[sample] Client-side flow control (#37604)

Closes #37604

PiperOrigin-RevId: 677954309

examples/cpp/flow_control/BUILD

@@ -14,6 +14,33 @@
 
 licenses(["notice"])
 
+cc_binary(
+    name = "client_flow_control_client",
+    srcs = ["client_flow_control_client.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//:grpc++_reflection",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+    ],
+)
+
+cc_binary(
+    name = "client_flow_control_server",
+    srcs = ["client_flow_control_server.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//:grpc++_reflection",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+        "@com_google_absl//absl/strings:str_format",
+    ],
+)
+
 cc_binary(
     name = "server_flow_control_client",
     srcs = ["server_flow_control_client.cc"],

examples/cpp/flow_control/CMakeLists.txt

@@ -59,6 +59,7 @@ target_link_libraries(hw_grpc_proto
 
 # Targets greeter_[async_](client|server)
 foreach(_target
+  client_flow_control_client client_flow_control_server
   server_flow_control_client server_flow_control_server)
   add_executable(${_target} "${_target}.cc")
   target_link_libraries(${_target}

examples/cpp/flow_control/client_flow_control_client.cc

@@ -0,0 +1,126 @@
+/*
+ *
+ * Copyright 2024 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 <cstddef>
+#include <ostream>
+#include <string>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+
+#include <grpc/grpc.h>
+#include <grpcpp/ext/proto_server_reflection_plugin.h>
+#include <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(std::string, target, "localhost:50051", "Server address");
+
+using grpc::CallbackServerContext;
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerUnaryReactor;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+namespace {
+
+// Sends requests as quickly as possible and times how long it takes to perform
+// the write operation.
+class GreeterClientReactor final
+    : public grpc::ClientBidiReactor<helloworld::HelloRequest,
+                                     helloworld::HelloReply> {
+ public:
+  explicit GreeterClientReactor(int reqs, size_t req_size) : reqs_(reqs) {
+    req_.set_name(std::string(req_size, '*'));
+  }
+
+  void Start() {
+    absl::MutexLock lock(&mu_);
+    StartCall();
+    Write();
+  }
+
+  ~GreeterClientReactor() override {
+    absl::MutexLock lock(&mu_);
+    mu_.Await(absl::Condition(+[](bool* done) { return *done; }, &done_));
+  }
+
+  void OnWriteDone(bool ok) override {
+    absl::MutexLock lock(&mu_);
+    std::cout << "Writing took " << absl::Now() - *time_ << std::endl;
+    time_ = absl::nullopt;
+    if (ok) {
+      Write();
+    }
+  }
+
+  void OnDone(const grpc::Status& status) override {
+    if (status.ok()) {
+      std::cout << "Done\n";
+    } else {
+      std::cout << "Done with error: [" << status.error_code() << "] "
+                << status.error_message() << "\n";
+    }
+    absl::MutexLock lock(&mu_);
+    done_ = true;
+  }
+
+ private:
+  void Write() ABSL_EXCLUSIVE_LOCKS_REQUIRED(&mu_) {
+    if (reqs_ == 0) {
+      StartWritesDone();
+      return;
+    }
+    --reqs_;
+    StartWrite(&req_);
+    time_ = absl::Now();
+  }
+
+  absl::Mutex mu_;
+  bool done_ ABSL_GUARDED_BY(&mu_) = false;
+  HelloRequest req_;
+  size_t reqs_;
+  absl::optional<absl::Time> time_ ABSL_GUARDED_BY(mu_);
+};
+
+}  // namespace
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  grpc::ChannelArguments channel_arguments;
+  auto channel = grpc::CreateCustomChannel(absl::GetFlag(FLAGS_target),
+                                           grpc::InsecureChannelCredentials(),
+                                           channel_arguments);
+  auto stub = Greeter::NewStub(channel);
+  // Send 10 requests with 3Mb payload. This will eventually fill the buffer
+  // and make
+  GreeterClientReactor reactor(10, 3 * 1024 * 1024);
+  grpc::ClientContext context;
+  stub->async()->SayHelloBidiStream(&context, &reactor);
+  reactor.Start();
+  return 0;
+}

examples/cpp/flow_control/client_flow_control_server.cc

@@ -0,0 +1,111 @@
+/*
+ *
+ * Copyright 2021 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 <cstddef>
+#include <cstdint>
+#include <iostream>
+#include <string>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/strings/str_format.h"
+
+#include <grpcpp/ext/proto_server_reflection_plugin.h>
+#include <grpcpp/grpcpp.h>
+#include <grpcpp/health_check_service_interface.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");
+ABSL_FLAG(size_t, quota, 20, "Resource quota, in megabytes");
+
+namespace {
+
+//
+// Server reactor that is slow to read incoming messages, causing the buffers
+// to fill.
+//
+class SlowReadingBidiReactor final
+    : public grpc::ServerBidiReactor<helloworld::HelloRequest,
+                                     helloworld::HelloReply> {
+ public:
+  SlowReadingBidiReactor() { StartRead(&req_); }
+
+  void OnReadDone(bool ok) override {
+    std::cout << "Recieved request with " << req_.name().length()
+              << " bytes name\n";
+    if (!ok) {
+      Finish(grpc::Status::OK);
+      return;
+    }
+    sleep(1);
+    StartRead(&req_);
+  }
+
+  void OnDone() override {
+    std::cout << "Done\n";
+    delete this;
+  }
+
+ private:
+  absl::Mutex mu_;
+  helloworld::HelloRequest req_;
+};
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public helloworld::Greeter::CallbackService {
+  grpc::ServerBidiReactor<helloworld::HelloRequest, helloworld::HelloReply>*
+  SayHelloBidiStream(grpc::CallbackServerContext* /* context */) override {
+    return new SlowReadingBidiReactor();
+  }
+};
+
+}  // namespace
+
+void RunServer(uint16_t port) {
+  std::string server_address = absl::StrFormat("0.0.0.0:%d", port);
+  GreeterServiceImpl service;
+
+  grpc::EnableDefaultHealthCheckService(true);
+  grpc::reflection::InitProtoReflectionServerBuilderPlugin();
+  grpc::ServerBuilder builder;
+  // Listen on the given address without any authentication mechanism.
+  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
+  // Register "service" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* service.
+  builder.RegisterService(&service);
+  grpc::ResourceQuota quota;
+  quota.Resize(absl::GetFlag(FLAGS_quota) * 1024 * 1024);
+  // Finally assemble the server.
+  auto server = builder.BuildAndStart();
+  std::cout << "Server listening on " << server_address << std::endl;
+
+  // Wait for the server to shutdown. Note that some other thread must be
+  // responsible for shutting down the server for this call to ever return.
+  server->Wait();
+}
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  RunServer(absl::GetFlag(FLAGS_port));
+  return 0;
+}