Raise libevent dependency to 2.0.10-stable or newer

Only some very ancient distributions don't ship with Libevent 2 anymore,
even the oldest supported Ubuntu LTS version has it. This allows us to
get rid of a lot of compat code.

Makefile.am

@@ -176,7 +176,7 @@ coverage-html-full: all
 	genhtml --branch-coverage -o "$(HTML_COVER_DIR)" "$(HTML_COVER_DIR)/lcov.info"
 
 # Avoid strlcpy.c, strlcat.c, aes.c, OpenBSD_malloc_Linux.c, sha256.c,
-# eventdns.[hc], tinytest*.[ch]
+# tinytest*.[ch]
 check-spaces:
 	$(top_srcdir)/scripts/maint/checkSpace.pl -C \
 		$(top_srcdir)/src/common/*.[ch] \

configure.ac

@@ -481,7 +481,7 @@ TOR_SEARCH_LIBRARY(libevent, $trylibeventdir, [-levent $STATIC_LIBEVENT_FLAGS $T
 #endif
 #include <sys/time.h>
 #include <sys/types.h>
-#include <event.h>], [
+#include <event2/event.h>], [
 #ifdef _WIN32
 #include <winsock2.h>
 #endif
@@ -500,21 +500,10 @@ save_CPPFLAGS="$CPPFLAGS"
 LIBS="-levent $STATIC_LIBEVENT_FLAGS $TOR_LIB_WS32 $LIBS"
 LDFLAGS="$TOR_LDFLAGS_libevent $LDFLAGS"
 CPPFLAGS="$TOR_CPPFLAGS_libevent $CPPFLAGS"
-AC_CHECK_FUNCS([event_get_version_number \
-                evutil_secure_rng_set_urandom_device_file \
-                evutil_secure_rng_init \
-               ])
-AC_CHECK_MEMBERS([struct event.min_heap_idx], , ,
-[#include <event.h>
-])
-
-AC_CHECK_HEADERS(event2/event.h event2/dns.h event2/bufferevent_ssl.h)
+AC_CHECK_FUNCS([evutil_secure_rng_set_urandom_device_file])
 
 LIBS="$STATIC_LIBEVENT_FLAGS $TOR_LIB_WS32 $save_LIBS"
 
-AM_CONDITIONAL(USE_EXTERNAL_EVDNS,
-  test "x$ac_cv_header_event2_dns_h" = "xyes")
-
 if test "$enable_static_libevent" = "yes"; then
    if test "$tor_cv_library_libevent_dir" = "(system)"; then
      AC_MSG_ERROR("You must specify an explicit --with-libevent-dir=x option when using --enable-static-libevent")
@@ -541,32 +530,34 @@ LIBS="$save_LIBS"
 LDFLAGS="$save_LDFLAGS"
 CPPFLAGS="$save_CPPFLAGS"
 
-dnl This isn't the best test for Libevent 2.0.3-alpha.  Once it's released,
-dnl we can do much better.
-if test "$enable_bufferevents" = "yes"; then
-  if test "$ac_cv_header_event2_bufferevent_ssl_h" != "yes"; then
-    AC_MSG_ERROR([You've asked for bufferevent support, but you're using a version of Libevent without SSL support.  This won't work.  We need Libevent 2.0.8-rc or later, and you don't seem to even have Libevent 2.0.3-alpha.])
-  else
-
-    CPPFLAGS="$CPPFLAGS $TOR_CPPFLAGS_libevent"
-
-    # Check for the right version.  First see if version detection works.
-    AC_MSG_CHECKING([whether we can detect the Libevent version])
-    AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+dnl Check that libevent is at least at version 2.0.10, the first stable
+dnl release of its series
+CPPFLAGS="$CPPFLAGS $TOR_CPPFLAGS_libevent"
+AC_MSG_CHECKING([whether Libevent is new enough])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 #include <event2/event.h>
-#if !defined(LIBEVENT_VERSION_NUMBER) || LIBEVENT_VERSION_NUMBER < 10
+#if !defined(LIBEVENT_VERSION_NUMBER) || LIBEVENT_VERSION_NUMBER < 0x02000a00
 #error
 int x = y(zz);
 #else
 int x = 1;
 #endif
-  ])], [event_version_number_works=yes; AC_MSG_RESULT([yes]) ],
-     [event_version_number_works=no;  AC_MSG_RESULT([no])])
-    if test "$event_version_number_works" != "yes"; then
-      AC_MSG_WARN([Version detection on Libevent seems broken.  Your Libevent installation is probably screwed up or very old.])
-    else
-      AC_MSG_CHECKING([whether Libevent is new enough for bufferevents])
-      AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+])], [ AC_MSG_RESULT([yes]) ],
+   [ AC_MSG_RESULT([no])
+     AC_MSG_ERROR([Libevent is not new enough.  We require 2.0.10-stable or later]) ] )
+
+LIBS="$save_LIBS"
+LDFLAGS="$save_LDFLAGS"
+CPPFLAGS="$save_CPPFLAGS"
+
+dnl bufferents require version 2.0.13
+if test "$enable_bufferevents" = "yes"; then
+   AC_CHECK_HEADERS(event2/bufferevent_ssl.h)
+
+   CPPFLAGS="$CPPFLAGS $TOR_CPPFLAGS_libevent"
+
+   AC_MSG_CHECKING([whether Libevent is new enough for bufferevents])
+   AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 #include <event2/event.h>
 #if !defined(LIBEVENT_VERSION_NUMBER) || LIBEVENT_VERSION_NUMBER < 0x02000d00
 #error
@@ -577,8 +568,6 @@ int x = 1;
    ])], [ AC_MSG_RESULT([yes]) ],
       [ AC_MSG_RESULT([no])
         AC_MSG_ERROR([Libevent does not seem new enough to support bufferevents.  We require 2.0.13-stable or later]) ] )
-    fi
-  fi
 fi
 
