text: /*
   *
   * Copyright 2016 gRPC authors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   */
  
  #include <grpc/support/port_platform.h>
  
  #if GRPC_ARES == 1
  
  #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
  #include "src/core/lib/iomgr/sockaddr.h"
  
  #include <string.h>
  #include <sys/types.h>
  
  #include <ares.h>
  #include <grpc/support/alloc.h>
  #include <grpc/support/log.h>
  #include <grpc/support/string_util.h>
  #include <grpc/support/time.h>
  
  #include <address_sorting/address_sorting.h>
  #include "src/core/ext/filters/client_channel/parse_address.h"
  #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver.h"
  #include "src/core/lib/gpr/string.h"
  #include "src/core/lib/gprpp/host_port.h"
  #include "src/core/lib/iomgr/combiner.h"
  #include "src/core/lib/iomgr/error.h"
  #include "src/core/lib/iomgr/executor.h"
  #include "src/core/lib/iomgr/iomgr_internal.h"
  #include "src/core/lib/iomgr/nameser.h"
  #include "src/core/lib/iomgr/sockaddr_utils.h"
  
  using grpc_core::ServerAddress;
  using grpc_core::ServerAddressList;
  
  grpc_core::TraceFlag grpc_trace_cares_address_sorting(false,
                                                        "cares_address_sorting");
  
  grpc_core::TraceFlag grpc_trace_cares_resolver(false, "cares_resolver");
  
  struct grpc_ares_request {
    /** indicates the DNS server to use, if specified */
    struct ares_addr_port_node dns_server_addr;
    /** following members are set in grpc_resolve_address_ares_impl */
    /** closure to call when the request completes */
    grpc_closure* on_done;
    /** the pointer to receive the resolved addresses */
    std::unique_ptr<grpc_core::ServerAddressList>* addresses_out;
    /** the pointer to receive the service config in JSON */
    char** service_config_json_out;
    /** the evernt driver used by this request */
    grpc_ares_ev_driver* ev_driver;
    /** number of ongoing queries */
    size_t pending_queries;
  
    /** the errors explaining query failures, appended to in query callbacks */
    grpc_error* error;
  };
  
  typedef struct grpc_ares_hostbyname_request {
    /** following members are set in create_hostbyname_request_locked
     */
    /** the top-level request instance */
    grpc_ares_request* parent_request;
    /** host to resolve, parsed from the name to resolve */
    char* host;
    /** port to fill in sockaddr_in, parsed from the name to resolve */
    uint16_t port;
    /** is it a grpclb address */
    bool is_balancer;
  } grpc_ares_hostbyname_request;
  
  static void log_address_sorting_list(const ServerAddressList& addresses,
                                       const char* input_output_str) {
    for (size_t i = 0; i < addresses.size(); i++) {
      char* addr_str;
      if (grpc_sockaddr_to_string(&addr_str, &addresses[i].address(), true)) {
        gpr_log(GPR_INFO, "c-ares address sorting: %s[%" PRIuPTR "]=%s",
                input_output_str, i, addr_str);
        gpr_free(addr_str);
      } else {
        gpr_log(GPR_INFO,
                "c-ares address sorting: %s[%" PRIuPTR "]=<unprintable>",
                input_output_str, i);
      }
    }
  }
  
  void grpc_cares_wrapper_address_sorting_sort(ServerAddressList* addresses) {
    if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_cares_address_sorting)) {
      log_address_sorting_list(*addresses, "input");
    }
    address_sorting_sortable* sortables = (address_sorting_sortable*)gpr_zalloc(
        sizeof(address_sorting_sortable) * addresses->size());
    for (size_t i = 0; i < addresses->size(); ++i) {
      sortables[i].user_data = &(*addresses)[i];
      memcpy(&sortables[i].dest_addr.addr, &(*addresses)[i].address().addr,
             (*addresses)[i].address().len);
      sortables[i].dest_addr.len = (*addresses)[i].address().len;
    }
    address_sorting_rfc_6724_sort(sortables, addresses->size());
    ServerAddressList sorted;
    sorted.reserve(addresses->size());
    for (size_t i = 0; i < addresses->size(); ++i) {
      sorted.emplace_back(*static_cast<ServerAddress*>(sortables[i].user_data));
    }
    gpr_free(sortables);
    *addresses = std::move(sorted);
    if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_cares_address_sorting)) {
      log_address_sorting_list(*addresses, "output");
    }
  }
  
