addr_t *dir_addr = &req->dir_addr_port.addr;
  const int or_port = req->or_addr_port.port;
  const int dir_port = req->dir_addr_port.port;

  const dir_indirection_t indirection = req->indirection;

  tor_assert(reason);
  *reason = NULL;

  /* Reasons why we must use begindir */
  if (!dir_port) {
    *reason = "(using begindir - directory with no DirPort)";
    return 1; /* We don't know a DirPort -- must begindir. */
  }
  /* Reasons why we can't possibly use begindir */
  if (!or_port) {
    *reason = "directory with unknown ORPort";
    return 0; /* We don't know an ORPort -- no chance. */
  }
  if (indirection == DIRIND_DIRECT_CONN ||
      indirection == DIRIND_ANON_DIRPORT) {
    *reason = "DirPort connection";
    return 0;
  }
  if (indirection == DIRIND_ONEHOP) {
    /* We're firewalled and want a direct OR connection */
    if (!fascist_firewall_allows_address_addr(or_addr, or_port,
                                              FIREWALL_OR_CONNECTION, 0, 0)) {
      *reason = "ORPort not reachable";
      return 0;
    }
  }
  /* Reasons why we want to avoid using begindir */
  if (indirection == DIRIND_ONEHOP) {
    if (!directory_must_use_begindir(options)) {
      *reason = "in relay mode";
      return 0;
    }
  }
  /* DIRIND_ONEHOP on a client, or DIRIND_ANONYMOUS
   */
  *reason = "(using begindir)";
  return 1;
}

/**
 * Create and return a new directory_request_t with purpose
 * <b>dir_purpose</b>.
 */
directory_request_t *
directory_request_new(uint8_t dir_purpose)
{
  tor_assert(dir_purpose >= DIR_PURPOSE_MIN_);
  tor_assert(dir_purpose <= DIR_PURPOSE_MAX_);
  tor_assert(dir_purpose != DIR_PURPOSE_SERVER);
  tor_assert(dir_purpose != DIR_PURPOSE_HAS_FETCHED_RENDDESC_V2);

  directory_request_t *result = tor_malloc_zero(sizeof(*result));
  tor_addr_make_null(&result->or_addr_port.addr, AF_INET);
  result->or_addr_port.port = 0;
  tor_addr_make_null(&result->dir_addr_port.addr, AF_INET);
  result->dir_addr_port.port = 0;
  result->dir_purpose = dir_purpose;
  result->router_purpose = ROUTER_PURPOSE_GENERAL;
  result->indirection = DIRIND_ONEHOP;
  return result;
}
/**
 * Release all resources held by <b>req</b>.
 */
void
directory_request_free(directory_request_t *req)
{
  if (req == NULL)
    return;
  config_free_lines(req->additional_headers);
  tor_free(req);
}
/**
 * Set the address and OR port to use for this directory request.  If there is
 * no OR port, we'll have to connect over the dirport.  (If there are both,
 * the indirection setting determins which to use.)
 */
void
directory_request_set_or_addr_port(directory_request_t *req,
                                   const tor_addr_port_t *p)
{
  memcpy(&req->or_addr_port, p, sizeof(*p));
}
/**
 * Set the address and dirport to use for this directory request.  If there
 * is no dirport, we'll have to connect over the OR port.  (If there are both,
 * the indirection setting determins which to use.)
 */
void
directory_request_set_dir_addr_port(directory_request_t *req,
                                    const tor_addr_port_t *p)
{
  memcpy(&req->dir_addr_port, p, sizeof(*p));
}
/**
 * Set the RSA identity digest of the directory to use for this directory
 * request.
 */
void
directory_request_set_directory_id_digest(directory_request_t *req,
                                          const char *digest)
{
  memcpy(req->digest, digest, DIGEST_LEN);
}
/**
 * Set the router purpose associated with uploaded and downloaded router
 * descriptors and extrainfo documents in this directory request.  The purpose
 * must be one of ROUTER_PURPOSE_GENERAL (the default) or
 * ROUTER_PURPOSE_BRIDGE.
 */
void
directory_request_set_router_purpose(directory_request_t *req,
                                     uint8_t router_purpose)
{
  tor_assert(router_purpose == ROUTER_PURPOSE_GENERAL ||
             router_purpose == ROUTER_PURPOSE_BRIDGE);
  // assert that it actually makes sense to set this purpose, given
  // the dir_purpose.
  req->router_purpose = router_purpose;
}
/**
 * Set the indirection to be used for the directory request.  The indirection
 * parameter configures whether to connect to a DirPort or ORPort, and whether
 * to anonymize the connection.  DIRIND_ONEHOP (use ORPort, don't anonymize)
 * is the default.  See dir_indirection_t for more information.
 */
void
directory_request_set_indirection(directory_request_t *req,
                                  dir_indirection_t indirection)
{
  req->indirection = indirection;
}

/**
 * Set a pointer to the resource to request from a directory.  Different
 * request types use resources to indicate different components of their URL.
 * Note that only an alias to <b>resource</b> is stored, so the
 * <b>resource</b> must outlive the request.
 */
void
directory_request_set_resource(directory_request_t *req,
                               const char *resource)
{
  req->resource = resource;
}
/**
 * Set a pointer to the payload to include with this directory request, along
 * with its length.  Note that only an alias to <b>payload</b> is stored, so
 * the <b>payload</b> must outlive the request.
 */
void
directory_request_set_payload(directory_request_t *req,
                              const char *payload,
                              size_t payload_len)
{
  tor_assert(DIR_PURPOSE_IS_UPLOAD(req->dir_purpose));

  req->payload = payload;
  req->payload_len = payload_len;
}
/**
 * Set an if-modified-since date to send along with the request.  The
 * default is 0 (meaning, send no if-modified-since header).
 */
void
directory_request_set_if_modified_since(directory_request_t *req,
                                        time_t if_modified_since)
{
  req->if_modified_since = if_modified_since;
}

/** Include a header of name <b>key</b> with content <b>val</b> in the
 * request. Neither may include newlines or other odd characters. Their
 * ordering is not currently guaranteed.
 *
 * Note that, as elsewhere in this module, header keys include a trailing
 * colon and space.
 */
void
directory_request_add_header(directory_request_t *req,
                             const char *key,
                             const char *val)
{
  config_line_prepend(&req->additional_headers, key, val);
}
/**
 * Set an object containing HS data to be associated with this request.  Note
 * that only an alias to <b>query</b> is stored, so the <b>query</b> object
 * must outlive the request.
 */
void
directory_request_set_rend_query(directory_request_t *req,
                                 const rend_data_t *query)
{
  if (query) {
    tor_assert(req->dir_purpose == DIR_PURPOSE_FETCH_RENDDESC_V2 ||
               req->dir_purpose == DIR_PURPOSE_UPLOAD_RENDDESC_V2);
  }
  req->rend_query = query;
}
/** Set a static circuit_guard_state_t object to affliate with the request in
 * <b>req</b>.  This object will receive notification when the attempt to
 * connect to the guard either succeeds or fails. */
void
directory_request_set_guard_state(directory_request_t *req,
                                  circuit_guard_state_t *state)
{
  req->guard_state = state;
}

/**
 * Internal: Return true if any information for contacting the directory in
 * <b>req</b> has been set, other than by the routerstatus. */
static int
directory_request_dir_contact_info_specified(const directory_request_t *req)
{
  /* We only check for ports here, since we don't use an addr unless the port
   * is set */
  return (req->or_addr_port.port ||
          req->dir_addr_port.port ||
          ! tor_digest_is_zero(req->digest));
}

/**
 * Set the routerstatus to use for the directory associated with this
 * request.  If this option is set, then no other function to set the
 * directory's address or identity should be called.
 */
void
directory_request_set_routerstatus(directory_request_t *req,
                                   const routerstatus_t *status)
{
  req->routerstatus = status;
}
/**
 * Helper: update the addresses, ports, and identities in <b>req</b>
 * from the routerstatus object in <b>req</b>.  Return 0 on success.
 * On failure, warn and return -1.
 */
static int
directory_request_set_dir_from_routerstatus(directory_request_t *req)

{
  const routerstatus_t *status = req->routerstatus;
  if (BUG(status == NULL))
    return -1;
  const or_options_t *options = get_options();
  const node_t *node;
  tor_addr_port_t use_or_ap, use_dir_ap;
  const int anonymized_connection = dirind_is_anon(req->indirection);

  tor_assert(status != NULL);

  node = node_get_by_id(status->identity_digest);

  /* XXX The below check is wrong: !node means it's not in the consensus,
   * but we haven't checked if we have a descriptor for it -- and also,
   * we only care about the descriptor if it's a begindir-style anonymized
   * connection. */
  if (!node && anonymized_connection) {
    log_info(LD_DIR, "Not sending anonymized request to directory '%s'; we "
             "don't have its router descriptor.",
             routerstatus_describe(status));
    return -1;
  }

  if (options->ExcludeNodes && options->StrictNodes &&
      routerset_contains_routerstatus(options->ExcludeNodes, status, -1)) {
    log_warn(LD_DIR, "Wanted to contact directory mirror %s for %s, but "
             "it's in our ExcludedNodes list and StrictNodes is set. "
             "Skipping. This choice might make your Tor not work.",
             routerstatus_describe(status),
             dir_conn_purpose_to_string(req->dir_purpose));
    return -1;
  }

    /* At this point, if we are a client making a direct connection to a
   * directory server, we have selected a server that has at least one address
   * allowed by ClientUseIPv4/6 and Reachable{"",OR,Dir}Addresses. This
   * selection uses the preference in ClientPreferIPv6{OR,Dir}Port, if
   * possible. (If UseBridges is set, clients always use IPv6, and prefer it
   * by default.)
   *
   * Now choose an address that we can use to connect to the directory server.
   */
  if (directory_choose_address_routerstatus(status,
                                            req->indirection, &use_or_ap,
                                            &use_dir_ap) < 0) {
    return -1;
  }

  directory_request_set_or_addr_port(req, &use_or_ap);
  directory_request_set_dir_addr_port(req, &use_dir_ap);
  directory_request_set_directory_id_digest(req, status->identity_digest);
  return 0;
}

/**
 * Launch the provided directory request, configured in <b>request</b>.
 * After this function is called, you can free <b>request</b>.
 */
MOCK_IMPL(void,
directory_initiate_request,(directory_request_t *request))
{
  tor_assert(request);
  if (request->routerstatus) {
    tor_assert_nonfatal(
               ! directory_request_dir_contact_info_specified(request));
    if (directory_request_set_dir_from_routerstatus(request) < 0) {
      return;
    }
  }

  const tor_addr_port_t *or_addr_port = &request->or_addr_port;
  const tor_addr_port_t *dir_addr_port = &request->dir_addr_port;
  const char *digest = request->digest;
  const uint8_t dir_purpose = request->dir_purpose;
  const uint8_t router_purpose = request->router_purpose;
  const dir_indirection_t indirection = request->indirection;
  const char *resource = request->resource;
  const rend_data_t *rend_query = request->rend_query;
  circuit_guard_state_t *guard_state = request->guard_state;

  tor_assert(or_addr_port->port || dir_addr_port->port);
  tor_assert(digest);

  dir_connection_t *conn;
  const or_options_t *options = get_options();
  int socket_error = 0;
  const char *begindir_reason = NULL;
  /* Should the connection be to a relay's OR port (and inside that we will
   * send our directory request)? */
  const int use_begindir =
    directory_command_should_use_begindir(options, request, &begindir_reason);

  /* Will the connection go via a three-hop Tor circuit? Note that this
   * is separate from whether it will use_begindir. */
  const int anonymized_connection = dirind_is_anon(indirection);

  /* What is the address we want to make the directory request to? If
   * we're making a begindir request this is the ORPort of the relay
   * we're contacting; if not a begindir request, this is its DirPort.
   * Note that if anonymized_connection is true, we won't be initiating
   * a connection directly to this address. */
  tor_addr_t addr;
  tor_addr_copy(&addr, &(use_begindir ? or_addr_port : dir_addr_port)->addr);
  uint16_t port = (use_begindir ? or_addr_port : dir_addr_port)->port;

  log_debug(LD_DIR, "anonymized %d, use_begindir %d.",
            anonymized_connection, use_begindir);

  log_debug(LD_DIR, "Initiating %s", dir_conn_purpose_to_string(dir_purpose));

  if (purpose_needs_anonymity(dir_purpose, router_purpose, resource)) {
    tor_assert(anonymized_connection ||
               rend_non_anonymous_mode_enabled(options));
  }

  /* use encrypted begindir connections for everything except relays
   * this provides better protection for directory fetches */
  if (!use_begindir && directory_must_use_begindir(options)) {
    log_warn(LD_BUG, "Client could not use begindir connection: %s",
             begindir_reason ? begindir_reason : "(NULL)");
    return;
  }

  /* ensure that we don't make direct connections when a SOCKS server is
   * configured. */
  if (!anonymized_connection && !use_begindir && !options->HTTPProxy &&
      (options->Socks4Proxy || options->Socks5Proxy)) {
    log_warn(LD_DIR, "Cannot connect to a directory server through a "
                     "SOCKS proxy!");
    return;
  }

  /* Make sure that the destination addr and port we picked is viable. */
  if (!port || tor_addr_is_null(&addr)) {
    static int logged_backtrace = 0;
    log_warn(LD_DIR,
             "Cannot make an outgoing %sconnection without a remote %sPort.",
             use_begindir ? "begindir " : "",
             use_begindir ? "OR" : "Dir");
    if (!logged_backtrace) {
      log_backtrace(LOG_INFO, LD_BUG, "Address came from");
      logged_backtrace = 1;
    }
    return;
  }

  conn = dir_connection_new(tor_addr_family(&addr));

  /* set up conn so it's got all the data we need to remember */
  tor_addr_copy(&conn->base_.addr, &addr);
  conn->base_.port = port;
  conn->base_.address = tor_addr_to_str_dup(&addr);
  memcpy(conn->identity_digest, digest, DIGEST_LEN);

  conn->base_.purpose = dir_purpose;
  conn->router_purpose = router_purpose;

  /* give it an initial state */
  conn->base_.state = DIR_CONN_STATE_CONNECTING;

  /* decide whether we can learn our IP address from this conn */
  /* XXXX This is a bad name for this field now. */
  conn->dirconn_direct = !anonymized_connection;

  /* copy rendezvous data, if any */
  if (rend_query)
    conn->rend_data = rend_data_dup(rend_query);

  if (!anonymized_connection && !use_begindir) {
    /* then we want to connect to dirport directly */

    if (options->HTTPProxy) {
      tor_addr_copy(&addr, &options->HTTPProxyAddr);
      port = options->HTTPProxyPort;
    }

    // In this case we should not have picked a directory guard.
    if (BUG(guard_state)) {
      entry_guard_cancel(&guard_state);
    }

    switch (connection_connect(TO_CONN(conn), conn->base_.address, &addr,
                               port, &socket_error)) {
      case -1:
        connection_mark_for_close(TO_CONN(conn));
        return;
      case 1:
        /* start flushing conn */
        conn->base_.state = DIR_CONN_STATE_CLIENT_SENDING;
        /* fall through */
      case 0:
        /* queue the command on the outbuf */
        directory_send_command(conn, 1, request);
        connection_watch_events(TO_CONN(conn), READ_EVENT | WRITE_EVENT);
        /* writable indicates finish, readable indicates broken link,
           error indicates broken link in windowsland. */
    }
  } else {
    /* We will use a Tor circuit (maybe 1-hop, maybe 3-hop, maybe with
     * begindir, maybe not with begindir) */

    entry_connection_t *linked_conn;

    /* Anonymized tunneled connections can never share a circuit.
     * One-hop directory connections can share circuits with each other
     * but nothing else. */
    int iso_flags = anonymized_connection ? ISO_STREAM : ISO_SESSIONGRP;

    /* If it's an anonymized connection, remember the fact that we
     * wanted it for later: maybe we'll want it again soon. */
    if (anonymized_connection && use_begindir)
      rep_hist_note_used_internal(time(NULL), 0, 1);
    else if (anonymized_connection && !use_begindir)
      rep_hist_note_used_port(time(NULL), conn->base_.port);

    // In this case we should not have a directory guard; we'll
    // get a regular guard later when we build the circuit.
    if (BUG(anonymized_connection && guard_state)) {
      entry_guard_cancel(&guard_state);
    }

    conn->guard_state = guard_state;

    /* make an AP connection
     * populate it and add it at the right state
     * hook up both sides
     */
    linked_conn =
      connection_ap_make_link(TO_CONN(conn),
                              conn->base_.address, conn->base_.port,
                              digest,
                              SESSION_GROUP_DIRCONN, iso_flags,
                              use_begindir, !anonymized_connection);
    if (!linked_conn) {
      log_warn(LD_NET,"Making tunnel to dirserver failed.");
      connection_mark_for_close(TO_CONN(conn));
      return;
    }

    if (connection_add(TO_CONN(conn)) < 0) {
      log_warn(LD_NET,"Unable to add connection for link to dirserver.");
      connection_mark_for_close(TO_CONN(conn));
      return;
    }
    conn->base_.state = DIR_CONN_STATE_CLIENT_SENDING;
    /* queue the command on the outbuf */
    directory_send_command(conn, 0, request);

    connection_watch_events(TO_CONN(conn), READ_EVENT|WRITE_EVENT);
    connection_start_reading(ENTRY_TO_CONN(linked_conn));
  }
}

/** Return true iff anything we say on <b>conn</b> is being encrypted before
 * we send it to the client/server. */
int
connection_dir_is_encrypted(const dir_connection_t *conn)
{
  /* Right now it's sufficient to see if conn is or has been linked, since
   * the only thing it could be linked to is an edge connection on a
   * circuit, and the only way it could have been unlinked is at the edge
   * connection getting closed.
   */
  return TO_CONN(conn)->linked;
}

/** Helper for sorting
 *
 * sort strings alphabetically
 */
static int
compare_strs_(const void **a, const void **b)
{
  const char *s1 = *a, *s2 = *b;
  return strcmp(s1, s2);
}

#define CONDITIONAL_CONSENSUS_FPR_LEN 3
#if (CONDITIONAL_CONSENSUS_FPR_LEN > DIGEST_LEN)
#error "conditional consensus fingerprint length is larger than digest length"
#endif

/** Return the URL we should use for a consensus download.
 *
 * Use the "conditional consensus downloading" feature described in
 * dir-spec.txt, i.e.
 * GET .../consensus/<b>fpr</b>+<b>fpr</b>+<b>fpr</b>
 *
 * If 'resource' is provided, it is the name of a consensus flavor to request.
 */
static char *
directory_get_consensus_url(const char *resource)
{
  char *url = NULL;
  const char *hyphen, *flavor;
  if (resource==NULL || strcmp(resource, "ns")==0) {
    flavor = ""; /* Request ns consensuses as "", so older servers will work*/
    hyphen = "";
  } else {
    flavor = resource;
    hyphen = "-";
  }

  {
    char *authority_id_list;
    smartlist_t *authority_digests = smartlist_new();

    SMARTLIST_FOREACH_BEGIN(router_get_trusted_dir_servers(),
                            dir_server_t *, ds) {
        char *hex;
        if (!(ds->type & V3_DIRINFO))
          continue;

        hex = tor_malloc(2*CONDITIONAL_CONSENSUS_FPR_LEN+1);
        base16_encode(hex, 2*CONDITIONAL_CONSENSUS_FPR_LEN+1,
                      ds->v3_identity_digest, CONDITIONAL_CONSENSUS_FPR_LEN);
        smartlist_add(authority_digests, hex);
    } SMARTLIST_FOREACH_END(ds);
    smartlist_sort(authority_digests, compare_strs_);
    authority_id_list = smartlist_join_strings(authority_digests,
                                               "+", 0, NULL);

    tor_asprintf(&url, "/tor/status-vote/current/consensus%s%s/%s.z",
                 hyphen, flavor, authority_id_list);

    SMARTLIST_FOREACH(authority_digests, char *, cp, tor_free(cp));
    smartlist_free(authority_digests);
    tor_free(authority_id_list);
  }
  return url;
}

/**
 * Copies the ipv6 from source to destination, subject to buffer size limit
 * size. If decorate is true, makes sure the copied address is decorated.
 */
static void
copy_ipv6_address(char* destination, const char* source, size_t len,
                  int decorate) {
  tor_assert(destination);
  tor_assert(source);

  if (decorate && source[0] != '[') {
    tor_snprintf(destination, len, "[%s]", source);
  } else {
    strlcpy(destination, source, len);
  }
}

