test/cpp/grpclb/grpclb_test.cc

/*
 *
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 * modification, are permitted provided that the following conditions are
 * met:
 *
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 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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#include <cinttypes>
#include <cstdarg>
#include <cstdint>
#include <cstring>
#include <string>

#include <grpc/grpc.h>
#include <grpc/support/alloc.h>
#include <grpc/support/host_port.h>
#include <grpc/support/log.h>
#include <grpc/support/string_util.h>
#include <grpc/support/sync.h>
#include <grpc/support/thd.h>
#include <grpc/support/time.h>

extern "C" {
#include "src/core/ext/client_config/client_channel.h"
#include "src/core/lib/channel/channel_stack.h"
#include "src/core/lib/support/string.h"
#include "src/core/lib/support/tmpfile.h"
#include "src/core/lib/surface/channel.h"
#include "src/core/lib/surface/server.h"
#include "test/core/end2end/cq_verifier.h"
#include "test/core/util/port.h"
#include "test/core/util/test_config.h"
}

#include "src/proto/grpc/lb/v1/load_balancer.pb.h"

#define NUM_BACKENDS 4

// TODO(dgq): Other scenarios in need of testing:
// - Send an empty serverlist update and verify that the client request blocks
//   until a new serverlist with actual contents is available.
// - Send identical serverlist update
// - Test reception of invalid serverlist
// - Test pinging
// - Test against a non-LB server. That server should return UNIMPLEMENTED and
//   the call should fail.
// - Random LB server closing the stream unexpectedly.

namespace grpc {
namespace {

typedef struct client_fixture {
  grpc_channel *client;
  char *server_uri;
  grpc_completion_queue *cq;
} client_fixture;

typedef struct server_fixture {
  grpc_server *server;
  grpc_call *server_call;
  grpc_completion_queue *cq;
  char *servers_hostport;
  int port;
  gpr_thd_id tid;
  int num_calls_serviced;
} server_fixture;

typedef struct test_fixture {
  server_fixture lb_server;
  server_fixture lb_backends[NUM_BACKENDS];
  client_fixture client;
  int lb_server_update_delay_ms;
} test_fixture;

static void *tag(intptr_t t) { return (void *)t; }

static gpr_slice build_response_payload_slice(
    const char *host, int *ports, size_t nports,
    int64_t expiration_interval_secs, int32_t expiration_interval_nanos) {
  // server_list {
  //   servers {
  //     ip_address: "127.0.0.1"
  //     port: ...
  //     load_balance_token: "token..."
  //   }
  //   ...
  // }
  grpc::lb::v1::LoadBalanceResponse response;
  auto *serverlist = response.mutable_server_list();

  if (expiration_interval_secs > 0 || expiration_interval_nanos > 0) {
    auto *expiration_interval = serverlist->mutable_expiration_interval();
    if (expiration_interval_secs > 0) {
      expiration_interval->set_seconds(expiration_interval_secs);
    }
    if (expiration_interval_nanos > 0) {
      expiration_interval->set_nanos(expiration_interval_nanos);
    }
  }
  for (size_t i = 0; i < nports; i++) {
    auto *server = serverlist->add_servers();
    server->set_ip_address(host);
    server->set_port(ports[i]);
    // The following long long int cast is meant to work around the
    // disfunctional implementation of std::to_string in gcc 4.4, which doesn't
    // have a version for int but does have one for long long int.
    server->set_load_balance_token("token" +
                                   std::to_string((long long int)ports[i]));
  }

  gpr_log(GPR_INFO, "generating response: %s",
          response.ShortDebugString().c_str());

  const gpr_slice response_slice =
      gpr_slice_from_copied_string(response.SerializeAsString().c_str());
  return response_slice;
}

static void drain_cq(grpc_completion_queue *cq) {
  grpc_event ev;
  do {
    ev = grpc_completion_queue_next(cq, GRPC_TIMEOUT_SECONDS_TO_DEADLINE(5),
                                    NULL);
  } while (ev.type != GRPC_QUEUE_SHUTDOWN);
}

static void sleep_ms(int delay_ms) {
  gpr_sleep_until(gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
                               gpr_time_from_millis(delay_ms, GPR_TIMESPAN)));
}