  static void grpc_ares_request_ref_locked(grpc_ares_request* r) {
    r->pending_queries++;
  }
  
  static void grpc_ares_request_unref_locked(grpc_ares_request* r) {
    r->pending_queries--;
    if (r->pending_queries == 0u) {
      grpc_ares_ev_driver_on_queries_complete_locked(r->ev_driver);
    }
  }
  
  void grpc_ares_complete_request_locked(grpc_ares_request* r) {
    /* Invoke on_done callback and destroy the
       request */
    r->ev_driver = nullptr;
    ServerAddressList* addresses = r->addresses_out->get();
    if (addresses != nullptr) {
      grpc_cares_wrapper_address_sorting_sort(addresses);
      GRPC_ERROR_UNREF(r->error);
      r->error = GRPC_ERROR_NONE;
      // TODO(apolcyn): allow c-ares to return a service config
      // with no addresses along side it
    }
    grpc_core::ExecCtx::Run(DEBUG_LOCATION, r->on_done, r->error);
  }
  
  static grpc_ares_hostbyname_request* create_hostbyname_request_locked(
      grpc_ares_request* parent_request, char* host, uint16_t port,
      bool is_balancer) {
    GRPC_CARES_TRACE_LOG(
        "request:%p create_hostbyname_request_locked host:%s port:%d "
        "is_balancer:%d",
        parent_request, host, port, is_balancer);
    grpc_ares_hostbyname_request* hr = static_cast<grpc_ares_hostbyname_request*>(
        gpr_zalloc(sizeof(grpc_ares_hostbyname_request)));
    hr->parent_request = parent_request;
    hr->host = gpr_strdup(host);
    hr->port = port;
    hr->is_balancer = is_balancer;
    grpc_ares_request_ref_locked(parent_request);
    return hr;
  }
  
  static void destroy_hostbyname_request_locked(
      grpc_ares_hostbyname_request* hr) {
    grpc_ares_request_unref_locked(hr->parent_request);
    gpr_free(hr->host);
    gpr_free(hr);
  }
  
  static void on_hostbyname_done_locked(void* arg, int status, int /*timeouts*/,
                                        struct hostent* hostent) {
    grpc_ares_hostbyname_request* hr =
        static_cast<grpc_ares_hostbyname_request*>(arg);
    grpc_ares_request* r = hr->parent_request;
    if (status == ARES_SUCCESS) {
      GRPC_CARES_TRACE_LOG(
          "request:%p on_hostbyname_done_locked host=%s ARES_SUCCESS", r,
          hr->host);
      if (*r->addresses_out == nullptr) {
        *r->addresses_out = grpc_core::MakeUnique<ServerAddressList>();
      }
      ServerAddressList& addresses = **r->addresses_out;
      for (size_t i = 0; hostent->h_addr_list[i] != nullptr; ++i) {
        grpc_core::InlinedVector<grpc_arg, 2> args_to_add;
        if (hr->is_balancer) {
          args_to_add.emplace_back(grpc_channel_arg_integer_create(
              const_cast<char*>(GRPC_ARG_ADDRESS_IS_BALANCER), 1));
          args_to_add.emplace_back(grpc_channel_arg_string_create(
              const_cast<char*>(GRPC_ARG_ADDRESS_BALANCER_NAME), hr->host));
        }
        grpc_channel_args* args = grpc_channel_args_copy_and_add(
            nullptr, args_to_add.data(), args_to_add.size());
        switch (hostent->h_addrtype) {
          case AF_INET6: {
            size_t addr_len = sizeof(struct sockaddr_in6);
            struct sockaddr_in6 addr;
            memset(&addr, 0, addr_len);
            memcpy(&addr.sin6_addr, hostent->h_addr_list[i],
                   sizeof(struct in6_addr));
            addr.sin6_family = static_cast<unsigned char>(hostent->h_addrtype);
            addr.sin6_port = hr->port;
            addresses.emplace_back(&addr, addr_len, args);
            char output[INET6_ADDRSTRLEN];
            ares_inet_ntop(AF_INET6, &addr.sin6_addr, output, INET6_ADDRSTRLEN);
            GRPC_CARES_TRACE_LOG(
                "request:%p c-ares resolver gets a AF_INET6 result: \n"
                "  addr: %s\n  port: %d\n  sin6_scope_id: %d\n",
                r, output, ntohs(hr->port), addr.sin6_scope_id);
            break;
          }
          case AF_INET: {
            size_t addr_len = sizeof(struct sockaddr_in);
            struct sockaddr_in addr;
            memset(&addr, 0, addr_len);
            memcpy(&addr.sin_addr, hostent->h_addr_list[i],
                   sizeof(struct in_addr));
            addr.sin_family = static_cast<unsigned char>(hostent->h_addrtype);
            addr.sin_port = hr->port;
            addresses.emplace_back(&addr, addr_len, args);
            char output[INET_ADDRSTRLEN];
            ares_inet_ntop(AF_INET, &addr.sin_addr, output, INET_ADDRSTRLEN);
            GRPC_CARES_TRACE_LOG(
                "request:%p c-ares resolver gets a AF_INET result: \n"
                "  addr: %s\n  port: %d\n",
                r, output, ntohs(hr->port));
            break;
          }
        }
      }
    } else {
      char* error_msg;
      gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
                   ares_strerror(status));
      GRPC_CARES_TRACE_LOG("request:%p on_hostbyname_done_locked host=%s %s", r,
                           hr->host, error_msg);
      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
      gpr_free(error_msg);
      r->error = grpc_error_add_child(error, r->error);
    }
    destroy_hostbyname_request_locked(hr);
  }
  