/** Queue an appropriate HTTP command for <b>request</b> on
 * <b>conn</b>-\>outbuf.  If <b>direct</b> is true, we're making a
 * non-anonymized connection to the dirport.
 */
static void
directory_send_command(dir_connection_t *conn,
                       const int direct,
                       const directory_request_t *req)
{
  tor_assert(req);
  const int purpose = req->dir_purpose;
  const char *resource = req->resource;
  const char *payload = req->payload;
  const size_t payload_len = req->payload_len;
  const time_t if_modified_since = req->if_modified_since;
  const int anonymized_connection = dirind_is_anon(req->indirection);

  char proxystring[256];
  char hoststring[128];
  /* NEEDS to be the same size hoststring.
   Will be decorated with brackets around it if it is ipv6. */
  char decorated_address[128];
  smartlist_t *headers = smartlist_new();
  char *url;
  char *accept_encoding;
  size_t url_len;
  char request[8192];
  size_t request_len, total_request_len = 0;
  const char *httpcommand = NULL;

  tor_assert(conn);
  tor_assert(conn->base_.type == CONN_TYPE_DIR);

  tor_free(conn->requested_resource);
  if (resource)
    conn->requested_resource = tor_strdup(resource);

  /* decorate the ip address if it is ipv6 */
  if (strchr(conn->base_.address, ':')) {
    copy_ipv6_address(decorated_address, conn->base_.address,
                      sizeof(decorated_address), 1);
  } else {
    strlcpy(decorated_address, conn->base_.address, sizeof(decorated_address));
  }

  /* come up with a string for which Host: we want */
  if (conn->base_.port == 80) {
    strlcpy(hoststring, decorated_address, sizeof(hoststring));
  } else {
    tor_snprintf(hoststring, sizeof(hoststring), "%s:%d",
                 decorated_address, conn->base_.port);
  }

  /* Format if-modified-since */
  if (if_modified_since) {
    char b[RFC1123_TIME_LEN+1];
    format_rfc1123_time(b, if_modified_since);
    smartlist_add_asprintf(headers, "If-Modified-Since: %s\r\n", b);
  }

  /* come up with some proxy lines, if we're using one. */
  if (direct && get_options()->HTTPProxy) {
    char *base64_authenticator=NULL;
    const char *authenticator = get_options()->HTTPProxyAuthenticator;

    tor_snprintf(proxystring, sizeof(proxystring),"http://%s", hoststring);
    if (authenticator) {
      base64_authenticator = alloc_http_authenticator(authenticator);
      if (!base64_authenticator)
        log_warn(LD_BUG, "Encoding http authenticator failed");
    }
    if (base64_authenticator) {
      smartlist_add_asprintf(headers,
                   "Proxy-Authorization: Basic %s\r\n",
                   base64_authenticator);
      tor_free(base64_authenticator);
    }
  } else {
    proxystring[0] = 0;
  }

  if (! anonymized_connection) {
    /* Add Accept-Encoding. */
    accept_encoding = accept_encoding_header();
    smartlist_add_asprintf(headers, "Accept-Encoding: %s\r\n",
                           accept_encoding);
    tor_free(accept_encoding);
  }

  /* Add additional headers, if any */
  {
    config_line_t *h;
    for (h = req->additional_headers; h; h = h->next) {
      smartlist_add_asprintf(headers, "%s%s\r\n", h->key, h->value);
    }
  }

  switch (purpose) {
    case DIR_PURPOSE_FETCH_CONSENSUS:
      /* resource is optional.  If present, it's a flavor name */
      tor_assert(!payload);
      httpcommand = "GET";
      url = directory_get_consensus_url(resource);
      log_info(LD_DIR, "Downloading consensus from %s using %s",
               hoststring, url);
      break;
    case DIR_PURPOSE_FETCH_CERTIFICATE:
      tor_assert(resource);
      tor_assert(!payload);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/keys/%s", resource);
      break;
    case DIR_PURPOSE_FETCH_STATUS_VOTE:
      tor_assert(resource);
      tor_assert(!payload);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/status-vote/next/%s.z", resource);
      break;
    case DIR_PURPOSE_FETCH_DETACHED_SIGNATURES:
      tor_assert(!resource);
      tor_assert(!payload);
      httpcommand = "GET";
      url = tor_strdup("/tor/status-vote/next/consensus-signatures.z");
      break;
    case DIR_PURPOSE_FETCH_SERVERDESC:
      tor_assert(resource);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/server/%s", resource);
      break;
    case DIR_PURPOSE_FETCH_EXTRAINFO:
      tor_assert(resource);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/extra/%s", resource);
      break;
    case DIR_PURPOSE_FETCH_MICRODESC:
      tor_assert(resource);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/micro/%s", resource);
      break;
    case DIR_PURPOSE_UPLOAD_DIR: {
      const char *why = router_get_descriptor_gen_reason();
      tor_assert(!resource);
      tor_assert(payload);
      httpcommand = "POST";
      url = tor_strdup("/tor/");
      if (why) {
        smartlist_add_asprintf(headers, "X-Desc-Gen-Reason: %s\r\n", why);
      }
      break;
    }
    case DIR_PURPOSE_UPLOAD_VOTE:
      tor_assert(!resource);
      tor_assert(payload);
      httpcommand = "POST";
      url = tor_strdup("/tor/post/vote");
      break;
    case DIR_PURPOSE_UPLOAD_SIGNATURES:
      tor_assert(!resource);
      tor_assert(payload);
      httpcommand = "POST";
      url = tor_strdup("/tor/post/consensus-signature");
      break;
    case DIR_PURPOSE_FETCH_RENDDESC_V2:
      tor_assert(resource);
      tor_assert(strlen(resource) <= REND_DESC_ID_V2_LEN_BASE32);
      tor_assert(!payload);
      httpcommand = "GET";
      tor_asprintf(&url, "/tor/rendezvous2/%s", resource);
      break;
    case DIR_PURPOSE_UPLOAD_RENDDESC_V2:
      tor_assert(!resource);
      tor_assert(payload);
      httpcommand = "POST";
      url = tor_strdup("/tor/rendezvous2/publish");
      break;
    default:
      tor_assert(0);
      return;
  }

  /* warn in the non-tunneled case */
  if (direct && (strlen(proxystring) + strlen(url) >= 4096)) {
    log_warn(LD_BUG,
             "Squid does not like URLs longer than 4095 bytes, and this "
             "one is %d bytes long: %s%s",
             (int)(strlen(proxystring) + strlen(url)), proxystring, url);
  }

  tor_snprintf(request, sizeof(request), "%s %s", httpcommand, proxystring);

  request_len = strlen(request);
  total_request_len += request_len;
  connection_write_to_buf(request, request_len, TO_CONN(conn));

  url_len = strlen(url);
  total_request_len += url_len;
  connection_write_to_buf(url, url_len, TO_CONN(conn));
  tor_free(url);

  if (!strcmp(httpcommand, "POST") || payload) {
    smartlist_add_asprintf(headers, "Content-Length: %lu\r\n",
                 payload ? (unsigned long)payload_len : 0);
  }

  {
    char *header = smartlist_join_strings(headers, "", 0, NULL);
    tor_snprintf(request, sizeof(request), " HTTP/1.0\r\nHost: %s\r\n%s\r\n",
                 hoststring, header);
    tor_free(header);
  }

  request_len = strlen(request);
  total_request_len += request_len;
  connection_write_to_buf(request, request_len, TO_CONN(conn));

  if (payload) {
    /* then send the payload afterwards too */
    connection_write_to_buf(payload, payload_len, TO_CONN(conn));
    total_request_len += payload_len;
  }

  SMARTLIST_FOREACH(headers, char *, h, tor_free(h));
  smartlist_free(headers);

  log_debug(LD_DIR,
            "Sent request to directory server '%s:%d': "
            "(purpose: %d, request size: " U64_FORMAT ", "
            "payload size: " U64_FORMAT ")",
            conn->base_.address, conn->base_.port,
            conn->base_.purpose,
            U64_PRINTF_ARG(total_request_len),
            U64_PRINTF_ARG(payload ? payload_len : 0));
}

/** Parse an HTTP request string <b>headers</b> of the form
 * \verbatim
 * "\%s [http[s]://]\%s HTTP/1..."
 * \endverbatim
 * If it's well-formed, strdup the second \%s into *<b>url</b>, and
 * nul-terminate it. If the url doesn't start with "/tor/", rewrite it
 * so it does. Return 0.
 * Otherwise, return -1.
 */
STATIC int
parse_http_url(const char *headers, char **url)
{
  char *s, *start, *tmp;

  s = (char *)eat_whitespace_no_nl(headers);
  if (!*s) return -1;
  s = (char *)find_whitespace(s); /* get past GET/POST */
  if (!*s) return -1;
  s = (char *)eat_whitespace_no_nl(s);
  if (!*s) return -1;
  start = s; /* this is it, assuming it's valid */
  s = (char *)find_whitespace(start);
  if (!*s) return -1;

  /* tolerate the http[s] proxy style of putting the hostname in the url */
  if (s-start >= 4 && !strcmpstart(start,"http")) {
    tmp = start + 4;
    if (*tmp == 's')
      tmp++;
    if (s-tmp >= 3 && !strcmpstart(tmp,"://")) {
      tmp = strchr(tmp+3, '/');
      if (tmp && tmp < s) {
        log_debug(LD_DIR,"Skipping over 'http[s]://hostname/' string");
        start = tmp;
      }
    }
  }

  /* Check if the header is well formed (next sequence
   * should be HTTP/1.X\r\n). Assumes we're supporting 1.0? */
  {
    unsigned minor_ver;
    char ch;
    char *e = (char *)eat_whitespace_no_nl(s);
    if (2 != tor_sscanf(e, "HTTP/1.%u%c", &minor_ver, &ch)) {
      return -1;
    }
    if (ch != '\r')
      return -1;
  }

  if (s-start < 5 || strcmpstart(start,"/tor/")) { /* need to rewrite it */
    *url = tor_malloc(s - start + 5);
    strlcpy(*url,"/tor", s-start+5);
    strlcat((*url)+4, start, s-start+1);
  } else {
    *url = tor_strndup(start, s-start);
  }
  return 0;
}

/** Return a copy of the first HTTP header in <b>headers</b> whose key is
 * <b>which</b>.  The key should be given with a terminating colon and space;
 * this function copies everything after, up to but not including the
 * following \\r\\n. */
static char *
http_get_header(const char *headers, const char *which)
{
  const char *cp = headers;
  while (cp) {
    if (!strcasecmpstart(cp, which)) {
      char *eos;
      cp += strlen(which);
      if ((eos = strchr(cp,'\r')))
        return tor_strndup(cp, eos-cp);
      else
        return tor_strdup(cp);
    }
    cp = strchr(cp, '\n');
    if (cp)
      ++cp;
  }
  return NULL;
}

/** If <b>headers</b> indicates that a proxy was involved, then rewrite
 * <b>conn</b>-\>address to describe our best guess of the address that
 * originated this HTTP request. */
static void
http_set_address_origin(const char *headers, connection_t *conn)
{
  char *fwd;

  fwd = http_get_header(headers, "Forwarded-For: ");
  if (!fwd)
    fwd = http_get_header(headers, "X-Forwarded-For: ");
  if (fwd) {
    tor_addr_t toraddr;
    if (tor_addr_parse(&toraddr,fwd) == -1 ||
        tor_addr_is_internal(&toraddr,0)) {
      log_debug(LD_DIR, "Ignoring local/internal IP %s", escaped(fwd));
      tor_free(fwd);
      return;
    }

    tor_free(conn->address);
    conn->address = tor_strdup(fwd);
    tor_free(fwd);
  }
}

/** Parse an HTTP response string <b>headers</b> of the form
 * \verbatim
 * "HTTP/1.\%d \%d\%s\r\n...".
 * \endverbatim
 *
 * If it's well-formed, assign the status code to *<b>code</b> and
 * return 0.  Otherwise, return -1.
 *
 * On success: If <b>date</b> is provided, set *date to the Date
 * header in the http headers, or 0 if no such header is found.  If
 * <b>compression</b> is provided, set *<b>compression</b> to the
 * compression method given in the Content-Encoding header, or 0 if no
 * such header is found, or -1 if the value of the header is not
 * recognized.  If <b>reason</b> is provided, strdup the reason string
 * into it.
 */
int
parse_http_response(const char *headers, int *code, time_t *date,
                    compress_method_t *compression, char **reason)
{
  unsigned n1, n2;
  char datestr[RFC1123_TIME_LEN+1];
  smartlist_t *parsed_headers;
  tor_assert(headers);
  tor_assert(code);

  while (TOR_ISSPACE(*headers)) headers++; /* tolerate leading whitespace */

  if (tor_sscanf(headers, "HTTP/1.%u %u", &n1, &n2) < 2 ||
      (n1 != 0 && n1 != 1) ||
      (n2 < 100 || n2 >= 600)) {
    log_warn(LD_HTTP,"Failed to parse header %s",escaped(headers));
    return -1;
  }
  *code = n2;

  parsed_headers = smartlist_new();
  smartlist_split_string(parsed_headers, headers, "\n",
                         SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, -1);
  if (reason) {
    smartlist_t *status_line_elements = smartlist_new();
    tor_assert(smartlist_len(parsed_headers));
    smartlist_split_string(status_line_elements,
                           smartlist_get(parsed_headers, 0),
                           " ", SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, 3);
    tor_assert(smartlist_len(status_line_elements) <= 3);
    if (smartlist_len(status_line_elements) == 3) {
      *reason = smartlist_get(status_line_elements, 2);
      smartlist_set(status_line_elements, 2, NULL); /* Prevent free */
    }
    SMARTLIST_FOREACH(status_line_elements, char *, cp, tor_free(cp));
    smartlist_free(status_line_elements);
  }
  if (date) {
    *date = 0;
    SMARTLIST_FOREACH(parsed_headers, const char *, s,
      if (!strcmpstart(s, "Date: ")) {
        strlcpy(datestr, s+6, sizeof(datestr));
        /* This will do nothing on failure, so we don't need to check
           the result.   We shouldn't warn, since there are many other valid
           date formats besides the one we use. */
        parse_rfc1123_time(datestr, date);
        break;
      });
  }
  if (compression) {
    const char *enc = NULL;
    SMARTLIST_FOREACH(parsed_headers, const char *, s,
      if (!strcmpstart(s, "Content-Encoding: ")) {
        enc = s+18; break;
      });

    if (enc == NULL)
      *compression = NO_METHOD;
    else {
      *compression = compression_method_get_by_name(enc);

      if (*compression == UNKNOWN_METHOD)
        log_info(LD_HTTP, "Unrecognized content encoding: %s. Trying to deal.",
                 escaped(enc));
    }
  }
  SMARTLIST_FOREACH(parsed_headers, char *, s, tor_free(s));
  smartlist_free(parsed_headers);

  return 0;
}

/** Return true iff <b>body</b> doesn't start with a plausible router or
 * network-status or microdescriptor opening.  This is a sign of possible
 * compression. */
static int
body_is_plausible(const char *body, size_t len, int purpose)
{
  int i;
  if (len == 0)
    return 1; /* empty bodies don't need decompression */
  if (len < 32)
    return 0;
  if (purpose == DIR_PURPOSE_FETCH_MICRODESC) {
    return (!strcmpstart(body,"onion-key"));
  }

  if (!strcmpstart(body,"router") ||
      !strcmpstart(body,"network-status"))
    return 1;
  for (i=0;i<32;++i) {
    if (!TOR_ISPRINT(body[i]) && !TOR_ISSPACE(body[i]))
      return 0;
  }

  return 1;
}

/** Called when we've just fetched a bunch of router descriptors in
 * <b>body</b>.  The list <b>which</b>, if present, holds digests for
 * descriptors we requested: descriptor digests if <b>descriptor_digests</b>
 * is true, or identity digests otherwise.  Parse the descriptors, validate
 * them, and annotate them as having purpose <b>purpose</b> and as having been
 * downloaded from <b>source</b>.
 *
 * Return the number of routers actually added. */
static int
load_downloaded_routers(const char *body, smartlist_t *which,
                        int descriptor_digests,
                        int router_purpose,
                        const char *source)
{
  char buf[256];
  char time_buf[ISO_TIME_LEN+1];
  int added = 0;
  int general = router_purpose == ROUTER_PURPOSE_GENERAL;
  format_iso_time(time_buf, time(NULL));
  tor_assert(source);

  if (tor_snprintf(buf, sizeof(buf),
                   "@downloaded-at %s\n"
                   "@source %s\n"
                   "%s%s%s", time_buf, escaped(source),
                   !general ? "@purpose " : "",
                   !general ? router_purpose_to_string(router_purpose) : "",
                   !general ? "\n" : "")<0)
    return added;

  added = router_load_routers_from_string(body, NULL, SAVED_NOWHERE, which,
                                  descriptor_digests, buf);
  if (added && general)
    control_event_bootstrap(BOOTSTRAP_STATUS_LOADING_DESCRIPTORS,
                            count_loading_descriptors_progress());
  return added;
}

/** A structure to hold arguments passed into each directory response
 * handler */
typedef struct response_handler_args_t {
  int status_code;
  const char *reason;
  const char *body;
  size_t body_len;
  const char *headers;
} response_handler_args_t;

static int handle_response_fetch_consensus(dir_connection_t *,
                                           const response_handler_args_t *);
static int handle_response_fetch_certificate(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_fetch_status_vote(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_fetch_detached_signatures(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_fetch_desc(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_fetch_microdesc(dir_connection_t *,
                                           const response_handler_args_t *);
static int handle_response_upload_dir(dir_connection_t *,
                                      const response_handler_args_t *);
static int handle_response_upload_vote(dir_connection_t *,
                                       const response_handler_args_t *);
static int handle_response_upload_signatures(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_fetch_renddesc_v2(dir_connection_t *,
                                             const response_handler_args_t *);
static int handle_response_upload_renddesc_v2(dir_connection_t *,
                                              const response_handler_args_t *);

/** We are a client, and we've finished reading the server's
 * response. Parse it and act appropriately.
 *
 * If we're still happy with using this directory server in the future, return
 * 0. Otherwise return -1; and the caller should consider trying the request
 * again.
 *
 * The caller will take care of marking the connection for close.
 */
static int
connection_dir_client_reached_eof(dir_connection_t *conn)
{
  char *body = NULL;
  char *headers = NULL;
  char *reason = NULL;
  size_t body_len = 0;
  int status_code;
  time_t date_header = 0;
  long apparent_skew;
  compress_method_t compression;
  int plausible;
  int skewed = 0;
  int rv;
  int allow_partial = (conn->base_.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
                       conn->base_.purpose == DIR_PURPOSE_FETCH_EXTRAINFO ||
                       conn->base_.purpose == DIR_PURPOSE_FETCH_MICRODESC);
  size_t received_bytes;
  const int anonymized_connection =
    purpose_needs_anonymity(conn->base_.purpose,
                            conn->router_purpose,
                            conn->requested_resource);

  received_bytes = connection_get_inbuf_len(TO_CONN(conn));

  switch (connection_fetch_from_buf_http(TO_CONN(conn),
                              &headers, MAX_HEADERS_SIZE,
                              &body, &body_len, MAX_DIR_DL_SIZE,
                              allow_partial)) {
    case -1: /* overflow */
      log_warn(LD_PROTOCOL,
               "'fetch' response too large (server '%s:%d'). Closing.",
               conn->base_.address, conn->base_.port);
      return -1;
    case 0:
      log_info(LD_HTTP,
               "'fetch' response not all here, but we're at eof. Closing.");
      return -1;
    /* case 1, fall through */
  }

  if (parse_http_response(headers, &status_code, &date_header,
                          &compression, &reason) < 0) {
    log_warn(LD_HTTP,"Unparseable headers (server '%s:%d'). Closing.",
             conn->base_.address, conn->base_.port);

    rv = -1;
    goto done;
  }
  if (!reason) reason = tor_strdup("[no reason given]");

  tor_log(LOG_DEBUG, LD_DIR,
            "Received response from directory server '%s:%d': %d %s "
            "(purpose: %d, response size: " U64_FORMAT
#ifdef MEASUREMENTS_21206
            ", data cells received: %d, data cells sent: %d"
#endif
            ", compression: %d)",
            conn->base_.address, conn->base_.port, status_code,
            escaped(reason), conn->base_.purpose,
            U64_PRINTF_ARG(received_bytes),
#ifdef MEASUREMENTS_21206
            conn->data_cells_received, conn->data_cells_sent,
#endif
            compression);

  if (conn->guard_state) {
    /* we count the connection as successful once we can read from it.  We do
     * not, however, delay use of the circuit here, since it's just for a
     * one-hop directory request. */
    /* XXXXprop271 note that this will not do the right thing for other
     * waiting circuits that would be triggered by this circuit becoming
     * complete/usable. But that's ok, I think.
     */
    entry_guard_succeeded(&conn->guard_state);
    circuit_guard_state_free(conn->guard_state);
    conn->guard_state = NULL;
  }

