/*
 *
 * Copyright 2017 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>

#include <errno.h>
#include <fcntl.h>
#include <string.h>

#include <string>
#include <thread>
#include <vector>

#include <gmock/gmock.h>

#include "absl/flags/flag.h"
#include "absl/memory/memory.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"

#include <grpc/grpc.h>
#include <grpc/impl/codegen/grpc_types.h>
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/sync.h>
#include <grpc/support/time.h>

#include "src/core/ext/filters/client_channel/client_channel.h"
#include "src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_balancer_addresses.h"
#include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
#include "src/core/lib/address_utils/parse_address.h"
#include "src/core/lib/address_utils/sockaddr_utils.h"
#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/config/core_configuration.h"
#include "src/core/lib/gpr/string.h"
#include "src/core/lib/gprpp/host_port.h"
#include "src/core/lib/gprpp/orphanable.h"
#include "src/core/lib/iomgr/executor.h"
#include "src/core/lib/iomgr/iomgr.h"
#include "src/core/lib/iomgr/resolve_address.h"
#include "src/core/lib/iomgr/socket_utils.h"
#include "src/core/lib/iomgr/work_serializer.h"
#include "src/core/lib/resolver/resolver.h"
#include "src/core/lib/resolver/resolver_registry.h"
#include "src/core/lib/resolver/server_address.h"
#include "test/core/util/fake_udp_and_tcp_server.h"
#include "test/core/util/port.h"
#include "test/core/util/test_config.h"
#include "test/cpp/util/subprocess.h"
#include "test/cpp/util/test_config.h"

// TODO(unknown): pull in different headers when enabling this
// test on windows. Also set BAD_SOCKET_RETURN_VAL
// to INVALID_SOCKET on windows.
#ifdef GPR_WINDOWS
#include "src/core/lib/iomgr/sockaddr_windows.h"
#include "src/core/lib/iomgr/socket_windows.h"
#include "src/core/lib/iomgr/tcp_windows.h"
#define BAD_SOCKET_RETURN_VAL INVALID_SOCKET
#else
#include "src/core/lib/iomgr/sockaddr_posix.h"
#define BAD_SOCKET_RETURN_VAL (-1)
#endif

using std::vector;
using testing::UnorderedElementsAreArray;

ABSL_FLAG(std::string, target_name, "", "Target name to resolve.");
ABSL_FLAG(std::string, do_ordered_address_comparison, "",
          "Whether or not to compare resolved addresses to expected "
          "addresses using an ordered comparison. This is useful for "
          "testing certain behaviors that involve sorting of resolved "
          "addresses. Note it would be better if this argument was a "
          "bool flag, but it's a string for ease of invocation from "
          "the generated python test runner.");
ABSL_FLAG(std::string, expected_addrs, "",
          "List of expected backend or balancer addresses in the form "
          "'<ip0:port0>,<is_balancer0>;<ip1:port1>,<is_balancer1>;...'. "
          "'is_balancer' should be bool, i.e. true or false.");
ABSL_FLAG(std::string, expected_chosen_service_config, "",
          "Expected service config json string that gets chosen (no "
          "whitespace). Empty for none.");
ABSL_FLAG(std::string, expected_service_config_error, "",
          "Expected service config error. Empty for none.");
ABSL_FLAG(std::string, local_dns_server_address, "",
          "Optional. This address is placed as the uri authority if present.");
// TODO(Capstan): Is this worth making `bool` now with Abseil flags?
ABSL_FLAG(
    std::string, enable_srv_queries, "",
    "Whether or not to enable SRV queries for the ares resolver instance."
    "It would be better if this arg could be bool, but the way that we "
    "generate "
    "the python script runner doesn't allow us to pass a gflags bool to this "
    "binary.");
// TODO(Capstan): Is this worth making `bool` now with Abseil flags?
ABSL_FLAG(
    std::string, enable_txt_queries, "",
    "Whether or not to enable TXT queries for the ares resolver instance."
    "It would be better if this arg could be bool, but the way that we "
    "generate "
    "the python script runner doesn't allow us to pass a gflags bool to this "
    "binary.");
// TODO(Capstan): Is this worth making `bool` now with Abseil flags?
ABSL_FLAG(
    std::string, inject_broken_nameserver_list, "",
    "Whether or not to configure c-ares to use a broken nameserver list, in "
    "which "
    "the first nameserver in the list is non-responsive, but the second one "
    "works, i.e "
    "serves the expected DNS records; using for testing such a real scenario."
    "It would be better if this arg could be bool, but the way that we "
    "generate "
    "the python script runner doesn't allow us to pass a gflags bool to this "
    "binary.");
ABSL_FLAG(std::string, expected_lb_policy, "",
          "Expected lb policy name that appears in resolver result channel "
          "arg. Empty for none.");