  static void on_srv_query_done_locked(void* arg, int status, int /*timeouts*/,
                                       unsigned char* abuf, int alen) {
    grpc_ares_request* r = static_cast<grpc_ares_request*>(arg);
    if (status == ARES_SUCCESS) {
      GRPC_CARES_TRACE_LOG("request:%p on_srv_query_done_locked ARES_SUCCESS", r);
      struct ares_srv_reply* reply;
      const int parse_status = ares_parse_srv_reply(abuf, alen, &reply);
      GRPC_CARES_TRACE_LOG("request:%p ares_parse_srv_reply: %d", r,
                           parse_status);
      if (parse_status == ARES_SUCCESS) {
        ares_channel* channel =
            grpc_ares_ev_driver_get_channel_locked(r->ev_driver);
        for (struct ares_srv_reply* srv_it = reply; srv_it != nullptr;
             srv_it = srv_it->next) {
          if (grpc_ares_query_ipv6()) {
            grpc_ares_hostbyname_request* hr = create_hostbyname_request_locked(
                r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
            ares_gethostbyname(*channel, hr->host, AF_INET6,
                               on_hostbyname_done_locked, hr);
          }
          grpc_ares_hostbyname_request* hr = create_hostbyname_request_locked(
              r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
          ares_gethostbyname(*channel, hr->host, AF_INET,
                             on_hostbyname_done_locked, hr);
          grpc_ares_ev_driver_start_locked(r->ev_driver);
        }
      }
      if (reply != nullptr) {
        ares_free_data(reply);
      }
    } else {
      char* error_msg;
      gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
                   ares_strerror(status));
      GRPC_CARES_TRACE_LOG("request:%p on_srv_query_done_locked %s", r,
                           error_msg);
      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
      gpr_free(error_msg);
      r->error = grpc_error_add_child(error, r->error);
    }
    grpc_ares_request_unref_locked(r);
  }
  
  static const char g_service_config_attribute_prefix[] = "grpc_config=";
  