 LIBS="$save_LIBS"

scripts/maint/redox.py

@@ -33,8 +33,6 @@
 # files that we've snarfed in from somebody else, whose C we do no intend
 # to document for them.
 SKIP_FILES = [ "OpenBSD_malloc_Linux.c",
-               "eventdns.c",
-               "eventdns.h",
                "strlcat.c",
                "strlcpy.c",
                "sha256.c",

src/common/compat_libevent.c

@@ -19,15 +19,11 @@
 #include "util.h"
 #include "torlog.h"
 
-#ifdef HAVE_EVENT2_EVENT_H
 #include <event2/event.h>
 #include <event2/thread.h>
 #ifdef USE_BUFFEREVENTS
 #include <event2/bufferevent.h>
 #endif
-#else
-#include <event.h>
-#endif
 
 /** A string which, if it appears in a libevent log, should be ignored. */
 static const char *suppress_msg = NULL;
@@ -69,6 +65,7 @@ configure_libevent_logging(void)
 {
   event_set_log_callback(libevent_logging_callback);
 }
+
 /** Ignore any libevent log message that contains <b>msg</b>. */
 void
 suppress_libevent_log_msg(const char *msg)
@@ -76,44 +73,6 @@ suppress_libevent_log_msg(const char *msg)
   suppress_msg = msg;
 }
 
-#ifndef HAVE_EVENT2_EVENT_H
-/** Work-alike replacement for event_new() on pre-Libevent-2.0 systems. */
-struct event *
-tor_event_new(struct event_base *base, int sock, short what,
-              void (*cb)(int, short, void *), void *arg)
-{
-  struct event *e = tor_malloc_zero(sizeof(struct event));
-  event_set(e, sock, what, cb, arg);
-  if (! base)
-    base = tor_libevent_get_base();
-  event_base_set(base, e);
-  return e;
-}
-/** Work-alike replacement for evtimer_new() on pre-Libevent-2.0 systems. */
-struct event *
-tor_evtimer_new(struct event_base *base,
-                void (*cb)(int, short, void *), void *arg)
-{
-  return tor_event_new(base, -1, 0, cb, arg);
-}
-/** Work-alike replacement for evsignal_new() on pre-Libevent-2.0 systems. */
-struct event *
-tor_evsignal_new(struct event_base * base, int sig,
-                 void (*cb)(int, short, void *), void *arg)
-{
-  return tor_event_new(base, sig, EV_SIGNAL|EV_PERSIST, cb, arg);
-}
-/** Work-alike replacement for event_free() on pre-Libevent-2.0 systems,
- * except tolerate tor_event_free(NULL). */
-void
-tor_event_free(struct event *ev)
-{
-  if (ev == NULL)
-    return;
-  event_del(ev);
-  tor_free(ev);
-}
-#else
 /* Wrapper for event_free() that tolerates tor_event_free(NULL) */
 void
 tor_event_free(struct event *ev)
@@ -122,7 +81,6 @@ tor_event_free(struct event *ev)
     return;
   event_free(ev);
 }
-#endif
 