namespace {

class GrpcLBAddress final {
 public:
  GrpcLBAddress(std::string address, bool is_balancer)
      : is_balancer(is_balancer), address(std::move(address)) {}

  bool operator==(const GrpcLBAddress& other) const {
    return this->is_balancer == other.is_balancer &&
           this->address == other.address;
  }

  bool operator!=(const GrpcLBAddress& other) const {
    return !(*this == other);
  }

  bool is_balancer;
  std::string address;
};

vector<GrpcLBAddress> ParseExpectedAddrs(std::string expected_addrs) {
  std::vector<GrpcLBAddress> out;
  while (!expected_addrs.empty()) {
    // get the next <ip>,<port> (v4 or v6)
    size_t next_comma = expected_addrs.find(',');
    if (next_comma == std::string::npos) {
      gpr_log(GPR_ERROR,
              "Missing ','. Expected_addrs arg should be a semicolon-separated "
              "list of <ip-port>,<bool> pairs. Left-to-be-parsed arg is |%s|",
              expected_addrs.c_str());
      abort();
    }
    std::string next_addr = expected_addrs.substr(0, next_comma);
    expected_addrs = expected_addrs.substr(next_comma + 1, std::string::npos);
    // get the next is_balancer 'bool' associated with this address
    size_t next_semicolon = expected_addrs.find(';');
    bool is_balancer = false;
    gpr_parse_bool_value(expected_addrs.substr(0, next_semicolon).c_str(),
                         &is_balancer);
    out.emplace_back(GrpcLBAddress(next_addr, is_balancer));
    if (next_semicolon == std::string::npos) {
      break;
    }
    expected_addrs =
        expected_addrs.substr(next_semicolon + 1, std::string::npos);
  }
  if (out.empty()) {
    gpr_log(GPR_ERROR,
            "expected_addrs arg should be a semicolon-separated list of "
            "<ip-port>,<bool> pairs");
    abort();
  }
  return out;
}

gpr_timespec TestDeadline(void) {
  return grpc_timeout_seconds_to_deadline(100);
}

struct ArgsStruct {
  gpr_event ev;
  gpr_atm done_atm;
  gpr_mu* mu;
  grpc_pollset* pollset;
  grpc_pollset_set* pollset_set;
  std::shared_ptr<grpc_core::WorkSerializer> lock;
  grpc_channel_args* channel_args;
  vector<GrpcLBAddress> expected_addrs;
  std::string expected_service_config_string;
  std::string expected_service_config_error;
  std::string expected_lb_policy;
};

void ArgsInit(ArgsStruct* args) {
  gpr_event_init(&args->ev);
  args->pollset = static_cast<grpc_pollset*>(gpr_zalloc(grpc_pollset_size()));
  grpc_pollset_init(args->pollset, &args->mu);
  args->pollset_set = grpc_pollset_set_create();
  grpc_pollset_set_add_pollset(args->pollset_set, args->pollset);
  args->lock = std::make_shared<grpc_core::WorkSerializer>();
  gpr_atm_rel_store(&args->done_atm, 0);
  args->channel_args = nullptr;
}