  static void on_txt_done_locked(void* arg, int status, int /*timeouts*/,
                                 unsigned char* buf, int len) {
    char* error_msg;
    grpc_ares_request* r = static_cast<grpc_ares_request*>(arg);
    const size_t prefix_len = sizeof(g_service_config_attribute_prefix) - 1;
    struct ares_txt_ext* result = nullptr;
    struct ares_txt_ext* reply = nullptr;
    grpc_error* error = GRPC_ERROR_NONE;
    if (status != ARES_SUCCESS) goto fail;
    GRPC_CARES_TRACE_LOG("request:%p on_txt_done_locked ARES_SUCCESS", r);
    status = ares_parse_txt_reply_ext(buf, len, &reply);
    if (status != ARES_SUCCESS) goto fail;
    // Find service config in TXT record.
    for (result = reply; result != nullptr; result = result->next) {
      if (result->record_start &&
          memcmp(result->txt, g_service_config_attribute_prefix, prefix_len) ==
              0) {
        break;
      }
    }
    // Found a service config record.
    if (result != nullptr) {
      size_t service_config_len = result->length - prefix_len;
      *r->service_config_json_out =
          static_cast<char*>(gpr_malloc(service_config_len + 1));
      memcpy(*r->service_config_json_out, result->txt + prefix_len,
             service_config_len);
      for (result = result->next; result != nullptr && !result->record_start;
           result = result->next) {
        *r->service_config_json_out = static_cast<char*>(
            gpr_realloc(*r->service_config_json_out,
                        service_config_len + result->length + 1));
        memcpy(*r->service_config_json_out + service_config_len, result->txt,
               result->length);
        service_config_len += result->length;
      }
      (*r->service_config_json_out)[service_config_len] = '\0';
      GRPC_CARES_TRACE_LOG("request:%p found service config: %s", r,
                           *r->service_config_json_out);
    }
    // Clean up.
    ares_free_data(reply);
    goto done;
  fail:
    gpr_asprintf(&error_msg, "C-ares TXT lookup status is not ARES_SUCCESS: %s",
                 ares_strerror(status));
    error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
    GRPC_CARES_TRACE_LOG("request:%p on_txt_done_locked %s", r, error_msg);
    gpr_free(error_msg);
    r->error = grpc_error_add_child(error, r->error);
  done:
    grpc_ares_request_unref_locked(r);
  }
  