static void start_lb_server(server_fixture *sf, int *ports, size_t nports,
                            int update_delay_ms) {
  grpc_call *s;
  cq_verifier *cqv = cq_verifier_create(sf->cq);
  grpc_op ops[6];
  grpc_op *op;
  grpc_metadata_array request_metadata_recv;
  grpc_call_details call_details;
  grpc_call_error error;
  int was_cancelled = 2;
  grpc_byte_buffer *request_payload_recv;
  grpc_byte_buffer *response_payload;

  memset(ops, 0, sizeof(ops));
  grpc_metadata_array_init(&request_metadata_recv);
  grpc_call_details_init(&call_details);

  error = grpc_server_request_call(sf->server, &s, &call_details,
                                   &request_metadata_recv, sf->cq, sf->cq,
                                   tag(200));
  GPR_ASSERT(GRPC_CALL_OK == error);
  gpr_log(GPR_INFO, "LB Server[%s] up", sf->servers_hostport);
  cq_expect_completion(cqv, tag(200), 1);
  cq_verify(cqv);
  gpr_log(GPR_INFO, "LB Server[%s] after tag 200", sf->servers_hostport);

  op = ops;
  op->op = GRPC_OP_SEND_INITIAL_METADATA;
  op->data.send_initial_metadata.count = 0;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  op->op = GRPC_OP_RECV_CLOSE_ON_SERVER;
  op->data.recv_close_on_server.cancelled = &was_cancelled;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(201), NULL);
  GPR_ASSERT(GRPC_CALL_OK == error);
  gpr_log(GPR_INFO, "LB Server[%s] after tag 201", sf->servers_hostport);

  // receive request for backends
  op = ops;
  op->op = GRPC_OP_RECV_MESSAGE;
  op->data.recv_message = &request_payload_recv;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(202), NULL);
  GPR_ASSERT(GRPC_CALL_OK == error);
  cq_expect_completion(cqv, tag(202), 1);
  cq_verify(cqv);
  gpr_log(GPR_INFO, "LB Server[%s] after RECV_MSG", sf->servers_hostport);
  // TODO(dgq): validate request.
  grpc_byte_buffer_destroy(request_payload_recv);
  gpr_slice response_payload_slice;
  for (int i = 0; i < 2; i++) {
    if (i == 0) {
      // First half of the ports.
      response_payload_slice =
          build_response_payload_slice("127.0.0.1", ports, nports / 2, -1, -1);
    } else {
      // Second half of the ports.
      sleep_ms(update_delay_ms);
      response_payload_slice =
          build_response_payload_slice("127.0.0.1", ports + (nports / 2),
                                       (nports + 1) / 2 /* ceil */, -1, -1);
    }

    response_payload = grpc_raw_byte_buffer_create(&response_payload_slice, 1);
    op = ops;
    op->op = GRPC_OP_SEND_MESSAGE;
    op->data.send_message = response_payload;
    op->flags = 0;
    op->reserved = NULL;
    op++;
    error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(203), NULL);
    GPR_ASSERT(GRPC_CALL_OK == error);
    cq_expect_completion(cqv, tag(203), 1);
    cq_verify(cqv);
    gpr_log(GPR_INFO, "LB Server[%s] after SEND_MESSAGE, iter %d",
            sf->servers_hostport, i);

    grpc_byte_buffer_destroy(response_payload);
    gpr_slice_unref(response_payload_slice);
  }
  gpr_log(GPR_INFO, "LB Server[%s] shutting down", sf->servers_hostport);

  op = ops;
  op->op = GRPC_OP_SEND_STATUS_FROM_SERVER;
  op->data.send_status_from_server.trailing_metadata_count = 0;
  op->data.send_status_from_server.status = GRPC_STATUS_OK;
  op->data.send_status_from_server.status_details = "xyz";
  op->flags = 0;
  op->reserved = NULL;
  op++;
  error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(204), NULL);
  GPR_ASSERT(GRPC_CALL_OK == error);

  cq_expect_completion(cqv, tag(201), 1);
  cq_expect_completion(cqv, tag(204), 1);
  cq_verify(cqv);
  gpr_log(GPR_INFO, "LB Server[%s] after tag 204. All done. LB server out",
          sf->servers_hostport);

  grpc_call_destroy(s);

  cq_verifier_destroy(cqv);

  grpc_metadata_array_destroy(&request_metadata_recv);
  grpc_call_details_destroy(&call_details);
}