  /* now check if it's got any hints for us about our IP address. */
  if (conn->dirconn_direct) {
    char *guess = http_get_header(headers, X_ADDRESS_HEADER);
    if (guess) {
      router_new_address_suggestion(guess, conn);
      tor_free(guess);
    }
  }

  if (date_header > 0) {
    /* The date header was written very soon after we sent our request,
     * so compute the skew as the difference between sending the request
     * and the date header.  (We used to check now-date_header, but that's
     * inaccurate if we spend a lot of time downloading.)
     */
    apparent_skew = conn->base_.timestamp_lastwritten - date_header;
    if (labs(apparent_skew)>ALLOW_DIRECTORY_TIME_SKEW) {
      int trusted = router_digest_is_trusted_dir(conn->identity_digest);
      clock_skew_warning(TO_CONN(conn), apparent_skew, trusted, LD_HTTP,
                         "directory", "DIRSERV");
      skewed = 1; /* don't check the recommended-versions line */
    } else {
      log_debug(LD_HTTP, "Time on received directory is within tolerance; "
                "we are %ld seconds skewed.  (That's okay.)", apparent_skew);
    }
  }
  (void) skewed; /* skewed isn't used yet. */

  if (status_code == 503) {
    routerstatus_t *rs;
    dir_server_t *ds;
    const char *id_digest = conn->identity_digest;
    log_info(LD_DIR,"Received http status code %d (%s) from server "
             "'%s:%d'. I'll try again soon.",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    time_t now = approx_time();
    if ((rs = router_get_mutable_consensus_status_by_id(id_digest)))
      rs->last_dir_503_at = now;
    if ((ds = router_get_fallback_dirserver_by_digest(id_digest)))
      ds->fake_status.last_dir_503_at = now;

    rv = -1;
    goto done;
  }

  plausible = body_is_plausible(body, body_len, conn->base_.purpose);
  if (compression != NO_METHOD || !plausible) {
    char *new_body = NULL;
    size_t new_len = 0;
    compress_method_t guessed = detect_compression_method(body, body_len);
    if (compression == UNKNOWN_METHOD || guessed != compression) {
      /* Tell the user if we don't believe what we're told about compression.*/
      const char *description1, *description2;

      description1 = compression_method_get_human_name(compression);

      if (BUG(description1 == NULL))
        description1 = compression_method_get_human_name(UNKNOWN_METHOD);

      if (guessed == UNKNOWN_METHOD && !plausible)
        description2 = "confusing binary junk";
      else
        description2 = compression_method_get_human_name(guessed);

      log_info(LD_HTTP, "HTTP body from server '%s:%d' was labeled as %s, "
               "but it seems to be %s.%s",
               conn->base_.address, conn->base_.port, description1,
               description2,
               (compression>0 && guessed>0)?"  Trying both.":"");
    }

    /* Try declared compression first if we can.
     * tor_compress_supports_method() also returns true for NO_METHOD.
     * Ensure that the server is not sending us data compressed using a
     * compression method that is not allowed for anonymous connections. */
    if (anonymized_connection &&
        ! allowed_anonymous_connection_compression_method(compression)) {
      warn_disallowed_anonymous_compression_method(compression);
      rv = -1;
      goto done;
    }

    if (tor_compress_supports_method(compression))
      tor_uncompress(&new_body, &new_len, body, body_len, compression,
                     !allow_partial, LOG_PROTOCOL_WARN);

    /* Okay, if that didn't work, and we think that it was compressed
     * differently, try that. */
    if (anonymized_connection &&
        ! allowed_anonymous_connection_compression_method(guessed)) {
      warn_disallowed_anonymous_compression_method(guessed);
      rv = -1;
      goto done;
    }

    if (!new_body && tor_compress_supports_method(guessed) &&
        compression != guessed)
      tor_uncompress(&new_body, &new_len, body, body_len, guessed,
                     !allow_partial, LOG_PROTOCOL_WARN);
    /* If we're pretty sure that we have a compressed directory, and
     * we didn't manage to uncompress it, then warn and bail. */
    if (!plausible && !new_body) {
      log_fn(LOG_PROTOCOL_WARN, LD_HTTP,
             "Unable to decompress HTTP body (server '%s:%d').",
             conn->base_.address, conn->base_.port);
      rv = -1;
      goto done;
    }
    if (new_body) {
      tor_free(body);
      body = new_body;
      body_len = new_len;
    }
  }

  response_handler_args_t args;
  memset(&args, 0, sizeof(args));
  args.status_code = status_code;
  args.reason = reason;
  args.body = body;
  args.body_len = body_len;
  args.headers = headers;

  switch (conn->base_.purpose) {
    case DIR_PURPOSE_FETCH_CONSENSUS:
      rv = handle_response_fetch_consensus(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_CERTIFICATE:
      rv = handle_response_fetch_certificate(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_STATUS_VOTE:
      rv = handle_response_fetch_status_vote(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_DETACHED_SIGNATURES:
      rv = handle_response_fetch_detached_signatures(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_SERVERDESC:
    case DIR_PURPOSE_FETCH_EXTRAINFO:
      rv = handle_response_fetch_desc(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_MICRODESC:
      rv = handle_response_fetch_microdesc(conn, &args);
      break;
    case DIR_PURPOSE_FETCH_RENDDESC_V2:
      rv = handle_response_fetch_renddesc_v2(conn, &args);
      break;
    case DIR_PURPOSE_UPLOAD_DIR:
      rv = handle_response_upload_dir(conn, &args);
      break;
    case DIR_PURPOSE_UPLOAD_SIGNATURES:
      rv = handle_response_upload_signatures(conn, &args);
      break;
    case DIR_PURPOSE_UPLOAD_VOTE:
      rv = handle_response_upload_vote(conn, &args);
      break;
    case DIR_PURPOSE_UPLOAD_RENDDESC_V2:
      rv = handle_response_upload_renddesc_v2(conn, &args);
      break;
    default:
      tor_assert_nonfatal_unreached();
      rv = -1;
      break;
  }

 done:
  tor_free(body);
  tor_free(headers);
  tor_free(reason);
  return rv;
}

/**
 * Handler function: processes a response to a request for a networkstatus
 * consensus document by checking the consensus, storing it, and marking
 * router requests as reachable.
 **/
static int
handle_response_fetch_consensus(dir_connection_t *conn,
                                const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_CONSENSUS);
  const int status_code = args->status_code;
  const char *body = args->body;
  const size_t body_len = args->body_len;
  const char *reason = args->reason;
  const time_t now = approx_time();

  const char *consensus;
  char *new_consensus = NULL;
  const char *sourcename;

  int r;
  const char *flavname = conn->requested_resource;
  if (status_code != 200) {
    int severity = (status_code == 304) ? LOG_INFO : LOG_WARN;
    tor_log(severity, LD_DIR,
            "Received http status code %d (%s) from server "
            "'%s:%d' while fetching consensus directory.",
            status_code, escaped(reason), conn->base_.address,
            conn->base_.port);
    networkstatus_consensus_download_failed(status_code, flavname);
    return -1;
  }

  if (looks_like_a_consensus_diff(body, body_len)) {
    /* First find our previous consensus. Maybe it's in ram, maybe not. */
    cached_dir_t *cd = dirserv_get_consensus(flavname);
    const char *consensus_body;
    char *owned_consensus = NULL;
    if (cd) {
      consensus_body = cd->dir;
    } else {
      owned_consensus = networkstatus_read_cached_consensus(flavname);
      consensus_body = owned_consensus;
    }
    if (!consensus_body) {
      log_warn(LD_DIR, "Received a consensus diff, but we can't find "
               "any %s-flavored consensus in our current cache.",flavname);
      networkstatus_consensus_download_failed(0, flavname);
      // XXXX if this happens too much, see below
      return -1;
    }

    new_consensus = consensus_diff_apply(consensus_body, body);
    tor_free(owned_consensus);
    if (new_consensus == NULL) {
      log_warn(LD_DIR, "Could not apply consensus diff received from server "
               "'%s:%d'", conn->base_.address, conn->base_.port);
      // XXXX If this happens too many times, we should maybe not use
      // XXXX this directory for diffs any more?
      networkstatus_consensus_download_failed(0, flavname);
      return -1;
    }
    log_info(LD_DIR, "Applied consensus diff (size %d) from server "
             "'%s:%d', resulting in a new consensus document (size %d).",
             (int)body_len, conn->base_.address, conn->base_.port,
             (int)strlen(new_consensus));
    consensus = new_consensus;
    sourcename = "generated based on a diff";
  } else {
    log_info(LD_DIR,"Received consensus directory (body size %d) from server "
             "'%s:%d'", (int)body_len, conn->base_.address, conn->base_.port);
    consensus = body;
    sourcename = "downloaded";
  }

  if ((r=networkstatus_set_current_consensus(consensus, flavname, 0,
                                             conn->identity_digest))<0) {
    log_fn(r<-1?LOG_WARN:LOG_INFO, LD_DIR,
           "Unable to load %s consensus directory %s from "
           "server '%s:%d'. I'll try again soon.",
           flavname, sourcename, conn->base_.address, conn->base_.port);
    networkstatus_consensus_download_failed(0, flavname);
    tor_free(new_consensus);
    return -1;
  }

  /* If we launched other fetches for this consensus, cancel them. */
  connection_dir_close_consensus_fetches(conn, flavname);

  /* launches router downloads as needed */
  routers_update_all_from_networkstatus(now, 3);
  update_microdescs_from_networkstatus(now);
  update_microdesc_downloads(now);
  directory_info_has_arrived(now, 0, 0);
  if (authdir_mode_v3(get_options())) {
    sr_act_post_consensus(
                     networkstatus_get_latest_consensus_by_flavor(FLAV_NS));
  }
  log_info(LD_DIR, "Successfully loaded consensus.");

  tor_free(new_consensus);
  return 0;
}

/**
 * Handler function: processes a response to a request for one or more
 * authority certificates
 **/
static int
handle_response_fetch_certificate(dir_connection_t *conn,
                                  const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_CERTIFICATE);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

  if (status_code != 200) {
    log_warn(LD_DIR,
             "Received http status code %d (%s) from server "
             "'%s:%d' while fetching \"/tor/keys/%s\".",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port, conn->requested_resource);
    connection_dir_download_cert_failed(conn, status_code);
    return -1;
  }
  log_info(LD_DIR,"Received authority certificates (body size %d) from "
           "server '%s:%d'",
           (int)body_len, conn->base_.address, conn->base_.port);

  /*
   * Tell trusted_dirs_load_certs_from_string() whether it was by fp
   * or fp-sk pair.
   */
  int src_code = -1;
  if (!strcmpstart(conn->requested_resource, "fp/")) {
    src_code = TRUSTED_DIRS_CERTS_SRC_DL_BY_ID_DIGEST;
  } else if (!strcmpstart(conn->requested_resource, "fp-sk/")) {
    src_code = TRUSTED_DIRS_CERTS_SRC_DL_BY_ID_SK_DIGEST;
  }

  if (src_code != -1) {
    if (trusted_dirs_load_certs_from_string(body, src_code, 1,
                                            conn->identity_digest)<0) {
      log_warn(LD_DIR, "Unable to parse fetched certificates");
      /* if we fetched more than one and only some failed, the successful
       * ones got flushed to disk so it's safe to call this on them */
      connection_dir_download_cert_failed(conn, status_code);
    } else {
      time_t now = approx_time();
      directory_info_has_arrived(now, 0, 0);
      log_info(LD_DIR, "Successfully loaded certificates from fetch.");
    }
  } else {
    log_warn(LD_DIR,
             "Couldn't figure out what to do with fetched certificates for "
             "unknown resource %s",
             conn->requested_resource);
    connection_dir_download_cert_failed(conn, status_code);
  }
  return 0;
}

/**
 * Handler function: processes a response to a request for an authority's
 * current networkstatus vote.
 **/
static int
handle_response_fetch_status_vote(dir_connection_t *conn,
                                  const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_STATUS_VOTE);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

  const char *msg;
  int st;
  log_info(LD_DIR,"Got votes (body size %d) from server %s:%d",
           (int)body_len, conn->base_.address, conn->base_.port);
  if (status_code != 200) {
    log_warn(LD_DIR,
             "Received http status code %d (%s) from server "
             "'%s:%d' while fetching \"/tor/status-vote/next/%s.z\".",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port, conn->requested_resource);
    return -1;
  }
  dirvote_add_vote(body, &msg, &st);
  if (st > 299) {
    log_warn(LD_DIR, "Error adding retrieved vote: %s", msg);
  } else {
    log_info(LD_DIR, "Added vote(s) successfully [msg: %s]", msg);
  }

  return 0;
}

/**
 * Handler function: processes a response to a request for the signatures
 * that an authority knows about on a given consensus.
 **/
static int
handle_response_fetch_detached_signatures(dir_connection_t *conn,
                                          const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_DETACHED_SIGNATURES);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

  const char *msg = NULL;
  log_info(LD_DIR,"Got detached signatures (body size %d) from server %s:%d",
           (int)body_len, conn->base_.address, conn->base_.port);
  if (status_code != 200) {
    log_warn(LD_DIR,
        "Received http status code %d (%s) from server '%s:%d' while fetching "
        "\"/tor/status-vote/next/consensus-signatures.z\".",
        status_code, escaped(reason), conn->base_.address,
        conn->base_.port);
    return -1;
  }
  if (dirvote_add_signatures(body, conn->base_.address, &msg)<0) {
    log_warn(LD_DIR, "Problem adding detached signatures from %s:%d: %s",
             conn->base_.address, conn->base_.port, msg?msg:"???");
  }

  return 0;
}

/**
 * Handler function: processes a response to a request for a group of server
 * descriptors or an extrainfo documents.
 **/
static int
handle_response_fetch_desc(dir_connection_t *conn,
                           const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_SERVERDESC ||
             conn->base_.purpose == DIR_PURPOSE_FETCH_EXTRAINFO);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

  int was_ei = conn->base_.purpose == DIR_PURPOSE_FETCH_EXTRAINFO;
  smartlist_t *which = NULL;
  int n_asked_for = 0;
  int descriptor_digests = conn->requested_resource &&
    !strcmpstart(conn->requested_resource,"d/");
  log_info(LD_DIR,"Received %s (body size %d) from server '%s:%d'",
           was_ei ? "extra server info" : "server info",
           (int)body_len, conn->base_.address, conn->base_.port);
  if (conn->requested_resource &&
      (!strcmpstart(conn->requested_resource,"d/") ||
       !strcmpstart(conn->requested_resource,"fp/"))) {
    which = smartlist_new();
    dir_split_resource_into_fingerprints(conn->requested_resource +
                                         (descriptor_digests ? 2 : 3),
                                         which, NULL, 0);
    n_asked_for = smartlist_len(which);
  }
  if (status_code != 200) {
    int dir_okay = status_code == 404 ||
      (status_code == 400 && !strcmp(reason, "Servers unavailable."));
    /* 404 means that it didn't have them; no big deal.
     * Older (pre-0.1.1.8) servers said 400 Servers unavailable instead. */
    log_fn(dir_okay ? LOG_INFO : LOG_WARN, LD_DIR,
           "Received http status code %d (%s) from server '%s:%d' "
           "while fetching \"/tor/server/%s\". I'll try again soon.",
           status_code, escaped(reason), conn->base_.address,
           conn->base_.port, conn->requested_resource);
    if (!which) {
      connection_dir_download_routerdesc_failed(conn);
    } else {
      dir_routerdesc_download_failed(which, status_code,
                                     conn->router_purpose,
                                     was_ei, descriptor_digests);
      SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
      smartlist_free(which);
    }
    return dir_okay ? 0 : -1;
  }
  /* Learn the routers, assuming we requested by fingerprint or "all"
   * or "authority".
   *
   * We use "authority" to fetch our own descriptor for
   * testing, and to fetch bridge descriptors for bootstrapping. Ignore
   * the output of "authority" requests unless we are using bridges,
   * since otherwise they'll be the response from reachability tests,
   * and we don't really want to add that to our routerlist. */
  if (which || (conn->requested_resource &&
                (!strcmpstart(conn->requested_resource, "all") ||
                 (!strcmpstart(conn->requested_resource, "authority") &&
                  get_options()->UseBridges)))) {
    /* as we learn from them, we remove them from 'which' */
    if (was_ei) {
      router_load_extrainfo_from_string(body, NULL, SAVED_NOWHERE, which,
                                        descriptor_digests);
    } else {
      //router_load_routers_from_string(body, NULL, SAVED_NOWHERE, which,
      //                       descriptor_digests, conn->router_purpose);
      if (load_downloaded_routers(body, which, descriptor_digests,
                                  conn->router_purpose,
                                  conn->base_.address)) {
        time_t now = approx_time();
        directory_info_has_arrived(now, 0, 0);
      }
    }
  }
  if (which) { /* mark remaining ones as failed */
    log_info(LD_DIR, "Received %d/%d %s requested from %s:%d",
             n_asked_for-smartlist_len(which), n_asked_for,
             was_ei ? "extra-info documents" : "router descriptors",
             conn->base_.address, (int)conn->base_.port);
    if (smartlist_len(which)) {
      dir_routerdesc_download_failed(which, status_code,
                                     conn->router_purpose,
                                     was_ei, descriptor_digests);
    }
    SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
    smartlist_free(which);
  }
  if (directory_conn_is_self_reachability_test(conn))
    router_dirport_found_reachable();

  return 0;
}

/**
 * Handler function: processes a response to a request for a group of
 * microdescriptors
 **/
static int
handle_response_fetch_microdesc(dir_connection_t *conn,
                                const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_MICRODESC);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

  smartlist_t *which = NULL;
  log_info(LD_DIR,"Received answer to microdescriptor request (status %d, "
           "body size %d) from server '%s:%d'",
           status_code, (int)body_len, conn->base_.address,
           conn->base_.port);
  tor_assert(conn->requested_resource &&
             !strcmpstart(conn->requested_resource, "d/"));
  which = smartlist_new();
  dir_split_resource_into_fingerprints(conn->requested_resource+2,
                                       which, NULL,
                                       DSR_DIGEST256|DSR_BASE64);
  if (status_code != 200) {
    log_info(LD_DIR, "Received status code %d (%s) from server "
             "'%s:%d' while fetching \"/tor/micro/%s\".  I'll try again "
             "soon.",
             status_code, escaped(reason), conn->base_.address,
             (int)conn->base_.port, conn->requested_resource);
    dir_microdesc_download_failed(which, status_code);
    SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
    smartlist_free(which);
    return 0;
  } else {
    smartlist_t *mds;
    time_t now = approx_time();
    mds = microdescs_add_to_cache(get_microdesc_cache(),
                                  body, body+body_len, SAVED_NOWHERE, 0,
                                  now, which);
    if (smartlist_len(which)) {
      /* Mark remaining ones as failed. */
      dir_microdesc_download_failed(which, status_code);
    }
    if (mds && smartlist_len(mds)) {
      control_event_bootstrap(BOOTSTRAP_STATUS_LOADING_DESCRIPTORS,
                              count_loading_descriptors_progress());
      directory_info_has_arrived(now, 0, 1);
    }
    SMARTLIST_FOREACH(which, char *, cp, tor_free(cp));
    smartlist_free(which);
    smartlist_free(mds);
  }

  return 0;
}

/**
 * Handler function: processes a response to a POST request to upload our
 * router descriptor.
 **/
static int
handle_response_upload_dir(dir_connection_t *conn,
                           const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_UPLOAD_DIR);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *headers = args->headers;

  switch (status_code) {
  case 200: {
    dir_server_t *ds =
      router_get_trusteddirserver_by_digest(conn->identity_digest);
    char *rejected_hdr = http_get_header(headers,
                                         "X-Descriptor-Not-New: ");
    if (rejected_hdr) {
      if (!strcmp(rejected_hdr, "Yes")) {
        log_info(LD_GENERAL,
                 "Authority '%s' declined our descriptor (not new)",
                 ds->nickname);
        /* XXXX use this information; be sure to upload next one
         * sooner. -NM */
        /* XXXX++ On further thought, the task above implies that we're
         * basing our regenerate-descriptor time on when we uploaded the
         * last descriptor, not on the published time of the last
         * descriptor.  If those are different, that's a bad thing to
         * do. -NM */
      }
      tor_free(rejected_hdr);
    }
    log_info(LD_GENERAL,"eof (status 200) after uploading server "
             "descriptor: finished.");
    control_event_server_status(
                   LOG_NOTICE, "ACCEPTED_SERVER_DESCRIPTOR DIRAUTH=%s:%d",
                   conn->base_.address, conn->base_.port);

    ds->has_accepted_serverdesc = 1;
    if (directories_have_accepted_server_descriptor())
      control_event_server_status(LOG_NOTICE, "GOOD_SERVER_DESCRIPTOR");
  }
    break;
  case 400:
    log_warn(LD_GENERAL,"http status 400 (%s) response from "
             "dirserver '%s:%d'. Please correct.",
             escaped(reason), conn->base_.address, conn->base_.port);
    control_event_server_status(LOG_WARN,
                    "BAD_SERVER_DESCRIPTOR DIRAUTH=%s:%d REASON=\"%s\"",
                    conn->base_.address, conn->base_.port, escaped(reason));
    break;
  default:
    log_warn(LD_GENERAL,
             "HTTP status %d (%s) was unexpected while uploading "
             "descriptor to server '%s:%d'. Possibly the server is "
             "misconfigured?",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    break;
  }
  /* return 0 in all cases, since we don't want to mark any
   * dirservers down just because they don't like us. */

  return 0;
}

/**
 * Handler function: processes a response to POST request to upload our
 * own networkstatus vote.
 **/
static int
handle_response_upload_vote(dir_connection_t *conn,
                            const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_UPLOAD_VOTE);
  const int status_code = args->status_code;
  const char *reason = args->reason;

  switch (status_code) {
  case 200: {
    log_notice(LD_DIR,"Uploaded a vote to dirserver %s:%d",
               conn->base_.address, conn->base_.port);
  }
    break;
  case 400:
    log_warn(LD_DIR,"http status 400 (%s) response after uploading "
             "vote to dirserver '%s:%d'. Please correct.",
             escaped(reason), conn->base_.address, conn->base_.port);
    break;
  default:
    log_warn(LD_GENERAL,
             "HTTP status %d (%s) was unexpected while uploading "
             "vote to server '%s:%d'.",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    break;
  }
  /* return 0 in all cases, since we don't want to mark any
   * dirservers down just because they don't like us. */
  return 0;
}

