connection_edge.c

/* Copyright 2001 Matej Pfajfar.
 * Copyright 2001-2004 Roger Dingledine.
 * Copyright 2004-2005 Roger Dingledine, Nick Mathewson. */
/* See LICENSE for licensing information */
/* $Id$ */
const char connection_edge_c_id[] = "$Id$";

/**
 * \file connection_edge.c
 * \brief Handle edge streams.
 **/

#include "or.h"

static addr_policy_t *socks_policy = NULL;
/* List of exit_redirect_t */
static smartlist_t *redirect_exit_list = NULL;

static int connection_ap_handshake_process_socks(connection_t *conn);

/** An AP stream has failed/finished. If it hasn't already sent back
 * a socks reply, send one now (based on endreason). Also set
 * has_sent_end to 1, and mark the conn.
 */
void
_connection_mark_unattached_ap(connection_t *conn, int endreason,
                               int line, const char *file)
{
  tor_assert(conn->type == CONN_TYPE_AP);
  conn->has_sent_end = 1; /* no circ yet */

  if (conn->marked_for_close) {
    /* This call will warn as appropriate. */
    _connection_mark_for_close(conn, line, file);
    return;
  }

  if (!conn->socks_request->has_finished) {
    socks5_reply_status_t socksreason =
      connection_edge_end_reason_socks5_response(endreason);

    if (endreason == END_STREAM_REASON_ALREADY_SOCKS_REPLIED)
      warn(LD_BUG,"Bug: stream (marked at %s:%d) sending two socks replies?",
           file, line);

    if (conn->socks_request->command == SOCKS_COMMAND_CONNECT)
      connection_ap_handshake_socks_reply(conn, NULL, 0, socksreason);
    else
      connection_ap_handshake_socks_resolved(conn,RESOLVED_TYPE_ERROR,0,NULL,-1);
  }

  _connection_mark_for_close(conn, line, file);
  conn->hold_open_until_flushed = 1;
}

/** There was an EOF. Send an end and mark the connection for close.
 */
int
connection_edge_reached_eof(connection_t *conn)
{
#ifdef HALF_OPEN
  /* eof reached; we're done reading, but we might want to write more. */
  conn->done_receiving = 1;
  shutdown(conn->s, 0); /* XXX check return, refactor NM */
  if (conn->done_sending) {
    connection_edge_end(conn, END_STREAM_REASON_DONE, conn->cpath_layer);
    connection_mark_for_close(conn);
  } else {
    connection_edge_send_command(conn, circuit_get_by_edge_conn(conn),
                                 RELAY_COMMAND_END,
                                 NULL, 0, conn->cpath_layer);
  }
  return 0;
#else
  if (buf_datalen(conn->inbuf) && connection_state_is_open(conn)) {
    /* it still has stuff to process. don't let it die yet. */
    return 0;
  }
  info(LD_EDGE,"conn (fd %d) reached eof. Closing.", conn->s);
  if (!conn->marked_for_close) {
    /* only mark it if not already marked. it's possible to
     * get the 'end' right around when the client hangs up on us. */
    connection_edge_end(conn, END_STREAM_REASON_DONE, conn->cpath_layer);
    if (conn->socks_request) /* eof, so don't send a socks reply back */
      conn->socks_request->has_finished = 1;
    connection_mark_for_close(conn);
  }
  return 0;
#endif
}

/** Handle new bytes on conn->inbuf based on state:
 *   - If it's waiting for socks info, try to read another step of the
 *     socks handshake out of conn->inbuf.
 *   - If it's open, then package more relay cells from the stream.
 *   - Else, leave the bytes on inbuf alone for now.
 *
 * Mark and return -1 if there was an unexpected error with the conn,
 * else return 0.
 */
int
connection_edge_process_inbuf(connection_t *conn, int package_partial)
{
  tor_assert(conn);
  tor_assert(CONN_IS_EDGE(conn));

  switch (conn->state) {
    case AP_CONN_STATE_SOCKS_WAIT:
      if (connection_ap_handshake_process_socks(conn) < 0) {
        /* already marked */
        return -1;
      }
      return 0;
    case AP_CONN_STATE_OPEN:
    case EXIT_CONN_STATE_OPEN:
      if (connection_edge_package_raw_inbuf(conn, package_partial) < 0) {
        /* (We already sent an end cell if possible) */
        connection_mark_for_close(conn);
        return -1;
      }
      return 0;
    case EXIT_CONN_STATE_CONNECTING:
    case AP_CONN_STATE_RENDDESC_WAIT:
    case AP_CONN_STATE_CIRCUIT_WAIT:
    case AP_CONN_STATE_CONNECT_WAIT:
    case AP_CONN_STATE_RESOLVE_WAIT:
    case AP_CONN_STATE_CONTROLLER_WAIT:
      info(LD_EDGE,"data from edge while in '%s' state. Leaving it on buffer.",
             conn_state_to_string(conn->type, conn->state));
      return 0;
  }
  warn(LD_BUG,"Bug: Got unexpected state %d. Closing.",conn->state);
  tor_fragile_assert();
  connection_edge_end(conn, END_STREAM_REASON_INTERNAL, conn->cpath_layer);
  connection_mark_for_close(conn);
  return -1;
}