  void grpc_dns_lookup_ares_continue_after_check_localhost_and_ip_literals_locked(
      grpc_ares_request* r, const char* dns_server, const char* name,
      const char* default_port, grpc_pollset_set* interested_parties,
      bool check_grpclb, int query_timeout_ms, grpc_core::Combiner* combiner) {
    grpc_error* error = GRPC_ERROR_NONE;
    grpc_ares_hostbyname_request* hr = nullptr;
    ares_channel* channel = nullptr;
    /* parse name, splitting it into host and port parts */
    grpc_core::UniquePtr<char> host;
    grpc_core::UniquePtr<char> port;
    grpc_core::SplitHostPort(name, &host, &port);
    if (host == nullptr) {
      error = grpc_error_set_str(
          GRPC_ERROR_CREATE_FROM_STATIC_STRING("unparseable host:port"),
          GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
      goto error_cleanup;
    } else if (port == nullptr) {
      if (default_port == nullptr) {
        error = grpc_error_set_str(
            GRPC_ERROR_CREATE_FROM_STATIC_STRING("no port in name"),
            GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
        goto error_cleanup;
      }
      port.reset(gpr_strdup(default_port));
    }
    error = grpc_ares_ev_driver_create_locked(&r->ev_driver, interested_parties,
                                              query_timeout_ms, combiner, r);
    if (error != GRPC_ERROR_NONE) goto error_cleanup;
    channel = grpc_ares_ev_driver_get_channel_locked(r->ev_driver);
    // If dns_server is specified, use it.
    if (dns_server != nullptr) {
      GRPC_CARES_TRACE_LOG("request:%p Using DNS server %s", r, dns_server);
      grpc_resolved_address addr;
      if (grpc_parse_ipv4_hostport(dns_server, &addr, false /* log_errors */)) {
        r->dns_server_addr.family = AF_INET;
        struct sockaddr_in* in = reinterpret_cast<struct sockaddr_in*>(addr.addr);
        memcpy(&r->dns_server_addr.addr.addr4, &in->sin_addr,
               sizeof(struct in_addr));
        r->dns_server_addr.tcp_port = grpc_sockaddr_get_port(&addr);
        r->dns_server_addr.udp_port = grpc_sockaddr_get_port(&addr);
      } else if (grpc_parse_ipv6_hostport(dns_server, &addr,
                                          false /* log_errors */)) {
        r->dns_server_addr.family = AF_INET6;
        struct sockaddr_in6* in6 =
            reinterpret_cast<struct sockaddr_in6*>(addr.addr);
        memcpy(&r->dns_server_addr.addr.addr6, &in6->sin6_addr,
               sizeof(struct in6_addr));
        r->dns_server_addr.tcp_port = grpc_sockaddr_get_port(&addr);
        r->dns_server_addr.udp_port = grpc_sockaddr_get_port(&addr);
      } else {
        error = grpc_error_set_str(
            GRPC_ERROR_CREATE_FROM_STATIC_STRING("cannot parse authority"),
            GRPC_ERROR_STR_TARGET_ADDRESS, grpc_slice_from_copied_string(name));
        goto error_cleanup;
      }
      int status = ares_set_servers_ports(*channel, &r->dns_server_addr);
      if (status != ARES_SUCCESS) {
        char* error_msg;
        gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
                     ares_strerror(status));
        error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
        gpr_free(error_msg);
        goto error_cleanup;
      }
    }
    r->pending_queries = 1;
    if (grpc_ares_query_ipv6()) {
      hr = create_hostbyname_request_locked(r, host.get(),
                                            grpc_strhtons(port.get()),
                                            /*is_balancer=*/false);
      ares_gethostbyname(*channel, hr->host, AF_INET6, on_hostbyname_done_locked,
                         hr);
    }
    hr =
        create_hostbyname_request_locked(r, host.get(), grpc_strhtons(port.get()),
                                         /*is_balancer=*/false);
    ares_gethostbyname(*channel, hr->host, AF_INET, on_hostbyname_done_locked,
                       hr);
    if (check_grpclb) {
      /* Query the SRV record */
      grpc_ares_request_ref_locked(r);
      char* service_name;
      gpr_asprintf(&service_name, "_grpclb._tcp.%s", host.get());
      ares_query(*channel, service_name, ns_c_in, ns_t_srv,
                 on_srv_query_done_locked, r);
      gpr_free(service_name);
    }
    if (r->service_config_json_out != nullptr) {
      grpc_ares_request_ref_locked(r);
      char* config_name;
      gpr_asprintf(&config_name, "_grpc_config.%s", host.get());
      ares_search(*channel, config_name, ns_c_in, ns_t_txt, on_txt_done_locked,
                  r);
      gpr_free(config_name);
    }
    grpc_ares_ev_driver_start_locked(r->ev_driver);
    grpc_ares_request_unref_locked(r);
    return;
  
  error_cleanup:
    grpc_core::ExecCtx::Run(DEBUG_LOCATION, r->on_done, error);
  }
  
  static bool inner_resolve_as_ip_literal_locked(
      const char* name, const char* default_port,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs,
      grpc_core::UniquePtr<char>* host, grpc_core::UniquePtr<char>* port,
      grpc_core::UniquePtr<char>* hostport) {
    grpc_core::SplitHostPort(name, host, port);
    if (*host == nullptr) {
      gpr_log(GPR_ERROR,
              "Failed to parse %s to host:port while attempting to resolve as ip "
              "literal.",
              name);
      return false;
    }
    if (*port == nullptr) {
      if (default_port == nullptr) {
        gpr_log(GPR_ERROR,
                "No port or default port for %s while attempting to resolve as "
                "ip literal.",
                name);
        return false;
      }
      port->reset(gpr_strdup(default_port));
    }
    grpc_resolved_address addr;
    GPR_ASSERT(grpc_core::JoinHostPort(hostport, host->get(), atoi(port->get())));
    if (grpc_parse_ipv4_hostport(hostport->get(), &addr,
                                 false /* log errors */) ||
        grpc_parse_ipv6_hostport(hostport->get(), &addr,
                                 false /* log errors */)) {
      GPR_ASSERT(*addrs == nullptr);
      *addrs = grpc_core::MakeUnique<ServerAddressList>();
      (*addrs)->emplace_back(addr.addr, addr.len, nullptr /* args */);
      return true;
    }
    return false;
  }
  