/**
 * Handler function: processes a response to POST request to upload our
 * view of the signatures on the current consensus.
 **/
static int
handle_response_upload_signatures(dir_connection_t *conn,
                                  const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_UPLOAD_SIGNATURES);
  const int status_code = args->status_code;
  const char *reason = args->reason;

  switch (status_code) {
  case 200: {
    log_notice(LD_DIR,"Uploaded signature(s) to dirserver %s:%d",
               conn->base_.address, conn->base_.port);
  }
    break;
  case 400:
    log_warn(LD_DIR,"http status 400 (%s) response after uploading "
             "signatures to dirserver '%s:%d'. Please correct.",
             escaped(reason), conn->base_.address, conn->base_.port);
    break;
  default:
    log_warn(LD_GENERAL,
             "HTTP status %d (%s) was unexpected while uploading "
             "signatures to server '%s:%d'.",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    break;
  }
  /* return 0 in all cases, since we don't want to mark any
   * dirservers down just because they don't like us. */

  return 0;
}

/**
 * Handler function: processes a response to a request for a v2 hidden service
 * descriptor.
 **/
static int
handle_response_fetch_renddesc_v2(dir_connection_t *conn,
                                  const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_FETCH_RENDDESC_V2);
  const int status_code = args->status_code;
  const char *reason = args->reason;
  const char *body = args->body;
  const size_t body_len = args->body_len;

#define SEND_HS_DESC_FAILED_EVENT(reason)                               \
  (control_event_hs_descriptor_failed(conn->rend_data,                  \
                                      conn->identity_digest,            \
                                      reason))
#define SEND_HS_DESC_FAILED_CONTENT()                                   \
  (control_event_hs_descriptor_content(                                 \
                                rend_data_get_address(conn->rend_data), \
                                conn->requested_resource,               \
                                conn->identity_digest,                  \
                                NULL))

  tor_assert(conn->rend_data);
  log_info(LD_REND,"Received rendezvous descriptor (body size %d, status %d "
           "(%s))",
           (int)body_len, status_code, escaped(reason));
  switch (status_code) {
  case 200:
    {
      rend_cache_entry_t *entry = NULL;

      if (rend_cache_store_v2_desc_as_client(body,
                                             conn->requested_resource,
                                             conn->rend_data, &entry) < 0) {
        log_warn(LD_REND,"Fetching v2 rendezvous descriptor failed. "
                 "Retrying at another directory.");
        /* We'll retry when connection_about_to_close_connection()
         * cleans this dir conn up. */
        SEND_HS_DESC_FAILED_EVENT("BAD_DESC");
        SEND_HS_DESC_FAILED_CONTENT();
      } else {
        char service_id[REND_SERVICE_ID_LEN_BASE32 + 1];
        /* Should never be NULL here if we found the descriptor. */
        tor_assert(entry);
        rend_get_service_id(entry->parsed->pk, service_id);

        /* success. notify pending connections about this. */
        log_info(LD_REND, "Successfully fetched v2 rendezvous "
                 "descriptor.");
        control_event_hs_descriptor_received(service_id,
                                             conn->rend_data,
                                             conn->identity_digest);
        control_event_hs_descriptor_content(service_id,
                                            conn->requested_resource,
                                            conn->identity_digest,
                                            body);
        conn->base_.purpose = DIR_PURPOSE_HAS_FETCHED_RENDDESC_V2;
        rend_client_desc_trynow(service_id);
        memwipe(service_id, 0, sizeof(service_id));
      }
      break;
    }
  case 404:
    /* Not there. We'll retry when
     * connection_about_to_close_connection() cleans this conn up. */
    log_info(LD_REND,"Fetching v2 rendezvous descriptor failed: "
             "Retrying at another directory.");
    SEND_HS_DESC_FAILED_EVENT("NOT_FOUND");
    SEND_HS_DESC_FAILED_CONTENT();
    break;
  case 400:
    log_warn(LD_REND, "Fetching v2 rendezvous descriptor failed: "
             "http status 400 (%s). Dirserver didn't like our "
             "v2 rendezvous query? Retrying at another directory.",
             escaped(reason));
    SEND_HS_DESC_FAILED_EVENT("QUERY_REJECTED");
    SEND_HS_DESC_FAILED_CONTENT();
    break;
  default:
    log_warn(LD_REND, "Fetching v2 rendezvous descriptor failed: "
             "http status %d (%s) response unexpected while "
             "fetching v2 hidden service descriptor (server '%s:%d'). "
             "Retrying at another directory.",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    SEND_HS_DESC_FAILED_EVENT("UNEXPECTED");
    SEND_HS_DESC_FAILED_CONTENT();
    break;
  }

  return 0;
}

/**
 * Handler function: processes a response to a POST request to upload a v2
 * hidden service descriptor.
 **/
static int
handle_response_upload_renddesc_v2(dir_connection_t *conn,
                                   const response_handler_args_t *args)
{
  tor_assert(conn->base_.purpose == DIR_PURPOSE_UPLOAD_RENDDESC_V2);
  const int status_code = args->status_code;
  const char *reason = args->reason;

#define SEND_HS_DESC_UPLOAD_FAILED_EVENT(reason)                        \
    (control_event_hs_descriptor_upload_failed(                         \
                                conn->identity_digest,                  \
                                rend_data_get_address(conn->rend_data), \
                                reason))

  log_info(LD_REND,"Uploaded rendezvous descriptor (status %d "
           "(%s))",
           status_code, escaped(reason));
  /* Without the rend data, we'll have a problem identifying what has been
   * uploaded for which service. */
  tor_assert(conn->rend_data);
  switch (status_code) {
  case 200:
    log_info(LD_REND,
             "Uploading rendezvous descriptor: finished with status "
             "200 (%s)", escaped(reason));
    control_event_hs_descriptor_uploaded(conn->identity_digest,
                                   rend_data_get_address(conn->rend_data));
    rend_service_desc_has_uploaded(conn->rend_data);
    break;
  case 400:
    log_warn(LD_REND,"http status 400 (%s) response from dirserver "
             "'%s:%d'. Malformed rendezvous descriptor?",
             escaped(reason), conn->base_.address, conn->base_.port);
    SEND_HS_DESC_UPLOAD_FAILED_EVENT("UPLOAD_REJECTED");
    break;
  default:
    log_warn(LD_REND,"http status %d (%s) response unexpected (server "
             "'%s:%d').",
             status_code, escaped(reason), conn->base_.address,
             conn->base_.port);
    SEND_HS_DESC_UPLOAD_FAILED_EVENT("UNEXPECTED");
    break;
  }

  return 0;
}

/** Called when a directory connection reaches EOF. */
int
connection_dir_reached_eof(dir_connection_t *conn)
{
  int retval;
  if (conn->base_.state != DIR_CONN_STATE_CLIENT_READING) {
    log_info(LD_HTTP,"conn reached eof, not reading. [state=%d] Closing.",
             conn->base_.state);
    connection_close_immediate(TO_CONN(conn)); /* error: give up on flushing */
    connection_mark_for_close(TO_CONN(conn));
    return -1;
  }

  retval = connection_dir_client_reached_eof(conn);
  if (retval == 0) /* success */
    conn->base_.state = DIR_CONN_STATE_CLIENT_FINISHED;
  connection_mark_for_close(TO_CONN(conn));
  return retval;
}

/** If any directory object is arriving, and it's over 10MB large, we're
 * getting DoS'd.  (As of 0.1.2.x, raw directories are about 1MB, and we never
 * ask for more than 96 router descriptors at a time.)
 */
#define MAX_DIRECTORY_OBJECT_SIZE (10*(1<<20))

#define MAX_VOTE_DL_SIZE (MAX_DIRECTORY_OBJECT_SIZE * 5)

/** Read handler for directory connections.  (That's connections <em>to</em>
 * directory servers and connections <em>at</em> directory servers.)
 */
int
connection_dir_process_inbuf(dir_connection_t *conn)
{
  size_t max_size;
  tor_assert(conn);
  tor_assert(conn->base_.type == CONN_TYPE_DIR);

  /* Directory clients write, then read data until they receive EOF;
   * directory servers read data until they get an HTTP command, then
   * write their response (when it's finished flushing, they mark for
   * close).
   */

  /* If we're on the dirserver side, look for a command. */
  if (conn->base_.state == DIR_CONN_STATE_SERVER_COMMAND_WAIT) {
    if (directory_handle_command(conn) < 0) {
      connection_mark_for_close(TO_CONN(conn));
      return -1;
    }
    return 0;
  }

  max_size =
    (TO_CONN(conn)->purpose == DIR_PURPOSE_FETCH_STATUS_VOTE) ?
    MAX_VOTE_DL_SIZE : MAX_DIRECTORY_OBJECT_SIZE;

  if (connection_get_inbuf_len(TO_CONN(conn)) > max_size) {
    log_warn(LD_HTTP,
             "Too much data received from directory connection (%s): "
             "denial of service attempt, or you need to upgrade?",
             conn->base_.address);
    connection_mark_for_close(TO_CONN(conn));
    return -1;
  }

  if (!conn->base_.inbuf_reached_eof)
    log_debug(LD_HTTP,"Got data, not eof. Leaving on inbuf.");
  return 0;
}

/** Called when we're about to finally unlink and free a directory connection:
 * perform necessary accounting and cleanup */
void
connection_dir_about_to_close(dir_connection_t *dir_conn)
{
  connection_t *conn = TO_CONN(dir_conn);

  if (conn->state < DIR_CONN_STATE_CLIENT_FINISHED) {
    /* It's a directory connection and connecting or fetching
     * failed: forget about this router, and maybe try again. */
    connection_dir_request_failed(dir_conn);
  }
  /* If we were trying to fetch a v2 rend desc and did not succeed,
   * retry as needed. (If a fetch is successful, the connection state
   * is changed to DIR_PURPOSE_HAS_FETCHED_RENDDESC_V2 to mark that
   * refetching is unnecessary.) */
  if (conn->purpose == DIR_PURPOSE_FETCH_RENDDESC_V2 &&
      dir_conn->rend_data &&
      strlen(rend_data_get_address(dir_conn->rend_data)) ==
             REND_SERVICE_ID_LEN_BASE32)
    rend_client_refetch_v2_renddesc(dir_conn->rend_data);
}

/** Create an http response for the client <b>conn</b> out of
 * <b>status</b> and <b>reason_phrase</b>. Write it to <b>conn</b>.
 */
static void
write_http_status_line(dir_connection_t *conn, int status,
                       const char *reason_phrase)
{
  char buf[256];
  if (tor_snprintf(buf, sizeof(buf), "HTTP/1.0 %d %s\r\n\r\n",
      status, reason_phrase ? reason_phrase : "OK") < 0) {
    log_warn(LD_BUG,"status line too long.");
    return;
  }
  log_debug(LD_DIRSERV,"Wrote status 'HTTP/1.0 %d %s'", status, reason_phrase);
  connection_write_to_buf(buf, strlen(buf), TO_CONN(conn));
}

/** Write the header for an HTTP/1.0 response onto <b>conn</b>-\>outbuf,
 * with <b>type</b> as the Content-Type.
 *
 * If <b>length</b> is nonnegative, it is the Content-Length.
 * If <b>encoding</b> is provided, it is the Content-Encoding.
 * If <b>cache_lifetime</b> is greater than 0, the content may be cached for
 * up to cache_lifetime seconds.  Otherwise, the content may not be cached. */
static void
write_http_response_header_impl(dir_connection_t *conn, ssize_t length,
                           const char *type, const char *encoding,
                           const char *extra_headers,
                           long cache_lifetime)
{
  char date[RFC1123_TIME_LEN+1];
  char tmp[1024];
  char *cp;
  time_t now = time(NULL);

  tor_assert(conn);

  format_rfc1123_time(date, now);
  cp = tmp;
  tor_snprintf(cp, sizeof(tmp),
               "HTTP/1.0 200 OK\r\nDate: %s\r\n",
               date);
  cp += strlen(tmp);
  if (type) {
    tor_snprintf(cp, sizeof(tmp)-(cp-tmp), "Content-Type: %s\r\n", type);
    cp += strlen(cp);
  }
  if (!is_local_addr(&conn->base_.addr)) {
    /* Don't report the source address for a nearby/private connection.
     * Otherwise we tend to mis-report in cases where incoming ports are
     * being forwarded to a Tor server running behind the firewall. */
    tor_snprintf(cp, sizeof(tmp)-(cp-tmp),
                 X_ADDRESS_HEADER "%s\r\n", conn->base_.address);
    cp += strlen(cp);
  }
  if (encoding) {
    tor_snprintf(cp, sizeof(tmp)-(cp-tmp),
                 "Content-Encoding: %s\r\n", encoding);
    cp += strlen(cp);
  }
  if (length >= 0) {
    tor_snprintf(cp, sizeof(tmp)-(cp-tmp),
                 "Content-Length: %ld\r\n", (long)length);
    cp += strlen(cp);
  }
  if (cache_lifetime > 0) {
    char expbuf[RFC1123_TIME_LEN+1];
    format_rfc1123_time(expbuf, (time_t)(now + cache_lifetime));
    /* We could say 'Cache-control: max-age=%d' here if we start doing
     * http/1.1 */
    tor_snprintf(cp, sizeof(tmp)-(cp-tmp),
                 "Expires: %s\r\n", expbuf);
    cp += strlen(cp);
  } else if (cache_lifetime == 0) {
    /* We could say 'Cache-control: no-cache' here if we start doing
     * http/1.1 */
    strlcpy(cp, "Pragma: no-cache\r\n", sizeof(tmp)-(cp-tmp));
    cp += strlen(cp);
  }
  if (extra_headers) {
    strlcpy(cp, extra_headers, sizeof(tmp)-(cp-tmp));
    cp += strlen(cp);
  }
  if (sizeof(tmp)-(cp-tmp) > 3)
    memcpy(cp, "\r\n", 3);
  else
    tor_assert(0);
  connection_write_to_buf(tmp, strlen(tmp), TO_CONN(conn));
}

/** As write_http_response_header_impl, but sets encoding and content-typed
 * based on whether the response will be <b>compressed</b> or not. */
static void
write_http_response_headers(dir_connection_t *conn, ssize_t length,
                            compress_method_t method,
                            const char *extra_headers, long cache_lifetime)
{
  const char *methodname = compression_method_get_name(method);
  const char *doctype;
  if (method == NO_METHOD)
    doctype = "text/plain";
  else
    doctype = "application/octet-stream";
  write_http_response_header_impl(conn, length,
                                  doctype,
                                  methodname,
                                  extra_headers,
                                  cache_lifetime);
}

/** As write_http_response_headers, but assumes extra_headers is NULL */
static void
write_http_response_header(dir_connection_t *conn, ssize_t length,
                           compress_method_t method,
                           long cache_lifetime)
{
  write_http_response_headers(conn, length, method, NULL, cache_lifetime);
}

/** Array of compression methods to use (if supported) for serving
 * precompressed data, ordered from best to worst. */
static compress_method_t srv_meth_pref_precompressed[] = {
  LZMA_METHOD,
  ZSTD_METHOD,
  ZLIB_METHOD,
  GZIP_METHOD,
  NO_METHOD
};

/** Array of compression methods to use (if supported) for serving
 * streamed data, ordered from best to worst. */
static compress_method_t srv_meth_pref_streaming_compression[] = {
  ZSTD_METHOD,
  ZLIB_METHOD,
  GZIP_METHOD,
  NO_METHOD
};

/** Array of allowed compression methods to use (if supported) when receiving a
 * response from a request that was required to be anonymous. */
static compress_method_t client_meth_allowed_anonymous_compression[] = {
  ZLIB_METHOD,
  GZIP_METHOD,
  NO_METHOD
};

/** Parse the compression methods listed in an Accept-Encoding header <b>h</b>,
 * and convert them to a bitfield where compression method x is supported if
 * and only if 1 &lt;&lt; x is set in the bitfield. */
STATIC unsigned
parse_accept_encoding_header(const char *h)
{
  unsigned result = (1u << NO_METHOD);
  smartlist_t *methods = smartlist_new();
  smartlist_split_string(methods, h, ",",
             SPLIT_SKIP_SPACE|SPLIT_STRIP_SPACE|SPLIT_IGNORE_BLANK, 0);

  SMARTLIST_FOREACH_BEGIN(methods, const char *, m) {
    compress_method_t method = compression_method_get_by_name(m);
    if (method != UNKNOWN_METHOD) {
      tor_assert(((unsigned)method) < 8*sizeof(unsigned));
      result |= (1u << method);
    }
  } SMARTLIST_FOREACH_END(m);
  SMARTLIST_FOREACH_BEGIN(methods, char *, m) {
    tor_free(m);
  } SMARTLIST_FOREACH_END(m);
  smartlist_free(methods);
  return result;
}

/** Array of compression methods to use (if supported) for requesting
 * compressed data, ordered from best to worst. */
static compress_method_t client_meth_pref[] = {
  LZMA_METHOD,
  ZSTD_METHOD,
  ZLIB_METHOD,
  GZIP_METHOD,
  NO_METHOD
};