/** This edge needs to be closed, because its circuit has closed.
 * Mark it for close and return 0.
 */
int
connection_edge_destroy(uint16_t circ_id, connection_t *conn)
{
  tor_assert(CONN_IS_EDGE(conn));

  if (!conn->marked_for_close) {
    info(LD_EDGE,
         "CircID %d: At an edge. Marking connection for close.", circ_id);
    if (conn->type == CONN_TYPE_AP) {
      connection_mark_unattached_ap(conn, END_STREAM_REASON_DESTROY);
    } else {
      conn->has_sent_end = 1; /* we're closing the circuit, nothing to send to */
      connection_mark_for_close(conn);
      conn->hold_open_until_flushed = 1;
    }
  }
  conn->cpath_layer = NULL;
  conn->on_circuit = NULL;
  return 0;
}

/** Send a relay end cell from stream <b>conn</b> to conn's circuit,
 * with a destination of cpath_layer. (If cpath_layer is NULL, the
 * destination is the circuit's origin.) Mark the relay end cell as
 * closing because of <b>reason</b>.
 *
 * Return -1 if this function has already been called on this conn,
 * else return 0.
 */
int
connection_edge_end(connection_t *conn, char reason, crypt_path_t *cpath_layer)
{
  char payload[RELAY_PAYLOAD_SIZE];
  size_t payload_len=1;
  circuit_t *circ;

  if (conn->has_sent_end) {
    warn(LD_BUG,"Harmless bug: Calling connection_edge_end (reason %d) on an already ended stream?", reason);
    tor_fragile_assert();
    return -1;
  }

  if (conn->marked_for_close) {
    warn(LD_BUG,"Bug: called on conn that's already marked for close at %s:%d.",
           conn->marked_for_close_file, conn->marked_for_close);
    return 0;
  }

  payload[0] = reason;
  if (reason == END_STREAM_REASON_EXITPOLICY &&
      !connection_edge_is_rendezvous_stream(conn)) {
    set_uint32(payload+1, htonl(conn->addr));
    set_uint32(payload+5, htonl(MAX_DNS_ENTRY_AGE)); /* XXXXfill with a real TTL*/
    payload_len += 8;
  }

  circ = circuit_get_by_edge_conn(conn);
  if (circ && !circ->marked_for_close) {
    debug(LD_EDGE,"Marking conn (fd %d) and sending end.",conn->s);
    connection_edge_send_command(conn, circ, RELAY_COMMAND_END,
                                 payload, payload_len, cpath_layer);
  } else {
    debug(LD_EDGE,"Marking conn (fd %d); no circ to send end.",conn->s);
  }

  conn->has_sent_end = 1;
  return 0;
}

/** An error has just occured on an operation on an edge connection
 * <b>conn</b>.  Extract the errno; convert it to an end reason, and send
 * an appropriate relay end cell to <b>cpath_layer</b>.
 **/
int
connection_edge_end_errno(connection_t *conn, crypt_path_t *cpath_layer)
{
  uint8_t reason;
  tor_assert(conn);
  reason = (uint8_t)errno_to_end_reason(tor_socket_errno(conn->s));
  return connection_edge_end(conn, reason, cpath_layer);
}

/** Connection <b>conn</b> has finished writing and has no bytes left on
 * its outbuf.
 *
 * If it's in state 'open', stop writing, consider responding with a
 * sendme, and return.
 * Otherwise, stop writing and return.
 *
 * If <b>conn</b> is broken, mark it for close and return -1, else
 * return 0.
 */
int
connection_edge_finished_flushing(connection_t *conn)
{
  tor_assert(conn);
  tor_assert(CONN_IS_EDGE(conn));

  switch (conn->state) {
    case AP_CONN_STATE_OPEN:
    case EXIT_CONN_STATE_OPEN:
      connection_stop_writing(conn);
      connection_edge_consider_sending_sendme(conn);
      return 0;
    case AP_CONN_STATE_SOCKS_WAIT:
    case AP_CONN_STATE_RENDDESC_WAIT:
    case AP_CONN_STATE_CIRCUIT_WAIT:
    case AP_CONN_STATE_CONNECT_WAIT:
    case AP_CONN_STATE_CONTROLLER_WAIT:
      connection_stop_writing(conn);
      return 0;
    default:
      warn(LD_BUG,"BUG: called in unexpected state %d.", conn->state);
      tor_fragile_assert();
      return -1;
  }
  return 0;
}