static void start_backend_server(server_fixture *sf) {
  grpc_call *s;
  cq_verifier *cqv;
  grpc_op ops[6];
  grpc_op *op;
  grpc_metadata_array request_metadata_recv;
  grpc_call_details call_details;
  grpc_call_error error;
  int was_cancelled;
  grpc_byte_buffer *request_payload_recv;
  grpc_byte_buffer *response_payload;
  grpc_event ev;

  while (true) {
    memset(ops, 0, sizeof(ops));
    cqv = cq_verifier_create(sf->cq);
    was_cancelled = 2;
    grpc_metadata_array_init(&request_metadata_recv);
    grpc_call_details_init(&call_details);

    error = grpc_server_request_call(sf->server, &s, &call_details,
                                     &request_metadata_recv, sf->cq, sf->cq,
                                     tag(100));
    GPR_ASSERT(GRPC_CALL_OK == error);
    gpr_log(GPR_INFO, "Server[%s] up", sf->servers_hostport);
    ev = grpc_completion_queue_next(sf->cq,
                                    GRPC_TIMEOUT_SECONDS_TO_DEADLINE(60), NULL);
    if (!ev.success) {
      gpr_log(GPR_INFO, "Server[%s] being torn down", sf->servers_hostport);
      cq_verifier_destroy(cqv);
      grpc_metadata_array_destroy(&request_metadata_recv);
      grpc_call_details_destroy(&call_details);
      return;
    }
    GPR_ASSERT(ev.type == GRPC_OP_COMPLETE);
    gpr_log(GPR_INFO, "Server[%s] after tag 100", sf->servers_hostport);

    op = ops;
    op->op = GRPC_OP_SEND_INITIAL_METADATA;
    op->data.send_initial_metadata.count = 0;
    op->flags = 0;
    op->reserved = NULL;
    op++;
    op->op = GRPC_OP_RECV_CLOSE_ON_SERVER;
    op->data.recv_close_on_server.cancelled = &was_cancelled;
    op->flags = 0;
    op->reserved = NULL;
    op++;
    error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(101), NULL);
    GPR_ASSERT(GRPC_CALL_OK == error);
    gpr_log(GPR_INFO, "Server[%s] after tag 101", sf->servers_hostport);

    bool exit = false;
    gpr_slice response_payload_slice =
        gpr_slice_from_copied_string("hello you");
    while (!exit) {
      op = ops;
      op->op = GRPC_OP_RECV_MESSAGE;
      op->data.recv_message = &request_payload_recv;
      op->flags = 0;
      op->reserved = NULL;
      op++;
      error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(102), NULL);
      GPR_ASSERT(GRPC_CALL_OK == error);
      ev = grpc_completion_queue_next(
          sf->cq, GRPC_TIMEOUT_SECONDS_TO_DEADLINE(3), NULL);
      if (ev.type == GRPC_OP_COMPLETE && ev.success) {
        GPR_ASSERT(ev.tag = tag(102));
        if (request_payload_recv == NULL) {
          exit = true;
          gpr_log(GPR_INFO,
                  "Server[%s] recv \"close\" from client, exiting. Call #%d",
                  sf->servers_hostport, sf->num_calls_serviced);
        }
      } else {
        gpr_log(GPR_INFO, "Server[%s] forced to shutdown. Call #%d",
                sf->servers_hostport, sf->num_calls_serviced);
        exit = true;
      }
      gpr_log(GPR_INFO, "Server[%s] after tag 102. Call #%d",
              sf->servers_hostport, sf->num_calls_serviced);

      if (!exit) {
        response_payload =
            grpc_raw_byte_buffer_create(&response_payload_slice, 1);
        op = ops;
        op->op = GRPC_OP_SEND_MESSAGE;
        op->data.send_message = response_payload;
        op->flags = 0;
        op->reserved = NULL;
        op++;
        error =
            grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(103), NULL);
        GPR_ASSERT(GRPC_CALL_OK == error);
        ev = grpc_completion_queue_next(
            sf->cq, GRPC_TIMEOUT_SECONDS_TO_DEADLINE(3), NULL);
        if (ev.type == GRPC_OP_COMPLETE && ev.success) {
          GPR_ASSERT(ev.tag = tag(103));
        } else {
          gpr_log(GPR_INFO, "Server[%s] forced to shutdown. Call #%d",
                  sf->servers_hostport, sf->num_calls_serviced);
          exit = true;
        }
        gpr_log(GPR_INFO, "Server[%s] after tag 103. Call #%d",
                sf->servers_hostport, sf->num_calls_serviced);
        grpc_byte_buffer_destroy(response_payload);
      }

