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

 *                                  _   _ ____  _

 *  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"

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

 * Only for threaded name resolves builds

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

#ifdef USE_RESOLV_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

#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 "curl_addrinfo.h"

#include "curl_trc.h"

#include "url.h"

#include "multiif.h"

#include "curl_threads.h"

#include "progress.h"

#include "rand.h"

#include "select.h"

#include "thrdqueue.h"

#include "vdns/hostip.h"

#include "vdns/httpsrr.h"

#include "curlx/strparse.h"

#include "curlx/wait.h"

#ifdef USE_ARES

#include <ares.h>

#ifdef USE_HTTPSRR

#define USE_HTTPSRR_ARES  /* the combo */

#endif

#endif

/*

 * 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

}

#ifdef CURLVERBOSE

#define CURL_ASYN_ITEM_DESC_LEN   64

#define async_item_description(x)   (x)->description

#else

#define async_item_description(x)   NULL

#endif

struct async_thrdd_item {

  struct Curl_addrinfo *res;

#ifdef CURLVERBOSE

  char description[CURL_ASYN_ITEM_DESC_LEN];

#endif

  int sockerr;

  uint32_t mid;

  uint32_t resolv_id;

  uint16_t port;

  uint8_t transport;

  uint8_t dns_queries;

  BIT(negative); /* resolver answered that the name does not exist */

#ifdef DEBUGBUILD

  uint32_t delay_ms;

  uint32_t delay_fail_ms;

  BIT(dbg_negative);

#endif

  char hostname[1];

};

/* Give up reference to add_ctx */

static void async_thrdd_item_destroy(struct async_thrdd_item *item)

{

  if(item) {

    if(item->res)

      Curl_freeaddrinfo(item->res);

    curlx_free(item);

  }

}

/* Initialize context for threaded resolver */

static struct async_thrdd_item *async_thrdd_item_create(

  struct Curl_easy *data,

  uint32_t resolv_id, uint8_t dns_queries,

  const char *hostname, uint16_t port,

  uint8_t transport)

{

  size_t hostlen = strlen(hostname);

  struct async_thrdd_item *item;

  item = curlx_calloc(1, sizeof(*item) + hostlen);

  if(!item)

    return NULL;

  if(hostlen) /* null-terminator of name already in struct size */

    memcpy(item->hostname, hostname, hostlen);

  item->mid = data->mid;

  item->resolv_id = resolv_id;

  item->dns_queries = dns_queries;

  item->port = port;

  item->transport = transport;

#ifdef CURLVERBOSE

  curl_msnprintf(item->description, sizeof(item->description),

                 "[%" FMT_OFF_T "/%u] %s %s:%u",

                 data->id, item->resolv_id,

                 Curl_resolv_query_str(dns_queries),

                 item->hostname, item->port);

#endif

#ifdef DEBUGBUILD

  {

    const char *p = getenv("CURL_DBG_RESOLV_DELAY");

    if(p) {

      curl_off_t l;

      if(!curlx_str_number(&p, &l, UINT32_MAX)) {

        item->delay_ms = (uint32_t)l;

      }

    }

    p = getenv("CURL_DBG_RESOLV_FAIL_DELAY");

    if(p) {

      curl_off_t l;

      if(!curlx_str_number(&p, &l, UINT32_MAX)) {

        unsigned char c = 0;

        Curl_rand_bytes(data, FALSE, &c, 1);

        item->delay_fail_ms = (uint32_t)l + c;

      }

    }

    if(getenv("CURL_DBG_RESOLV_FAIL_NEGATIVE"))

      item->dbg_negative = TRUE;

  }

#endif

  return item;

}

#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_resolv_async *async = user_data;

  struct async_thrdd_ctx *thrdd = async ? &async->thrdd : NULL;

  (void)timeouts;

  if(!thrdd)

    return;

  async->dns_responses |= CURL_DNSQ_HTTPS;

  async->queries_ongoing--;

  async->done = !async->queries_ongoing;

  if((ARES_SUCCESS == status) && dnsrec)

    async->result = Curl_httpsrr_from_ares(dnsrec, &async->httpsrr);