 /** Global event base for use by the main thread. */
 static struct event_base *the_event_base = NULL;
@@ -158,7 +116,6 @@ tor_libevent_initialize(tor_libevent_cfg *torcfg)
   /* some paths below don't use torcfg, so avoid unused variable warnings */
   (void)torcfg;
 
-#ifdef HAVE_EVENT2_EVENT_H
   {
     int attempts = 0;
     int using_threads;
@@ -190,16 +147,12 @@ tor_libevent_initialize(tor_libevent_cfg *torcfg)
       event_config_set_flag(cfg, EVENT_BASE_FLAG_NOLOCK);
     }
 
-#if defined(LIBEVENT_VERSION_NUMBER) && LIBEVENT_VERSION_NUMBER >= V(2,0,7)
     if (torcfg->num_cpus > 0)
       event_config_set_num_cpus_hint(cfg, torcfg->num_cpus);
-#endif
 
-#if LIBEVENT_VERSION_NUMBER >= V(2,0,9)
     /* We can enable changelist support with epoll, since we don't give
      * Libevent any dup'd fds.  This lets us avoid some syscalls. */
     event_config_set_flag(cfg, EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST);
-#endif
 
     the_event_base = event_base_new_with_config(cfg);
 
@@ -223,9 +176,6 @@ tor_libevent_initialize(tor_libevent_cfg *torcfg)
       goto retry;
     }
   }
-#else
-  the_event_base = event_init();
-#endif
 
   if (!the_event_base) {
     /* LCOV_EXCL_START */
@@ -255,62 +205,7 @@ tor_libevent_get_base, (void))
 const char *
 tor_libevent_get_method(void)
 {
-#ifdef HAVE_EVENT2_EVENT_H
   return event_base_get_method(the_event_base);
-#else
-  return event_get_method();
-#endif
-}
-
-/** Return the le_version_t for the version of libevent specified in the
- * string <b>v</b>.  If the version is very new or uses an unrecognized
- * version, format, return LE_OTHER. */
-STATIC le_version_t
-tor_decode_libevent_version(const char *v)
-{
-  unsigned major, minor, patchlevel;
-  char c, e, extra;
-  int fields;
-
-  /* Try the new preferred "1.4.11-stable" format.
-   * Also accept "1.4.14b-stable". */
-  fields = tor_sscanf(v, "%u.%u.%u%c%c", &major, &minor, &patchlevel, &c, &e);
-  if (fields == 3 ||
-      ((fields == 4 || fields == 5 ) && (c == '-' || c == '_')) ||
-      (fields == 5 && TOR_ISALPHA(c) && (e == '-' || e == '_'))) {
-    return V(major,minor,patchlevel);
-  }
-
-  /* Try the old "1.3e" format. */
-  fields = tor_sscanf(v, "%u.%u%c%c", &major, &minor, &c, &extra);
-  if (fields == 3 && TOR_ISALPHA(c)) {
-    return V_OLD(major, minor, c);
-  } else if (fields == 2) {
-    return V(major, minor, 0);
-  }
-
-  return LE_OTHER;
-}
-
-/** Return an integer representing the binary interface of a Libevent library.
- * Two different versions with different numbers are sure not to be binary
- * compatible.  Two different versions with the same numbers have a decent
- * chance of binary compatibility.*/
-STATIC int
-le_versions_compatibility(le_version_t v)
-{
-  if (v == LE_OTHER)
-    return 0;
-  if (v < V_OLD(1,0,'c'))
-    return 1;
-  else if (v < V(1,4,0))
-    return 2;
-  else if (v < V(1,4,99))
-    return 3;
-  else if (v < V(2,0,1))
-    return 4;
-  else /* Everything 2.0 and later should be compatible. */
-    return 5;
 }
 
 /** Return a string representation of the version of the currently running
@@ -321,101 +216,14 @@ tor_libevent_get_version_str(void)
   return event_get_version();
 }
 