      grpc_byte_buffer_destroy(request_payload_recv);
    }
    ++sf->num_calls_serviced;

    gpr_log(GPR_INFO, "Server[%s] OUT OF THE LOOP", sf->servers_hostport);
    gpr_slice_unref(response_payload_slice);

    op = ops;
    op->op = GRPC_OP_SEND_STATUS_FROM_SERVER;
    op->data.send_status_from_server.trailing_metadata_count = 0;
    op->data.send_status_from_server.status = GRPC_STATUS_OK;
    op->data.send_status_from_server.status_details = "Backend server out a-ok";
    op->flags = 0;
    op->reserved = NULL;
    op++;
    error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(104), NULL);
    GPR_ASSERT(GRPC_CALL_OK == error);

    cq_expect_completion(cqv, tag(101), 1);
    cq_expect_completion(cqv, tag(104), 1);
    cq_verify(cqv);
    gpr_log(GPR_INFO, "Server[%s] DONE. After servicing %d calls",
            sf->servers_hostport, sf->num_calls_serviced);

    grpc_call_destroy(s);
    cq_verifier_destroy(cqv);
    grpc_metadata_array_destroy(&request_metadata_recv);
    grpc_call_details_destroy(&call_details);
  }
}

static void perform_request(client_fixture *cf) {
  grpc_call *c;
  cq_verifier *cqv = cq_verifier_create(cf->cq);
  grpc_op ops[6];
  grpc_op *op;
  grpc_metadata_array initial_metadata_recv;
  grpc_metadata_array trailing_metadata_recv;
  grpc_status_code status;
  grpc_call_error error;
  char *details = NULL;
  size_t details_capacity = 0;
  grpc_byte_buffer *request_payload;
  grpc_byte_buffer *response_payload_recv;
  int i;

  memset(ops, 0, sizeof(ops));
  gpr_slice request_payload_slice = gpr_slice_from_copied_string("hello world");

  c = grpc_channel_create_call(cf->client, NULL, GRPC_PROPAGATE_DEFAULTS,
                               cf->cq, "/foo", "foo.test.google.fr:1234",
                               GRPC_TIMEOUT_SECONDS_TO_DEADLINE(1000), NULL);
  gpr_log(GPR_INFO, "Call 0x%" PRIxPTR " created", (intptr_t)c);
  GPR_ASSERT(c);
  char *peer;

  grpc_metadata_array_init(&initial_metadata_recv);
  grpc_metadata_array_init(&trailing_metadata_recv);

  op = ops;
  op->op = GRPC_OP_SEND_INITIAL_METADATA;
  op->data.send_initial_metadata.count = 0;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  op->op = GRPC_OP_RECV_INITIAL_METADATA;
  op->data.recv_initial_metadata = &initial_metadata_recv;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  op->op = GRPC_OP_RECV_STATUS_ON_CLIENT;
  op->data.recv_status_on_client.trailing_metadata = &trailing_metadata_recv;
  op->data.recv_status_on_client.status = &status;
  op->data.recv_status_on_client.status_details = &details;
  op->data.recv_status_on_client.status_details_capacity = &details_capacity;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  error = grpc_call_start_batch(c, ops, (size_t)(op - ops), tag(1), NULL);
  GPR_ASSERT(GRPC_CALL_OK == error);

  for (i = 0; i < 4; i++) {
    request_payload = grpc_raw_byte_buffer_create(&request_payload_slice, 1);

    op = ops;
    op->op = GRPC_OP_SEND_MESSAGE;
    op->data.send_message = request_payload;
    op->flags = 0;
    op->reserved = NULL;
    op++;
    op->op = GRPC_OP_RECV_MESSAGE;
    op->data.recv_message = &response_payload_recv;
    op->flags = 0;
    op->reserved = NULL;
    op++;
    error = grpc_call_start_batch(c, ops, (size_t)(op - ops), tag(2), NULL);
    GPR_ASSERT(GRPC_CALL_OK == error);

    peer = grpc_call_get_peer(c);
    cq_expect_completion(cqv, tag(2), 1);
    cq_verify(cqv);
    gpr_free(peer);

    grpc_byte_buffer_destroy(request_payload);
    grpc_byte_buffer_destroy(response_payload_recv);
  }