/** Connected handler for exit connections: start writing pending
 * data, deliver 'CONNECTED' relay cells as appropriate, and check
 * any pending data that may have been received. */
int
connection_edge_finished_connecting(connection_t *conn)
{
  char valbuf[INET_NTOA_BUF_LEN];
  struct in_addr in;

  tor_assert(conn);
  tor_assert(conn->type == CONN_TYPE_EXIT);
  tor_assert(conn->state == EXIT_CONN_STATE_CONNECTING);

  in.s_addr = htonl(conn->addr);
  tor_inet_ntoa(&in,valbuf,sizeof(valbuf));
  info(LD_EXIT,"Exit connection to %s:%u (%s) established.",
         safe_str(conn->address),conn->port,safe_str(valbuf));

  conn->state = EXIT_CONN_STATE_OPEN;
  connection_watch_events(conn, EV_READ); /* stop writing, continue reading */
  if (connection_wants_to_flush(conn)) /* in case there are any queued relay cells */
    connection_start_writing(conn);
  /* deliver a 'connected' relay cell back through the circuit. */
  if (connection_edge_is_rendezvous_stream(conn)) {
    if (connection_edge_send_command(conn, circuit_get_by_edge_conn(conn),
                                     RELAY_COMMAND_CONNECTED, NULL, 0, conn->cpath_layer) < 0)
      return 0; /* circuit is closed, don't continue */
  } else {
    char connected_payload[8];
    set_uint32(connected_payload, htonl(conn->addr));
    set_uint32(connected_payload+4,
               htonl(MAX_DNS_ENTRY_AGE)); /* XXXX fill with a real TTL */
    if (connection_edge_send_command(conn, circuit_get_by_edge_conn(conn),
        RELAY_COMMAND_CONNECTED, connected_payload, 8, conn->cpath_layer) < 0)
      return 0; /* circuit is closed, don't continue */
  }
  tor_assert(conn->package_window > 0);
  /* in case the server has written anything */
  return connection_edge_process_inbuf(conn, 1);
}

/** Find all general-purpose AP streams waiting for a response that sent
 * their begin/resolve cell >=15 seconds ago. Detach from their current circuit,
 * and mark their current circuit as unsuitable for new streams. Then call
 * connection_ap_handshake_attach_circuit() to attach to a new circuit (if
 * available) or launch a new one.
 *
 * For rendezvous streams, simply give up after 45 seconds (with no
 * retry attempt).
 */
void
connection_ap_expire_beginning(void)
{
  connection_t **carray;
  connection_t *conn;
  circuit_t *circ;
  int n, i;
  time_t now = time(NULL);
  or_options_t *options = get_options();

  get_connection_array(&carray, &n);

  for (i = 0; i < n; ++i) {
    conn = carray[i];
    if (conn->type != CONN_TYPE_AP)
      continue;
    if (conn->state == AP_CONN_STATE_CONTROLLER_WAIT) {
      if (now - conn->timestamp_lastread >= 120) {
        notice(LD_APP, "Closing unattached stream.");
        connection_mark_unattached_ap(conn, END_STREAM_REASON_TIMEOUT);
      }
      continue;
    }

    else if (conn->state != AP_CONN_STATE_RESOLVE_WAIT &&
        conn->state != AP_CONN_STATE_CONNECT_WAIT)
      continue;
    if (now - conn->timestamp_lastread < 15)
      continue;
    circ = circuit_get_by_edge_conn(conn);
    if (!circ) { /* it's vanished? */
      info(LD_APP,"Conn is waiting (address %s), but lost its circ.",
             safe_str(conn->socks_request->address));
      connection_mark_unattached_ap(conn, END_STREAM_REASON_TIMEOUT);
      continue;
    }
    if (circ->purpose == CIRCUIT_PURPOSE_C_REND_JOINED) {
      if (now - conn->timestamp_lastread > 45) {
        notice(LD_REND,"Rend stream is %d seconds late. Giving up on address '%s'.",
               (int)(now - conn->timestamp_lastread),
               safe_str(conn->socks_request->address));
        connection_edge_end(conn, END_STREAM_REASON_TIMEOUT, conn->cpath_layer);
        connection_mark_unattached_ap(conn, END_STREAM_REASON_TIMEOUT);
      }
      continue;
    }
    tor_assert(circ->purpose == CIRCUIT_PURPOSE_C_GENERAL);
    notice(LD_APP,"We tried for %d seconds to connect to '%s'. Retrying on a new circuit.",
           (int)(now - conn->timestamp_lastread),
           safe_str(conn->socks_request->address));
    /* send an end down the circuit */
    connection_edge_end(conn, END_STREAM_REASON_TIMEOUT, conn->cpath_layer);
    /* un-mark it as ending, since we're going to reuse it */
    conn->has_sent_end = 0;
    /* kludge to make us not try this circuit again, yet to allow
     * current streams on it to survive if they can: make it
     * unattractive to use for new streams */
    tor_assert(circ->timestamp_dirty);
    circ->timestamp_dirty -= options->MaxCircuitDirtiness;
    /* give our stream another 15 seconds to try */
    conn->timestamp_lastread += 15;
    /* move it back into 'pending' state, and try to attach. */
    if (connection_ap_detach_retriable(conn, circ)<0) {
      connection_mark_unattached_ap(conn, END_STREAM_REASON_CANT_ATTACH);
    }
  } /* end for */
}

