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 && !defined(GRPC_UV)
  
  #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
  #include "src/core/lib/iomgr/sockaddr.h"
  #include "src/core/lib/iomgr/socket_utils_posix.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 "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/host_port.h"
  #include "src/core/lib/gpr/string.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"
  
  static gpr_once g_basic_init = GPR_ONCE_INIT;
  static gpr_mu g_init_mu;
  
  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 */
    grpc_lb_addresses** lb_addrs_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 */
    gpr_refcount pending_queries;
  
    /** mutex guarding the rest of the state */
    gpr_mu mu;
    /** is there at least one successful query, set in on_done_cb */
    bool success;
    /** the errors explaining the request failure, set in on_done_cb */
    grpc_error* error;
  };
  
  typedef struct grpc_ares_hostbyname_request {
    /** following members are set in create_hostbyname_request */
    /** 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 do_basic_init(void) { gpr_mu_init(&g_init_mu); }
  
  static uint16_t strhtons(const char* port) {
    if (strcmp(port, "http") == 0) {
      return htons(80);
    } else if (strcmp(port, "https") == 0) {
      return htons(443);
    }
    return htons(static_cast<unsigned short>(atoi(port)));
  }
  
  static void grpc_ares_request_ref(grpc_ares_request* r) {
    gpr_ref(&r->pending_queries);
  }
  
  static void grpc_ares_request_unref(grpc_ares_request* r) {
    /* If there are no pending queries, invoke on_done callback and destroy the
       request */
    if (gpr_unref(&r->pending_queries)) {
      /* TODO(zyc): Sort results with RFC6724 before invoking on_done. */
      GRPC_CLOSURE_SCHED(r->on_done, r->error);
      gpr_mu_destroy(&r->mu);
      grpc_ares_ev_driver_destroy(r->ev_driver);
      gpr_free(r);
    }
  }
  
  static grpc_ares_hostbyname_request* create_hostbyname_request(
      grpc_ares_request* parent_request, char* host, uint16_t port,
      bool 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(parent_request);
    return hr;
  }
  
  static void destroy_hostbyname_request(grpc_ares_hostbyname_request* hr) {
    grpc_ares_request_unref(hr->parent_request);
    gpr_free(hr->host);
    gpr_free(hr);
  }
  
  static void on_hostbyname_done_cb(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;
    gpr_mu_lock(&r->mu);
    if (status == ARES_SUCCESS) {
      GRPC_ERROR_UNREF(r->error);
      r->error = GRPC_ERROR_NONE;
      r->success = true;
      grpc_lb_addresses** lb_addresses = r->lb_addrs_out;
      if (*lb_addresses == nullptr) {
        *lb_addresses = grpc_lb_addresses_create(0, nullptr);
      }
      size_t prev_naddr = (*lb_addresses)->num_addresses;
      size_t i;
      for (i = 0; hostent->h_addr_list[i] != nullptr; i++) {
      }
      (*lb_addresses)->num_addresses += i;
      (*lb_addresses)->addresses = static_cast<grpc_lb_address*>(
          gpr_realloc((*lb_addresses)->addresses,
                      sizeof(grpc_lb_address) * (*lb_addresses)->num_addresses));
      for (i = prev_naddr; i < (*lb_addresses)->num_addresses; i++) {
        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 - prev_naddr],
                   sizeof(struct in6_addr));
            addr.sin6_family = static_cast<sa_family_t>(hostent->h_addrtype);
            addr.sin6_port = hr->port;
            grpc_lb_addresses_set_address(
                *lb_addresses, i, &addr, addr_len,
                hr->is_balancer /* is_balancer */,
                hr->is_balancer ? hr->host : nullptr /* balancer_name */,
                nullptr /* user_data */);
            char output[INET6_ADDRSTRLEN];
            ares_inet_ntop(AF_INET6, &addr.sin6_addr, output, INET6_ADDRSTRLEN);
            gpr_log(GPR_DEBUG,
                    "c-ares resolver gets a AF_INET6 result: \n"
                    "  addr: %s\n  port: %d\n  sin6_scope_id: %d\n",
                    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 - prev_naddr],
                   sizeof(struct in_addr));
            addr.sin_family = static_cast<sa_family_t>(hostent->h_addrtype);
            addr.sin_port = hr->port;
            grpc_lb_addresses_set_address(
                *lb_addresses, i, &addr, addr_len,
                hr->is_balancer /* is_balancer */,
                hr->is_balancer ? hr->host : nullptr /* balancer_name */,
                nullptr /* user_data */);
            char output[INET_ADDRSTRLEN];
            ares_inet_ntop(AF_INET, &addr.sin_addr, output, INET_ADDRSTRLEN);
            gpr_log(GPR_DEBUG,
                    "c-ares resolver gets a AF_INET result: \n"
                    "  addr: %s\n  port: %d\n",
                    output, ntohs(hr->port));
            break;
          }
        }
      }
    } else if (!r->success) {
      char* error_msg;
      gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
                   ares_strerror(status));
      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
      gpr_free(error_msg);
      if (r->error == GRPC_ERROR_NONE) {
        r->error = error;
      } else {
        r->error = grpc_error_add_child(error, r->error);
      }
    }
    gpr_mu_unlock(&r->mu);
    destroy_hostbyname_request(hr);
  }
  