-#if defined(LIBEVENT_VERSION)
-#define HEADER_VERSION LIBEVENT_VERSION
-#elif defined(_EVENT_VERSION)
-#define HEADER_VERSION _EVENT_VERSION
-#endif
-
 /** Return a string representation of the version of Libevent that was used
 * at compilation time. */
 const char *
 tor_libevent_get_header_version_str(void)
 {
-  return HEADER_VERSION;
-}
-
-/** See whether the headers we were built against differ from the library we
- * linked against so much that we're likely to crash.  If so, warn the
- * user. */
-void
-tor_check_libevent_header_compatibility(void)
-{
-  (void) le_versions_compatibility;
-  (void) tor_decode_libevent_version;
-
-  /* In libevent versions before 2.0, it's hard to keep binary compatibility
-   * between upgrades, and unpleasant to detect when the version we compiled
-   * against is unlike the version we have linked against. Here's how. */
-#if defined(HEADER_VERSION)
-  /* We have a header-file version and a function-call version. Easy. */
-  if (strcmp(HEADER_VERSION, event_get_version())) {
-    le_version_t v1, v2;
-    int compat1 = -1, compat2 = -1;
-    int verybad;
-    v1 = tor_decode_libevent_version(HEADER_VERSION);
-    v2 = tor_decode_libevent_version(event_get_version());
-    compat1 = le_versions_compatibility(v1);
-    compat2 = le_versions_compatibility(v2);
-
-    verybad = compat1 != compat2;
-
-    tor_log(verybad ? LOG_WARN : LOG_NOTICE,
-        LD_GENERAL, "We were compiled with headers from version %s "
-        "of Libevent, but we're using a Libevent library that says it's "
-        "version %s.", HEADER_VERSION, event_get_version());
-    if (verybad)
-      log_warn(LD_GENERAL, "This will almost certainly make Tor crash.");
-    else
-      log_info(LD_GENERAL, "I think these versions are binary-compatible.");
-  }
-#else
-  /* event_get_version but no _EVENT_VERSION.  We might be in 1.4.0-beta or
-     earlier, where that's normal.  To see whether we were compiled with an
-     earlier version, let's see whether the struct event defines MIN_HEAP_IDX.
-  */
-#ifdef HAVE_STRUCT_EVENT_MIN_HEAP_IDX
-  /* The header files are 1.4.0-beta or later. If the version is not
-   * 1.4.0-beta, we are incompatible. */
-  {
-    if (strcmp(event_get_version(), "1.4.0-beta")) {
-      log_warn(LD_GENERAL, "It's a little hard to tell, but you seem to have "
-               "Libevent 1.4.0-beta header files, whereas you have linked "
-               "against Libevent %s.  This will probably make Tor crash.",
-               event_get_version());
-    }
-  }
-#else
-  /* Our headers are 1.3e or earlier. If the library version is not 1.4.x or
-     later, we're probably fine. */
-  {
-    const char *v = event_get_version();
-    if ((v[0] == '1' && v[2] == '.' && v[3] > '3') || v[0] > '1') {
-      log_warn(LD_GENERAL, "It's a little hard to tell, but you seem to have "
-               "Libevent header file from 1.3e or earlier, whereas you have "
-               "linked against Libevent %s.  This will probably make Tor "
-               "crash.", event_get_version());
-    }
-  }
-#endif
-
-  /* Your libevent is ancient. */
-#endif
+  return LIBEVENT_VERSION;
 }
 
-/*
-  If possible, we're going to try to use Libevent's periodic timer support,
-  since it does a pretty good job of making sure that periodic events get
-  called exactly M seconds apart, rather than starting each one exactly M
-  seconds after the time that the last one was run.
- */
-#ifdef HAVE_EVENT2_EVENT_H
-#define HAVE_PERIODIC
-#define PERIODIC_FLAGS EV_PERSIST
-#else
-#define PERIODIC_FLAGS 0
-#endif
-
 /** Represents a timer that's run every N microseconds by Libevent. */
 struct periodic_timer_t {
   /** Underlying event used to implement this periodic event. */
@@ -424,11 +232,6 @@ struct periodic_timer_t {
   void (*cb)(struct periodic_timer_t *, void *);
   /** User-supplied data for the callback */
   void *data;
-#ifndef HAVE_PERIODIC
-  /** If Libevent doesn't know how to invoke events every N microseconds,
-   * we'll need to remember the timeout interval here. */
-  struct timeval tv;
-#endif
 };
 
 /** Libevent callback to implement a periodic event. */
@@ -438,10 +241,6 @@ periodic_timer_cb(evutil_socket_t fd, short what, void *arg)
   periodic_timer_t *timer = arg;
   (void) what;
   (void) fd;
-#ifndef HAVE_PERIODIC
-  /** reschedule the event as needed. */
-  event_add(timer->ev, &timer->tv);
-#endif
   timer->cb(timer, timer->data);
 }
 