/** Tell any AP streams that are waiting for a new circuit that one is
 * available.
 */
void
connection_ap_attach_pending(void)
{
  connection_t **carray;
  connection_t *conn;
  int n, i;

  get_connection_array(&carray, &n);

  for (i = 0; i < n; ++i) {
    conn = carray[i];
    if (conn->marked_for_close ||
        conn->type != CONN_TYPE_AP ||
        conn->state != AP_CONN_STATE_CIRCUIT_WAIT)
      continue;
    if (connection_ap_handshake_attach_circuit(conn) < 0) {
      connection_mark_unattached_ap(conn, END_STREAM_REASON_CANT_ATTACH);
    }
  }
}

/** The AP connection <b>conn</b> has just failed while attaching or
 * sending a BEGIN or resolving on <b>circ</b>, but another circuit
 * might work.  Detach the circuit, and either reattach it, launch a
 * new circuit, tell the controller, or give up as a appropriate.
 *
 * Returns -1 on err, 1 on success, 0 on not-yet-sure.
 */
int
connection_ap_detach_retriable(connection_t *conn, circuit_t *circ)
{
  control_event_stream_status(conn, STREAM_EVENT_FAILED_RETRIABLE);
  conn->timestamp_lastread = time(NULL);
  if (! get_options()->LeaveStreamsUnattached) {
    conn->state = AP_CONN_STATE_CIRCUIT_WAIT;
    circuit_detach_stream(circ,conn);
    return connection_ap_handshake_attach_circuit(conn);
  } else {
    conn->state = AP_CONN_STATE_CONTROLLER_WAIT;
    circuit_detach_stream(circ,conn);
    return 0;
  }
}

/** A client-side struct to remember requests to rewrite addresses
 * to new addresses. These structs are stored the hash table
 * "addressmap" below.
 *
 * There are 5 ways to set an address mapping:
 * - A MapAddress command from the controller [permanent]
 * - An AddressMap directive in the torrc [permanent]
 * - When a TrackHostExits torrc directive is triggered [temporary]
 * - When a dns resolve succeeds [temporary]
 * - When a dns resolve fails [temporary]
 *
 * When an addressmap request is made but one is already registered,
 * the new one is replaced only if the currently registered one has
 * no "new_address" (that is, it's in the process of dns resolve),
 * or if the new one is permanent (expires==0 or 1).
 *
 * (We overload the 'expires' field, using "0" for mappings set via
 * the configuration file, "1" for mappings set from the control
 * interface, and other values for DNS mappings that can expire.)
 */
typedef struct {
  char *new_address;
  time_t expires;
  int num_resolve_failures;
} addressmap_entry_t;

/** Entry for mapping addresses to which virtual address we mapped them to. */
typedef struct {
  char *ipv4_address;
  char *hostname_address;
} virtaddress_entry_t;

/** A hash table to store client-side address rewrite instructions. */
static strmap_t *addressmap=NULL;
/**
 * Table mapping addresses to which virtual address, if any, we
 * assigned them to.
 *
 * We maintain the following invariant: if [A,B] is in
 * virtaddress_reversemap, then B must be a virtual address, and [A,B]
 * must be in addressmap.  We do not require that the converse hold:
 * if it fails, then we could end up mapping two virtual addresses to
 * the same address, which is no disaster.
 **/
static strmap_t *virtaddress_reversemap=NULL;

/** Initialize addressmap. */
void
addressmap_init(void)
{
  addressmap = strmap_new();
  virtaddress_reversemap = strmap_new();
}

/** Free the memory associated with the addressmap entry <b>_ent</b>. */
static void
addressmap_ent_free(void *_ent)
{
  addressmap_entry_t *ent = _ent;
  tor_free(ent->new_address);
  tor_free(ent);
}