/** Return a newly allocated string containing a comma separated list of
 * supported encodings. */
STATIC char *
accept_encoding_header(void)
{
  smartlist_t *methods = smartlist_new();
  char *header = NULL;
  compress_method_t method;
  unsigned i;

  for (i = 0; i < ARRAY_LENGTH(client_meth_pref); ++i) {
    method = client_meth_pref[i];
    if (tor_compress_supports_method(method))
      smartlist_add(methods, (char *)compression_method_get_name(method));
  }

  header = smartlist_join_strings(methods, ", ", 0, NULL);
  smartlist_free(methods);

  return header;
}

/** Decide whether a client would accept the consensus we have.
 *
 * Clients can say they only want a consensus if it's signed by more
 * than half the authorities in a list.  They pass this list in
 * the url as "...consensus/<b>fpr</b>+<b>fpr</b>+<b>fpr</b>".
 *
 * <b>fpr</b> may be an abbreviated fingerprint, i.e. only a left substring
 * of the full authority identity digest. (Only strings of even length,
 * i.e. encodings of full bytes, are handled correctly.  In the case
 * of an odd number of hex digits the last one is silently ignored.)
 *
 * Returns 1 if more than half of the requested authorities signed the
 * consensus, 0 otherwise.
 */
int
client_likes_consensus(const struct consensus_cache_entry_t *ent,
                       const char *want_url)
{
  smartlist_t *voters = smartlist_new();
  int need_at_least;
  int have = 0;

  if (consensus_cache_entry_get_voter_id_digests(ent, voters) != 0) {
    return 1; // We don't know the voters; assume the client won't mind. */
  }

  smartlist_t *want_authorities = smartlist_new();
  dir_split_resource_into_fingerprints(want_url, want_authorities, NULL, 0);
  need_at_least = smartlist_len(want_authorities)/2+1;

  SMARTLIST_FOREACH_BEGIN(want_authorities, const char *, want_digest) {

    SMARTLIST_FOREACH_BEGIN(voters, const char *, digest) {
      if (!strcasecmpstart(digest, want_digest)) {
        have++;
        break;
      };
    } SMARTLIST_FOREACH_END(digest);

    /* early exit, if we already have enough */
    if (have >= need_at_least)
      break;
  } SMARTLIST_FOREACH_END(want_digest);

  SMARTLIST_FOREACH(want_authorities, char *, d, tor_free(d));
  smartlist_free(want_authorities);
  SMARTLIST_FOREACH(voters, char *, cp, tor_free(cp));
  smartlist_free(voters);
  return (have >= need_at_least);
}

/** Return the compression level we should use for sending a compressed
 * response of size <b>n_bytes</b>. */
STATIC compression_level_t
choose_compression_level(ssize_t n_bytes)
{
  if (! have_been_under_memory_pressure()) {
    return HIGH_COMPRESSION; /* we have plenty of RAM. */
  } else if (n_bytes < 0) {
    return HIGH_COMPRESSION; /* unknown; might be big. */
  } else if (n_bytes < 1024) {
    return LOW_COMPRESSION;
  } else if (n_bytes < 2048) {
    return MEDIUM_COMPRESSION;
  } else {
    return HIGH_COMPRESSION;
  }
}

/** Information passed to handle a GET request. */
typedef struct get_handler_args_t {
  /** Bitmask of compression methods that the client said (or implied) it
   * supported. */
  unsigned compression_supported;
  /** If nonzero, the time included an if-modified-since header with this
   * value. */
  time_t if_modified_since;
  /** String containing the requested URL or resource. */
  const char *url;
  /** String containing the HTTP headers */
  const char *headers;
} get_handler_args_t;

/** Entry for handling an HTTP GET request.
 *
 * This entry matches a request if "string" is equal to the requested
 * resource, or if "is_prefix" is true and "string" is a prefix of the
 * requested resource.
 *
 * The 'handler' function is called to handle the request.  It receives
 * an arguments structure, and must return 0 on success or -1 if we should
 * close the connection.
 **/
typedef struct url_table_ent_s {
  const char *string;
  int is_prefix;
  int (*handler)(dir_connection_t *conn, const get_handler_args_t *args);
} url_table_ent_t;

static int handle_get_frontpage(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_current_consensus(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_status_vote(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_microdesc(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_descriptor(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_keys(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_hs_descriptor_v2(dir_connection_t *conn,
                                       const get_handler_args_t *args);
static int handle_get_robots(dir_connection_t *conn,
                                const get_handler_args_t *args);
static int handle_get_networkstatus_bridges(dir_connection_t *conn,
                                const get_handler_args_t *args);

/** Table for handling GET requests. */
static const url_table_ent_t url_table[] = {
  { "/tor/", 0, handle_get_frontpage },
  { "/tor/status-vote/current/consensus", 1, handle_get_current_consensus },
  { "/tor/status-vote/current/", 1, handle_get_status_vote },
  { "/tor/status-vote/next/", 1, handle_get_status_vote },
  { "/tor/micro/d/", 1, handle_get_microdesc },
  { "/tor/server/", 1, handle_get_descriptor },
  { "/tor/extra/", 1, handle_get_descriptor },
  { "/tor/keys/", 1, handle_get_keys },
  { "/tor/rendezvous2/", 1, handle_get_hs_descriptor_v2 },
  { "/tor/hs/3/", 1, handle_get_hs_descriptor_v3 },
  { "/tor/robots.txt", 0, handle_get_robots },
  { "/tor/networkstatus-bridges", 0, handle_get_networkstatus_bridges },
  { NULL, 0, NULL },
};

/** Helper function: called when a dirserver gets a complete HTTP GET
 * request.  Look for a request for a directory or for a rendezvous
 * service descriptor.  On finding one, write a response into
 * conn-\>outbuf.  If the request is unrecognized, send a 404.
 * Return 0 if we handled this successfully, or -1 if we need to close
 * the connection. */
MOCK_IMPL(STATIC int,
directory_handle_command_get,(dir_connection_t *conn, const char *headers,
                              const char *req_body, size_t req_body_len))
{
  char *url, *url_mem, *header;
  time_t if_modified_since = 0;
  int zlib_compressed_in_url;
  size_t url_len;
  unsigned compression_methods_supported;

  /* We ignore the body of a GET request. */
  (void)req_body;
  (void)req_body_len;

  log_debug(LD_DIRSERV,"Received GET command.");

  conn->base_.state = DIR_CONN_STATE_SERVER_WRITING;

  if (parse_http_url(headers, &url) < 0) {
    write_http_status_line(conn, 400, "Bad request");
    return 0;
  }
  if ((header = http_get_header(headers, "If-Modified-Since: "))) {
    struct tm tm;
    if (parse_http_time(header, &tm) == 0) {
      if (tor_timegm(&tm, &if_modified_since)<0) {
        if_modified_since = 0;
      } else {
        log_debug(LD_DIRSERV, "If-Modified-Since is '%s'.", escaped(header));
      }
    }
    /* The correct behavior on a malformed If-Modified-Since header is to
     * act as if no If-Modified-Since header had been given. */
    tor_free(header);
  }
  log_debug(LD_DIRSERV,"rewritten url as '%s'.", escaped(url));

  url_mem = url;
  url_len = strlen(url);

  zlib_compressed_in_url = url_len > 2 && !strcmp(url+url_len-2, ".z");
  if (zlib_compressed_in_url) {
    url[url_len-2] = '\0';
    url_len -= 2;
  }

  if ((header = http_get_header(headers, "Accept-Encoding: "))) {
    compression_methods_supported = parse_accept_encoding_header(header);
    tor_free(header);
  } else {
    compression_methods_supported = (1u << NO_METHOD);
  }
  if (zlib_compressed_in_url) {
    compression_methods_supported |= (1u << ZLIB_METHOD);
  }

  /* Remove all methods that we don't both support. */
  compression_methods_supported &= tor_compress_get_supported_method_bitmask();

  get_handler_args_t args;
  args.url = url;
  args.headers = headers;
  args.if_modified_since = if_modified_since;
  args.compression_supported = compression_methods_supported;

  int i, result = -1;
  for (i = 0; url_table[i].string; ++i) {
    int match;
    if (url_table[i].is_prefix) {
      match = !strcmpstart(url, url_table[i].string);
    } else {
      match = !strcmp(url, url_table[i].string);
    }
    if (match) {
      result = url_table[i].handler(conn, &args);
      goto done;
    }
  }

  /* we didn't recognize the url */
  write_http_status_line(conn, 404, "Not found");
  result = 0;

 done:
  tor_free(url_mem);
  return result;
}

/** Helper function for GET / or GET /tor/
 */
static int
handle_get_frontpage(dir_connection_t *conn, const get_handler_args_t *args)
{
  (void) args; /* unused */
  const char *frontpage = get_dirportfrontpage();

  if (frontpage) {
    size_t dlen;
    dlen = strlen(frontpage);
    /* Let's return a disclaimer page (users shouldn't use V1 anymore,
       and caches don't fetch '/', so this is safe). */

    /* [We don't check for write_bucket_low here, since we want to serve
     *  this page no matter what.] */
    write_http_response_header_impl(conn, dlen, "text/html", "identity",
                                    NULL, DIRPORTFRONTPAGE_CACHE_LIFETIME);
    connection_write_to_buf(frontpage, dlen, TO_CONN(conn));
  } else {
    write_http_status_line(conn, 404, "Not found");
  }
  return 0;
}

/** Warn that the cached consensus <b>consensus</b> of type
 * <b>flavor</b> is too old and will not be served to clients. Rate-limit the
 * warning to avoid logging an entry on every request.
 */
static void
warn_consensus_is_too_old(const struct consensus_cache_entry_t *consensus,
                          const char *flavor, time_t now)
{
#define TOO_OLD_WARNING_INTERVAL (60*60)
  static ratelim_t warned = RATELIM_INIT(TOO_OLD_WARNING_INTERVAL);
  char timestamp[ISO_TIME_LEN+1];
  time_t valid_until;
  char *dupes;

  if (consensus_cache_entry_get_valid_until(consensus, &valid_until))
    return;

  if ((dupes = rate_limit_log(&warned, now))) {
    format_local_iso_time(timestamp, valid_until);
    log_warn(LD_DIRSERV, "Our %s%sconsensus is too old, so we will not "
             "serve it to clients. It was valid until %s local time and we "
             "continued to serve it for up to 24 hours after it expired.%s",
             flavor ? flavor : "", flavor ? " " : "", timestamp, dupes);
    tor_free(dupes);
  }
}

/**
 * Parse a single hex-encoded sha3-256 digest from <b>hex</b> into
 * <b>digest</b>. Return 0 on success.  On failure, report that the hash came
 * from <b>location</b>, report that we are taking <b>action</b> with it, and
 * return -1.
 */
static int
parse_one_diff_hash(uint8_t *digest, const char *hex, const char *location,
                    const char *action)
{
  if (base16_decode((char*)digest, DIGEST256_LEN, hex, strlen(hex)) ==
      DIGEST256_LEN) {
    return 0;
  } else {
    log_fn(LOG_PROTOCOL_WARN, LD_DIR,
           "%s contained bogus digest %s; %s.",
           location, escaped(hex), action);
    return -1;
  }
}

/** If there is an X-Or-Diff-From-Consensus header included in <b>headers</b>,
 * set <b>digest_out<b> to a new smartlist containing every 256-bit
 * hex-encoded digest listed in that header and return 0.  Otherwise return
 * -1.  */
static int
parse_or_diff_from_header(smartlist_t **digests_out, const char *headers)
{
  char *hdr = http_get_header(headers, X_OR_DIFF_FROM_CONSENSUS_HEADER);
  if (hdr == NULL) {
    return -1;
  }
  smartlist_t *hex_digests = smartlist_new();
  *digests_out = smartlist_new();
  smartlist_split_string(hex_digests, hdr, " ",
                         SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, -1);
  SMARTLIST_FOREACH_BEGIN(hex_digests, const char *, hex) {
    uint8_t digest[DIGEST256_LEN];
    if (!parse_one_diff_hash(digest, hex, "X-Or-Diff-From-Consensus header",
                             "ignoring")) {
      smartlist_add(*digests_out, tor_memdup(digest, sizeof(digest)));
    }
  } SMARTLIST_FOREACH_END(hex);
  SMARTLIST_FOREACH(hex_digests, char *, cp, tor_free(cp));
  smartlist_free(hex_digests);
  tor_free(hdr);
  return 0;
}

/** Fallback compression method.  The fallback compression method is used in
 * case a client requests a non-compressed document. We only store compressed
 * documents, so we use this compression method to fetch the document and let
 * the spooling system do the streaming decompression.
 */
#define FALLBACK_COMPRESS_METHOD ZLIB_METHOD

/**
 * Try to find the best consensus diff possible in order to serve a client
 * request for a diff from one of the consensuses in <b>digests</b> to the
 * current consensus of flavor <b>flav</b>.  The client supports the
 * compression methods listed in the <b>compression_methods</b> bitfield:
 * place the method chosen (if any) into <b>compression_used_out</b>.
 */
static struct consensus_cache_entry_t *
find_best_diff(const smartlist_t *digests, int flav,
               unsigned compression_methods,
               compress_method_t *compression_used_out)
{
  struct consensus_cache_entry_t *result = NULL;

  SMARTLIST_FOREACH_BEGIN(digests, const uint8_t *, diff_from) {
    unsigned u;
    for (u = 0; u < ARRAY_LENGTH(srv_meth_pref_precompressed); ++u) {
      compress_method_t method = srv_meth_pref_precompressed[u];
      if (0 == (compression_methods & (1u<<method)))
        continue; // client doesn't like this one, or we don't have it.
      if (consdiffmgr_find_diff_from(&result, flav, DIGEST_SHA3_256,
                                     diff_from, DIGEST256_LEN,
                                     method) == CONSDIFF_AVAILABLE) {
        tor_assert_nonfatal(result);
        *compression_used_out = method;
        return result;
      }
    }
  } SMARTLIST_FOREACH_END(diff_from);

  SMARTLIST_FOREACH_BEGIN(digests, const uint8_t *, diff_from) {
    if (consdiffmgr_find_diff_from(&result, flav, DIGEST_SHA3_256, diff_from,
          DIGEST256_LEN, FALLBACK_COMPRESS_METHOD) == CONSDIFF_AVAILABLE) {
      tor_assert_nonfatal(result);
      *compression_used_out = FALLBACK_COMPRESS_METHOD;
      return result;
    }
  } SMARTLIST_FOREACH_END(diff_from);

  return NULL;
}

/** Lookup the cached consensus document by the flavor found in <b>flav</b>.
 * The prefered set of compression methods should be listed in the
 * <b>compression_methods</b> bitfield. The compression method chosen (if any)
 * is stored in <b>compression_used_out</b>. */
static struct consensus_cache_entry_t *
find_best_consensus(int flav,
                    unsigned compression_methods,
                    compress_method_t *compression_used_out)
{
  struct consensus_cache_entry_t *result = NULL;
  unsigned u;

  for (u = 0; u < ARRAY_LENGTH(srv_meth_pref_precompressed); ++u) {
    compress_method_t method = srv_meth_pref_precompressed[u];

    if (0 == (compression_methods & (1u<<method)))
      continue;

    if (consdiffmgr_find_consensus(&result, flav,
                                   method) == CONSDIFF_AVAILABLE) {
      tor_assert_nonfatal(result);
      *compression_used_out = method;
      return result;
    }
  }

  if (consdiffmgr_find_consensus(&result, flav,
        FALLBACK_COMPRESS_METHOD) == CONSDIFF_AVAILABLE) {
    tor_assert_nonfatal(result);
    *compression_used_out = FALLBACK_COMPRESS_METHOD;
    return result;
  }

  return NULL;
}

/** Try to find the best supported compression method possible from a given
 * <b>compression_methods</b>. Return NO_METHOD if no mutually supported
 * compression method could be found. */
static compress_method_t
find_best_compression_method(unsigned compression_methods, int stream)
{
  unsigned u;
  compress_method_t *methods;
  size_t length;

  if (stream) {
    methods = srv_meth_pref_streaming_compression;
    length = ARRAY_LENGTH(srv_meth_pref_streaming_compression);
  } else {
    methods = srv_meth_pref_precompressed;
    length = ARRAY_LENGTH(srv_meth_pref_precompressed);
  }

  for (u = 0; u < length; ++u) {
    compress_method_t method = methods[u];
    if (compression_methods & (1u<<method))
      return method;
  }

  return NO_METHOD;
}

/** Check if the given compression method is allowed for a connection that is
 * supposed to be anonymous. Returns 1 if the compression method is allowed,
 * otherwise 0. */
STATIC int
allowed_anonymous_connection_compression_method(compress_method_t method)
{
  unsigned u;

  for (u = 0; u < ARRAY_LENGTH(client_meth_allowed_anonymous_compression);
       ++u) {
    compress_method_t allowed_method =
      client_meth_allowed_anonymous_compression[u];

    if (! tor_compress_supports_method(allowed_method))
      continue;

    if (method == allowed_method)
      return 1;
  }

  return 0;
}

/** Log a warning when a remote server has sent us a document using a
 * compression method that is not allowed for anonymous directory requests. */
STATIC void
warn_disallowed_anonymous_compression_method(compress_method_t method)
{
  log_fn(LOG_PROTOCOL_WARN, LD_HTTP,
         "Received a %s HTTP response, which is not "
         "allowed for anonymous directory requests.",
         compression_method_get_human_name(method));
}

/** Encodes the results of parsing a consensus request to figure out what
 * consensus, and possibly what diffs, the user asked for. */
typedef struct {
  /** name of the flavor to retrieve. */
  char *flavor;
  /** flavor to retrive, as enum. */
  consensus_flavor_t flav;
  /** plus-separated list of authority fingerprints; see
   * client_likes_consensus(). Aliases the URL in the request passed to
   * parse_consensus_request(). */
  const char *want_fps;
  /** Optionally, a smartlist of sha3 digests-as-signed of the consensuses
   * to return a diff from. */
  smartlist_t *diff_from_digests;
  /** If true, never send a full consensus. If there is no diff, send
   * a 404 instead. */
  int diff_only;
} parsed_consensus_request_t;

/** Remove all data held in <b>req</b>. Do not free <b>req</b> itself, since
 * it is stack-allocated. */
static void
parsed_consensus_request_clear(parsed_consensus_request_t *req)
{
  if (!req)
    return;
  tor_free(req->flavor);
  if (req->diff_from_digests) {
    SMARTLIST_FOREACH(req->diff_from_digests, uint8_t *, d, tor_free(d));
    smartlist_free(req->diff_from_digests);
  }
  memset(req, 0, sizeof(parsed_consensus_request_t));
}

/**
 * Parse the URL and relevant headers of <b>args</b> for a current-consensus
 * request to learn what flavor of consensus we want, what keys it must be
 * signed with, and what diffs we would accept (or demand) instead. Return 0
 * on success and -1 on failure.
 */
static int
parse_consensus_request(parsed_consensus_request_t *out,
                        const get_handler_args_t *args)
{
  const char *url = args->url;
  memset(out, 0, sizeof(parsed_consensus_request_t));
  out->flav = FLAV_NS;

  const char CONSENSUS_URL_PREFIX[] = "/tor/status-vote/current/consensus/";
  const char CONSENSUS_FLAVORED_PREFIX[] =
    "/tor/status-vote/current/consensus-";

  /* figure out the flavor if any, and who we wanted to sign the thing */
  const char *after_flavor = NULL;

  if (!strcmpstart(url, CONSENSUS_FLAVORED_PREFIX)) {
    const char *f, *cp;
    f = url + strlen(CONSENSUS_FLAVORED_PREFIX);
    cp = strchr(f, '/');
    if (cp) {
      after_flavor = cp+1;
      out->flavor = tor_strndup(f, cp-f);
    } else {
      out->flavor = tor_strdup(f);
    }
    int flav = networkstatus_parse_flavor_name(out->flavor);
    if (flav < 0)
      flav = FLAV_NS;
    out->flav = flav;
  } else {
    if (!strcmpstart(url, CONSENSUS_URL_PREFIX))
      after_flavor = url+strlen(CONSENSUS_URL_PREFIX);
  }

  /* see whether we've been asked explicitly for a diff from an older
   * consensus. (The user might also have said that a diff would be okay,
   * via X-Or-Diff-From-Consensus */
  const char DIFF_COMPONENT[] = "diff/";
  char *diff_hash_in_url = NULL;
  if (after_flavor && !strcmpstart(after_flavor, DIFF_COMPONENT)) {
    after_flavor += strlen(DIFF_COMPONENT);
    const char *cp = strchr(after_flavor, '/');
    if (cp) {
      diff_hash_in_url = tor_strndup(after_flavor, cp-after_flavor);
      out->want_fps = cp+1;
    } else {
      diff_hash_in_url = tor_strdup(after_flavor);
      out->want_fps = NULL;
    }
  } else {
    out->want_fps = after_flavor;
  }

  if (diff_hash_in_url) {
    uint8_t diff_from[DIGEST256_LEN];
    out->diff_from_digests = smartlist_new();
    out->diff_only = 1;
    int ok = !parse_one_diff_hash(diff_from, diff_hash_in_url, "URL",
                                  "rejecting");
    tor_free(diff_hash_in_url);
    if (ok) {
      smartlist_add(out->diff_from_digests,
                    tor_memdup(diff_from, DIGEST256_LEN));
    } else {
      return -1;
    }
  } else {
    parse_or_diff_from_header(&out->diff_from_digests, args->headers);
  }

  return 0;
}

/** Helper function for GET /tor/status-vote/current/consensus
 */
static int
handle_get_current_consensus(dir_connection_t *conn,
                             const get_handler_args_t *args)
{
  const compress_method_t compress_method =
    find_best_compression_method(args->compression_supported, 0);
  const time_t if_modified_since = args->if_modified_since;
  int clear_spool = 0;