void DoNothing(void* /*arg*/, grpc_error_handle /*error*/) {}

void ArgsFinish(ArgsStruct* args) {
  GPR_ASSERT(gpr_event_wait(&args->ev, TestDeadline()));
  grpc_pollset_set_del_pollset(args->pollset_set, args->pollset);
  grpc_pollset_set_destroy(args->pollset_set);
  grpc_closure DoNothing_cb;
  GRPC_CLOSURE_INIT(&DoNothing_cb, DoNothing, nullptr,
                    grpc_schedule_on_exec_ctx);
  grpc_pollset_shutdown(args->pollset, &DoNothing_cb);
  // exec_ctx needs to be flushed before calling grpc_pollset_destroy()
  grpc_channel_args_destroy(args->channel_args);
  grpc_core::ExecCtx::Get()->Flush();
  grpc_pollset_destroy(args->pollset);
  gpr_free(args->pollset);
}

gpr_timespec NSecondDeadline(int seconds) {
  return gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
                      gpr_time_from_seconds(seconds, GPR_TIMESPAN));
}

void PollPollsetUntilRequestDone(ArgsStruct* args) {
  // Use a 20-second timeout to give room for the tests that involve
  // a non-responsive name server (c-ares uses a ~5 second query timeout
  // for that server before succeeding with the healthy one).
  gpr_timespec deadline = NSecondDeadline(20);
  while (true) {
    bool done = gpr_atm_acq_load(&args->done_atm) != 0;
    if (done) {
      break;
    }
    gpr_timespec time_left =
        gpr_time_sub(deadline, gpr_now(GPR_CLOCK_REALTIME));
    gpr_log(GPR_DEBUG, "done=%d, time_left=%" PRId64 ".%09d", done,
            time_left.tv_sec, time_left.tv_nsec);
    GPR_ASSERT(gpr_time_cmp(time_left, gpr_time_0(GPR_TIMESPAN)) >= 0);
    grpc_pollset_worker* worker = nullptr;
    grpc_core::ExecCtx exec_ctx;
    gpr_mu_lock(args->mu);
    GRPC_LOG_IF_ERROR(
        "pollset_work",
        grpc_pollset_work(
            args->pollset, &worker,
            grpc_core::Timestamp::FromTimespecRoundUp(NSecondDeadline(1))));
    gpr_mu_unlock(args->mu);
  }
  gpr_event_set(&args->ev, reinterpret_cast<void*>(1));
}

void CheckServiceConfigResultLocked(const char* service_config_json,
                                    absl::Status service_config_error,
                                    ArgsStruct* args) {
  if (!args->expected_service_config_string.empty()) {
    ASSERT_NE(service_config_json, nullptr);
    EXPECT_EQ(service_config_json, args->expected_service_config_string);
  }
  if (args->expected_service_config_error.empty()) {
    EXPECT_TRUE(service_config_error.ok());
  } else {
    EXPECT_THAT(service_config_error.ToString(),
                testing::HasSubstr(args->expected_service_config_error));
  }
}

void CheckLBPolicyResultLocked(const grpc_channel_args* channel_args,
                               ArgsStruct* args) {
  const grpc_arg* lb_policy_arg =
      grpc_channel_args_find(channel_args, GRPC_ARG_LB_POLICY_NAME);
  if (!args->expected_lb_policy.empty()) {
    GPR_ASSERT(lb_policy_arg != nullptr);
    GPR_ASSERT(lb_policy_arg->type == GRPC_ARG_STRING);
    EXPECT_EQ(lb_policy_arg->value.string, args->expected_lb_policy);
  } else {
    GPR_ASSERT(lb_policy_arg == nullptr);
  }
}

