add pick_first_unary

src/proto/grpc/testing/messages.proto

@@ -77,6 +77,9 @@ message SimpleRequest {
 
   // Whether the server should expect this request to be compressed.
   BoolValue expect_compressed = 8;
+
+  // Whether SimpleResponse should include server_id.
+  bool fill_server_id = 9;
 }
 
 // Unary response, as configured by the request.
@@ -88,6 +91,10 @@ message SimpleResponse {
   string username = 2;
   // OAuth scope.
   string oauth_scope = 3;
+
+  // Server ID. This must be unique among different server instances,
+  // but the same across all RPC's made to a particular server instance.
+  string server_id = 4;
 }
 
 // Client-streaming request.

test/cpp/interop/client.cc

@@ -222,6 +222,8 @@ int main(int argc, char** argv) {
       &grpc::testing::InteropClient::DoTimeoutOnSleepingServer, &client);
   actions["empty_stream"] =
       std::bind(&grpc::testing::InteropClient::DoEmptyStream, &client);
+  actions["pick_first_unary"] =
+      std::bind(&grpc::testing::InteropClient::DoPickFirstUnary, &client);
   if (FLAGS_use_tls) {
     actions["compute_engine_creds"] =
         std::bind(&grpc::testing::InteropClient::DoComputeEngineCreds, &client,

test/cpp/interop/client_helper.cc

@@ -105,6 +105,13 @@ std::shared_ptr<Channel> CreateChannelForTestCase(
     creds = FLAGS_custom_credentials_type == "google_default_credentials"
                 ? nullptr
                 : AccessTokenCredentials(GetOauth2AccessToken());
+  } else if (test_case == "pick_first_unary") {
+    ChannelArguments channel_args;
+    // force using pick first policy
+    channel_args.SetInt(GRPC_ARG_SERVICE_CONFIG_DISABLE_RESOLUTION, 0);
+    return CreateTestChannel(host_port, FLAGS_custom_credentials_type,
+                             FLAGS_server_host_override, !FLAGS_use_test_ca,
+                             creds, channel_args);
   }
   if (FLAGS_custom_credentials_type.empty()) {
     transport_security security_type =

test/cpp/interop/interop_client.cc

@@ -948,6 +948,29 @@ bool InteropClient::DoCacheableUnary() {
   return true;
 }
 
+bool InteropClient::DoPickFirstUnary() {
+  const int rpcCount = 100;
+  SimpleRequest request;
+  SimpleResponse response;
+  std::string first_server_id;
+  request.set_fill_server_id(true);
+  for (int i = 0; i < rpcCount; i++) {
+    ClientContext context;
+    Status s = serviceStub_.Get()->UnaryCall(&context, request, &response);
+    if (!AssertStatusOk(s, context.debug_error_string())) {
+      return false;
+    }
+    if (i == 0) {
+      first_server_id = response.server_id();
+      gpr_log(GPR_DEBUG, "first_user_id is %s", first_server_id.c_str());
+      continue;
+    }
+    GPR_ASSERT(response.server_id() == first_server_id);
+  }
+  gpr_log(GPR_DEBUG, "pick first unary successfully finished");
+  return true;
+}
+
 bool InteropClient::DoCustomMetadata() {
   const grpc::string kEchoInitialMetadataKey("x-grpc-test-echo-initial");
   const grpc::string kInitialMetadataValue("test_initial_metadata_value");

test/cpp/interop/interop_client.h

@@ -69,6 +69,8 @@ class InteropClient {
   bool DoUnimplementedMethod();
   bool DoUnimplementedService();
   bool DoCacheableUnary();
+  // all requests are sent to one server despite multiple servers are resolved
+  bool DoPickFirstUnary();
 
   // The following interop test are not yet part of the interop spec, and are
   // not implemented cross-language. They are considered experimental for now,