  /* v3 network status fetch. */
  long lifetime = NETWORKSTATUS_CACHE_LIFETIME;

  time_t now = time(NULL);
  parsed_consensus_request_t req;

  if (parse_consensus_request(&req, args) < 0) {
    write_http_status_line(conn, 404, "Couldn't parse request");
    goto done;
  }

  struct consensus_cache_entry_t *cached_consensus = NULL;

  compress_method_t compression_used = NO_METHOD;
  if (req.diff_from_digests) {
    cached_consensus = find_best_diff(req.diff_from_digests, req.flav,
                                      args->compression_supported,
                                      &compression_used);
  }

  if (req.diff_only && !cached_consensus) {
    write_http_status_line(conn, 404, "No such diff available");
    // XXXX warn_consensus_is_too_old(v, req.flavor, now);
    geoip_note_ns_response(GEOIP_REJECT_NOT_FOUND);
    goto done;
  }

  if (! cached_consensus) {
    cached_consensus = find_best_consensus(req.flav,
                                           args->compression_supported,
                                           &compression_used);
  }

  time_t fresh_until, valid_until;
  int have_fresh_until = 0, have_valid_until = 0;
  if (cached_consensus) {
    have_fresh_until =
      !consensus_cache_entry_get_fresh_until(cached_consensus, &fresh_until);
    have_valid_until =
      !consensus_cache_entry_get_valid_until(cached_consensus, &valid_until);
  }

  if (cached_consensus && have_valid_until &&
      !networkstatus_valid_until_is_reasonably_live(valid_until, now)) {
    write_http_status_line(conn, 404, "Consensus is too old");
    warn_consensus_is_too_old(cached_consensus, req.flavor, now);
    geoip_note_ns_response(GEOIP_REJECT_NOT_FOUND);
    goto done;
  }

  if (cached_consensus && req.want_fps &&
      !client_likes_consensus(cached_consensus, req.want_fps)) {
    write_http_status_line(conn, 404, "Consensus not signed by sufficient "
                           "number of requested authorities");
    geoip_note_ns_response(GEOIP_REJECT_NOT_ENOUGH_SIGS);
    goto done;
  }

  conn->spool = smartlist_new();
  clear_spool = 1;
  {
    spooled_resource_t *spooled;
    if (cached_consensus) {
      spooled = spooled_resource_new_from_cache_entry(cached_consensus);
      smartlist_add(conn->spool, spooled);
    }
  }

  lifetime = (have_fresh_until && fresh_until > now) ? fresh_until - now : 0;

  size_t size_guess = 0;
  int n_expired = 0;
  dirserv_spool_remove_missing_and_guess_size(conn, if_modified_since,
                                              compress_method != NO_METHOD,
                                              &size_guess,
                                              &n_expired);

  if (!smartlist_len(conn->spool) && !n_expired) {
    write_http_status_line(conn, 404, "Not found");
    geoip_note_ns_response(GEOIP_REJECT_NOT_FOUND);
    goto done;
  } else if (!smartlist_len(conn->spool)) {
    write_http_status_line(conn, 304, "Not modified");
    geoip_note_ns_response(GEOIP_REJECT_NOT_MODIFIED);
    goto done;
  }

  if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
    log_debug(LD_DIRSERV,
              "Client asked for network status lists, but we've been "
              "writing too many bytes lately. Sending 503 Dir busy.");
    write_http_status_line(conn, 503, "Directory busy, try again later");
    geoip_note_ns_response(GEOIP_REJECT_BUSY);
    goto done;
  }

  tor_addr_t addr;
  if (tor_addr_parse(&addr, (TO_CONN(conn))->address) >= 0) {
    geoip_note_client_seen(GEOIP_CLIENT_NETWORKSTATUS,
                           &addr, NULL,
                           time(NULL));
    geoip_note_ns_response(GEOIP_SUCCESS);
    /* Note that a request for a network status has started, so that we
     * can measure the download time later on. */
    if (conn->dirreq_id)
      geoip_start_dirreq(conn->dirreq_id, size_guess, DIRREQ_TUNNELED);
    else
      geoip_start_dirreq(TO_CONN(conn)->global_identifier, size_guess,
                         DIRREQ_DIRECT);
  }

  /* Use this header to tell caches that the response depends on the
   * X-Or-Diff-From-Consensus header (or lack thereof). */
  const char vary_header[] = "Vary: X-Or-Diff-From-Consensus\r\n";

  clear_spool = 0;

  // The compress_method might have been NO_METHOD, but we store the data
  // compressed. Decompress them using `compression_used`. See fallback code in
  // find_best_consensus() and find_best_diff().
  write_http_response_headers(conn, -1,
                             compress_method == NO_METHOD ?
                               NO_METHOD : compression_used,
                             vary_header,
                             smartlist_len(conn->spool) == 1 ? lifetime : 0);

  if (compress_method == NO_METHOD && smartlist_len(conn->spool))
    conn->compress_state = tor_compress_new(0, compression_used,
                                            HIGH_COMPRESSION);

  /* Prime the connection with some data. */
  const int initial_flush_result = connection_dirserv_flushed_some(conn);
  tor_assert_nonfatal(initial_flush_result == 0);
  goto done;

 done:
  parsed_consensus_request_clear(&req);
  if (clear_spool) {
    dir_conn_clear_spool(conn);
  }
  return 0;
}

/** Helper function for GET /tor/status-vote/{current,next}/...
 */
static int
handle_get_status_vote(dir_connection_t *conn, const get_handler_args_t *args)
{
  const char *url = args->url;
  const compress_method_t compress_method =
    find_best_compression_method(args->compression_supported, 1);
  {
    int current;
    ssize_t body_len = 0;
    ssize_t estimated_len = 0;
    smartlist_t *items = smartlist_new();
    smartlist_t *dir_items = smartlist_new();
    int lifetime = 60; /* XXXX?? should actually use vote intervals. */
    url += strlen("/tor/status-vote/");
    current = !strcmpstart(url, "current/");
    url = strchr(url, '/');
    tor_assert(url);
    ++url;
    if (!strcmp(url, "consensus")) {
      const char *item;
      tor_assert(!current); /* we handle current consensus specially above,
                             * since it wants to be spooled. */
      if ((item = dirvote_get_pending_consensus(FLAV_NS)))
        smartlist_add(items, (char*)item);
    } else if (!current && !strcmp(url, "consensus-signatures")) {
      /* XXXX the spec says that we should implement
       * current/consensus-signatures too.  It doesn't seem to be needed,
       * though. */
      const char *item;
      if ((item=dirvote_get_pending_detached_signatures()))
        smartlist_add(items, (char*)item);
    } else if (!strcmp(url, "authority")) {
      const cached_dir_t *d;
      int flags = DGV_BY_ID |
        (current ? DGV_INCLUDE_PREVIOUS : DGV_INCLUDE_PENDING);
      if ((d=dirvote_get_vote(NULL, flags)))
        smartlist_add(dir_items, (cached_dir_t*)d);
    } else {
      const cached_dir_t *d;
      smartlist_t *fps = smartlist_new();
      int flags;
      if (!strcmpstart(url, "d/")) {
        url += 2;
        flags = DGV_INCLUDE_PENDING | DGV_INCLUDE_PREVIOUS;
      } else {
        flags = DGV_BY_ID |
          (current ? DGV_INCLUDE_PREVIOUS : DGV_INCLUDE_PENDING);
      }
      dir_split_resource_into_fingerprints(url, fps, NULL,
                                           DSR_HEX|DSR_SORT_UNIQ);
      SMARTLIST_FOREACH(fps, char *, fp, {
          if ((d = dirvote_get_vote(fp, flags)))
            smartlist_add(dir_items, (cached_dir_t*)d);
          tor_free(fp);
        });
      smartlist_free(fps);
    }
    if (!smartlist_len(dir_items) && !smartlist_len(items)) {
      write_http_status_line(conn, 404, "Not found");
      goto vote_done;
    }
    SMARTLIST_FOREACH(dir_items, cached_dir_t *, d,
                      body_len += compress_method != NO_METHOD ?
                        d->dir_compressed_len : d->dir_len);
    estimated_len += body_len;
    SMARTLIST_FOREACH(items, const char *, item, {
        size_t ln = strlen(item);
        if (compress_method != NO_METHOD) {
          estimated_len += ln/2;
        } else {
          body_len += ln; estimated_len += ln;
        }
      });

    if (global_write_bucket_low(TO_CONN(conn), estimated_len, 2)) {
      write_http_status_line(conn, 503, "Directory busy, try again later");
      goto vote_done;
    }
    write_http_response_header(conn, body_len ? body_len : -1,
                 compress_method,
                 lifetime);

    if (smartlist_len(items)) {
      if (compress_method != NO_METHOD) {
        conn->compress_state = tor_compress_new(1, compress_method,
                           choose_compression_level(estimated_len));
        SMARTLIST_FOREACH(items, const char *, c,
                 connection_write_to_buf_compress(c, strlen(c), conn, 0));
        connection_write_to_buf_compress("", 0, conn, 1);
      } else {
        SMARTLIST_FOREACH(items, const char *, c,
                         connection_write_to_buf(c, strlen(c), TO_CONN(conn)));
      }
    } else {
      SMARTLIST_FOREACH(dir_items, cached_dir_t *, d,
          connection_write_to_buf(compress_method != NO_METHOD ?
                                    d->dir_compressed : d->dir,
                                  compress_method != NO_METHOD ?
                                    d->dir_compressed_len : d->dir_len,
                                  TO_CONN(conn)));
    }
  vote_done:
    smartlist_free(items);
    smartlist_free(dir_items);
    goto done;
  }
 done:
  return 0;
}

/** Helper function for GET /tor/micro/d/...
 */
static int
handle_get_microdesc(dir_connection_t *conn, const get_handler_args_t *args)
{
  const char *url = args->url;
  const compress_method_t compress_method =
    find_best_compression_method(args->compression_supported, 1);
  int clear_spool = 1;
  {
    conn->spool = smartlist_new();

    dir_split_resource_into_spoolable(url+strlen("/tor/micro/d/"),
                                      DIR_SPOOL_MICRODESC,
                                      conn->spool, NULL,
                                      DSR_DIGEST256|DSR_BASE64|DSR_SORT_UNIQ);

    size_t size_guess = 0;
    dirserv_spool_remove_missing_and_guess_size(conn, 0,
                                                compress_method != NO_METHOD,
                                                &size_guess, NULL);
    if (smartlist_len(conn->spool) == 0) {
      write_http_status_line(conn, 404, "Not found");
      goto done;
    }
    if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
      log_info(LD_DIRSERV,
               "Client asked for server descriptors, but we've been "
               "writing too many bytes lately. Sending 503 Dir busy.");
      write_http_status_line(conn, 503, "Directory busy, try again later");
      goto done;
    }

    clear_spool = 0;
    write_http_response_header(conn, -1,
                               compress_method,
                               MICRODESC_CACHE_LIFETIME);

    if (compress_method != NO_METHOD)
      conn->compress_state = tor_compress_new(1, compress_method,
                                      choose_compression_level(size_guess));

    const int initial_flush_result = connection_dirserv_flushed_some(conn);
    tor_assert_nonfatal(initial_flush_result == 0);
    goto done;
  }

 done:
  if (clear_spool) {
    dir_conn_clear_spool(conn);
  }
  return 0;
}

/** Helper function for GET /tor/{server,extra}/...
 */
static int
handle_get_descriptor(dir_connection_t *conn, const get_handler_args_t *args)
{
  const char *url = args->url;
  const compress_method_t compress_method =
    find_best_compression_method(args->compression_supported, 1);
  const or_options_t *options = get_options();
  int clear_spool = 1;
  if (!strcmpstart(url,"/tor/server/") ||
      (!options->BridgeAuthoritativeDir &&
       !options->BridgeRelay && !strcmpstart(url,"/tor/extra/"))) {
    int res;
    const char *msg = NULL;
    int cache_lifetime = 0;
    int is_extra = !strcmpstart(url,"/tor/extra/");
    url += is_extra ? strlen("/tor/extra/") : strlen("/tor/server/");
    dir_spool_source_t source;
    time_t publish_cutoff = 0;
    if (!strcmpstart(url, "d/")) {
      source =
        is_extra ? DIR_SPOOL_EXTRA_BY_DIGEST : DIR_SPOOL_SERVER_BY_DIGEST;
    } else {
      source =
        is_extra ? DIR_SPOOL_EXTRA_BY_FP : DIR_SPOOL_SERVER_BY_FP;
      /* We only want to apply a publish cutoff when we're requesting
       * resources by fingerprint. */
      publish_cutoff = time(NULL) - ROUTER_MAX_AGE_TO_PUBLISH;
    }

    conn->spool = smartlist_new();
    res = dirserv_get_routerdesc_spool(conn->spool, url,
                                       source,
                                       connection_dir_is_encrypted(conn),
                                       &msg);

    if (!strcmpstart(url, "all")) {
      cache_lifetime = FULL_DIR_CACHE_LIFETIME;
    } else if (smartlist_len(conn->spool) == 1) {
      cache_lifetime = ROUTERDESC_BY_DIGEST_CACHE_LIFETIME;
    }

    size_t size_guess = 0;
    int n_expired = 0;
    dirserv_spool_remove_missing_and_guess_size(conn, publish_cutoff,
                                                compress_method != NO_METHOD,
                                                &size_guess, &n_expired);

    /* If we are the bridge authority and the descriptor is a bridge
     * descriptor, remember that we served this descriptor for desc stats. */
    /* XXXX it's a bit of a kludge to have this here. */
    if (get_options()->BridgeAuthoritativeDir &&
        source == DIR_SPOOL_SERVER_BY_FP) {
      SMARTLIST_FOREACH_BEGIN(conn->spool, spooled_resource_t *, spooled) {
        const routerinfo_t *router =
          router_get_by_id_digest((const char *)spooled->digest);
        /* router can be NULL here when the bridge auth is asked for its own
         * descriptor. */
        if (router && router->purpose == ROUTER_PURPOSE_BRIDGE)
          rep_hist_note_desc_served(router->cache_info.identity_digest);
      } SMARTLIST_FOREACH_END(spooled);
    }

    if (res < 0 || size_guess == 0 || smartlist_len(conn->spool) == 0) {
      if (msg == NULL)
        msg = "Not found";
      write_http_status_line(conn, 404, msg);
    } else {
      if (global_write_bucket_low(TO_CONN(conn), size_guess, 2)) {
        log_info(LD_DIRSERV,
                 "Client asked for server descriptors, but we've been "
                 "writing too many bytes lately. Sending 503 Dir busy.");
        write_http_status_line(conn, 503, "Directory busy, try again later");
        dir_conn_clear_spool(conn);
        goto done;
      }
      write_http_response_header(conn, -1, compress_method, cache_lifetime);
      if (compress_method != NO_METHOD)
        conn->compress_state = tor_compress_new(1, compress_method,
                                        choose_compression_level(size_guess));
      clear_spool = 0;
      /* Prime the connection with some data. */
      int initial_flush_result = connection_dirserv_flushed_some(conn);
      tor_assert_nonfatal(initial_flush_result == 0);
    }
    goto done;
  }
 done:
  if (clear_spool)
    dir_conn_clear_spool(conn);
  return 0;
}

/** Helper function for GET /tor/keys/...
 */
static int
handle_get_keys(dir_connection_t *conn, const get_handler_args_t *args)
{
  const char *url = args->url;
  const compress_method_t compress_method =
    find_best_compression_method(args->compression_supported, 1);
  const time_t if_modified_since = args->if_modified_since;
  {
    smartlist_t *certs = smartlist_new();
    ssize_t len = -1;
    if (!strcmp(url, "/tor/keys/all")) {
      authority_cert_get_all(certs);
    } else if (!strcmp(url, "/tor/keys/authority")) {
      authority_cert_t *cert = get_my_v3_authority_cert();
      if (cert)
        smartlist_add(certs, cert);
    } else if (!strcmpstart(url, "/tor/keys/fp/")) {
      smartlist_t *fps = smartlist_new();
      dir_split_resource_into_fingerprints(url+strlen("/tor/keys/fp/"),
                                           fps, NULL,
                                           DSR_HEX|DSR_SORT_UNIQ);
      SMARTLIST_FOREACH(fps, char *, d, {
          authority_cert_t *c = authority_cert_get_newest_by_id(d);
          if (c) smartlist_add(certs, c);
          tor_free(d);
      });
      smartlist_free(fps);
    } else if (!strcmpstart(url, "/tor/keys/sk/")) {
      smartlist_t *fps = smartlist_new();
      dir_split_resource_into_fingerprints(url+strlen("/tor/keys/sk/"),
                                           fps, NULL,
                                           DSR_HEX|DSR_SORT_UNIQ);
      SMARTLIST_FOREACH(fps, char *, d, {
          authority_cert_t *c = authority_cert_get_by_sk_digest(d);
          if (c) smartlist_add(certs, c);
          tor_free(d);
      });
      smartlist_free(fps);
    } else if (!strcmpstart(url, "/tor/keys/fp-sk/")) {
      smartlist_t *fp_sks = smartlist_new();
      dir_split_resource_into_fingerprint_pairs(url+strlen("/tor/keys/fp-sk/"),
                                                fp_sks);
      SMARTLIST_FOREACH(fp_sks, fp_pair_t *, pair, {
          authority_cert_t *c = authority_cert_get_by_digests(pair->first,
                                                              pair->second);
          if (c) smartlist_add(certs, c);
          tor_free(pair);
      });
      smartlist_free(fp_sks);
    } else {
      write_http_status_line(conn, 400, "Bad request");
      goto keys_done;
    }
    if (!smartlist_len(certs)) {
      write_http_status_line(conn, 404, "Not found");
      goto keys_done;
    }
    SMARTLIST_FOREACH(certs, authority_cert_t *, c,
      if (c->cache_info.published_on < if_modified_since)
        SMARTLIST_DEL_CURRENT(certs, c));
    if (!smartlist_len(certs)) {
      write_http_status_line(conn, 304, "Not modified");
      goto keys_done;
    }
    len = 0;
    SMARTLIST_FOREACH(certs, authority_cert_t *, c,
                      len += c->cache_info.signed_descriptor_len);

    if (global_write_bucket_low(TO_CONN(conn),
                                compress_method != NO_METHOD ? len/2 : len,
                                2)) {
      write_http_status_line(conn, 503, "Directory busy, try again later");
      goto keys_done;
    }

    write_http_response_header(conn,
                               compress_method != NO_METHOD ? -1 : len,
                               compress_method,
                               60*60);
    if (compress_method != NO_METHOD) {
      conn->compress_state = tor_compress_new(1, compress_method,
                                              choose_compression_level(len));
      SMARTLIST_FOREACH(certs, authority_cert_t *, c,
            connection_write_to_buf_compress(
                c->cache_info.signed_descriptor_body,
                c->cache_info.signed_descriptor_len,
                conn, 0));
      connection_write_to_buf_compress("", 0, conn, 1);
    } else {
      SMARTLIST_FOREACH(certs, authority_cert_t *, c,
            connection_write_to_buf(c->cache_info.signed_descriptor_body,
                                    c->cache_info.signed_descriptor_len,
                                    TO_CONN(conn)));
    }
  keys_done:
    smartlist_free(certs);
    goto done;
  }
 done:
  return 0;
}

/** Helper function for GET /tor/rendezvous2/
 */
static int
handle_get_hs_descriptor_v2(dir_connection_t *conn,
                            const get_handler_args_t *args)
{
  const char *url = args->url;
  if (connection_dir_is_encrypted(conn)) {
    /* Handle v2 rendezvous descriptor fetch request. */
    const char *descp;
    const char *query = url + strlen("/tor/rendezvous2/");
    if (rend_valid_descriptor_id(query)) {
      log_info(LD_REND, "Got a v2 rendezvous descriptor request for ID '%s'",
               safe_str(escaped(query)));
      switch (rend_cache_lookup_v2_desc_as_dir(query, &descp)) {
        case 1: /* valid */
          write_http_response_header(conn, strlen(descp), NO_METHOD, 0);
          connection_write_to_buf(descp, strlen(descp), TO_CONN(conn));
          break;
        case 0: /* well-formed but not present */
          write_http_status_line(conn, 404, "Not found");
          break;
        case -1: /* not well-formed */
          write_http_status_line(conn, 400, "Bad request");
          break;
      }
    } else { /* not well-formed */
      write_http_status_line(conn, 400, "Bad request");
    }
    goto done;
  } else {
    /* Not encrypted! */
    write_http_status_line(conn, 404, "Not found");
  }
 done:
  return 0;
}