#ifdef GPR_WINDOWS
void OpenAndCloseSocketsStressLoop(int phony_port, gpr_event* done_ev) {
  sockaddr_in6 addr;
  memset(&addr, 0, sizeof(addr));
  addr.sin6_family = AF_INET6;
  addr.sin6_port = htons(phony_port);
  ((char*)&addr.sin6_addr)[15] = 1;
  for (;;) {
    if (gpr_event_get(done_ev)) {
      return;
    }
    std::vector<int> sockets;
    for (size_t i = 0; i < 50; i++) {
      SOCKET s = WSASocket(AF_INET6, SOCK_STREAM, IPPROTO_TCP, nullptr, 0,
                           WSA_FLAG_OVERLAPPED);
      ASSERT_TRUE(s != BAD_SOCKET_RETURN_VAL)
          << "Failed to create TCP ipv6 socket";
      gpr_log(GPR_DEBUG, "Opened socket: %d", s);
      char val = 1;
      ASSERT_TRUE(setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) !=
                  SOCKET_ERROR)
          << "Failed to set socketopt reuseaddr. WSA error: " +
                 std::to_string(WSAGetLastError());
      ASSERT_TRUE(grpc_tcp_set_non_block(s) == GRPC_ERROR_NONE)
          << "Failed to set socket non-blocking";
      ASSERT_TRUE(bind(s, (const sockaddr*)&addr, sizeof(addr)) != SOCKET_ERROR)
          << "Failed to bind socket " + std::to_string(s) +
                 " to [::1]:" + std::to_string(phony_port) +
                 ". WSA error: " + std::to_string(WSAGetLastError());
      ASSERT_TRUE(listen(s, 1) != SOCKET_ERROR)
          << "Failed to listen on socket " + std::to_string(s) +
                 ". WSA error: " + std::to_string(WSAGetLastError());
      sockets.push_back(s);
    }
    // Do a non-blocking accept followed by a close on all of those sockets.
    // Do this in a separate loop to try to induce a time window to hit races.
    for (size_t i = 0; i < sockets.size(); i++) {
      gpr_log(GPR_DEBUG, "non-blocking accept then close on %d", sockets[i]);
      ASSERT_TRUE(accept(sockets[i], nullptr, nullptr) == INVALID_SOCKET)
          << "Accept on phony socket unexpectedly accepted actual connection.";
      ASSERT_TRUE(WSAGetLastError() == WSAEWOULDBLOCK)
          << "OpenAndCloseSocketsStressLoop accept on socket " +
                 std::to_string(sockets[i]) +
                 " failed in "
                 "an unexpected way. "
                 "WSA error: " +
                 std::to_string(WSAGetLastError()) +
                 ". Socket use-after-close bugs are likely.";
      ASSERT_TRUE(closesocket(sockets[i]) != SOCKET_ERROR)
          << "Failed to close socket: " + std::to_string(sockets[i]) +
                 ". WSA error: " + std::to_string(WSAGetLastError());
    }
  }
  return;
}
#else
void OpenAndCloseSocketsStressLoop(int phony_port, gpr_event* done_ev) {
  // The goal of this loop is to catch socket
  // "use after close" bugs within the c-ares resolver by acting
  // like some separate thread doing I/O.
  // It's goal is to try to hit race conditions whereby:
  //    1) The c-ares resolver closes a socket.
  //    2) This loop opens a socket with (coincidentally) the same handle.
  //    3) the c-ares resolver mistakenly uses that same socket without
  //       realizing that its closed.
  //    4) This loop performs an operation on that socket that should
  //       succeed but instead fails because of what the c-ares
  //       resolver did in the meantime.
  sockaddr_in6 addr;
  memset(&addr, 0, sizeof(addr));
  addr.sin6_family = AF_INET6;
  addr.sin6_port = htons(phony_port);
  (reinterpret_cast<char*>(&addr.sin6_addr))[15] = 1;
  for (;;) {
    if (gpr_event_get(done_ev)) {
      return;
    }
    std::vector<int> sockets;
    // First open a bunch of sockets, bind and listen
    // '50' is an arbitrary number that, experimentally,
    // has a good chance of catching bugs.
    for (size_t i = 0; i < 50; i++) {
      int s = socket(AF_INET6, SOCK_STREAM, 0);
      int val = 1;
      ASSERT_TRUE(setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &val, sizeof(val)) ==
                  0)
          << "Failed to set socketopt reuseport";
      ASSERT_TRUE(setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) ==
                  0)
          << "Failed to set socket reuseaddr";
      ASSERT_TRUE(fcntl(s, F_SETFL, O_NONBLOCK) == 0)
          << "Failed to set socket non-blocking";
      ASSERT_TRUE(s != BAD_SOCKET_RETURN_VAL)
          << "Failed to create TCP ipv6 socket";
      gpr_log(GPR_DEBUG, "Opened fd: %d", s);
      ASSERT_TRUE(bind(s, (const sockaddr*)&addr, sizeof(addr)) == 0)
          << "Failed to bind socket " + std::to_string(s) +
                 " to [::1]:" + std::to_string(phony_port) +
                 ". errno: " + std::to_string(errno);
      ASSERT_TRUE(listen(s, 1) == 0) << "Failed to listen on socket " +
                                            std::to_string(s) +
                                            ". errno: " + std::to_string(errno);
      sockets.push_back(s);
    }
    // Do a non-blocking accept followed by a close on all of those sockets.
    // Do this in a separate loop to try to induce a time window to hit races.
    for (size_t i = 0; i < sockets.size(); i++) {
      gpr_log(GPR_DEBUG, "non-blocking accept then close on %d", sockets[i]);
      if (accept(sockets[i], nullptr, nullptr)) {
        // If e.g. a "shutdown" was called on this fd from another thread,
        // then this accept call should fail with an unexpected error.
        ASSERT_TRUE(errno == EAGAIN || errno == EWOULDBLOCK)
            << "OpenAndCloseSocketsStressLoop accept on socket " +
                   std::to_string(sockets[i]) +
                   " failed in "
                   "an unexpected way. "
                   "errno: " +
                   std::to_string(errno) +
                   ". Socket use-after-close bugs are likely.";
      }
      ASSERT_TRUE(close(sockets[i]) == 0)
          << "Failed to close socket: " + std::to_string(sockets[i]) +
                 ". errno: " + std::to_string(errno);
    }
  }
}
#endif