  gpr_slice_unref(request_payload_slice);

  op = ops;
  op->op = GRPC_OP_SEND_CLOSE_FROM_CLIENT;
  op->flags = 0;
  op->reserved = NULL;
  op++;
  error = grpc_call_start_batch(c, ops, (size_t)(op - ops), tag(3), NULL);
  GPR_ASSERT(GRPC_CALL_OK == error);

  cq_expect_completion(cqv, tag(1), 1);
  cq_expect_completion(cqv, tag(3), 1);
  cq_verify(cqv);
  peer = grpc_call_get_peer(c);
  gpr_log(GPR_INFO, "Client DONE WITH SERVER %s ", peer);
  gpr_free(peer);

  grpc_call_destroy(c);

  cq_verify_empty_timeout(cqv, 1);
  cq_verifier_destroy(cqv);

  grpc_metadata_array_destroy(&initial_metadata_recv);
  grpc_metadata_array_destroy(&trailing_metadata_recv);
  gpr_free(details);
}

static void setup_client(const char *server_hostport, client_fixture *cf) {
  cf->cq = grpc_completion_queue_create(NULL);
  cf->server_uri = gpr_strdup(server_hostport);
  cf->client = grpc_insecure_channel_create(cf->server_uri, NULL, NULL);
}

static void teardown_client(client_fixture *cf) {
  grpc_completion_queue_shutdown(cf->cq);
  drain_cq(cf->cq);
  grpc_completion_queue_destroy(cf->cq);
  cf->cq = NULL;
  grpc_channel_destroy(cf->client);
  cf->client = NULL;
  gpr_free(cf->server_uri);
}

static void setup_server(const char *host, server_fixture *sf) {
  int assigned_port;

  sf->cq = grpc_completion_queue_create(NULL);
  const char *colon_idx = strchr(host, ':');
  if (colon_idx) {
    const char *port_str = colon_idx + 1;
    sf->port = atoi(port_str);
    sf->servers_hostport = gpr_strdup(host);
  } else {
    sf->port = grpc_pick_unused_port_or_die();
    gpr_join_host_port(&sf->servers_hostport, host, sf->port);
  }

  sf->server = grpc_server_create(NULL, NULL);
  grpc_server_register_completion_queue(sf->server, sf->cq, NULL);
  GPR_ASSERT((assigned_port = grpc_server_add_insecure_http2_port(
                  sf->server, sf->servers_hostport)) > 0);
  GPR_ASSERT(sf->port == assigned_port);
  grpc_server_start(sf->server);
}

static void teardown_server(server_fixture *sf) {
  if (!sf->server) return;

  gpr_log(GPR_INFO, "Server[%s] shutting down", sf->servers_hostport);
  grpc_server_shutdown_and_notify(sf->server, sf->cq, tag(1000));
  GPR_ASSERT(grpc_completion_queue_pluck(
                 sf->cq, tag(1000), GRPC_TIMEOUT_SECONDS_TO_DEADLINE(5), NULL)
                 .type == GRPC_OP_COMPLETE);
  grpc_server_destroy(sf->server);
  gpr_thd_join(sf->tid);

  sf->server = NULL;
  grpc_completion_queue_shutdown(sf->cq);
  drain_cq(sf->cq);
  grpc_completion_queue_destroy(sf->cq);

  gpr_log(GPR_INFO, "Server[%s] bye bye", sf->servers_hostport);
  gpr_free(sf->servers_hostport);
}

static void fork_backend_server(void *arg) {
  server_fixture *sf = static_cast<server_fixture *>(arg);
  start_backend_server(sf);
}

static void fork_lb_server(void *arg) {
  test_fixture *tf = static_cast<test_fixture *>(arg);
  int ports[NUM_BACKENDS];
  for (int i = 0; i < NUM_BACKENDS; i++) {
    ports[i] = tf->lb_backends[i].port;
  }
  start_lb_server(&tf->lb_server, ports, NUM_BACKENDS,
                  tf->lb_server_update_delay_ms);
}

static void setup_test_fixture(test_fixture *tf,
                               int lb_server_update_delay_ms) {
  tf->lb_server_update_delay_ms = lb_server_update_delay_ms;

  gpr_thd_options options = gpr_thd_options_default();
  gpr_thd_options_set_joinable(&options);