  static void on_srv_query_done_cb(void* arg, int status, int timeouts,
                                   unsigned char* abuf, int alen) {
    grpc_ares_request* r = static_cast<grpc_ares_request*>(arg);
    grpc_core::ExecCtx exec_ctx;
    gpr_log(GPR_DEBUG, "on_query_srv_done_cb");
    if (status == ARES_SUCCESS) {
      gpr_log(GPR_DEBUG, "on_query_srv_done_cb ARES_SUCCESS");
      struct ares_srv_reply* reply;
      const int parse_status = ares_parse_srv_reply(abuf, alen, &reply);
      if (parse_status == ARES_SUCCESS) {
        ares_channel* channel = grpc_ares_ev_driver_get_channel(r->ev_driver);
        for (struct ares_srv_reply* srv_it = reply; srv_it != nullptr;
             srv_it = srv_it->next) {
          if (grpc_ipv6_loopback_available()) {
            grpc_ares_hostbyname_request* hr = create_hostbyname_request(
                r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
            ares_gethostbyname(*channel, hr->host, AF_INET6,
                               on_hostbyname_done_cb, hr);
          }
          grpc_ares_hostbyname_request* hr = create_hostbyname_request(
              r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
          ares_gethostbyname(*channel, hr->host, AF_INET, on_hostbyname_done_cb,
                             hr);
          grpc_ares_ev_driver_start(r->ev_driver);
        }
      }
      if (reply != nullptr) {
        ares_free_data(reply);
      }
    } else if (!r->success) {
      char* error_msg;
      gpr_asprintf(&error_msg, "C-ares status is not ARES_SUCCESS: %s",
                   ares_strerror(status));
      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
      gpr_free(error_msg);
      if (r->error == GRPC_ERROR_NONE) {
        r->error = error;
      } else {
        r->error = grpc_error_add_child(error, r->error);
      }
    }
    grpc_ares_request_unref(r);
  }
  
  static const char g_service_config_attribute_prefix[] = "grpc_config=";
  
  static void on_txt_done_cb(void* arg, int status, int timeouts,
                             unsigned char* buf, int len) {
    gpr_log(GPR_DEBUG, "on_txt_done_cb");
    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;
    gpr_mu_lock(&r->mu);
    if (status != ARES_SUCCESS) goto fail;
    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';
      gpr_log(GPR_INFO, "found service config: %s", *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);
    gpr_free(error_msg);
    if (r->error == GRPC_ERROR_NONE) {
      r->error = error;
    } else {
      r->error = grpc_error_add_child(error, r->error);
    }
  done:
    gpr_mu_unlock(&r->mu);
    grpc_ares_request_unref(r);
  }
  
  static grpc_ares_request* grpc_dns_lookup_ares_impl(
      const char* dns_server, const char* name, const char* default_port,
      grpc_pollset_set* interested_parties, grpc_closure* on_done,
      grpc_lb_addresses** addrs, bool check_grpclb, char** service_config_json) {
    grpc_error* error = GRPC_ERROR_NONE;
    grpc_ares_hostbyname_request* hr = nullptr;
    grpc_ares_request* r = nullptr;
    ares_channel* channel = nullptr;
    /* TODO(zyc): Enable tracing after #9603 is checked in */
    /* if (grpc_dns_trace) {
        gpr_log(GPR_DEBUG, "resolve_address (blocking): name=%s, default_port=%s",
                name, default_port);
       } */
  
    /* parse name, splitting it into host and port parts */
    char* host;
    char* port;
    gpr_split_host_port(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 = gpr_strdup(default_port);
    }
  
    grpc_ares_ev_driver* ev_driver;
    error = grpc_ares_ev_driver_create(&ev_driver, interested_parties);
    if (error != GRPC_ERROR_NONE) goto error_cleanup;
  
    r = static_cast<grpc_ares_request*>(gpr_zalloc(sizeof(grpc_ares_request)));
    gpr_mu_init(&r->mu);
    r->ev_driver = ev_driver;
    r->on_done = on_done;
    r->lb_addrs_out = addrs;
    r->service_config_json_out = service_config_json;
    r->success = false;
    r->error = GRPC_ERROR_NONE;
    channel = grpc_ares_ev_driver_get_channel(r->ev_driver);
  