/** Helper function for GET /tor/hs/3/<z>. Only for version 3.
 */
STATIC int
handle_get_hs_descriptor_v3(dir_connection_t *conn,
                            const get_handler_args_t *args)
{
  int retval;
  const char *desc_str = NULL;
  const char *pubkey_str = NULL;
  const char *url = args->url;

  /* Reject unencrypted dir connections */
  if (!connection_dir_is_encrypted(conn)) {
    write_http_status_line(conn, 404, "Not found");
    goto done;
  }

  /* After the path prefix follows the base64 encoded blinded pubkey which we
   * use to get the descriptor from the cache. Skip the prefix and get the
   * pubkey. */
  tor_assert(!strcmpstart(url, "/tor/hs/3/"));
  pubkey_str = url + strlen("/tor/hs/3/");
  retval = hs_cache_lookup_as_dir(HS_VERSION_THREE,
                                  pubkey_str, &desc_str);
  if (retval <= 0 || desc_str == NULL) {
    write_http_status_line(conn, 404, "Not found");
    goto done;
  }

  /* Found requested descriptor! Pass it to this nice client. */
  write_http_response_header(conn, strlen(desc_str), NO_METHOD, 0);
  connection_write_to_buf(desc_str, strlen(desc_str), TO_CONN(conn));

 done:
  return 0;
}

/** Helper function for GET /tor/networkstatus-bridges
 */
static int
handle_get_networkstatus_bridges(dir_connection_t *conn,
                                 const get_handler_args_t *args)
{
  const char *headers = args->headers;

  const or_options_t *options = get_options();
  if (options->BridgeAuthoritativeDir &&
      options->BridgePassword_AuthDigest_ &&
      connection_dir_is_encrypted(conn)) {
    char *status;
    char digest[DIGEST256_LEN];

    char *header = http_get_header(headers, "Authorization: Basic ");
    if (header)
      crypto_digest256(digest, header, strlen(header), DIGEST_SHA256);

    /* now make sure the password is there and right */
    if (!header ||
        tor_memneq(digest,
                   options->BridgePassword_AuthDigest_, DIGEST256_LEN)) {
      write_http_status_line(conn, 404, "Not found");
      tor_free(header);
      goto done;
    }
    tor_free(header);

    /* all happy now. send an answer. */
    status = networkstatus_getinfo_by_purpose("bridge", time(NULL));
    size_t dlen = strlen(status);
    write_http_response_header(conn, dlen, NO_METHOD, 0);
    connection_write_to_buf(status, dlen, TO_CONN(conn));
    tor_free(status);
    goto done;
  }
 done:
  return 0;
}

/** Helper function for GET robots.txt or /tor/robots.txt */
static int
handle_get_robots(dir_connection_t *conn, const get_handler_args_t *args)
{
  (void)args;
  {
    const char robots[] = "User-agent: *\r\nDisallow: /\r\n";
    size_t len = strlen(robots);
    write_http_response_header(conn, len, NO_METHOD, ROBOTS_CACHE_LIFETIME);
    connection_write_to_buf(robots, len, TO_CONN(conn));
  }
  return 0;
}

/* Given the <b>url</b> from a POST request, try to extract the version number
 * using the provided <b>prefix</b>. The version should be after the prefix and
 * ending with the seperator "/". For instance:
 *      /tor/hs/3/publish
 *
 * On success, <b>end_pos</b> points to the position right after the version
 * was found. On error, it is set to NULL.
 *
 * Return version on success else negative value. */
STATIC int
parse_hs_version_from_post(const char *url, const char *prefix,
                           const char **end_pos)
{
  int ok;
  unsigned long version;
  const char *start;
  char *end = NULL;

  tor_assert(url);
  tor_assert(prefix);
  tor_assert(end_pos);

  /* Check if the prefix does start the url. */
  if (strcmpstart(url, prefix)) {
    goto err;
  }
  /* Move pointer to the end of the prefix string. */
  start = url + strlen(prefix);
  /* Try this to be the HS version and if we are still at the separator, next
   * will be move to the right value. */
  version = tor_parse_long(start, 10, 0, INT_MAX, &ok, &end);
  if (!ok) {
    goto err;
  }

  *end_pos = end;
  return (int) version;
 err:
  *end_pos = NULL;
  return -1;
}

/* Handle the POST request for a hidden service descripror. The request is in
 * <b>url</b>, the body of the request is in <b>body</b>. Return 200 on success
 * else return 400 indicating a bad request. */
STATIC int
handle_post_hs_descriptor(const char *url, const char *body)
{
  int version;
  const char *end_pos;

  tor_assert(url);
  tor_assert(body);

  version = parse_hs_version_from_post(url, "/tor/hs/", &end_pos);
  if (version < 0) {
    goto err;
  }

  /* We have a valid version number, now make sure it's a publish request. Use
   * the end position just after the version and check for the command. */
  if (strcmpstart(end_pos, "/publish")) {
    goto err;
  }

  switch (version) {
  case HS_VERSION_THREE:
    if (hs_cache_store_as_dir(body) < 0) {
      goto err;
    }
    log_info(LD_REND, "Publish request for HS descriptor handled "
                      "successfully.");
    break;
  default:
    /* Unsupported version, return a bad request. */
    goto err;
  }

  return 200;
 err:
  /* Bad request. */
  return 400;
}

/** Helper function: called when a dirserver gets a complete HTTP POST
 * request.  Look for an uploaded server descriptor or rendezvous
 * service descriptor.  On finding one, process it and write a
 * response into conn-\>outbuf.  If the request is unrecognized, send a
 * 400.  Always return 0. */
MOCK_IMPL(STATIC int,
directory_handle_command_post,(dir_connection_t *conn, const char *headers,
                               const char *body, size_t body_len))
{
  char *url = NULL;
  const or_options_t *options = get_options();

  log_debug(LD_DIRSERV,"Received POST command.");

  conn->base_.state = DIR_CONN_STATE_SERVER_WRITING;

  if (!public_server_mode(options)) {
    log_info(LD_DIR, "Rejected dir post request from %s "
             "since we're not a public relay.", conn->base_.address);
    write_http_status_line(conn, 503, "Not acting as a public relay");
    goto done;
  }

  if (parse_http_url(headers, &url) < 0) {
    write_http_status_line(conn, 400, "Bad request");
    return 0;
  }
  log_debug(LD_DIRSERV,"rewritten url as '%s'.", escaped(url));

  /* Handle v2 rendezvous service publish request. */
  if (connection_dir_is_encrypted(conn) &&
      !strcmpstart(url,"/tor/rendezvous2/publish")) {
    if (rend_cache_store_v2_desc_as_dir(body) < 0) {
      log_warn(LD_REND, "Rejected v2 rend descriptor (body size %d) from %s.",
               (int)body_len, conn->base_.address);
      write_http_status_line(conn, 400,
                             "Invalid v2 service descriptor rejected");
    } else {
      write_http_status_line(conn, 200, "Service descriptor (v2) stored");
      log_info(LD_REND, "Handled v2 rendezvous descriptor post: accepted");
    }
    goto done;
  }

  /* Handle HS descriptor publish request. */
  /* XXX: This should be disabled with a consensus param until we want to
   * the prop224 be deployed and thus use. */
  if (connection_dir_is_encrypted(conn) && !strcmpstart(url, "/tor/hs/")) {
    const char *msg = "HS descriptor stored successfully.";

    /* We most probably have a publish request for an HS descriptor. */
    int code = handle_post_hs_descriptor(url, body);
    if (code != 200) {
      msg = "Invalid HS descriptor. Rejected.";
    }
    write_http_status_line(conn, code, msg);
    goto done;
  }

  if (!authdir_mode(options)) {
    /* we just provide cached directories; we don't want to
     * receive anything. */
    write_http_status_line(conn, 400, "Nonauthoritative directory does not "
                           "accept posted server descriptors");
    goto done;
  }

  if (authdir_mode_handles_descs(options, -1) &&
      !strcmp(url,"/tor/")) { /* server descriptor post */
    const char *msg = "[None]";
    uint8_t purpose = authdir_mode_bridge(options) ?
                      ROUTER_PURPOSE_BRIDGE : ROUTER_PURPOSE_GENERAL;
    was_router_added_t r = dirserv_add_multiple_descriptors(body, purpose,
                                             conn->base_.address, &msg);
    tor_assert(msg);

    if (r == ROUTER_ADDED_SUCCESSFULLY) {
      write_http_status_line(conn, 200, msg);
    } else if (WRA_WAS_OUTDATED(r)) {
      write_http_response_header_impl(conn, -1, NULL, NULL,
                                      "X-Descriptor-Not-New: Yes\r\n", -1);
    } else {
      log_info(LD_DIRSERV,
               "Rejected router descriptor or extra-info from %s "
               "(\"%s\").",
               conn->base_.address, msg);
      write_http_status_line(conn, 400, msg);
    }
    goto done;
  }

  if (authdir_mode_v3(options) &&
      !strcmp(url,"/tor/post/vote")) { /* v3 networkstatus vote */
    const char *msg = "OK";
    int status;
    if (dirvote_add_vote(body, &msg, &status)) {
      write_http_status_line(conn, status, "Vote stored");
    } else {
      tor_assert(msg);
      log_warn(LD_DIRSERV, "Rejected vote from %s (\"%s\").",
               conn->base_.address, msg);
      write_http_status_line(conn, status, msg);
    }
    goto done;
  }

  if (authdir_mode_v3(options) &&
      !strcmp(url,"/tor/post/consensus-signature")) { /* sigs on consensus. */
    const char *msg = NULL;
    if (dirvote_add_signatures(body, conn->base_.address, &msg)>=0) {
      write_http_status_line(conn, 200, msg?msg:"Signatures stored");
    } else {
      log_warn(LD_DIR, "Unable to store signatures posted by %s: %s",
               conn->base_.address, msg?msg:"???");
      write_http_status_line(conn, 400, msg?msg:"Unable to store signatures");
    }
    goto done;
  }

  /* we didn't recognize the url */
  write_http_status_line(conn, 404, "Not found");

 done:
  tor_free(url);
  return 0;
}

/** Called when a dirserver receives data on a directory connection;
 * looks for an HTTP request.  If the request is complete, remove it
 * from the inbuf, try to process it; otherwise, leave it on the
 * buffer.  Return a 0 on success, or -1 on error.
 */
STATIC int
directory_handle_command(dir_connection_t *conn)
{
  char *headers=NULL, *body=NULL;
  size_t body_len=0;
  int r;

  tor_assert(conn);
  tor_assert(conn->base_.type == CONN_TYPE_DIR);

  switch (connection_fetch_from_buf_http(TO_CONN(conn),
                              &headers, MAX_HEADERS_SIZE,
                              &body, &body_len, MAX_DIR_UL_SIZE, 0)) {
    case -1: /* overflow */
      log_warn(LD_DIRSERV,
               "Request too large from address '%s' to DirPort. Closing.",
               safe_str(conn->base_.address));
      return -1;
    case 0:
      log_debug(LD_DIRSERV,"command not all here yet.");
      return 0;
    /* case 1, fall through */
  }

  http_set_address_origin(headers, TO_CONN(conn));
  // we should escape headers here as well,
  // but we can't call escaped() twice, as it uses the same buffer
  //log_debug(LD_DIRSERV,"headers %s, body %s.", headers, escaped(body));

  if (!strncasecmp(headers,"GET",3))
    r = directory_handle_command_get(conn, headers, body, body_len);
  else if (!strncasecmp(headers,"POST",4))
    r = directory_handle_command_post(conn, headers, body, body_len);
  else {
    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
           "Got headers %s with unknown command. Closing.",
           escaped(headers));
    r = -1;
  }

  tor_free(headers); tor_free(body);
  return r;
}

/** Write handler for directory connections; called when all data has
 * been flushed.  Close the connection or wait for a response as
 * appropriate.
 */
int
connection_dir_finished_flushing(dir_connection_t *conn)
{
  tor_assert(conn);
  tor_assert(conn->base_.type == CONN_TYPE_DIR);

  /* Note that we have finished writing the directory response. For direct
   * connections this means we're done; for tunneled connections it's only
   * an intermediate step. */
  if (conn->dirreq_id)
    geoip_change_dirreq_state(conn->dirreq_id, DIRREQ_TUNNELED,
                              DIRREQ_FLUSHING_DIR_CONN_FINISHED);
  else
    geoip_change_dirreq_state(TO_CONN(conn)->global_identifier,
                              DIRREQ_DIRECT,
                              DIRREQ_FLUSHING_DIR_CONN_FINISHED);
  switch (conn->base_.state) {
    case DIR_CONN_STATE_CONNECTING:
    case DIR_CONN_STATE_CLIENT_SENDING:
      log_debug(LD_DIR,"client finished sending command.");
      conn->base_.state = DIR_CONN_STATE_CLIENT_READING;
      return 0;
    case DIR_CONN_STATE_SERVER_WRITING:
      if (conn->spool) {
        log_warn(LD_BUG, "Emptied a dirserv buffer, but it's still spooling!");
        connection_mark_for_close(TO_CONN(conn));
      } else {
        log_debug(LD_DIRSERV, "Finished writing server response. Closing.");
        connection_mark_for_close(TO_CONN(conn));
      }
      return 0;
    default:
      log_warn(LD_BUG,"called in unexpected state %d.",
               conn->base_.state);
      tor_fragile_assert();
      return -1;
  }
  return 0;
}

/* We just got a new consensus! If there are other in-progress requests
 * for this consensus flavor (for example because we launched several in
 * parallel), cancel them.
 *
 * We do this check here (not just in
 * connection_ap_handshake_attach_circuit()) to handle the edge case where
 * a consensus fetch begins and ends before some other one tries to attach to
 * a circuit, in which case the other one won't know that we're all happy now.
 *
 * Don't mark the conn that just gave us the consensus -- otherwise we
 * would end up double-marking it when it cleans itself up.
 */
static void
connection_dir_close_consensus_fetches(dir_connection_t *except_this_one,
                                       const char *resource)
{
  smartlist_t *conns_to_close =
    connection_dir_list_by_purpose_and_resource(DIR_PURPOSE_FETCH_CONSENSUS,
                                                resource);
  SMARTLIST_FOREACH_BEGIN(conns_to_close, dir_connection_t *, d) {
    if (d == except_this_one)
      continue;
    log_info(LD_DIR, "Closing consensus fetch (to %s) since one "
             "has just arrived.", TO_CONN(d)->address);
    connection_mark_for_close(TO_CONN(d));
  } SMARTLIST_FOREACH_END(d);
  smartlist_free(conns_to_close);
}

/** Connected handler for directory connections: begin sending data to the
 * server, and return 0.
 * Only used when connections don't immediately connect. */
int
connection_dir_finished_connecting(dir_connection_t *conn)
{
  tor_assert(conn);
  tor_assert(conn->base_.type == CONN_TYPE_DIR);
  tor_assert(conn->base_.state == DIR_CONN_STATE_CONNECTING);

  log_debug(LD_HTTP,"Dir connection to router %s:%u established.",
            conn->base_.address,conn->base_.port);

  /* start flushing conn */
  conn->base_.state = DIR_CONN_STATE_CLIENT_SENDING;
  return 0;
}

/** Decide which download schedule we want to use based on descriptor type
 * in <b>dls</b> and <b>options</b>.
 * Then return a list of int pointers defining download delays in seconds.
 * Helper function for download_status_increment_failure(),
 * download_status_reset(), and download_status_increment_attempt(). */
STATIC const smartlist_t *
find_dl_schedule(download_status_t *dls, const or_options_t *options)
{
  const int dir_server = dir_server_mode(options);
  const int multi_d = networkstatus_consensus_can_use_multiple_directories(
                                                                    options);
  const int we_are_bootstrapping = networkstatus_consensus_is_bootstrapping(
                                                                 time(NULL));
  const int use_fallbacks = networkstatus_consensus_can_use_extra_fallbacks(
                                                                    options);
  switch (dls->schedule) {
    case DL_SCHED_GENERIC:
      if (dir_server) {
        return options->TestingServerDownloadSchedule;
      } else {
        return options->TestingClientDownloadSchedule;
      }
    case DL_SCHED_CONSENSUS:
      if (!multi_d) {
        return options->TestingServerConsensusDownloadSchedule;
      } else {
        if (we_are_bootstrapping) {
          if (!use_fallbacks) {
            /* A bootstrapping client without extra fallback directories */
            return
             options->ClientBootstrapConsensusAuthorityOnlyDownloadSchedule;
          } else if (dls->want_authority) {
            /* A bootstrapping client with extra fallback directories, but
             * connecting to an authority */
            return
             options->ClientBootstrapConsensusAuthorityDownloadSchedule;
          } else {
            /* A bootstrapping client connecting to extra fallback directories
             */
            return
              options->ClientBootstrapConsensusFallbackDownloadSchedule;
          }
        } else {
          return options->TestingClientConsensusDownloadSchedule;
        }
      }
    case DL_SCHED_BRIDGE:
      return options->TestingBridgeDownloadSchedule;
    default:
      tor_assert(0);
  }

  /* Impossible, but gcc will fail with -Werror without a `return`. */
  return NULL;
}

/** Decide which minimum and maximum delay step we want to use based on
 * descriptor type in <b>dls</b> and <b>options</b>.
 * Helper function for download_status_schedule_get_delay(). */
STATIC void
find_dl_min_and_max_delay(download_status_t *dls, const or_options_t *options,
                          int *min, int *max)
{
  tor_assert(dls);
  tor_assert(options);
  tor_assert(min);
  tor_assert(max);

  /*
   * For now, just use the existing schedule config stuff and pick the
   * first/last entries off to get min/max delay for backoff purposes
   */
  const smartlist_t *schedule = find_dl_schedule(dls, options);
  tor_assert(schedule != NULL && smartlist_len(schedule) >= 2);
  *min = *((int *)(smartlist_get(schedule, 0)));
  if (dls->backoff == DL_SCHED_DETERMINISTIC)
    *max = *((int *)((smartlist_get(schedule, smartlist_len(schedule) - 1))));
  else
    *max = INT_MAX;
}

/** Advance one delay step.  The algorithm is to use the previous delay to
 * compute an increment, we construct a value uniformly at random between
 * delay and MAX(delay*2,delay+1).  We then clamp that value to be no larger
 * than max_delay, and return it.
 *
 * Requires that delay is less than INT_MAX, and delay is in [0,max_delay].
 */
STATIC int
next_random_exponential_delay(int delay, int max_delay)
{
  /* Check preconditions */
  if (BUG(max_delay < 0))
    max_delay = 0;
  if (BUG(delay > max_delay))
    delay = max_delay;
  if (delay == INT_MAX)
    return INT_MAX; /* prevent overflow */
  if (BUG(delay < 0))
    delay = 0;

  /* How much are we willing to add to the delay? */
  int max_increment;
  int multiplier = 3; /* no more than quadruple the previous delay */
  if (get_options()->TestingTorNetwork) {
    /* Decrease the multiplier in testing networks. This reduces the variance,
     * so that bootstrap is more reliable. */
    multiplier = 2; /* no more than triple the previous delay */
  }

  if (delay && delay < (INT_MAX-1) / multiplier) {
    max_increment = delay * multiplier;
  } else if (delay) {
    max_increment = INT_MAX-1;
  } else {
    max_increment = 1;
  }

  if (BUG(max_increment < 1))
    max_increment = 1;

  /* the + 1 here is so that we always wait longer than last time. */
  int increment = crypto_rand_int(max_increment)+1;

  if (increment < max_delay - delay)
    return delay + increment;
  else
    return max_delay;
}