class ResultHandler : public grpc_core::Resolver::ResultHandler {
 public:
  static std::unique_ptr<grpc_core::Resolver::ResultHandler> Create(
      ArgsStruct* args) {
    return std::unique_ptr<grpc_core::Resolver::ResultHandler>(
        new ResultHandler(args));
  }

  explicit ResultHandler(ArgsStruct* args) : args_(args) {}

  void ReportResult(grpc_core::Resolver::Result result) override {
    CheckResult(result);
    gpr_atm_rel_store(&args_->done_atm, 1);
    gpr_mu_lock(args_->mu);
    GRPC_LOG_IF_ERROR("pollset_kick",
                      grpc_pollset_kick(args_->pollset, nullptr));
    gpr_mu_unlock(args_->mu);
  }

  virtual void CheckResult(const grpc_core::Resolver::Result& /*result*/) {}

 protected:
  ArgsStruct* args_struct() const { return args_; }

 private:
  ArgsStruct* args_;
};

class CheckingResultHandler : public ResultHandler {
 public:
  static std::unique_ptr<grpc_core::Resolver::ResultHandler> Create(
      ArgsStruct* args) {
    return std::unique_ptr<grpc_core::Resolver::ResultHandler>(
        new CheckingResultHandler(args));
  }

  explicit CheckingResultHandler(ArgsStruct* args) : ResultHandler(args) {}

  void CheckResult(const grpc_core::Resolver::Result& result) override {
    ASSERT_TRUE(result.addresses.ok()) << result.addresses.status().ToString();
    ArgsStruct* args = args_struct();
    std::vector<GrpcLBAddress> found_lb_addrs;
    AddActualAddresses(*result.addresses, /*is_balancer=*/false,
                       &found_lb_addrs);
    const grpc_core::ServerAddressList* balancer_addresses =
        grpc_core::FindGrpclbBalancerAddressesInChannelArgs(*result.args);
    if (balancer_addresses != nullptr) {
      AddActualAddresses(*balancer_addresses, /*is_balancer=*/true,
                         &found_lb_addrs);
    }
    gpr_log(GPR_INFO,
            "found %" PRIdPTR " backend addresses and %" PRIdPTR
            " balancer addresses",
            result.addresses->size(),
            balancer_addresses == nullptr ? 0L : balancer_addresses->size());
    if (args->expected_addrs.size() != found_lb_addrs.size()) {
      gpr_log(GPR_DEBUG,
              "found lb addrs size is: %" PRIdPTR
              ". expected addrs size is %" PRIdPTR,
              found_lb_addrs.size(), args->expected_addrs.size());
      abort();
    }
    if (absl::GetFlag(FLAGS_do_ordered_address_comparison) == "True") {
      EXPECT_EQ(args->expected_addrs, found_lb_addrs);
    } else if (absl::GetFlag(FLAGS_do_ordered_address_comparison) == "False") {
      EXPECT_THAT(args->expected_addrs,
                  UnorderedElementsAreArray(found_lb_addrs));
    } else {
      gpr_log(GPR_ERROR,
              "Invalid for setting for --do_ordered_address_comparison. "
              "Have %s, want True or False",
              absl::GetFlag(FLAGS_do_ordered_address_comparison).c_str());
      GPR_ASSERT(0);
    }
    if (!result.service_config.ok()) {
      CheckServiceConfigResultLocked(nullptr, result.service_config.status(),