  static bool resolve_as_ip_literal_locked(
      const char* name, const char* default_port,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs) {
    grpc_core::UniquePtr<char> host;
    grpc_core::UniquePtr<char> port;
    grpc_core::UniquePtr<char> hostport;
    bool out = inner_resolve_as_ip_literal_locked(name, default_port, addrs,
                                                  &host, &port, &hostport);
    return out;
  }
  
  static bool target_matches_localhost_inner(const char* name,
                                             grpc_core::UniquePtr<char>* host,
                                             grpc_core::UniquePtr<char>* port) {
    if (!grpc_core::SplitHostPort(name, host, port)) {
      gpr_log(GPR_ERROR, "Unable to split host and port for name: %s", name);
      return false;
    }
    if (gpr_stricmp(host->get(), "localhost") == 0) {
      return true;
    } else {
      return false;
    }
  }
  
  static bool target_matches_localhost(const char* name) {
    grpc_core::UniquePtr<char> host;
    grpc_core::UniquePtr<char> port;
    return target_matches_localhost_inner(name, &host, &port);
  }
  
  #ifdef GRPC_ARES_RESOLVE_LOCALHOST_MANUALLY
  static bool inner_maybe_resolve_localhost_manually_locked(
      const char* name, const char* default_port,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs,
      grpc_core::UniquePtr<char>* host, grpc_core::UniquePtr<char>* port) {
    grpc_core::SplitHostPort(name, host, port);
    if (*host == nullptr) {
      gpr_log(GPR_ERROR,
              "Failed to parse %s into host:port during manual localhost "
              "resolution check.",
              name);
      return false;
    }
    if (*port == nullptr) {
      if (default_port == nullptr) {
        gpr_log(GPR_ERROR,
                "No port or default port for %s during manual localhost "
                "resolution check.",
                name);
        return false;
      }
      port->reset(gpr_strdup(default_port));
    }
    if (gpr_stricmp(host->get(), "localhost") == 0) {
      GPR_ASSERT(*addrs == nullptr);
      *addrs = grpc_core::MakeUnique<grpc_core::ServerAddressList>();
      uint16_t numeric_port = grpc_strhtons(port->get());
      // Append the ipv6 loopback address.
      struct sockaddr_in6 ipv6_loopback_addr;
      memset(&ipv6_loopback_addr, 0, sizeof(ipv6_loopback_addr));
      ((char*)&ipv6_loopback_addr.sin6_addr)[15] = 1;
      ipv6_loopback_addr.sin6_family = AF_INET6;
      ipv6_loopback_addr.sin6_port = numeric_port;
      (*addrs)->emplace_back(&ipv6_loopback_addr, sizeof(ipv6_loopback_addr),
                             nullptr /* args */);
      // Append the ipv4 loopback address.
      struct sockaddr_in ipv4_loopback_addr;
      memset(&ipv4_loopback_addr, 0, sizeof(ipv4_loopback_addr));
      ((char*)&ipv4_loopback_addr.sin_addr)[0] = 0x7f;
      ((char*)&ipv4_loopback_addr.sin_addr)[3] = 0x01;
      ipv4_loopback_addr.sin_family = AF_INET;
      ipv4_loopback_addr.sin_port = numeric_port;
      (*addrs)->emplace_back(&ipv4_loopback_addr, sizeof(ipv4_loopback_addr),
                             nullptr /* args */);
      // Let the address sorter figure out which one should be tried first.
      grpc_cares_wrapper_address_sorting_sort(addrs->get());
      return true;
    }
    return false;
  }
  
  static bool grpc_ares_maybe_resolve_localhost_manually_locked(
      const char* name, const char* default_port,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs) {
    grpc_core::UniquePtr<char> host;
    grpc_core::UniquePtr<char> port;
    return inner_maybe_resolve_localhost_manually_locked(name, default_port,
                                                         addrs, &host, &port);
  }
  #else  /* GRPC_ARES_RESOLVE_LOCALHOST_MANUALLY */
  static bool grpc_ares_maybe_resolve_localhost_manually_locked(
      const char* /*name*/, const char* /*default_port*/,
      std::unique_ptr<grpc_core::ServerAddressList>* /*addrs*/) {
    return false;
  }
  #endif /* GRPC_ARES_RESOLVE_LOCALHOST_MANUALLY */
  