/** Free storage held by a virtaddress_entry_t* entry in <b>ent</b> */
static void
addressmap_virtaddress_ent_free(void *_ent)
{
  virtaddress_entry_t *ent = _ent;
  tor_free(ent->ipv4_address);
  tor_free(ent->hostname_address);
  tor_free(ent);
}

/** Free storage held by a virtaddress_entry_t* entry in <b>ent</b> */
static void
addressmap_virtaddress_remove(const char *address, addressmap_entry_t *ent)
{
  if (ent && ent->new_address && address_is_in_virtual_range(ent->new_address)) {
    virtaddress_entry_t *ve =
      strmap_get(virtaddress_reversemap, ent->new_address);
    /*log_fn(LOG_NOTICE,"remove reverse mapping for %s",ent->new_address);*/
    if (ve) {
      if (!strcmp(address, ve->ipv4_address))
        tor_free(ve->ipv4_address);
      if (!strcmp(address, ve->hostname_address))
        tor_free(ve->hostname_address);
      if (!ve->ipv4_address && !ve->hostname_address) {
        tor_free(ve);
        strmap_remove(virtaddress_reversemap, ent->new_address);
      }
    }
  }
}

/* DOCDOC */
static void
addressmap_ent_remove(const char *address, addressmap_entry_t *ent)
{
  addressmap_virtaddress_remove(address, ent);
  addressmap_ent_free(ent);
}

/** Remove all entries from the addressmap that were set via the
 * configuration file or the command line. */
void
addressmap_clear_configured(void)
{
  addressmap_get_mappings(NULL, 0, 0);
}

/** Remove all entries from the addressmap that are set to expire, ever. */
void
addressmap_clear_transient(void)
{
  addressmap_get_mappings(NULL, 2, TIME_MAX);
}

/** Clean out entries from the addressmap cache that were
 * added long enough ago that they are no longer valid.
 */
void
addressmap_clean(time_t now)
{
  addressmap_get_mappings(NULL, 2, now);
}

/** Free all the elements in the addressmap, and free the addressmap
 * itself. */
void
addressmap_free_all(void)
{
  if (addressmap) {
    strmap_free(addressmap, addressmap_ent_free);
    addressmap = NULL;
  }
  if (virtaddress_reversemap) {
    strmap_free(virtaddress_reversemap, addressmap_virtaddress_ent_free);
    virtaddress_reversemap = NULL;
  }
}

/** Look at address, and rewrite it until it doesn't want any
 * more rewrites; but don't get into an infinite loop.
 * Don't write more than maxlen chars into address.
 */
void
addressmap_rewrite(char *address, size_t maxlen)
{
  addressmap_entry_t *ent;
  int rewrites;

  for (rewrites = 0; rewrites < 16; rewrites++) {
    ent = strmap_get(addressmap, address);

    if (!ent || !ent->new_address)
      return; /* done, no rewrite needed */

    info(LD_APP, "Addressmap: rewriting '%s' to '%s'",
         safe_str(address), safe_str(ent->new_address));
    strlcpy(address, ent->new_address, maxlen);
  }
  warn(LD_CONFIG,"Loop detected: we've rewritten '%s' 16 times! Using it as-is.",
         safe_str(address));
  /* it's fine to rewrite a rewrite, but don't loop forever */
}

/** Return 1 if <b>address</b> is already registered, else return 0 */
int
addressmap_already_mapped(const char *address)
{
  return strmap_get(addressmap, address) ? 1 : 0;
}

/** Register a request to map <b>address</b> to <b>new_address</b>,
 * which will expire on <b>expires</b> (or 0 if never expires from
 * config file, 1 if never expires from controller, 2 if never expires
 * (virtual address mapping) from the controller.)
 *
 * <b>new_address</b> should be a newly dup'ed string, which we'll use or
 * free as appropriate. We will leave address alone.
 *
 * If <b>new_address</b> is NULL, or equal to <b>address</b>, remove
 * any mappings that exist from <b>address</b>.
 */
void
addressmap_register(const char *address, char *new_address, time_t expires)
{
  addressmap_entry_t *ent;

  ent = strmap_get(addressmap, address);
  if (!new_address || !strcasecmp(address,new_address)) {
    /* Remove the mapping, if any. */
    tor_free(new_address);
    if (ent) {
      addressmap_ent_remove(address,ent);
      strmap_remove(addressmap, address);
    }
    return;
  }
  if (!ent) { /* make a new one and register it */
    ent = tor_malloc_zero(sizeof(addressmap_entry_t));
    strmap_set(addressmap, address, ent);
  } else if (ent->new_address) { /* we need to clean up the old mapping. */
    if (expires > 1) {
      info(LD_APP,"Temporary addressmap ('%s' to '%s') not performed, since it's already mapped to '%s'",
      safe_str(address), safe_str(new_address), safe_str(ent->new_address));
      tor_free(new_address);
      return;
    }
    if (address_is_in_virtual_range(ent->new_address) &&
        expires != 2) {
      /* XXX This isn't the perfect test; we want to avoid removing
       * mappings set from the control interface _as virtual mapping */
      addressmap_virtaddress_remove(address, ent);
    }
    tor_free(ent->new_address);
  } /* else { we have an in-progress resolve with no mapping. } */