@@ -459,16 +258,13 @@ periodic_timer_new(struct event_base *base,
   tor_assert(tv);
   tor_assert(cb);
   timer = tor_malloc_zero(sizeof(periodic_timer_t));
-  if (!(timer->ev = tor_event_new(base, -1, PERIODIC_FLAGS,
+  if (!(timer->ev = tor_event_new(base, -1, EV_PERSIST,
                                   periodic_timer_cb, timer))) {
     tor_free(timer);
     return NULL;
   }
   timer->cb = cb;
   timer->data = data;
-#ifndef HAVE_PERIODIC
-  memcpy(&timer->tv, tv, sizeof(struct timeval));
-#endif
   event_add(timer->ev, (struct timeval *)tv); /*drop const for old libevent*/
   return timer;
 }
@@ -539,7 +335,6 @@ int
 tor_init_libevent_rng(void)
 {
   int rv = 0;
-#ifdef HAVE_EVUTIL_SECURE_RNG_INIT
   char buf[256];
   if (evutil_secure_rng_init() < 0) {
     rv = -1;
@@ -547,7 +342,6 @@ tor_init_libevent_rng(void)
   crypto_rand(buf, 32);
   evutil_secure_rng_add_bytes(buf, 32);
   evutil_secure_rng_get_bytes(buf, sizeof(buf));
-#endif
   return rv;
 }
 

src/common/compat_libevent.h

@@ -15,32 +15,17 @@ struct ev_token_bucket_cfg;
 struct bufferevent_rate_limit_group;
 #endif
 
-#ifdef HAVE_EVENT2_EVENT_H
 #include <event2/util.h>
-#elif !defined(EVUTIL_SOCKET_DEFINED)
-#define EVUTIL_SOCKET_DEFINED
-#define evutil_socket_t int
-#endif
 
 void configure_libevent_logging(void);
 void suppress_libevent_log_msg(const char *msg);
 
-#ifdef HAVE_EVENT2_EVENT_H
 #define tor_event_new     event_new
 #define tor_evtimer_new   evtimer_new
 #define tor_evsignal_new  evsignal_new
 #define tor_evdns_add_server_port(sock, tcp, cb, data) \
   evdns_add_server_port_with_base(tor_libevent_get_base(), \
   (sock),(tcp),(cb),(data));
-#else
-struct event *tor_event_new(struct event_base * base, evutil_socket_t sock,
-           short what, void (*cb)(evutil_socket_t, short, void *), void *arg);
-struct event *tor_evtimer_new(struct event_base * base,
-            void (*cb)(evutil_socket_t, short, void *), void *arg);
-struct event *tor_evsignal_new(struct event_base * base, int sig,
-            void (*cb)(evutil_socket_t, short, void *), void *arg);
-#define tor_evdns_add_server_port evdns_add_server_port
-#endif
 
 void tor_event_free(struct event *ev);
 
@@ -99,9 +84,7 @@ void tor_gettimeofday_cached_monotonic(struct timeval *tv);
     byte is unused.
 
     This is equivalent to the format of LIBEVENT_VERSION_NUMBER on Libevent
-    2.0.1 or later.  For versions of Libevent before 1.4.0, which followed the
-    format of "1.0, 1.0a, 1.0b", we define 1.0 to be equivalent to 1.0.0, 1.0a
-    to be equivalent to 1.0.1, and so on.
+    2.0.1 or later.
 */
 typedef uint32_t le_version_t;
 
@@ -109,23 +92,10 @@ typedef uint32_t le_version_t;
 /** Macros: returns the number of a libevent version as a le_version_t */
 #define V(major, minor, patch) \
   (((major) << 24) | ((minor) << 16) | ((patch) << 8))
-#define V_OLD(major, minor, patch) \
-  V((major), (minor), (patch)-'a'+1)
 /** @} */
 
-/** Represetns a version of libevent so old we can't figure out what version
- * it is. */
-#define LE_OLD V(0,0,0)
-/** Represents a version of libevent so weird we can't figure out what version
- * it is. */
-#define LE_OTHER V(0,0,99)
-
 STATIC void
 libevent_logging_callback(int severity, const char *msg);
-STATIC le_version_t
-tor_decode_libevent_version(const char *v);
-STATIC int
-le_versions_compatibility(le_version_t v);
 #endif
 
 #endif

src/common/procmon.c

@@ -10,11 +10,7 @@
 
 #include "util.h"
 
-#ifdef HAVE_EVENT2_EVENT_H
 #include <event2/event.h>
-#else
-#include <event.h>
-#endif
 