}

/* Initialize the c-ares channel used for the HTTPS RR side-query, without

 * submitting any query on it yet. */

static CURLcode async_rr_init(struct Curl_easy *data,

                              struct Curl_resolv_async *async)

{

  struct async_thrdd_ctx *thrdd = &async->thrdd;

  int status;

  (void)data;

  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 DEBUGBUILD

  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

  return CURLE_OK;

}

/* Submit the HTTPS RR query on the already initialized channel. */

static CURLcode async_rr_start(struct Curl_easy *data,

                               struct Curl_resolv_async *async)

{

  struct async_thrdd_ctx *thrdd = &async->thrdd;

  char *https_name = NULL;

  CURLcode result = CURLE_OK;

  if(async->peer->port != 443) {

    https_name = curl_maprintf("_%u._https.%s",

                               async->peer->port, async->peer->hostname);

    if(!https_name) {

      result = CURLE_OUT_OF_MEMORY;

      goto out;

    }

  }

  async->queries_ongoing++;

  ares_query_dnsrec(thrdd->rr.channel,

                    https_name ? https_name : async->peer->hostname,

                    ARES_CLASS_IN, ARES_REC_TYPE_HTTPS,

                    async_thrdd_rr_done, async, NULL);

  CURL_TRC_DNS(data, "[HTTPS] query records for %s",

               https_name ? https_name : async->peer->hostname);

out:

  curlx_free(https_name);

  return result;

}

#endif

void Curl_async_thrdd_shutdown(struct Curl_easy *data,

                               struct Curl_resolv_async *async)

{

  Curl_async_thrdd_destroy(data, async);

}

struct async_thrdd_match_ctx {

  uint32_t mid;

  uint32_t resolv_id;

};

static bool async_thrdd_match_item(void *qitem, void *match_data)

{

  const struct async_thrdd_match_ctx *ctx = match_data;

  struct async_thrdd_item *item = qitem;

  return (item->mid == ctx->mid) && (item->resolv_id == ctx->resolv_id);

}

void Curl_async_thrdd_destroy(struct Curl_easy *data,

                              struct Curl_resolv_async *async)

{

  (void)data;

  if(async->queries_ongoing && !async->done &&

     data->multi && data->multi->resolv_thrdq) {

    /* Remove any resolve items still queued */

    struct async_thrdd_match_ctx mctx;

    mctx.mid = data->mid;

    mctx.resolv_id = async->id;

    Curl_thrdq_clear(data->multi->resolv_thrdq,

                     async_thrdd_match_item, &mctx);

  }

#ifdef USE_HTTPSRR_ARES

  if(async->thrdd.rr.channel) {

    ares_destroy(async->thrdd.rr.channel);

    async->thrdd.rr.channel = NULL;

  }

#endif

  async_thrdd_item_destroy(async->thrdd.res_A);

  async->thrdd.res_A = NULL;

  async_thrdd_item_destroy(async->thrdd.res_AAAA);

  async->thrdd.res_AAAA = NULL;

}

/*

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

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

 */

CURLcode Curl_async_await(struct Curl_easy *data, uint32_t resolv_id,

                          struct Curl_dns_entry **pdns)

{

  struct Curl_resolv_async *async = Curl_async_get(data, resolv_id);

  struct async_thrdd_ctx *thrdd = async ? &async->thrdd : NULL;

  timediff_t milli, ms;

  CURLcode result = CURLE_AGAIN;

  if(!thrdd)

    return CURLE_FAILED_INIT;

  while(result == CURLE_AGAIN) {

    while(async->queries_ongoing && !async->done) {

      Curl_async_thrdd_multi_process(data->multi);

      if(async->done)

        break;

      ms = curlx_ptimediff_ms(Curl_pgrs_now(data), &async->start);

      if(ms < 3)

        milli = 0;

      else if(ms <= 50)

        milli = ms / 3;

      else if(ms <= 250)

        milli = 50;

      else

        milli = 200;

