/***************************************************************************

 *                                  _   _ ____  _

 *  Project                     ___| | | |  _ \| |

 *                             / __| | | | |_) | |

 *                            | (__| |_| |  _ <| |___

 *                             \___|\___/|_| \_\_____|

 *

 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.

 *

 * This software is licensed as described in the file COPYING, which

 * you should have received as part of this distribution. The terms

 * are also available at https://curl.se/docs/copyright.html.

 *

 * You may opt to use, copy, modify, merge, publish, distribute and/or sell

 * copies of the Software, and permit persons to whom the Software is

 * furnished to do so, under the terms of the COPYING file.

 *

 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY

 * KIND, either express or implied.

 *

 * SPDX-License-Identifier: curl

 *

 ***************************************************************************/

#include "curl_setup.h"

#include "socketpair.h"

/***********************************************************************

 * Only for threaded name resolves builds

 **********************************************************************/

#ifdef CURLRES_THREADED

#ifdef HAVE_NETINET_IN_H

#include <netinet/in.h>

#endif

#ifdef HAVE_NETDB_H

#include <netdb.h>

#endif

#ifdef HAVE_ARPA_INET_H

#include <arpa/inet.h>

#endif

#ifdef __VMS

#include <in.h>

#include <inet.h>

#endif

#if defined(USE_THREADS_POSIX) && defined(HAVE_PTHREAD_H)

#  include <pthread.h>

#endif

#ifdef HAVE_GETADDRINFO

#  define RESOLVER_ENOMEM  EAI_MEMORY  /* = WSA_NOT_ENOUGH_MEMORY on Windows */

#else

#  define RESOLVER_ENOMEM  SOCKENOMEM

#endif

#include "urldata.h"

#include "cfilters.h"

#include "sendf.h"

#include "hostip.h"

#include "hash.h"

#include "share.h"

#include "url.h"

#include "multiif.h"

#include "curl_threads.h"

#include "select.h"

#include "strdup.h"

#ifdef USE_ARES

#include <ares.h>

#ifdef USE_HTTPSRR

#define USE_HTTPSRR_ARES  /* the combo */

#endif

#endif

/* The last 2 #include files should be in this order */

#include "curl_memory.h"

#include "memdebug.h"

/*

 * Curl_async_global_init()

 * Called from curl_global_init() to initialize global resolver environment.

 * Does nothing here.

 */

int Curl_async_global_init(void)

{

#if defined(USE_ARES) && defined(CARES_HAVE_ARES_LIBRARY_INIT)

  if(ares_library_init(ARES_LIB_INIT_ALL)) {

    return CURLE_FAILED_INIT;

  }

#endif

  return CURLE_OK;

}

/*

 * Curl_async_global_cleanup()

 * Called from curl_global_cleanup() to destroy global resolver environment.

 * Does nothing here.

 */

void Curl_async_global_cleanup(void)

{

#if defined(USE_ARES) && defined(CARES_HAVE_ARES_LIBRARY_INIT)

  ares_library_cleanup();

#endif

}

static void async_thrdd_destroy(struct Curl_easy *);

static void async_thrdd_shutdown(struct Curl_easy *);

CURLcode Curl_async_get_impl(struct Curl_easy *data, void **impl)

{

  (void)data;

  *impl = NULL;

  return CURLE_OK;

}

/* Give up reference to add_ctx */

static void addr_ctx_unlink(struct async_thrdd_addr_ctx **paddr_ctx,

                            struct Curl_easy *data)

{

  struct async_thrdd_addr_ctx *addr_ctx = *paddr_ctx;

  bool destroy;

  (void)data;

  if(!addr_ctx)

    return;

  Curl_mutex_acquire(&addr_ctx->mutx);

  if(!data)  /* called by resolving thread */

    addr_ctx->thrd_done = TRUE;

  DEBUGASSERT(addr_ctx->ref_count);

  --addr_ctx->ref_count;

  destroy = !addr_ctx->ref_count;

  Curl_mutex_release(&addr_ctx->mutx);

  if(destroy) {

    Curl_mutex_destroy(&addr_ctx->mutx);

    free(addr_ctx->hostname);

    if(addr_ctx->res)

      Curl_freeaddrinfo(addr_ctx->res);

#ifndef CURL_DISABLE_SOCKETPAIR

#ifndef USE_EVENTFD

    wakeup_close(addr_ctx->sock_pair[1]);