  ent->new_address = new_address;
  ent->expires = expires==2 ? 1 : expires;
  ent->num_resolve_failures = 0;

  info(LD_CONFIG, "Addressmap: (re)mapped '%s' to '%s'",
       safe_str(address), safe_str(ent->new_address));
  control_event_address_mapped(address, ent->new_address, expires);
}

/** An attempt to resolve <b>address</b> failed at some OR.
 * Increment the number of resolve failures we have on record
 * for it, and then return that number.
 */
int
client_dns_incr_failures(const char *address)
{
  addressmap_entry_t *ent = strmap_get(addressmap, address);
  if (!ent) {
    ent = tor_malloc_zero(sizeof(addressmap_entry_t));
    ent->expires = time(NULL)+MAX_DNS_ENTRY_AGE;
    strmap_set(addressmap,address,ent);
  }
  ++ent->num_resolve_failures;
  info(LD_APP, "Address %s now has %d resolve failures.",
         safe_str(address), ent->num_resolve_failures);
  return ent->num_resolve_failures;
}

/** If <b>address</b> is in the client dns addressmap, reset
 * the number of resolve failures we have on record for it.
 * This is used when we fail a stream because it won't resolve:
 * otherwise future attempts on that address will only try once.
 */
void
client_dns_clear_failures(const char *address)
{
  addressmap_entry_t *ent = strmap_get(addressmap, address);
  if (ent)
    ent->num_resolve_failures = 0;
}

/** Record the fact that <b>address</b> resolved to <b>val</b>.
 * We can now use this in subsequent streams via addressmap_rewrite()
 * so we can more correctly choose an exit that will allow <b>address</b>.
 *
 * If <b>exitname</b> is defined, then append the addresses with
 * ".exitname.exit" before registering the mapping.
 *
 * If <b>ttl</b> is nonnegative, the mapping will be valid for
 * <b>ttl</b>seconds.
 */
void
client_dns_set_addressmap(const char *address, uint32_t val, const char *exitname,
                          int ttl)
{
  struct in_addr in;
  char extendedaddress[MAX_SOCKS_ADDR_LEN+MAX_HEX_NICKNAME_LEN+10];
  char valbuf[INET_NTOA_BUF_LEN];
  char extendedval[INET_NTOA_BUF_LEN+MAX_HEX_NICKNAME_LEN+10];

  tor_assert(address); tor_assert(val);

  if (ttl<0 || ttl>MAX_DNS_ENTRY_AGE)
    ttl = MAX_DNS_ENTRY_AGE;

  if (tor_inet_aton(address, &in))
    return; /* If address was an IP address already, don't add a mapping. */
  in.s_addr = htonl(val);
  tor_inet_ntoa(&in,valbuf,sizeof(valbuf));
  if (exitname) {
    tor_snprintf(extendedaddress, sizeof(extendedaddress),
                 "%s.%s.exit", address, exitname);
    tor_snprintf(extendedval, sizeof(extendedval),
                 "%s.%s.exit", valbuf, exitname);
  } else {
    tor_snprintf(extendedaddress, sizeof(extendedaddress),
                 "%s", address);
    tor_snprintf(extendedval, sizeof(extendedval),
                 "%s", valbuf);
  }
  addressmap_register(extendedaddress, tor_strdup(extendedval), time(NULL) + ttl);
}

/* Currently, we hand out 127.192.0.1 through 127.254.254.254.
 * These addresses should map to localhost, so even if the
 * application accidentally tried to connect to them directly (not
 * via Tor), it wouldn't get too far astray.
 *
 * Eventually, we should probably make this configurable.
 */
#define MIN_UNUSED_IPV4 0x7fc00001u
#define MAX_UNUSED_IPV4 0x7ffefefeu

/**
 * Return true iff <b>addr</b> is likely to have been returned by
 * client_dns_get_unused_address.
 **/
int
address_is_in_virtual_range(const char *address)
{
  struct in_addr in;
  tor_assert(address);
  if (!strcasecmpend(address, ".virtual")) {
    return 1;
  } else if (tor_inet_aton(address, &in)) {
    uint32_t addr = ntohl(in.s_addr);
    if (addr >= MIN_UNUSED_IPV4 && addr <= MAX_UNUSED_IPV4)
      return 1;
  }
  return 0;
}