                                     args);
    } else if (*result.service_config == nullptr) {
      CheckServiceConfigResultLocked(nullptr, absl::OkStatus(), args);
    } else {
      CheckServiceConfigResultLocked(
          std::string((*result.service_config)->json_string()).c_str(),
          absl::OkStatus(), args);
    }
    if (args->expected_service_config_string.empty()) {
      CheckLBPolicyResultLocked(result.args, args);
    }
  }

 private:
  static void AddActualAddresses(const grpc_core::ServerAddressList& addresses,
                                 bool is_balancer,
                                 std::vector<GrpcLBAddress>* out) {
    for (size_t i = 0; i < addresses.size(); i++) {
      const grpc_core::ServerAddress& addr = addresses[i];
      std::string str =
          grpc_sockaddr_to_string(&addr.address(), true /* normalize */);
      gpr_log(GPR_INFO, "%s", str.c_str());
      out->emplace_back(GrpcLBAddress(std::move(str), is_balancer));
    }
  }
};

int g_fake_non_responsive_dns_server_port = -1;

/* This function will configure any ares_channel created by the c-ares based
 * resolver. This is useful to effectively mock /etc/resolv.conf settings
 * (and equivalent on Windows), which unit tests don't have write permissions.
 */
void InjectBrokenNameServerList(ares_channel channel) {
  struct ares_addr_port_node dns_server_addrs[2];
  memset(dns_server_addrs, 0, sizeof(dns_server_addrs));
  std::string unused_host;
  std::string local_dns_server_port;
  GPR_ASSERT(grpc_core::SplitHostPort(
      absl::GetFlag(FLAGS_local_dns_server_address).c_str(), &unused_host,
      &local_dns_server_port));
  gpr_log(GPR_DEBUG,
          "Injecting broken nameserver list. Bad server address:|[::1]:%d|. "
          "Good server address:%s",
          g_fake_non_responsive_dns_server_port,
          absl::GetFlag(FLAGS_local_dns_server_address).c_str());
  // Put the non-responsive DNS server at the front of c-ares's nameserver list.
  dns_server_addrs[0].family = AF_INET6;
  (reinterpret_cast<char*>(&dns_server_addrs[0].addr.addr6))[15] = 0x1;
  dns_server_addrs[0].tcp_port = g_fake_non_responsive_dns_server_port;
  dns_server_addrs[0].udp_port = g_fake_non_responsive_dns_server_port;
  dns_server_addrs[0].next = &dns_server_addrs[1];
  // Put the actual healthy DNS server after the first one. The expectation is
  // that the resolver will timeout the query to the non-responsive DNS server
  // and will skip over to this healthy DNS server, without causing any DNS
  // resolution errors.
  dns_server_addrs[1].family = AF_INET;
  (reinterpret_cast<char*>(&dns_server_addrs[1].addr.addr4))[0] = 0x7f;
  (reinterpret_cast<char*>(&dns_server_addrs[1].addr.addr4))[3] = 0x1;
  dns_server_addrs[1].tcp_port = atoi(local_dns_server_port.c_str());
  dns_server_addrs[1].udp_port = atoi(local_dns_server_port.c_str());
  dns_server_addrs[1].next = nullptr;
  GPR_ASSERT(ares_set_servers_ports(channel, dns_server_addrs) == ARES_SUCCESS);
}