#endif

    wakeup_close(addr_ctx->sock_pair[0]);

#endif

    free(addr_ctx);

  }

  *paddr_ctx = NULL;

}

/* Initialize context for threaded resolver */

static struct async_thrdd_addr_ctx *

addr_ctx_create(struct Curl_easy *data,

                const char *hostname, int port,

                const struct addrinfo *hints)

{

  struct async_thrdd_addr_ctx *addr_ctx = calloc(1, sizeof(*addr_ctx));

  if(!addr_ctx)

    return NULL;

  addr_ctx->thread_hnd = curl_thread_t_null;

  addr_ctx->port = port;

  addr_ctx->ref_count = 1;

#ifdef HAVE_GETADDRINFO

  DEBUGASSERT(hints);

  addr_ctx->hints = *hints;

#else

  (void)hints;

#endif

  Curl_mutex_init(&addr_ctx->mutx);

#ifndef CURL_DISABLE_SOCKETPAIR

  /* create socket pair or pipe */

  if(wakeup_create(addr_ctx->sock_pair, FALSE) < 0) {

    addr_ctx->sock_pair[0] = CURL_SOCKET_BAD;

    addr_ctx->sock_pair[1] = CURL_SOCKET_BAD;

    goto err_exit;

  }

#endif

  addr_ctx->sock_error = 0;

  /* Copying hostname string because original can be destroyed by parent

   * thread during gethostbyname execution.

   */

  addr_ctx->hostname = strdup(hostname);

  if(!addr_ctx->hostname)

    goto err_exit;

  return addr_ctx;

err_exit:

  addr_ctx_unlink(&addr_ctx, data);

  return NULL;

}

#ifdef HAVE_GETADDRINFO

/*

 * getaddrinfo_thread() resolves a name and then exits.

 *

 * For builds without ARES, but with USE_IPV6, create a resolver thread

 * and wait on it.

 */

static CURL_THREAD_RETURN_T CURL_STDCALL getaddrinfo_thread(void *arg)

{

  struct async_thrdd_addr_ctx *addr_ctx = arg;

  bool do_abort;

  Curl_mutex_acquire(&addr_ctx->mutx);

  do_abort = addr_ctx->do_abort;

  Curl_mutex_release(&addr_ctx->mutx);

  if(!do_abort) {

    char service[12];

    int rc;

    curl_msnprintf(service, sizeof(service), "%d", addr_ctx->port);

    rc = Curl_getaddrinfo_ex(addr_ctx->hostname, service,

                             &addr_ctx->hints, &addr_ctx->res);

    if(rc) {

      addr_ctx->sock_error = SOCKERRNO ? SOCKERRNO : rc;

      if(addr_ctx->sock_error == 0)

        addr_ctx->sock_error = RESOLVER_ENOMEM;

    }

    else {

      Curl_addrinfo_set_port(addr_ctx->res, addr_ctx->port);

    }

    Curl_mutex_acquire(&addr_ctx->mutx);

    do_abort = addr_ctx->do_abort;

    Curl_mutex_release(&addr_ctx->mutx);

#ifndef CURL_DISABLE_SOCKETPAIR

    if(!do_abort) {

#ifdef USE_EVENTFD

      const uint64_t buf[1] = { 1 };

#else

      const char buf[1] = { 1 };

#endif

      /* Thread is done, notify transfer */

      if(wakeup_write(addr_ctx->sock_pair[1], buf, sizeof(buf)) < 0) {

        /* update sock_error to errno */

        addr_ctx->sock_error = SOCKERRNO;

      }

    }

#endif

  }

  addr_ctx_unlink(&addr_ctx, NULL);

  return 0;

}

#else /* HAVE_GETADDRINFO */

/*

 * gethostbyname_thread() resolves a name and then exits.