  static grpc_ares_request* grpc_dns_lookup_ares_locked_impl(
      const char* dns_server, const char* name, const char* default_port,
      grpc_pollset_set* interested_parties, grpc_closure* on_done,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs, bool check_grpclb,
      char** service_config_json, int query_timeout_ms,
      grpc_core::Combiner* combiner) {
    grpc_ares_request* r =
        static_cast<grpc_ares_request*>(gpr_zalloc(sizeof(grpc_ares_request)));
    r->ev_driver = nullptr;
    r->on_done = on_done;
    r->addresses_out = addrs;
    r->service_config_json_out = service_config_json;
    r->error = GRPC_ERROR_NONE;
    r->pending_queries = 0;
    GRPC_CARES_TRACE_LOG(
        "request:%p c-ares grpc_dns_lookup_ares_locked_impl name=%s, "
        "default_port=%s",
        r, name, default_port);
    // Early out if the target is an ipv4 or ipv6 literal.
    if (resolve_as_ip_literal_locked(name, default_port, addrs)) {
      grpc_ares_complete_request_locked(r);
      return r;
    }
    // Early out if the target is localhost and we're on Windows.
    if (grpc_ares_maybe_resolve_localhost_manually_locked(name, default_port,
                                                          addrs)) {
      grpc_ares_complete_request_locked(r);
      return r;
    }
    // Don't query for SRV and TXT records if the target is "localhost", so
    // as to cut down on lookups over the network, especially in tests:
    // https://github.com/grpc/proposal/pull/79
    if (target_matches_localhost(name)) {
      check_grpclb = false;
      r->service_config_json_out = nullptr;
    }
    // Look up name using c-ares lib.
    grpc_dns_lookup_ares_continue_after_check_localhost_and_ip_literals_locked(
        r, dns_server, name, default_port, interested_parties, check_grpclb,
        query_timeout_ms, combiner);
    return r;
  }
  
  grpc_ares_request* (*grpc_dns_lookup_ares_locked)(
      const char* dns_server, const char* name, const char* default_port,
      grpc_pollset_set* interested_parties, grpc_closure* on_done,
      std::unique_ptr<grpc_core::ServerAddressList>* addrs, bool check_grpclb,
      char** service_config_json, int query_timeout_ms,
      grpc_core::Combiner* combiner) = grpc_dns_lookup_ares_locked_impl;
  
  static void grpc_cancel_ares_request_locked_impl(grpc_ares_request* r) {
    GPR_ASSERT(r != nullptr);
    if (r->ev_driver != nullptr) {
      grpc_ares_ev_driver_shutdown_locked(r->ev_driver);
    }
  }
  
  void (*grpc_cancel_ares_request_locked)(grpc_ares_request* r) =
      grpc_cancel_ares_request_locked_impl;
  
  // ares_library_init and ares_library_cleanup are currently no-op except under
  // Windows. Calling them may cause race conditions when other parts of the
  // binary calls these functions concurrently.
  #ifdef GPR_WINDOWS
  grpc_error* grpc_ares_init(void) {
    int status = ares_library_init(ARES_LIB_INIT_ALL);
    if (status != ARES_SUCCESS) {
      char* error_msg;
      gpr_asprintf(&error_msg, "ares_library_init failed: %s",
                   ares_strerror(status));
      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
      gpr_free(error_msg);
      return error;
    }
    return GRPC_ERROR_NONE;
  }
  
  void grpc_ares_cleanup(void) { ares_library_cleanup(); }
  #else
  grpc_error* grpc_ares_init(void) { return GRPC_ERROR_NONE; }
  void grpc_ares_cleanup(void) {}
  #endif  // GPR_WINDOWS
  