/** Return a newly allocated string holding an address of <b>type</b>
 * (one of RESOLVED_TYPE_{IPV4|HOSTNAME}) that has not yet been mapped,
 * and that is very unlikely to be the address of any real host.
 */
static char *
addressmap_get_virtual_address(int type)
{
  char buf[64];
  static uint32_t next_ipv4 = MIN_UNUSED_IPV4;
  struct in_addr in;

  if (type == RESOLVED_TYPE_HOSTNAME) {
    char rand[10];
    do {
      crypto_rand(rand, sizeof(rand));
      base32_encode(buf,sizeof(buf),rand,sizeof(rand));
      strlcat(buf, ".virtual", sizeof(buf));
    } while (strmap_get(addressmap, buf));
    return tor_strdup(buf);
  } else if (type == RESOLVED_TYPE_IPV4) {
    while (1) {
      /* Don't hand out any .0 or .255 address. */
      while ((next_ipv4 & 0xff) == 0 ||
             (next_ipv4 & 0xff) == 0xff)
        ++next_ipv4;
      in.s_addr = htonl(next_ipv4);
      tor_inet_ntoa(&in, buf, sizeof(buf));
      if (!strmap_get(addressmap, buf))
        break;

      ++next_ipv4;
      if (next_ipv4 > MAX_UNUSED_IPV4)
        next_ipv4 = MIN_UNUSED_IPV4;
    }
    return tor_strdup(buf);
  } else {
    warn(LD_BUG, "Called with unsupported address type (%d)", type);
    return NULL;
  }
}

/** A controller has requested that we map some address of type
 * <b>type</b> to the address <b>new_address</b>.  Choose an address
 * that is unlikely to be used, and map it, and return it in a newly
 * allocated string.  If another address of the same type is already
 * mapped to <b>new_address</b>, try to return a copy of that address.
 *
 * The string in <b>new_address</b> may be freed, or inserted into a map
 * as appropriate.
 **/
const char *
addressmap_register_virtual_address(int type, char *new_address)
{
  char **addrp;
  virtaddress_entry_t *vent;

  tor_assert(new_address);
  tor_assert(addressmap);
  tor_assert(virtaddress_reversemap);

  vent = strmap_get(virtaddress_reversemap, new_address);
  if (!vent) {
    vent = tor_malloc_zero(sizeof(virtaddress_entry_t));
    strmap_set(virtaddress_reversemap, new_address, vent);
  }

  addrp = (type == RESOLVED_TYPE_IPV4) ?
    &vent->ipv4_address : &vent->hostname_address;
  if (*addrp) {
    addressmap_entry_t *ent = strmap_get(addressmap, *addrp);
    if (ent && ent->new_address && !strcasecmp(new_address, ent->new_address)) {
      tor_free(new_address);
      return tor_strdup(*addrp);
    } else
      warn(LD_BUG, "Internal confusion: I thought that '%s' was mapped to by '%s', but '%s' really maps to '%s'. This is a harmless bug.",
           safe_str(new_address), safe_str(*addrp), safe_str(*addrp),
           ent?safe_str(ent->new_address):"(nothing)");
  }

  tor_free(*addrp);
  *addrp = addressmap_get_virtual_address(type);
  addressmap_register(*addrp, new_address, 2);

#if 0
  {
    /* Try to catch possible bugs */
    addressmap_entry_t *ent;
    ent = strmap_get(addressmap, *addrp);
    tor_assert(ent);
    tor_assert(!strcasecmp(ent->new_address,new_address));
    vent = strmap_get(virtaddress_reversemap, new_address);
    tor_assert(vent);
    tor_assert(!strcasecmp(*addrp,
                           (type == RESOLVED_TYPE_IPV4) ?
                           vent->ipv4_address : vent->hostname_address));
    log_fn(LOG_INFO, "Map from %s to %s okay.",
           safe_str(*addrp),safe_str(new_address));
  }
#endif

  return *addrp;
}

/** Return 1 if <b>address</b> has funny characters in it like
 * colons. Return 0 if it's fine.
 */
static int
address_is_invalid_destination(const char *address)
{
  /* FFFF should flesh this out */
  if (strchr(address,':'))
    return 1;
  return 0;
}