 */

static CURL_THREAD_RETURN_T CURL_STDCALL gethostbyname_thread(void *arg)

{

  struct async_thrdd_addr_ctx *addr_ctx = arg;

  bool do_abort;

  Curl_mutex_acquire(&addr_ctx->mutx);

  do_abort = addr_ctx->do_abort;

  Curl_mutex_release(&addr_ctx->mutx);

  if(!do_abort) {

    addr_ctx->res = Curl_ipv4_resolve_r(addr_ctx->hostname, addr_ctx->port);

    if(!addr_ctx->res) {

      addr_ctx->sock_error = SOCKERRNO;

      if(addr_ctx->sock_error == 0)

        addr_ctx->sock_error = RESOLVER_ENOMEM;

    }

    Curl_mutex_acquire(&addr_ctx->mutx);

    do_abort = addr_ctx->do_abort;

    Curl_mutex_release(&addr_ctx->mutx);

#ifndef CURL_DISABLE_SOCKETPAIR

    if(!do_abort) {

#ifdef USE_EVENTFD

      const uint64_t buf[1] = { 1 };

#else

      const char buf[1] = { 1 };

#endif

      /* Thread is done, notify transfer */

      if(wakeup_write(addr_ctx->sock_pair[1], buf, sizeof(buf)) < 0) {

        /* update sock_error to errno */

        addr_ctx->sock_error = SOCKERRNO;

      }

    }

#endif

  }

  addr_ctx_unlink(&addr_ctx, NULL);

  return 0;

}

#endif /* HAVE_GETADDRINFO */

/*

 * async_thrdd_destroy() cleans up async resolver data and thread handle.

 */

static void async_thrdd_destroy(struct Curl_easy *data)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  struct async_thrdd_addr_ctx *addr = thrdd->addr;

#ifdef USE_HTTPSRR_ARES

  if(thrdd->rr.channel) {

    ares_destroy(thrdd->rr.channel);

    thrdd->rr.channel = NULL;

  }

  Curl_httpsrr_cleanup(&thrdd->rr.hinfo);

#endif

  if(thrdd->addr && (thrdd->addr->thread_hnd != curl_thread_t_null)) {

    bool done;

    Curl_mutex_acquire(&addr->mutx);

#ifndef CURL_DISABLE_SOCKETPAIR

    if(!addr->do_abort)

      Curl_multi_will_close(data, addr->sock_pair[0]);

#endif

    addr->do_abort = TRUE;

    done = addr->thrd_done;

    Curl_mutex_release(&addr->mutx);

    if(done) {

      Curl_thread_join(&addr->thread_hnd);

      CURL_TRC_DNS(data, "async_thrdd_destroy, thread joined");

    }

    else {

      /* thread is still running. Detach it. */

      Curl_thread_destroy(&addr->thread_hnd);

      CURL_TRC_DNS(data, "async_thrdd_destroy, thread detached");

    }

  }

  /* release our reference to the shared context */

  addr_ctx_unlink(&thrdd->addr, data);

}

#ifdef USE_HTTPSRR_ARES

static void async_thrdd_rr_done(void *user_data, ares_status_t status,

                                size_t timeouts,

                                const ares_dns_record_t *dnsrec)

{

  struct Curl_easy *data = user_data;

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  (void)timeouts;

  thrdd->rr.done = TRUE;

  if((ARES_SUCCESS != status) || !dnsrec)

    return;

  thrdd->rr.result = Curl_httpsrr_from_ares(data, dnsrec, &thrdd->rr.hinfo);

}

static CURLcode async_rr_start(struct Curl_easy *data)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  int status;

  DEBUGASSERT(!thrdd->rr.channel);

  status = ares_init_options(&thrdd->rr.channel, NULL, 0);

  if(status != ARES_SUCCESS) {

    thrdd->rr.channel = NULL;

    return CURLE_FAILED_INIT;

  }

#ifdef CURLDEBUG

  if(getenv("CURL_DNS_SERVER")) {

    const char *servers = getenv("CURL_DNS_SERVER");

    status = ares_set_servers_ports_csv(thrdd->rr.channel, servers);

    if(status)

      return CURLE_FAILED_INIT;

  }

#endif

  memset(&thrdd->rr.hinfo, 0, sizeof(thrdd->rr.hinfo));

  thrdd->rr.hinfo.port = -1;

  ares_query_dnsrec(thrdd->rr.channel,

                    data->conn->host.name, ARES_CLASS_IN,

                    ARES_REC_TYPE_HTTPS,

                    async_thrdd_rr_done, data, NULL);

  CURL_TRC_DNS(data, "Issued HTTPS-RR request for %s", data->conn->host.name);

  return CURLE_OK;

}

#endif

/*

 * async_thrdd_init() starts a new thread that performs the actual

 * resolve. This function returns before the resolve is done.

 *

 * Returns FALSE in case of failure, otherwise TRUE.