void StartResolvingLocked(grpc_core::Resolver* r) { r->StartLocked(); }

void RunResolvesRelevantRecordsTest(
    std::unique_ptr<grpc_core::Resolver::ResultHandler> (*CreateResultHandler)(
        ArgsStruct* args)) {
  grpc_core::ExecCtx exec_ctx;
  ArgsStruct args;
  ArgsInit(&args);
  args.expected_addrs = ParseExpectedAddrs(absl::GetFlag(FLAGS_expected_addrs));
  args.expected_service_config_string =
      absl::GetFlag(FLAGS_expected_chosen_service_config);
  args.expected_service_config_error =
      absl::GetFlag(FLAGS_expected_service_config_error);
  args.expected_lb_policy = absl::GetFlag(FLAGS_expected_lb_policy);
  // maybe build the address with an authority
  std::string whole_uri;
  gpr_log(GPR_DEBUG,
          "resolver_component_test: --inject_broken_nameserver_list: %s",
          absl::GetFlag(FLAGS_inject_broken_nameserver_list).c_str());
  std::unique_ptr<grpc_core::testing::FakeUdpAndTcpServer>
      fake_non_responsive_dns_server;
  if (absl::GetFlag(FLAGS_inject_broken_nameserver_list) == "True") {
    fake_non_responsive_dns_server = absl::make_unique<
        grpc_core::testing::FakeUdpAndTcpServer>(
        grpc_core::testing::FakeUdpAndTcpServer::AcceptMode::
            kWaitForClientToSendFirstBytes,
        grpc_core::testing::FakeUdpAndTcpServer::CloseSocketUponCloseFromPeer);
    g_fake_non_responsive_dns_server_port =
        fake_non_responsive_dns_server->port();
    grpc_ares_test_only_inject_config = InjectBrokenNameServerList;
    whole_uri = absl::StrCat("dns:///", absl::GetFlag(FLAGS_target_name));
  } else if (absl::GetFlag(FLAGS_inject_broken_nameserver_list) == "False") {
    gpr_log(GPR_INFO, "Specifying authority in uris to: %s",
            absl::GetFlag(FLAGS_local_dns_server_address).c_str());
    whole_uri = absl::StrFormat("dns://%s/%s",
                                absl::GetFlag(FLAGS_local_dns_server_address),
                                absl::GetFlag(FLAGS_target_name));
  } else {
    gpr_log(GPR_DEBUG, "Invalid value for --inject_broken_nameserver_list.");
    abort();
  }
  gpr_log(GPR_DEBUG, "resolver_component_test: --enable_srv_queries: %s",
          absl::GetFlag(FLAGS_enable_srv_queries).c_str());
  grpc_channel_args* resolver_args = nullptr;
  // By default, SRV queries are disabled, so tests that expect no SRV query
  // should avoid setting any channel arg. Test cases that do rely on the SRV
  // query must explicitly enable SRV though.
  if (absl::GetFlag(FLAGS_enable_srv_queries) == "True") {
    grpc_arg srv_queries_arg = grpc_channel_arg_integer_create(
        const_cast<char*>(GRPC_ARG_DNS_ENABLE_SRV_QUERIES), true);
    resolver_args =
        grpc_channel_args_copy_and_add(nullptr, &srv_queries_arg, 1);
  } else if (absl::GetFlag(FLAGS_enable_srv_queries) != "False") {
    gpr_log(GPR_DEBUG, "Invalid value for --enable_srv_queries.");
    abort();
  }
  gpr_log(GPR_DEBUG, "resolver_component_test: --enable_txt_queries: %s",
          absl::GetFlag(FLAGS_enable_txt_queries).c_str());
  // By default, TXT queries are disabled, so tests that expect no TXT query
  // should avoid setting any channel arg. Test cases that do rely on the TXT
  // query must explicitly enable TXT though.
  if (absl::GetFlag(FLAGS_enable_txt_queries) == "True") {
    // Unlike SRV queries, there isn't a channel arg specific to TXT records.
    // Rather, we use the resolver-agnostic "service config" resolution option,
    // for which c-ares has its own specific default value, which isn't
    // necessarily shared by other resolvers.
    grpc_arg txt_queries_arg = grpc_channel_arg_integer_create(
        const_cast<char*>(GRPC_ARG_SERVICE_CONFIG_DISABLE_RESOLUTION), false);
    grpc_channel_args* tmp_args =
        grpc_channel_args_copy_and_add(resolver_args, &txt_queries_arg, 1);
    grpc_channel_args_destroy(resolver_args);
    resolver_args = tmp_args;
  } else if (absl::GetFlag(FLAGS_enable_txt_queries) != "False") {
    gpr_log(GPR_DEBUG, "Invalid value for --enable_txt_queries.");
    abort();
  }
  // create resolver and resolve
  grpc_core::OrphanablePtr<grpc_core::Resolver> resolver =
      grpc_core::CoreConfiguration::Get().resolver_registry().CreateResolver(
          whole_uri.c_str(), resolver_args, args.pollset_set, args.lock,
          CreateResultHandler(&args));
  grpc_channel_args_destroy(resolver_args);
  auto* resolver_ptr = resolver.get();
  args.lock->Run([resolver_ptr]() { StartResolvingLocked(resolver_ptr); },
                 DEBUG_LOCATION);
  grpc_core::ExecCtx::Get()->Flush();
  PollPollsetUntilRequestDone(&args);
  ArgsFinish(&args);
}