  for (int i = 0; i < NUM_BACKENDS; ++i) {
    setup_server("127.0.0.1", &tf->lb_backends[i]);
    gpr_thd_new(&tf->lb_backends[i].tid, fork_backend_server,
                &tf->lb_backends[i], &options);
  }

  setup_server("127.0.0.1", &tf->lb_server);
  gpr_thd_new(&tf->lb_server.tid, fork_lb_server, &tf->lb_server, &options);

  char *server_uri;
  gpr_asprintf(&server_uri, "ipv4:%s?lb_policy=grpclb&lb_enabled=1",
               tf->lb_server.servers_hostport);
  setup_client(server_uri, &tf->client);
  gpr_free(server_uri);
}

static void teardown_test_fixture(test_fixture *tf) {
  teardown_client(&tf->client);
  for (int i = 0; i < NUM_BACKENDS; ++i) {
    teardown_server(&tf->lb_backends[i]);
  }
  teardown_server(&tf->lb_server);
}

// The LB server will send two updates: batch 1 and batch 2. Each batch
// contains
// two addresses, both of a valid and running backend server. Batch 1 is
// readily
// available and provided as soon as the client establishes the streaming
// call.
// Batch 2 is sent after a delay of \a lb_server_update_delay_ms
// milliseconds.
static test_fixture test_update(int lb_server_update_delay_ms) {
  gpr_log(GPR_INFO, "start %s(%d)", __func__, lb_server_update_delay_ms);
  test_fixture tf;
  memset(&tf, 0, sizeof(tf));
  setup_test_fixture(&tf, lb_server_update_delay_ms);
  perform_request(
      &tf.client);  // "consumes" 1st backend server of 1st serverlist
  perform_request(
      &tf.client);  // "consumes" 2nd backend server of 1st serverlist

  perform_request(
      &tf.client);  // "consumes" 1st backend server of 2nd serverlist
  perform_request(
      &tf.client);  // "consumes" 2nd backend server of 2nd serverlist

  teardown_test_fixture(&tf);
  gpr_log(GPR_INFO, "end %s(%d)", __func__, lb_server_update_delay_ms);
  return tf;
}

}  // namespace
}  // namespace grpc

int main(int argc, char **argv) {
  grpc_test_init(argc, argv);
  grpc_init();

  grpc::test_fixture tf_result;
  // Clients take a bit over one second to complete a call (the last part of the
  // call sleeps for 1 second while verifying the client's completion queue is
  // empty). Therefore:
  //
  // If the LB server waits 800ms before sending an update, it will arrive
  // before the first client request is done, skipping the second server from
  // batch 1 altogether: the 2nd client request will go to the 1st server of
  // batch 2 (ie, the third one out of the four total servers).
  tf_result = grpc::test_update(800);
  GPR_ASSERT(tf_result.lb_backends[0].num_calls_serviced == 1);
  GPR_ASSERT(tf_result.lb_backends[1].num_calls_serviced == 0);
  GPR_ASSERT(tf_result.lb_backends[2].num_calls_serviced == 2);
  GPR_ASSERT(tf_result.lb_backends[3].num_calls_serviced == 1);

  // If the LB server waits 1500ms, the update arrives after having picked the
  // 2nd server from batch 1 but before the next pick for the first server of
  // batch 2. All server are used.
  tf_result = grpc::test_update(1500);
  GPR_ASSERT(tf_result.lb_backends[0].num_calls_serviced == 1);
  GPR_ASSERT(tf_result.lb_backends[1].num_calls_serviced == 1);
  GPR_ASSERT(tf_result.lb_backends[2].num_calls_serviced == 1);
  GPR_ASSERT(tf_result.lb_backends[3].num_calls_serviced == 1);

  // If the LB server waits > 2000ms, the update arrives after the first two
  // request are done and the third pick is performed, which returns, in RR
  // fashion, the 1st server of the 1st update. Therefore, the second server of
  // batch 1 is hit at least one, whereas the first server of batch 2 is never
  // hit.
  tf_result = grpc::test_update(2500);
  GPR_ASSERT(tf_result.lb_backends[0].num_calls_serviced >= 1);
  GPR_ASSERT(tf_result.lb_backends[1].num_calls_serviced > 0);
  GPR_ASSERT(tf_result.lb_backends[2].num_calls_serviced > 0);
  GPR_ASSERT(tf_result.lb_backends[3].num_calls_serviced == 0);

  grpc_shutdown();
  return 0;
}