 */

static bool async_thrdd_init(struct Curl_easy *data,

                             const char *hostname, int port, int ip_version,

                             const struct addrinfo *hints)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  struct async_thrdd_addr_ctx *addr_ctx;

  /* !checksrc! disable ERRNOVAR 1 */

  int err = ENOMEM;

  if(thrdd->addr

#ifdef USE_HTTPSRR_ARES

     || thrdd->rr.channel

#endif

     ) {

    CURL_TRC_DNS(data, "starting new resolve, with previous not cleaned up");

    async_thrdd_destroy(data);

    DEBUGASSERT(!thrdd->addr);

#ifdef USE_HTTPSRR_ARES

    DEBUGASSERT(!thrdd->rr.channel);

#endif

  }

  data->state.async.dns = NULL;

  data->state.async.done = FALSE;

  data->state.async.port = port;

  data->state.async.ip_version = ip_version;

  free(data->state.async.hostname);

  data->state.async.hostname = strdup(hostname);

  if(!data->state.async.hostname)

    goto err_exit;

  addr_ctx = addr_ctx_create(data, hostname, port, hints);

  if(!addr_ctx)

    goto err_exit;

  thrdd->addr = addr_ctx;

  /* passing addr_ctx to the thread adds a reference */

  addr_ctx->ref_count = 2;

  addr_ctx->start = curlx_now();

#ifdef HAVE_GETADDRINFO

  addr_ctx->thread_hnd = Curl_thread_create(getaddrinfo_thread, addr_ctx);

#else

  addr_ctx->thread_hnd = Curl_thread_create(gethostbyname_thread, addr_ctx);

#endif

  if(addr_ctx->thread_hnd == curl_thread_t_null) {

    /* The thread never started */

    addr_ctx->ref_count = 1;

    addr_ctx->thrd_done = TRUE;

    err = errno;

    goto err_exit;

  }

#ifdef USE_HTTPSRR_ARES

  if(async_rr_start(data))

    infof(data, "Failed HTTPS RR operation");

#endif

  CURL_TRC_DNS(data, "resolve thread started for of %s:%d", hostname, port);

  return TRUE;

err_exit:

  CURL_TRC_DNS(data, "resolve thread failed init: %d", err);

  async_thrdd_destroy(data);

  CURL_SETERRNO(err);

  return FALSE;

}

static void async_thrdd_shutdown(struct Curl_easy *data)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  struct async_thrdd_addr_ctx *addr_ctx = thrdd->addr;

  bool done;

  if(!addr_ctx)

    return;

  if(addr_ctx->thread_hnd == curl_thread_t_null)

    return;

  Curl_mutex_acquire(&addr_ctx->mutx);

#ifndef CURL_DISABLE_SOCKETPAIR

    if(!addr_ctx->do_abort)

      Curl_multi_will_close(data, addr_ctx->sock_pair[0]);

#endif

  addr_ctx->do_abort = TRUE;

  done = addr_ctx->thrd_done;

  Curl_mutex_release(&addr_ctx->mutx);

  /* Wait for the thread to terminate if it is already marked done. If it is

     not done yet we cannot do anything here. We had tried pthread_cancel but

     it caused hanging and resource leaks (#18532). */

  if(done && (addr_ctx->thread_hnd != curl_thread_t_null)) {

    Curl_thread_join(&addr_ctx->thread_hnd);

    CURL_TRC_DNS(data, "async_thrdd_shutdown, thread joined");

  }

}

/*

 * 'entry' may be NULL and then no data is returned

 */

static CURLcode asyn_thrdd_await(struct Curl_easy *data,

                                 struct async_thrdd_addr_ctx *addr_ctx,

                                 struct Curl_dns_entry **entry)

{

  CURLcode result = CURLE_OK;

  if(addr_ctx->thread_hnd != curl_thread_t_null) {

    /* not interested in result? cancel, if still running... */

    if(!entry)

      async_thrdd_shutdown(data);

    if(addr_ctx->thread_hnd != curl_thread_t_null) {

      CURL_TRC_DNS(data, "resolve, wait for thread to finish");

      if(!Curl_thread_join(&addr_ctx->thread_hnd)) {

        DEBUGASSERT(0);

      }

    }

    if(entry)

      result = Curl_async_is_resolved(data, entry);

  }

  data->state.async.done = TRUE;

  if(entry)

    *entry = data->state.async.dns;

  return result;

}

/*

 * Until we gain a way to signal the resolver threads to stop early, we must

 * simply wait for them and ignore their results.