TEST(ResolverComponentTest, TestResolvesRelevantRecords) {
  RunResolvesRelevantRecordsTest(CheckingResultHandler::Create);
}

TEST(ResolverComponentTest, TestResolvesRelevantRecordsWithConcurrentFdStress) {
  // Start up background stress thread
  int phony_port = grpc_pick_unused_port_or_die();
  gpr_event done_ev;
  gpr_event_init(&done_ev);
  std::thread socket_stress_thread(OpenAndCloseSocketsStressLoop, phony_port,
                                   &done_ev);
  // Run the resolver test
  RunResolvesRelevantRecordsTest(ResultHandler::Create);
  // Shutdown and join stress thread
  gpr_event_set(&done_ev, reinterpret_cast<void*>(1));
  socket_stress_thread.join();
}

}  // namespace

int main(int argc, char** argv) {
  grpc_init();
  grpc::testing::TestEnvironment env(&argc, argv);
  ::testing::InitGoogleTest(&argc, argv);
  grpc::testing::InitTest(&argc, &argv, true);
  if (absl::GetFlag(FLAGS_target_name).empty()) {
    gpr_log(GPR_ERROR, "Missing target_name param.");
    abort();
  }
  auto result = RUN_ALL_TESTS();
  grpc_shutdown();
  return result;
}