      CURL_TRC_DNS(data, "await, waiting %" FMT_TIMEDIFF_T "ms", milli);

      curlx_wait_ms(milli);

    }

    result = Curl_async_take_result(data, async, pdns);

  }

  return result;

}

#ifdef HAVE_GETADDRINFO

/* Was the getaddrinfo() failure an authoritative negative answer,

   i.e. the resolver responded that the name (or its data) does not

   exist? Transient failures like EAI_AGAIN and local troubles must

   not count as negative answers. */

static bool gai_negative(int rc)

{

  switch(rc) {

#ifdef EAI_NONAME

  case EAI_NONAME:

#endif

#if defined(EAI_NODATA) && \

  (!defined(EAI_NONAME) || (EAI_NODATA != EAI_NONAME))

  case EAI_NODATA:

#endif

    return TRUE;

  default:

    return FALSE;

  }

}

/* Process the item, using Curl_getaddrinfo_ex() */

static void async_thrdd_item_process(void *arg)

{

  struct async_thrdd_item *item = arg;

  struct addrinfo hints;

  char service[12];

  int pf = PF_INET;

  int rc;

#ifdef DEBUGBUILD

  if(item->delay_ms) {

    curlx_wait_ms(item->delay_ms);

  }

  if(item->delay_fail_ms) {

    curlx_wait_ms(item->delay_fail_ms);

    item->negative = item->dbg_negative;

    return;

  }

#endif

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

#ifdef CURLRES_IPV6

  if(item->dns_queries & CURL_DNSQ_AAAA) {

    pf = (item->dns_queries & CURL_DNSQ_A) ? PF_UNSPEC : PF_INET6;

  }

#endif

  hints.ai_family = pf;

  hints.ai_socktype = Curl_socktype_for_transport(item->transport);

  hints.ai_protocol = Curl_protocol_for_transport(item->transport);

#ifdef __APPLE__

  /* If we leave `ai_flags == 0` then macOS is looking for IPV4MAPPED

   * when doing AAAA queries. We do not want this "help". */

  hints.ai_flags = AI_ADDRCONFIG;

#endif

  curl_msnprintf(service, sizeof(service), "%u", item->port);

#ifdef AI_NUMERICSERV

  hints.ai_flags |= AI_NUMERICSERV;

#endif

  rc = Curl_getaddrinfo_ex(item->hostname, service, &hints, &item->res);

  if(rc) {

    item->sockerr = SOCKERRNO ? SOCKERRNO : rc;

    if(item->sockerr == 0)

      item->sockerr = RESOLVER_ENOMEM;

    item->negative = gai_negative(rc);

  }

  else {

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

  }

}

#else /* HAVE_GETADDRINFO */

/* Process the item, using Curl_ipv4_resolve_r() */

static void async_thrdd_item_process(void *arg)

{

  struct async_thrdd_item *item = arg;

#ifdef DEBUGBUILD

  if(item->delay_ms) {

    curlx_wait_ms(item->delay_ms);

  }

  if(item->delay_fail_ms) {

    curlx_wait_ms(item->delay_fail_ms);

    item->negative = item->dbg_negative;

    return;

  }

#endif

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

  if(!item->res) {

    item->sockerr = SOCKERRNO;

    if(item->sockerr == 0)

      item->sockerr = RESOLVER_ENOMEM;

    /* this resolver cannot tell a transient failure from an

       authoritative negative answer, treat it as before */

    item->negative = TRUE;

  }

}

#endif /* HAVE_GETADDRINFO */

#ifdef ENABLE_INTERNAL_WAKEUP

static void async_thrdd_event(const struct curl_thrdq *tqueue,

                              Curl_thrdq_event ev,

                              void *user_data)

{

  struct Curl_multi *multi = user_data;

  (void)tqueue;

  switch(ev) {

  case CURL_THRDQ_EV_ITEM_DONE:

    Curl_multi_wakeup_internal(multi);

    break;

  default:

    break;

  }

}

#else

#define async_thrdd_event   NULL

#endif

static void async_thrdd_item_free(void *item)

{

  async_thrdd_item_destroy(item);