 */

void Curl_async_thrdd_shutdown(struct Curl_easy *data)

{

  async_thrdd_shutdown(data);

}

void Curl_async_thrdd_destroy(struct Curl_easy *data)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  if(thrdd->addr && !data->set.quick_exit) {

    (void)asyn_thrdd_await(data, thrdd->addr, NULL);

  }

  async_thrdd_destroy(data);

}

/*

 * Curl_async_await()

 *

 * Waits for a resolve to finish. This function should be avoided since using

 * this risk getting the multi interface to "hang".

 *

 * If 'entry' is non-NULL, make it point to the resolved dns entry

 *

 * Returns CURLE_COULDNT_RESOLVE_HOST if the host was not resolved,

 * CURLE_OPERATION_TIMEDOUT if a time-out occurred, or other errors.

 *

 * This is the version for resolves-in-a-thread.

 */

CURLcode Curl_async_await(struct Curl_easy *data,

                          struct Curl_dns_entry **entry)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  if(thrdd->addr)

    return asyn_thrdd_await(data, thrdd->addr, entry);

  return CURLE_FAILED_INIT;

}

/*

 * Curl_async_is_resolved() is called repeatedly to check if a previous

 * name resolve request has completed. It should also make sure to time-out if

 * the operation seems to take too long.

 */

CURLcode Curl_async_is_resolved(struct Curl_easy *data,

                                struct Curl_dns_entry **dns)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  bool done = FALSE;

  DEBUGASSERT(dns);

  *dns = NULL;

  if(data->state.async.done) {

    *dns = data->state.async.dns;

    CURL_TRC_DNS(data, "threaded: is_resolved(), already done, dns=%sfound",

                 *dns ? "" : "not ");

    return CURLE_OK;

  }

#ifdef USE_HTTPSRR_ARES

  /* best effort, ignore errors */

  if(thrdd->rr.channel)

    (void)Curl_ares_perform(thrdd->rr.channel, 0);

#endif

  DEBUGASSERT(thrdd->addr);

  if(!thrdd->addr)

    return CURLE_FAILED_INIT;

  Curl_mutex_acquire(&thrdd->addr->mutx);

  done = thrdd->addr->thrd_done;

  Curl_mutex_release(&thrdd->addr->mutx);

  if(done) {

    CURLcode result = CURLE_OK;

    data->state.async.done = TRUE;

    Curl_resolv_unlink(data, &data->state.async.dns);

    Curl_expire_done(data, EXPIRE_ASYNC_NAME);

    if(thrdd->addr->res) {

      data->state.async.dns =

        Curl_dnscache_mk_entry(data, thrdd->addr->res,

                               data->state.async.hostname, 0,

                               data->state.async.port, FALSE);

      thrdd->addr->res = NULL;

      if(!data->state.async.dns)

        result = CURLE_OUT_OF_MEMORY;

#ifdef USE_HTTPSRR_ARES

      if(thrdd->rr.channel) {

        result = thrdd->rr.result;

        if(!result) {

          struct Curl_https_rrinfo *lhrr;

          lhrr = Curl_httpsrr_dup_move(&thrdd->rr.hinfo);

          if(!lhrr)

            result = CURLE_OUT_OF_MEMORY;

          else

            data->state.async.dns->hinfo = lhrr;

        }

      }

#endif

      if(!result && data->state.async.dns)

        result = Curl_dnscache_add(data, data->state.async.dns);

    }

    if(!result && !data->state.async.dns)

      result = Curl_resolver_error(data, NULL);

    if(result)

      Curl_resolv_unlink(data, &data->state.async.dns);

    *dns = data->state.async.dns;

    CURL_TRC_DNS(data, "is_resolved() result=%d, dns=%sfound",

                 result, *dns ? "" : "not ");

    async_thrdd_shutdown(data);

    return result;

  }

  else {

    /* poll for name lookup done with exponential backoff up to 250ms */

    /* should be fine even if this converts to 32-bit */

    timediff_t elapsed = curlx_timediff(curlx_now(),

                                       data->progress.t_startsingle);

    if(elapsed < 0)

      elapsed = 0;

    if(thrdd->addr->poll_interval == 0)