/** Iterate over all address mapings which have expiry times between
 * min_expires and max_expires, inclusive.  If sl is provided, add an
 * "old-addr new-addr" string to sl for each mapping.  If sl is NULL,
 * remove the mappings.
 */
void
addressmap_get_mappings(smartlist_t *sl, time_t min_expires, time_t max_expires)
{
   strmap_iter_t *iter;
   const char *key;
   void *_val;
   addressmap_entry_t *val;

   if (!addressmap)
     addressmap_init();

   for (iter = strmap_iter_init(addressmap); !strmap_iter_done(iter); ) {
     strmap_iter_get(iter, &key, &_val);
     val = _val;
     if (val->expires >= min_expires && val->expires <= max_expires) {
       if (!sl) {
         iter = strmap_iter_next_rmv(addressmap,iter);
         addressmap_ent_remove(key, val);
         continue;
       } else if (val->new_address) {
         size_t len = strlen(key)+strlen(val->new_address)+2;
         char *line = tor_malloc(len);
         tor_snprintf(line, len, "%s %s", key, val->new_address);
         smartlist_add(sl, line);
       }
     }
     iter = strmap_iter_next(addressmap,iter);
   }
}

/** connection_edge_process_inbuf() found a conn in state
 * socks_wait. See if conn->inbuf has the right bytes to proceed with
 * the socks handshake.
 *
 * If the handshake is complete, and it's for a general circuit, then
 * try to attach it to a circuit (or launch one as needed). If it's for
 * a rendezvous circuit, then fetch a rendezvous descriptor first (or
 * attach/launch a circuit if the rendezvous descriptor is already here
 * and fresh enough).
 *
 * Return -1 if an unexpected error with conn (and it should be marked
 * for close), else return 0.
 */
static int
connection_ap_handshake_process_socks(connection_t *conn)
{
  socks_request_t *socks;
  int sockshere;
  hostname_type_t addresstype;
  or_options_t *options = get_options();
  int tor_should_handle_stream = !options->LeaveStreamsUnattached;

  tor_assert(conn);
  tor_assert(conn->type == CONN_TYPE_AP);
  tor_assert(conn->state == AP_CONN_STATE_SOCKS_WAIT);
  tor_assert(conn->socks_request);
  socks = conn->socks_request;

  debug(LD_APP,"entered.");

  sockshere = fetch_from_buf_socks(conn->inbuf, socks, options->TestSocks);
  if (sockshere == 0) {
    if (socks->replylen) {
      connection_write_to_buf(socks->reply, socks->replylen, conn);
      socks->replylen = 0; /* zero it out so we can do another round of negotiation */
    } else {
      debug(LD_APP,"socks handshake not all here yet.");
    }
    return 0;
  } else if (sockshere == -1) {
    if (socks->replylen) { /* we should send reply back */
      debug(LD_APP,"reply is already set for us. Using it.");
      connection_ap_handshake_socks_reply(conn, socks->reply, socks->replylen,
                                          SOCKS5_GENERAL_ERROR);
    } else {
      warn(LD_APP,"Fetching socks handshake failed. Closing.");
      connection_ap_handshake_socks_reply(conn, NULL, 0, SOCKS5_GENERAL_ERROR);
    }
    connection_mark_unattached_ap(conn, END_STREAM_REASON_ALREADY_SOCKS_REPLIED);
    return -1;
  } /* else socks handshake is done, continue processing */

  tor_strlower(socks->address); /* normalize it */
  debug(LD_APP,"Client asked for %s:%d", safe_str(socks->address),
         socks->port);

  /* For address map controls, remap the address */
  addressmap_rewrite(socks->address, sizeof(socks->address));

  if (tor_should_handle_stream &&
      address_is_in_virtual_range(socks->address)) {
    /* This address was probably handed out by client_dns_get_unmapped_address,
     * but the mapping was discarded for some reason.  We *don't* want to send
     * the address through tor; that's likely to fail, and may leak
     * information.
     */
    warn(LD_APP,"Missing mapping for virtual address '%s'. Refusing.",
           socks->address); /* don't safe_str() this yet. */
    connection_mark_unattached_ap(conn, END_STREAM_REASON_INTERNAL);
    return -1;
  }

  /* Parse the address provided by SOCKS.  Modify it in-place if it
   * specifies a hidden-service (.onion) or particular exit node (.exit).
   */
  addresstype = parse_extended_hostname(socks->address);

  if (tor_should_handle_stream && addresstype == BAD_HOSTNAME) {
    warn(LD_APP, "Invalid hostname %s; rejecting", socks->address);
    connection_mark_unattached_ap(conn, END_STREAM_REASON_TORPROTOCOL);
    return -1;
  }

  if (addresstype == EXIT_HOSTNAME) {
    /* foo.exit -- modify conn->chosen_exit_node to specify the exit
     * node, and conn->address to hold only the address portion.*/
    char *s = strrchr(socks->address,'.');
    if (s) {
      if (s[1] != '\0') {
        conn->chosen_exit_name = tor_strdup(s+1);
        *s = 0;
      } else {
        warn(LD_APP,"Malformed exit address '%s.exit'. Refusing.",
             safe_str(socks->address));