}

/* Create a thread queue for processing resolv items */

CURLcode Curl_async_thrdd_multi_init(struct Curl_multi *multi,

                                     uint32_t min_threads,

                                     uint32_t max_threads,

                                     uint32_t idle_time_ms)

{

  CURLcode result;

  DEBUGASSERT(!multi->resolv_thrdq);

  result = Curl_thrdq_create(&multi->resolv_thrdq, "DNS",

                             min_threads, max_threads, idle_time_ms,

                             async_thrdd_item_free,

                             async_thrdd_item_process,

                             async_thrdd_event,

                             multi);

#ifdef DEBUGBUILD

  if(!result) {

    const char *p = getenv("CURL_DBG_RESOLV_MAX_THREADS");

    if(p) {

      curl_off_t l;

      if(!curlx_str_number(&p, &l, UINT32_MAX)) {

        result = Curl_async_thrdd_multi_set_props(

          multi, min_threads, (uint32_t)l, idle_time_ms);

      }

    }

  }

#endif

  return result;

}

/* Tear down the thread queue, joining active threads or detaching them */

void Curl_async_thrdd_multi_destroy(struct Curl_multi *multi, bool join)

{

  if(multi->resolv_thrdq) {

#ifdef CURLVERBOSE

    CURL_TRC_DNS(multi->admin, "destroy thread queue+pool, join=%d", join);

    CURL_THRDQ_TRACE(multi->resolv_thrdq, multi->admin);

#endif

    Curl_thrdq_destroy(multi->resolv_thrdq, join);

    multi->resolv_thrdq = NULL;

  }

}

#ifdef CURLVERBOSE

static void async_thrdd_report_item(struct Curl_easy *data,

                                    struct async_thrdd_item *item)

{

  char buf[MAX_IPADR_LEN];

  struct dynbuf tmp;

  const char *sep = "";

  const struct Curl_addrinfo *ai = item->res;

  CURLcode result;

  int ai_family;

#ifdef USE_IPV6

  ai_family = (item->dns_queries & CURL_DNSQ_AAAA) ? AF_INET6 : AF_INET;

#else

  ai_family = AF_INET;

#endif

  if(!CURL_TRC_DNS_is_verbose(data))

    return;

  curlx_dyn_init(&tmp, 1024);

  for(; ai; ai = ai->ai_next) {

    if(ai->ai_family == ai_family) {

      Curl_printable_address(ai, buf, sizeof(buf));

      result = curlx_dyn_addf(&tmp, "%s%s", sep, buf);

      if(result) {

        CURL_TRC_DNS(data, "too many IP, cannot show");

        goto out;

      }

      sep = ", ";

    }

  }

  CURL_TRC_DNS(data, "Host %s:%u resolved IPv%c: %s",

               item->hostname, item->port,

               (item->dns_queries & CURL_DNSQ_AAAA) ? '6' : '4',

               (curlx_dyn_len(&tmp) ? curlx_dyn_ptr(&tmp) : "(none)"));

out:

  curlx_dyn_free(&tmp);

}

#endif /* CURLVERBOSE */

/* Process the receiving end of the thread queue, dispatching

 * processed items to their transfer when it can still be found

 * and has an `async` state present. Otherwise, destroy the item. */

void Curl_async_thrdd_multi_process(struct Curl_multi *multi)

{

  struct Curl_easy *data;

  void *qitem;

  while(!Curl_thrdq_recv(multi->resolv_thrdq, &qitem)) {

    /* dispatch resolve result */

    struct async_thrdd_item *item = qitem;

    struct Curl_resolv_async *async = NULL;

    data = Curl_multi_get_easy(multi, item->mid);

    if(data)

      async = Curl_async_get(data, item->resolv_id);

    if(async) {

      struct async_thrdd_item **pdest = &async->thrdd.res_A;

#ifdef CURLRES_IPV6

      if(item->dns_queries & CURL_DNSQ_AAAA)

        pdest = &async->thrdd.res_AAAA;

#endif

      if(!*pdest) {

        *pdest = item;

        item = NULL;