      /* Start at 1ms poll interval */

      thrdd->addr->poll_interval = 1;

    else if(elapsed >= thrdd->addr->interval_end)

      /* Back-off exponentially if last interval expired  */

      thrdd->addr->poll_interval *= 2;

    if(thrdd->addr->poll_interval > 250)

      thrdd->addr->poll_interval = 250;

    thrdd->addr->interval_end = elapsed + thrdd->addr->poll_interval;

    Curl_expire(data, thrdd->addr->poll_interval, EXPIRE_ASYNC_NAME);

    return CURLE_OK;

  }

}

CURLcode Curl_async_pollset(struct Curl_easy *data, struct easy_pollset *ps)

{

  struct async_thrdd_ctx *thrdd = &data->state.async.thrdd;

  CURLcode result = CURLE_OK;

  bool thrd_done;

#if !defined(USE_HTTPSRR_ARES) && defined(CURL_DISABLE_SOCKETPAIR)

  (void)ps;

#endif

#ifdef USE_HTTPSRR_ARES

  if(thrdd->rr.channel) {

    result = Curl_ares_pollset(data, thrdd->rr.channel, ps);

    if(result)

      return result;

  }

#endif

  if(!thrdd->addr)

    return result;

  Curl_mutex_acquire(&thrdd->addr->mutx);

  thrd_done = thrdd->addr->thrd_done;

  Curl_mutex_release(&thrdd->addr->mutx);

  if(!thrd_done) {

#ifndef CURL_DISABLE_SOCKETPAIR

  /* return read fd to client for polling the DNS resolution status */

    result = Curl_pollset_add_in(data, ps, thrdd->addr->sock_pair[0]);

#else

    timediff_t milli;

    timediff_t ms = curlx_timediff(curlx_now(), thrdd->addr->start);

    if(ms < 3)

      milli = 0;

    else if(ms <= 50)

      milli = ms/3;

    else if(ms <= 250)

      milli = 50;

    else

      milli = 200;

    Curl_expire(data, milli, EXPIRE_ASYNC_NAME);

#endif

  }

  return result;

}

#ifndef HAVE_GETADDRINFO

/*

 * Curl_async_getaddrinfo() - for platforms without getaddrinfo

 */

struct Curl_addrinfo *Curl_async_getaddrinfo(struct Curl_easy *data,

                                             const char *hostname,

                                             int port,

                                             int ip_version,

                                             int *waitp)

{

  (void)ip_version;

  *waitp = 0; /* default to synchronous response */

  /* fire up a new resolver thread! */

  if(async_thrdd_init(data, hostname, port, ip_version, NULL)) {

    *waitp = 1; /* expect asynchronous response */

    return NULL;

  }

  failf(data, "getaddrinfo() thread failed");

  return NULL;

}

#else /* !HAVE_GETADDRINFO */

/*

 * Curl_async_getaddrinfo() - for getaddrinfo

 */

struct Curl_addrinfo *Curl_async_getaddrinfo(struct Curl_easy *data,

                                             const char *hostname,

                                             int port,

                                             int ip_version,

                                             int *waitp)

{

  struct addrinfo hints;

  int pf = PF_INET;

  *waitp = 0; /* default to synchronous response */

  CURL_TRC_DNS(data, "init threaded resolve of %s:%d", hostname, port);

#ifdef CURLRES_IPV6

  if((ip_version != CURL_IPRESOLVE_V4) && Curl_ipv6works(data)) {

    /* The stack seems to be IPv6-enabled */

    if(ip_version == CURL_IPRESOLVE_V6)

      pf = PF_INET6;

    else

      pf = PF_UNSPEC;

  }

#else

  (void)ip_version;

#endif /* CURLRES_IPV6 */

  memset(&hints, 0, sizeof(hints));

  hints.ai_family = pf;

  hints.ai_socktype =

    (Curl_conn_get_transport(data, data->conn) == TRNSPRT_TCP) ?

    SOCK_STREAM : SOCK_DGRAM;

  /* fire up a new resolver thread! */

  if(async_thrdd_init(data, hostname, port, ip_version, &hints)) {

    *waitp = 1; /* expect asynchronous response */

    return NULL;

  }

  failf(data, "getaddrinfo() thread failed to start");

  return NULL;

}

#endif /* !HAVE_GETADDRINFO */

#endif /* CURLRES_THREADED */