  /*
   * grpc_resolve_address_ares related structs and functions
   */
  
  typedef struct grpc_resolve_address_ares_request {
    /* combiner that queries and related callbacks run under */
    grpc_core::Combiner* combiner;
    /** the pointer to receive the resolved addresses */
    grpc_resolved_addresses** addrs_out;
    /** currently resolving addresses */
    std::unique_ptr<ServerAddressList> addresses;
    /** closure to call when the resolve_address_ares request completes */
    grpc_closure* on_resolve_address_done;
    /** a closure wrapping on_resolve_address_done, which should be invoked when
       the grpc_dns_lookup_ares_locked operation is done. */
    grpc_closure on_dns_lookup_done_locked;
    /* target name */
    const char* name;
    /* default port to use if none is specified */
    const char* default_port;
    /* pollset_set to be driven by */
    grpc_pollset_set* interested_parties;
    /* underlying ares_request that the query is performed on */
    grpc_ares_request* ares_request = nullptr;
  } grpc_resolve_address_ares_request;
  
  static void on_dns_lookup_done_locked(void* arg, grpc_error* error) {
    grpc_resolve_address_ares_request* r =
        static_cast<grpc_resolve_address_ares_request*>(arg);
    gpr_free(r->ares_request);
    grpc_resolved_addresses** resolved_addresses = r->addrs_out;
    if (r->addresses == nullptr || r->addresses->empty()) {
      *resolved_addresses = nullptr;
    } else {
      *resolved_addresses = static_cast<grpc_resolved_addresses*>(
          gpr_zalloc(sizeof(grpc_resolved_addresses)));
      (*resolved_addresses)->naddrs = r->addresses->size();
      (*resolved_addresses)->addrs =
          static_cast<grpc_resolved_address*>(gpr_zalloc(
              sizeof(grpc_resolved_address) * (*resolved_addresses)->naddrs));
      for (size_t i = 0; i < (*resolved_addresses)->naddrs; ++i) {
        GPR_ASSERT(!(*r->addresses)[i].IsBalancer());
        memcpy(&(*resolved_addresses)->addrs[i], &(*r->addresses)[i].address(),
               sizeof(grpc_resolved_address));
      }
    }
    grpc_core::ExecCtx::Run(DEBUG_LOCATION, r->on_resolve_address_done,
                            GRPC_ERROR_REF(error));
    GRPC_COMBINER_UNREF(r->combiner, "on_dns_lookup_done_cb");
    delete r;
  }
  
  static void on_dns_lookup_done(void* arg, grpc_error* error) {
    grpc_resolve_address_ares_request* r =
        static_cast<grpc_resolve_address_ares_request*>(arg);
    r->combiner->Run(GRPC_CLOSURE_INIT(&r->on_dns_lookup_done_locked,
                                       on_dns_lookup_done_locked, r, nullptr),
                     GRPC_ERROR_REF(error));
  }
  
  static void grpc_resolve_address_invoke_dns_lookup_ares_locked(
      void* arg, grpc_error* /*unused_error*/) {
    grpc_resolve_address_ares_request* r =
        static_cast<grpc_resolve_address_ares_request*>(arg);
    GRPC_CLOSURE_INIT(&r->on_dns_lookup_done_locked, on_dns_lookup_done, r,
                      grpc_schedule_on_exec_ctx);
    r->ares_request = grpc_dns_lookup_ares_locked(
        nullptr /* dns_server */, r->name, r->default_port, r->interested_parties,
        &r->on_dns_lookup_done_locked, &r->addresses, false /* check_grpclb */,
        nullptr /* service_config_json */, GRPC_DNS_ARES_DEFAULT_QUERY_TIMEOUT_MS,
        r->combiner);
  }
  
  static void grpc_resolve_address_ares_impl(const char* name,
                                             const char* default_port,
                                             grpc_pollset_set* interested_parties,
                                             grpc_closure* on_done,
                                             grpc_resolved_addresses** addrs) {
    grpc_resolve_address_ares_request* r =
        new grpc_resolve_address_ares_request();
    r->combiner = grpc_combiner_create();
    r->addrs_out = addrs;
    r->on_resolve_address_done = on_done;
    r->name = name;
    r->default_port = default_port;
    r->interested_parties = interested_parties;
    r->combiner->Run(
        GRPC_CLOSURE_CREATE(grpc_resolve_address_invoke_dns_lookup_ares_locked, r,
                            nullptr),
        GRPC_ERROR_NONE);
  }
  
  void (*grpc_resolve_address_ares)(
      const char* name, const char* default_port,
      grpc_pollset_set* interested_parties, grpc_closure* on_done,
      grpc_resolved_addresses** addrs) = grpc_resolve_address_ares_impl;
  
  #endif /* GRPC_ARES == 1 */
  