      }

      else

        DEBUGASSERT(0); /* should not receive duplicates here */

      --async->queries_ongoing;

      Curl_multi_mark_dirty(data);

    }

    async_thrdd_item_free(item);

  }

  CURL_THRDQ_TRACE(multi->resolv_thrdq, multi->admin);

}

CURLcode Curl_async_thrdd_multi_set_props(struct Curl_multi *multi,

                                          uint32_t min_threads,

                                          uint32_t max_threads,

                                          uint32_t idle_time_ms)

{

  return Curl_thrdq_set_props(multi->resolv_thrdq,

                              min_threads, max_threads, idle_time_ms);

}

static CURLcode async_thrdd_query(struct Curl_easy *data,

                                  struct Curl_resolv_async *async,

                                  uint8_t dns_queries)

{

  struct async_thrdd_item *item;

  CURLcode result;

  item = async_thrdd_item_create(data, async->id, dns_queries,

                                 async->peer->hostname, async->peer->port,

                                 async->transport);

  if(!item) {

    result = CURLE_OUT_OF_MEMORY;

    goto out;

  }

  CURL_TRC_DNS(data, "queueing query %s", item->description);

  result = Curl_thrdq_send(data->multi->resolv_thrdq, item,

                           async_item_description(item), async->timeout_ms);

  if(result)

    goto out;

  item = NULL;

  async->queries_ongoing++;

out:

  if(item)

    async_thrdd_item_free(item);

  return result;

}

CURLcode Curl_async_getaddrinfo(struct Curl_easy *data,

                                struct Curl_resolv_async *async)

{

  CURLcode result = CURLE_FAILED_INIT;

  void *resolver = NULL;

  if(async->queries_ongoing || async->done)

    return CURLE_FAILED_INIT;

#ifdef USE_HTTPSRR_ARES

  DEBUGASSERT(!async->thrdd.rr.channel);

  if((async->dns_queries & CURL_DNSQ_HTTPS) && !async->is_ipaddr) {

    result = async_rr_init(data, async);

    if(result)

      goto out;

    resolver = async->thrdd.rr.channel;

  }

#endif

  result = Curl_resolv_announce_start(data, resolver);

  if(result)

    return result;

#ifdef USE_HTTPSRR_ARES

  if(resolver) {

    result = async_rr_start(data, async);

    if(result)

      goto out;

  }

#endif

#ifdef CURLRES_IPV6

  /* Do not start an AAAA query for an IPv4 address when

   * we will start an A query for it. */

  if((async->dns_queries & CURL_DNSQ_AAAA) &&

     !(async->is_ipv4addr && (async->dns_queries & CURL_DNSQ_A))) {

    result = async_thrdd_query(data, async, CURL_DNSQ_AAAA);

    if(result)

      goto out;

  }

#endif

  if(async->dns_queries & CURL_DNSQ_A) {

    result = async_thrdd_query(data, async, CURL_DNSQ_A);

    if(result)

      goto out;

  }

  CURL_THRDQ_TRACE(data->multi->resolv_thrdq, data);

out:

  if(!async->queries_ongoing)

    async->done = TRUE;

  if(result)

    CURL_TRC_DNS(data, "error queueing query %s:%d -> %d",

                 async->peer->hostname, async->peer->port, (int)result);

  return result;

}

CURLcode Curl_async_pollset(struct Curl_easy *data,

                            struct Curl_resolv_async *async,

                            struct easy_pollset *ps)

{

  timediff_t timeout_ms;

  timeout_ms = Curl_async_timeleft_ms(data, async);

#ifdef USE_HTTPSRR_ARES

  if(async->thrdd.rr.channel) {

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

    if(result)

      return result;

    timeout_ms = Curl_ares_timeout_ms(data, async, async->thrdd.rr.channel);

  }

#else

  (void)ps;

#endif

  if(!async->done) {

    const struct curltime *pnow = Curl_pgrs_now(data);