/** Find the current delay for dls based on schedule or min_delay/
 * max_delay if we're using exponential backoff.  If dls->backoff is
 * DL_SCHED_RANDOM_EXPONENTIAL, we must have 0 <= min_delay <= max_delay <=
 * INT_MAX, but schedule may be set to NULL; otherwise schedule is required.
 * This function sets dls->next_attempt_at based on now, and returns the delay.
 * Helper for download_status_increment_failure and
 * download_status_increment_attempt. */
STATIC int
download_status_schedule_get_delay(download_status_t *dls,
                                   const smartlist_t *schedule,
                                   int min_delay, int max_delay,
                                   time_t now)
{
  tor_assert(dls);
  /* We don't need a schedule if we're using random exponential backoff */
  tor_assert(dls->backoff == DL_SCHED_RANDOM_EXPONENTIAL ||
             schedule != NULL);
  /* If we're using random exponential backoff, we do need min/max delay */
  tor_assert(dls->backoff != DL_SCHED_RANDOM_EXPONENTIAL ||
             (min_delay >= 0 && max_delay >= min_delay));

  int delay = INT_MAX;
  uint8_t dls_schedule_position = (dls->increment_on
                                   == DL_SCHED_INCREMENT_ATTEMPT
                                   ? dls->n_download_attempts
                                   : dls->n_download_failures);

  if (dls->backoff == DL_SCHED_DETERMINISTIC) {
    if (dls_schedule_position < smartlist_len(schedule))
      delay = *(int *)smartlist_get(schedule, dls_schedule_position);
    else if (dls_schedule_position == IMPOSSIBLE_TO_DOWNLOAD)
      delay = INT_MAX;
    else
      delay = *(int *)smartlist_get(schedule, smartlist_len(schedule) - 1);
  } else if (dls->backoff == DL_SCHED_RANDOM_EXPONENTIAL) {
    /* Check if we missed a reset somehow */
    IF_BUG_ONCE(dls->last_backoff_position > dls_schedule_position) {
      dls->last_backoff_position = 0;
      dls->last_delay_used = 0;
    }

    if (dls_schedule_position > 0) {
      delay = dls->last_delay_used;

      while (dls->last_backoff_position < dls_schedule_position) {
        /* Do one increment step */
        delay = next_random_exponential_delay(delay, max_delay);
        /* Update our position */
        ++(dls->last_backoff_position);
      }
    } else {
      /* If we're just starting out, use the minimum delay */
      delay = min_delay;
    }

    /* Clamp it within min/max if we have them */
    if (min_delay >= 0 && delay < min_delay) delay = min_delay;
    if (max_delay != INT_MAX && delay > max_delay) delay = max_delay;

    /* Store it for next time */
    dls->last_backoff_position = dls_schedule_position;
    dls->last_delay_used = delay;
  }

  /* A negative delay makes no sense. Knowing that delay is
   * non-negative allows us to safely do the wrapping check below. */
  tor_assert(delay >= 0);

  /* Avoid now+delay overflowing TIME_MAX, by comparing with a subtraction
   * that won't overflow (since delay is non-negative). */
  if (delay < INT_MAX && now <= TIME_MAX - delay) {
    dls->next_attempt_at = now+delay;
  } else {
    dls->next_attempt_at = TIME_MAX;
  }

  return delay;
}

/* Log a debug message about item, which increments on increment_action, has
 * incremented dls_n_download_increments times. The message varies based on
 * was_schedule_incremented (if not, not_incremented_response is logged), and
 * the values of increment, dls_next_attempt_at, and now.
 * Helper for download_status_increment_failure and
 * download_status_increment_attempt. */
static void
download_status_log_helper(const char *item, int was_schedule_incremented,
                           const char *increment_action,
                           const char *not_incremented_response,
                           uint8_t dls_n_download_increments, int increment,
                           time_t dls_next_attempt_at, time_t now)
{
  if (item) {
    if (!was_schedule_incremented)
      log_debug(LD_DIR, "%s %s %d time(s); I'll try again %s.",
                item, increment_action, (int)dls_n_download_increments,
                not_incremented_response);
    else if (increment == 0)
      log_debug(LD_DIR, "%s %s %d time(s); I'll try again immediately.",
                item, increment_action, (int)dls_n_download_increments);
    else if (dls_next_attempt_at < TIME_MAX)
      log_debug(LD_DIR, "%s %s %d time(s); I'll try again in %d seconds.",
                item, increment_action, (int)dls_n_download_increments,
                (int)(dls_next_attempt_at-now));
    else
      log_debug(LD_DIR, "%s %s %d time(s); Giving up for a while.",
                item, increment_action, (int)dls_n_download_increments);
  }
}

/** Determine when a failed download attempt should be retried.
 * Called when an attempt to download <b>dls</b> has failed with HTTP status
 * <b>status_code</b>.  Increment the failure count (if the code indicates a
 * real failure, or if we're a server) and set <b>dls</b>-\>next_attempt_at to
 * an appropriate time in the future and return it.
 * If <b>dls->increment_on</b> is DL_SCHED_INCREMENT_ATTEMPT, increment the
 * failure count, and return a time in the far future for the next attempt (to
 * avoid an immediate retry). */
time_t
download_status_increment_failure(download_status_t *dls, int status_code,
                                  const char *item, int server, time_t now)
{
  (void) status_code; // XXXX no longer used.
  (void) server; // XXXX no longer used.
  int increment = -1;
  int min_delay = 0, max_delay = INT_MAX;

  tor_assert(dls);

  /* count the failure */
  if (dls->n_download_failures < IMPOSSIBLE_TO_DOWNLOAD-1) {
    ++dls->n_download_failures;
  }

  if (dls->increment_on == DL_SCHED_INCREMENT_FAILURE) {
    /* We don't find out that a failure-based schedule has attempted a
     * connection until that connection fails.
     * We'll never find out about successful connections, but this doesn't
     * matter, because schedules are reset after a successful download.
     */
    if (dls->n_download_attempts < IMPOSSIBLE_TO_DOWNLOAD-1)
      ++dls->n_download_attempts;

    /* only return a failure retry time if this schedule increments on failures
     */
    const smartlist_t *schedule = find_dl_schedule(dls, get_options());
    find_dl_min_and_max_delay(dls, get_options(), &min_delay, &max_delay);
    increment = download_status_schedule_get_delay(dls, schedule,
                                                   min_delay, max_delay, now);
  }

  download_status_log_helper(item, !dls->increment_on, "failed",
                             "concurrently", dls->n_download_failures,
                             increment, dls->next_attempt_at, now);

  if (dls->increment_on == DL_SCHED_INCREMENT_ATTEMPT) {
    /* stop this schedule retrying on failure, it will launch concurrent
     * connections instead */
    return TIME_MAX;
  } else {
    return dls->next_attempt_at;
  }
}

/** Determine when the next download attempt should be made when using an
 * attempt-based (potentially concurrent) download schedule.
 * Called when an attempt to download <b>dls</b> is being initiated.
 * Increment the attempt count and set <b>dls</b>-\>next_attempt_at to an
 * appropriate time in the future and return it.
 * If <b>dls->increment_on</b> is DL_SCHED_INCREMENT_FAILURE, don't increment
 * the attempts, and return a time in the far future (to avoid launching a
 * concurrent attempt). */
time_t
download_status_increment_attempt(download_status_t *dls, const char *item,
                                  time_t now)
{
  int delay = -1;
  int min_delay = 0, max_delay = INT_MAX;

  tor_assert(dls);

  if (dls->increment_on == DL_SCHED_INCREMENT_FAILURE) {
    /* this schedule should retry on failure, and not launch any concurrent
     attempts */
    log_warn(LD_BUG, "Tried to launch an attempt-based connection on a "
             "failure-based schedule.");
    return TIME_MAX;
  }

  if (dls->n_download_attempts < IMPOSSIBLE_TO_DOWNLOAD-1)
    ++dls->n_download_attempts;

  const smartlist_t *schedule = find_dl_schedule(dls, get_options());
  find_dl_min_and_max_delay(dls, get_options(), &min_delay, &max_delay);
  delay = download_status_schedule_get_delay(dls, schedule,
                                             min_delay, max_delay, now);

  download_status_log_helper(item, dls->increment_on, "attempted",
                             "on failure", dls->n_download_attempts,
                             delay, dls->next_attempt_at, now);

  return dls->next_attempt_at;
}

/** Reset <b>dls</b> so that it will be considered downloadable
 * immediately, and/or to show that we don't need it anymore.
 *
 * Must be called to initialise a download schedule, otherwise the zeroth item
 * in the schedule will never be used.
 *
 * (We find the zeroth element of the download schedule, and set
 * next_attempt_at to be the appropriate offset from 'now'. In most
 * cases this means setting it to 'now', so the item will be immediately
 * downloadable; in the case of bridge descriptors, the zeroth element
 * is an hour from now.) */
void
download_status_reset(download_status_t *dls)
{
  if (dls->n_download_failures == IMPOSSIBLE_TO_DOWNLOAD
      || dls->n_download_attempts == IMPOSSIBLE_TO_DOWNLOAD)
    return; /* Don't reset this. */

  const smartlist_t *schedule = find_dl_schedule(dls, get_options());

  dls->n_download_failures = 0;
  dls->n_download_attempts = 0;
  dls->next_attempt_at = time(NULL) + *(int *)smartlist_get(schedule, 0);
  dls->last_backoff_position = 0;
  dls->last_delay_used = 0;
  /* Don't reset dls->want_authority or dls->increment_on */
}

/** Return the number of failures on <b>dls</b> since the last success (if
 * any). */
int
download_status_get_n_failures(const download_status_t *dls)
{
  return dls->n_download_failures;
}

/** Return the number of attempts to download <b>dls</b> since the last success
 * (if any). This can differ from download_status_get_n_failures() due to
 * outstanding concurrent attempts. */
int
download_status_get_n_attempts(const download_status_t *dls)
{
  return dls->n_download_attempts;
}

/** Return the next time to attempt to download <b>dls</b>. */
time_t
download_status_get_next_attempt_at(const download_status_t *dls)
{
  return dls->next_attempt_at;
}

/** Called when one or more routerdesc (or extrainfo, if <b>was_extrainfo</b>)
 * fetches have failed (with uppercase fingerprints listed in <b>failed</b>,
 * either as descriptor digests or as identity digests based on
 * <b>was_descriptor_digests</b>).
 */
static void
dir_routerdesc_download_failed(smartlist_t *failed, int status_code,
                               int router_purpose,
                               int was_extrainfo, int was_descriptor_digests)
{
  char digest[DIGEST_LEN];
  time_t now = time(NULL);
  int server = directory_fetches_from_authorities(get_options());
  if (!was_descriptor_digests) {
    if (router_purpose == ROUTER_PURPOSE_BRIDGE) {
      tor_assert(!was_extrainfo);
      connection_dir_retry_bridges(failed);
    }
    return; /* FFFF should implement for other-than-router-purpose someday */
  }
  SMARTLIST_FOREACH_BEGIN(failed, const char *, cp) {
    download_status_t *dls = NULL;
    if (base16_decode(digest, DIGEST_LEN, cp, strlen(cp)) != DIGEST_LEN) {
      log_warn(LD_BUG, "Malformed fingerprint in list: %s", escaped(cp));
      continue;
    }
    if (was_extrainfo) {
      signed_descriptor_t *sd =
        router_get_by_extrainfo_digest(digest);
      if (sd)
        dls = &sd->ei_dl_status;
    } else {
      dls = router_get_dl_status_by_descriptor_digest(digest);
    }
    if (!dls || dls->n_download_failures >=
                get_options()->TestingDescriptorMaxDownloadTries)
      continue;
    download_status_increment_failure(dls, status_code, cp, server, now);
  } SMARTLIST_FOREACH_END(cp);

  /* No need to relaunch descriptor downloads here: we already do it
   * every 10 or 60 seconds (FOO_DESCRIPTOR_RETRY_INTERVAL) in main.c. */
}

/** Called when a connection to download microdescriptors has failed in whole
 * or in part. <b>failed</b> is a list of every microdesc digest we didn't
 * get. <b>status_code</b> is the http status code we received. Reschedule the
 * microdesc downloads as appropriate. */
static void
dir_microdesc_download_failed(smartlist_t *failed,
                              int status_code)
{
  networkstatus_t *consensus
    = networkstatus_get_latest_consensus_by_flavor(FLAV_MICRODESC);
  routerstatus_t *rs;
  download_status_t *dls;
  time_t now = time(NULL);
  int server = directory_fetches_from_authorities(get_options());

  if (! consensus)
    return;
  SMARTLIST_FOREACH_BEGIN(failed, const char *, d) {
    rs = router_get_mutable_consensus_status_by_descriptor_digest(consensus,d);
    if (!rs)
      continue;
    dls = &rs->dl_status;
    if (dls->n_download_failures >=
        get_options()->TestingMicrodescMaxDownloadTries)
      continue;
    {
      char buf[BASE64_DIGEST256_LEN+1];
      digest256_to_base64(buf, d);
      download_status_increment_failure(dls, status_code, buf,
                                        server, now);
    }
  } SMARTLIST_FOREACH_END(d);
}

/** Helper.  Compare two fp_pair_t objects, and return negative, 0, or
 * positive as appropriate. */
static int
compare_pairs_(const void **a, const void **b)
{
  const fp_pair_t *fp1 = *a, *fp2 = *b;
  int r;
  if ((r = fast_memcmp(fp1->first, fp2->first, DIGEST_LEN)))
    return r;
  else
    return fast_memcmp(fp1->second, fp2->second, DIGEST_LEN);
}

/** Divide a string <b>res</b> of the form FP1-FP2+FP3-FP4...[.z], where each
 * FP is a hex-encoded fingerprint, into a sequence of distinct sorted
 * fp_pair_t. Skip malformed pairs. On success, return 0 and add those
 * fp_pair_t into <b>pairs_out</b>.  On failure, return -1. */
int
dir_split_resource_into_fingerprint_pairs(const char *res,
                                          smartlist_t *pairs_out)
{
  smartlist_t *pairs_tmp = smartlist_new();
  smartlist_t *pairs_result = smartlist_new();

  smartlist_split_string(pairs_tmp, res, "+", 0, 0);
  if (smartlist_len(pairs_tmp)) {
    char *last = smartlist_get(pairs_tmp,smartlist_len(pairs_tmp)-1);
    size_t last_len = strlen(last);
    if (last_len > 2 && !strcmp(last+last_len-2, ".z")) {
      last[last_len-2] = '\0';
    }
  }
  SMARTLIST_FOREACH_BEGIN(pairs_tmp, char *, cp) {
    if (strlen(cp) != HEX_DIGEST_LEN*2+1) {
      log_info(LD_DIR,
             "Skipping digest pair %s with non-standard length.", escaped(cp));
    } else if (cp[HEX_DIGEST_LEN] != '-') {
      log_info(LD_DIR,
             "Skipping digest pair %s with missing dash.", escaped(cp));
    } else {
      fp_pair_t pair;
      if (base16_decode(pair.first, DIGEST_LEN,
                        cp, HEX_DIGEST_LEN) != DIGEST_LEN ||
          base16_decode(pair.second,DIGEST_LEN,
                        cp+HEX_DIGEST_LEN+1, HEX_DIGEST_LEN) != DIGEST_LEN) {
        log_info(LD_DIR, "Skipping non-decodable digest pair %s", escaped(cp));
      } else {
        smartlist_add(pairs_result, tor_memdup(&pair, sizeof(pair)));
      }
    }
    tor_free(cp);
  } SMARTLIST_FOREACH_END(cp);
  smartlist_free(pairs_tmp);

  /* Uniq-and-sort */
  smartlist_sort(pairs_result, compare_pairs_);
  smartlist_uniq(pairs_result, compare_pairs_, tor_free_);

  smartlist_add_all(pairs_out, pairs_result);
  smartlist_free(pairs_result);
  return 0;
}

/** Given a directory <b>resource</b> request, containing zero
 * or more strings separated by plus signs, followed optionally by ".z", store
 * the strings, in order, into <b>fp_out</b>.  If <b>compressed_out</b> is
 * non-NULL, set it to 1 if the resource ends in ".z", else set it to 0.
 *
 * If (flags & DSR_HEX), then delete all elements that aren't hex digests, and
 * decode the rest.  If (flags & DSR_BASE64), then use "-" rather than "+" as
 * a separator, delete all the elements that aren't base64-encoded digests,
 * and decode the rest.  If (flags & DSR_DIGEST256), these digests should be
 * 256 bits long; else they should be 160.
 *
 * If (flags & DSR_SORT_UNIQ), then sort the list and remove all duplicates.
 */
int
dir_split_resource_into_fingerprints(const char *resource,
                                     smartlist_t *fp_out, int *compressed_out,
                                     int flags)
{
  const int decode_hex = flags & DSR_HEX;
  const int decode_base64 = flags & DSR_BASE64;
  const int digests_are_256 = flags & DSR_DIGEST256;
  const int sort_uniq = flags & DSR_SORT_UNIQ;

  const int digest_len = digests_are_256 ? DIGEST256_LEN : DIGEST_LEN;
  const int hex_digest_len = digests_are_256 ?
    HEX_DIGEST256_LEN : HEX_DIGEST_LEN;
  const int base64_digest_len = digests_are_256 ?
    BASE64_DIGEST256_LEN : BASE64_DIGEST_LEN;
  smartlist_t *fp_tmp = smartlist_new();

  tor_assert(!(decode_hex && decode_base64));
  tor_assert(fp_out);

  smartlist_split_string(fp_tmp, resource, decode_base64?"-":"+", 0, 0);
  if (compressed_out)
    *compressed_out = 0;
  if (smartlist_len(fp_tmp)) {
    char *last = smartlist_get(fp_tmp,smartlist_len(fp_tmp)-1);
    size_t last_len = strlen(last);
    if (last_len > 2 && !strcmp(last+last_len-2, ".z")) {
      last[last_len-2] = '\0';
      if (compressed_out)
        *compressed_out = 1;
    }
  }
  if (decode_hex || decode_base64) {
    const size_t encoded_len = decode_hex ? hex_digest_len : base64_digest_len;
    int i;
    char *cp, *d = NULL;
    for (i = 0; i < smartlist_len(fp_tmp); ++i) {
      cp = smartlist_get(fp_tmp, i);
      if (strlen(cp) != encoded_len) {
        log_info(LD_DIR,
                 "Skipping digest %s with non-standard length.", escaped(cp));
        smartlist_del_keeporder(fp_tmp, i--);
        goto again;
      }
      d = tor_malloc_zero(digest_len);
      if (decode_hex ?
          (base16_decode(d, digest_len, cp, hex_digest_len) != digest_len) :
          (base64_decode(d, digest_len, cp, base64_digest_len)
                         != digest_len)) {
          log_info(LD_DIR, "Skipping non-decodable digest %s", escaped(cp));
          smartlist_del_keeporder(fp_tmp, i--);
          goto again;
      }
      smartlist_set(fp_tmp, i, d);
      d = NULL;
    again:
      tor_free(cp);
      tor_free(d);
    }
  }
  if (sort_uniq) {
    if (decode_hex || decode_base64) {
      if (digests_are_256) {
        smartlist_sort_digests256(fp_tmp);
        smartlist_uniq_digests256(fp_tmp);
      } else {
        smartlist_sort_digests(fp_tmp);
        smartlist_uniq_digests(fp_tmp);
      }
    } else {
      smartlist_sort_strings(fp_tmp);
      smartlist_uniq_strings(fp_tmp);
    }
  }
  smartlist_add_all(fp_out, fp_tmp);
  smartlist_free(fp_tmp);
  return 0;
}

/** As dir_split_resource_into_fingerprints, but instead fills
 * <b>spool_out</b> with a list of spoolable_resource_t for the resource
 * identified through <b>source</b>. */
int
dir_split_resource_into_spoolable(const char *resource,
                                  dir_spool_source_t source,
                                  smartlist_t *spool_out,
                                  int *compressed_out,
                                  int flags)
{
  smartlist_t *fingerprints = smartlist_new();

  tor_assert(flags & (DSR_HEX|DSR_BASE64));
  const size_t digest_len =
    (flags & DSR_DIGEST256) ? DIGEST256_LEN : DIGEST_LEN;

  int r = dir_split_resource_into_fingerprints(resource, fingerprints,
                                               compressed_out, flags);
  /* This is not a very efficient implementation XXXX */
  SMARTLIST_FOREACH_BEGIN(fingerprints, uint8_t *, digest) {
    spooled_resource_t *spooled =
      spooled_resource_new(source, digest, digest_len);
    if (spooled)
      smartlist_add(spool_out, spooled);
    tor_free(digest);
  } SMARTLIST_FOREACH_END(digest);

  smartlist_free(fingerprints);
  return r;
}