 #ifdef HAVE_SIGNAL_H
 #include <signal.h>
@@ -164,11 +160,7 @@ tor_validate_process_specifier(const char *process_spec,
 }
 
 /* XXXX we should use periodic_timer_new() for this stuff */
-#ifdef HAVE_EVENT2_EVENT_H
 #define PERIODIC_TIMER_FLAGS EV_PERSIST
-#else
-#define PERIODIC_TIMER_FLAGS (0)
-#endif
 
 /* DOCDOC poll_interval_tv */
 static struct timeval poll_interval_tv = {15, 0};
@@ -331,10 +323,6 @@ tor_process_monitor_poll_cb(evutil_socket_t unused1, short unused2,
 
   if (its_dead_jim) {
     procmon->cb(procmon->cb_arg);
-#ifndef HAVE_EVENT2_EVENT_H
-  } else {
-    evtimer_add(procmon->e, &poll_interval_tv);
-#endif
   }
 }
 #endif

src/common/timers.c

@@ -38,11 +38,7 @@
 #include "torlog.h"
 #include "util.h"
 
-#ifdef HAVE_EVENT2_EVENT_H
 #include <event2/event.h>
-#else
-#include <event.h>
-#endif
 
 struct timeout_cb {
   timer_cb_fn_t cb;

src/ext/README

@@ -11,13 +11,6 @@ strlcpy.c
     for strcat and strcpy.  These are nonstandard, and some libc
     implementations refuse to add them for religious reasons.
 
-eventdns.[ch]
-
-    A fork of Libevent's DNS implementation, used by Tor when Libevent
-    2.0 or later is not available.  Once Libevent 2.0 is required, we
-    should throw this away; it has diverged from evdns.[ch], and is
-    no longer easily mergeable.
-
 ht.h
 
     An implementation of a hash table in the style of Niels Provos's

src/ext/eventdns.h

-
-/*
- * The original DNS code is due to Adam Langley with heavy
- * modifications by Nick Mathewson.  Adam put his DNS software in the
- * public domain.  You can find his original copyright below.  Please,
- * aware that the code as part of libevent is governed by the 3-clause
- * BSD license above.
- *
- * This software is Public Domain. To view a copy of the public domain dedication,
- * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
- * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
- *
- * I ask and expect, but do not require, that all derivative works contain an
- * attribution similar to:
- *	Parts developed by Adam Langley <agl@imperialviolet.org>
- *
- * You may wish to replace the word "Parts" with something else depending on
- * the amount of original code.
- *
- * (Derivative works does not include programs which link against, run or include
- * the source verbatim in their source distributions)
- */
-
-/*
- * Welcome, gentle reader
- *
- * Async DNS lookups are really a whole lot harder than they should be,
- * mostly stemming from the fact that the libc resolver has never been
- * very good at them. Before you use this library you should see if libc
- * can do the job for you with the modern async call getaddrinfo_a
- * (see http://www.imperialviolet.org/page25.html#e498). Otherwise,
- * please continue.
- *
- * This code is based on libevent and you must call event_init before
- * any of the APIs in this file. You must also seed the OpenSSL random
- * source if you are using OpenSSL for ids (see below).
- *
- * This library is designed to be included and shipped with your source
- * code. You statically link with it. You should also test for the
- * existence of strtok_r and define HAVE_STRTOK_R if you have it.
- *
- * The DNS protocol requires a good source of id numbers and these
- * numbers should be unpredictable for spoofing reasons. There are
- * three methods for generating them here and you must define exactly
- * one of them. In increasing order of preference:
- *
- * DNS_USE_GETTIMEOFDAY_FOR_ID:
- *   Using the bottom 16 bits of the usec result from gettimeofday. This
- *   is a pretty poor solution but should work anywhere.
- * DNS_USE_CPU_CLOCK_FOR_ID:
- *  Using the bottom 16 bits of the nsec result from the CPU's time
- *  counter. This is better, but may not work everywhere. Requires
- *  POSIX realtime support and you'll need to link against -lrt on
- *  glibc systems at least.
- * DNS_USE_OPENSSL_FOR_ID:
- *  Uses the OpenSSL RAND_bytes call to generate the data. You must
- *  have seeded the pool before making any calls to this library.
- *
- * The library keeps track of the state of nameservers and will avoid
- * them when they go down. Otherwise it will round robin between them.
- *
- * Quick start guide:
- *	 #include "evdns.h"
- *	 void callback(int result, char type, int count, int ttl,
- *     void *addresses, void *arg);