#ifndef ENABLE_INTERNAL_WAKEUP

    timediff_t stutter_ms, elapsed_ms;

    elapsed_ms = curlx_ptimediff_ms(pnow, &async->start);

    if(elapsed_ms < 3)

      stutter_ms = 1;

    else if(elapsed_ms <= 50)

      stutter_ms = elapsed_ms / 3;

    else if(elapsed_ms <= 250)

      stutter_ms = 50;

    else

      stutter_ms = 200;

    timeout_ms = CURLMIN(stutter_ms, timeout_ms);

#else

    if(async->queries_ongoing &&

       !Curl_thrdq_check_started(data->multi->resolv_thrdq)) {

      /* The queue has items but starting a worker thread to process

         them just failed again; expire soon to check once more,

         instead of sleeping on the full resolve timeout. */

      CURL_TRC_DNS(data, "resolver thread start failed again, retrying");

      timeout_ms = CURLMIN(100, timeout_ms);

    }

#endif

    Curl_expire_set(data, EXPIRE_ASYNC_NAME, timeout_ms, pnow);

  }

  return CURLE_OK;

}

#if defined(USE_IPV6) && defined(HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID)

static bool async_thrdd_item_missing_scope(struct Curl_easy *data,

                                           struct async_thrdd_item *item)

{

  const struct Curl_addrinfo *ai;

  /* scope id already globally set */

  if(data->conn && data->conn->scope_id)

    return FALSE;

  for(ai = item->res; ai; ai = ai->ai_next) {

    if(ai->ai_family == AF_INET6) {

      struct sockaddr_in6 *sa6 = (void *)ai->ai_addr;

      if(IN6_IS_ADDR_LINKLOCAL(&sa6->sin6_addr) && !sa6->sin6_scope_id)

        return TRUE;

    }

  }

  return FALSE;

}

static void async_thrdd_item_strip_results(struct async_thrdd_item *item,

                                           int ai_family)

{

  struct Curl_addrinfo *ai = item->res, **panchor = &item->res;

  while(ai) {

    if(ai->ai_family == ai_family) {

      *panchor = ai->ai_next;

      ai->ai_next = NULL;

      Curl_freeaddrinfo(ai);

      ai = *panchor;

    }

    else {

      panchor = &ai->ai_next;

      ai = ai->ai_next;

    }

  }

}

#endif /* USE_IPV6 && HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID */

static CURLcode async_thrdd_check_done(struct Curl_easy *data,

                                       struct Curl_resolv_async *async)

{

  struct async_thrdd_ctx *thrdd = &async->thrdd;

  (void)data;

  if(thrdd->res_A && !thrdd->processed_A) {

    VERBOSE(async_thrdd_report_item(data, thrdd->res_A));

    /* move addrinfos to the async result member */

    async->dns_responses |= thrdd->res_A->dns_queries;

    async->ai_A = thrdd->res_A->res;

    thrdd->res_A->res = NULL;

    thrdd->processed_A = TRUE;

  }

  if(thrdd->res_AAAA && !thrdd->processed_AAAA) {

#if defined(USE_IPV6) && defined(HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID)

    /* do we accept the incoming AAAA response? */

    if(!(thrdd->res_AAAA->dns_queries & CURL_DNSQ_A) &&

       async_thrdd_item_missing_scope(data, thrdd->res_AAAA)) {

      /* We queried "only" AF_INET6. This may be problematic when the

       * result has ipv6 link-local addresses and did not give

       * any scope id for it. glibc has a long outstanding bug

       * <https://sourceware.org/bugzilla/show_bug.cgi?id=14413>

       * that gives scope ids only on AF_UNSPEC queries. */

      struct async_thrdd_item *item = thrdd->res_AAAA;

      CURLcode result;

      /* Reuse the item and queue it again, this time with added

       * CURL_DNSQ_A which resolves using AF_UNSPEC. */

      thrdd->res_AAAA = NULL;

      item->dns_queries |= CURL_DNSQ_A;

      if(item->res) {

        Curl_freeaddrinfo(item->res);

        item->res = NULL;

      }

      CURL_TRC_DNS(data, "re-queueing query %s for AF_UNSPEC resolve",

                   item->description);

      result = Curl_thrdq_send(data->multi->resolv_thrdq, item,

                               async_item_description(item),

                               async->timeout_ms);

      if(result) {

        async_thrdd_item_free(item);

        return result;