    // If dns_server is specified, use it.
    if (dns_server != nullptr) {
      gpr_log(GPR_INFO, "Using DNS server %s", 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));
        gpr_free(r);
        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);
        gpr_free(r);
        goto error_cleanup;
      }
    }
    gpr_ref_init(&r->pending_queries, 1);
    if (grpc_ipv6_loopback_available()) {
      hr = create_hostbyname_request(r, host, strhtons(port),
                                     false /* is_balancer */);
      ares_gethostbyname(*channel, hr->host, AF_INET6, on_hostbyname_done_cb, hr);
    }
    hr = create_hostbyname_request(r, host, strhtons(port),
                                   false /* is_balancer */);
    ares_gethostbyname(*channel, hr->host, AF_INET, on_hostbyname_done_cb, hr);
    if (check_grpclb) {
      /* Query the SRV record */
      grpc_ares_request_ref(r);
      char* service_name;
      gpr_asprintf(&service_name, "_grpclb._tcp.%s", host);
      ares_query(*channel, service_name, ns_c_in, ns_t_srv, on_srv_query_done_cb,
                 r);
      gpr_free(service_name);
    }
    if (service_config_json != nullptr) {
      grpc_ares_request_ref(r);
      char* config_name;
      gpr_asprintf(&config_name, "_grpc_config.%s", host);
      ares_search(*channel, config_name, ns_c_in, ns_t_txt, on_txt_done_cb, r);
      gpr_free(config_name);
    }
    /* TODO(zyc): Handle CNAME records here. */
    grpc_ares_ev_driver_start(r->ev_driver);
    grpc_ares_request_unref(r);
    gpr_free(host);
    gpr_free(port);
    return r;
  
  error_cleanup:
    GRPC_CLOSURE_SCHED(on_done, error);
    gpr_free(host);
    gpr_free(port);
    return nullptr;
  }
  
  grpc_ares_request* (*grpc_dns_lookup_ares)(
      const char* dns_server, const char* name, const char* default_port,
      grpc_pollset_set* interested_parties, grpc_closure* on_done,
      grpc_lb_addresses** addrs, bool check_grpclb,
      char** service_config_json) = grpc_dns_lookup_ares_impl;
  
  void grpc_cancel_ares_request(grpc_ares_request* r) {
    if (grpc_dns_lookup_ares == grpc_dns_lookup_ares_impl) {
      grpc_ares_ev_driver_shutdown(r->ev_driver);
    }
  }
  
  grpc_error* grpc_ares_init(void) {
    gpr_once_init(&g_basic_init, do_basic_init);
    gpr_mu_lock(&g_init_mu);
    int status = ares_library_init(ARES_LIB_INIT_ALL);
    gpr_mu_unlock(&g_init_mu);
  
    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) {
    gpr_mu_lock(&g_init_mu);
    ares_library_cleanup();
    gpr_mu_unlock(&g_init_mu);
  }
  
  /*
   * grpc_resolve_address_ares related structs and functions
   */
  
  typedef struct grpc_resolve_address_ares_request {
    /** the pointer to receive the resolved addresses */
    grpc_resolved_addresses** addrs_out;
    /** currently resolving lb addresses */
    grpc_lb_addresses* lb_addrs;
    /** closure to call when the resolve_address_ares request completes */
    grpc_closure* on_resolve_address_done;
    /** a closure wrapping on_dns_lookup_done_cb, which should be invoked when the
        grpc_dns_lookup_ares operation is done. */
    grpc_closure on_dns_lookup_done;
  } grpc_resolve_address_ares_request;
  
  static void on_dns_lookup_done_cb(void* arg, grpc_error* error) {
    grpc_resolve_address_ares_request* r =
        static_cast<grpc_resolve_address_ares_request*>(arg);
    grpc_resolved_addresses** resolved_addresses = r->addrs_out;
    if (r->lb_addrs == nullptr || r->lb_addrs->num_addresses == 0) {
      *resolved_addresses = nullptr;
    } else {
      *resolved_addresses = static_cast<grpc_resolved_addresses*>(
          gpr_zalloc(sizeof(grpc_resolved_addresses)));
      (*resolved_addresses)->naddrs = r->lb_addrs->num_addresses;
      (*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->lb_addrs->addresses[i].is_balancer);
        memcpy(&(*resolved_addresses)->addrs[i],
               &r->lb_addrs->addresses[i].address, sizeof(grpc_resolved_address));
      }
    }
    GRPC_CLOSURE_SCHED(r->on_resolve_address_done, GRPC_ERROR_REF(error));
    if (r->lb_addrs != nullptr) grpc_lb_addresses_destroy(r->lb_addrs);
    gpr_free(r);
  }
  
  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 =
        static_cast<grpc_resolve_address_ares_request*>(
            gpr_zalloc(sizeof(grpc_resolve_address_ares_request)));
    r->addrs_out = addrs;
    r->on_resolve_address_done = on_done;
    GRPC_CLOSURE_INIT(&r->on_dns_lookup_done, on_dns_lookup_done_cb, r,
                      grpc_schedule_on_exec_ctx);
    grpc_dns_lookup_ares(nullptr /* dns_server */, name, default_port,
                         interested_parties, &r->on_dns_lookup_done, &r->lb_addrs,
                         false /* check_grpclb */,
                         nullptr /* service_config_json */);
  }
  
  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 && !defined(GRPC_UV) */
  