      }

      async->queries_ongoing++;

      return CURLE_AGAIN;

    }

    /* accepting the AAAA result, strip it of any AF_INET entries,

     * as we might have resolved it with AF_UNSPEC. */

    async_thrdd_item_strip_results(thrdd->res_AAAA, AF_INET);

#endif /* USE_IPV6 && HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID */

    VERBOSE(async_thrdd_report_item(data, thrdd->res_AAAA));

    /* move addrinfos to the async result member */

    async->dns_responses |= thrdd->res_AAAA->dns_queries;

    async->ai_AAAA = thrdd->res_AAAA->res;

    thrdd->res_AAAA->res = NULL;

    thrdd->processed_AAAA = TRUE;

  }

  if(async->queries_ongoing)

    return CURLE_AGAIN;

  async->done = TRUE;

  return CURLE_OK;

}

/*

 * Curl_async_take_result() 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_take_result(struct Curl_easy *data,

                                struct Curl_resolv_async *async,

                                struct Curl_dns_entry **pdns)

{

  struct async_thrdd_ctx *thrdd = &async->thrdd;

  struct Curl_dns_entry *dns = NULL;

  CURLcode result = CURLE_OK;

  DEBUGASSERT(pdns);

  *pdns = NULL;

#ifdef USE_HTTPSRR_ARES

  /* best effort, ignore errors */

  if(thrdd->rr.channel)

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

#endif

#ifndef ENABLE_INTERNAL_WAKEUP

  Curl_async_thrdd_multi_process(data->multi);

#endif

  result = async_thrdd_check_done(data, async);

  if(result)

    return result;

  Curl_expire_clear(data, EXPIRE_ASYNC_NAME);

  /* A failure is an authoritative negative answer, eligible for

     negative caching, only when every A/AAAA query performed came

     back answering that the name does not exist. A query that

     failed transiently or never returned is not an answer. */

  {

    const uint8_t ip_queries =

      async->dns_queries & (CURL_DNSQ_A | CURL_DNSQ_AAAA);

    bool negative = (async->dns_responses & ip_queries) == ip_queries;

    if(thrdd->res_A && (async->ai_A || !thrdd->res_A->negative))

      negative = FALSE;

    if(thrdd->res_AAAA && (async->ai_AAAA || !thrdd->res_AAAA->negative))

      negative = FALSE;

    if(!thrdd->res_A && !thrdd->res_AAAA)

      negative = FALSE;

    async->negative_answer = negative;

  }

  if(async->result) {

    result = async->result;

    goto out;

  }

  if(async->ai_A || async->ai_AAAA) {

    dns = Curl_dnsc_mk_addr2(

      data, async->dns_queries, &async->ai_A, &async->ai_AAAA, async->peer);

    if(!dns) {

      result = CURLE_OUT_OF_MEMORY;

      goto out;

    }

  }

#ifdef USE_HTTPSRR_ARES

  if(!dns && thrdd->rr.channel) {

    Curl_httpsrr_trace(data, async->httpsrr);

    dns = Curl_dnsc_mk_https(data, &async->httpsrr, async->peer);

    if(!dns) {

      result = CURLE_OUT_OF_MEMORY;

      goto out;

    }

  }

#endif

  if(dns) {

    *pdns = dns;

    dns = NULL;

  }

  CURL_THRDQ_TRACE(data->multi->resolv_thrdq, data);

out:

  Curl_dns_entry_unlink(data, &dns);

  Curl_async_thrdd_shutdown(data, async);

  if(!result && !*pdns)

    result = Curl_async_failed(data, async, NULL);

  if(result &&

     (result != CURLE_COULDNT_RESOLVE_HOST) &&

     (result != CURLE_COULDNT_RESOLVE_PROXY)) {

    CURL_TRC_DNS(data, "Error %d resolving %s:%d",

                 (int)result, async->peer->hostname, async->peer->port);

  }

  return result;

}