[C++ Examples] Add an example for keepalive (#33191)

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doc/keepalive.md

@@ -25,6 +25,8 @@ On the client side, this does not have any effect.
 
 **IMPORTANT NOTE** - For keepalive to work properly and as intended, all of the above channel arguments should be configured appropriately. The client-side keepalive settings should also be in agreement with the server-side settings. If a client sends pings more often than the server is willing to accept, the connection will be terminated with a GOAWAY frame with "too_many_pings" as the debug data. 
 
+Please refer to the [C++ keepalive example](https://github.com/grpc/grpc/tree/master/examples/cpp/keepalive) for a sample way of setting these arguments.
+
 ### Defaults Values
 
 Channel Argument| Client|Server

examples/cpp/keepalive/BUILD

@@ -0,0 +1,41 @@
+# Copyright 2023 the 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.
+
+licenses(["notice"])
+
+cc_binary(
+    name = "greeter_callback_client",
+    srcs = ["greeter_callback_client.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+    ],
+)
+
+cc_binary(
+    name = "greeter_callback_server",
+    srcs = ["greeter_callback_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",
+    ],
+)

examples/cpp/keepalive/CMakeLists.txt

@@ -0,0 +1,70 @@
+# Copyright 2018 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.
+#
+# cmake build file for C++ helloworld example.
+# Assumes protobuf and gRPC have been installed using cmake.
+# See cmake_externalproject/CMakeLists.txt for all-in-one cmake build
+# that automatically builds all the dependencies before building helloworld.
+
+cmake_minimum_required(VERSION 3.8)
+
+project(HelloWorld C CXX)
+
+include(../cmake/common.cmake)
+
+# Proto file
+get_filename_component(hw_proto "../../protos/helloworld.proto" ABSOLUTE)
+get_filename_component(hw_proto_path "${hw_proto}" PATH)
+
+# Generated sources
+set(hw_proto_srcs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.pb.cc")
+set(hw_proto_hdrs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.pb.h")
+set(hw_grpc_srcs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.grpc.pb.cc")
+set(hw_grpc_hdrs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.grpc.pb.h")
+add_custom_command(
+      OUTPUT "${hw_proto_srcs}" "${hw_proto_hdrs}" "${hw_grpc_srcs}" "${hw_grpc_hdrs}"
+      COMMAND ${_PROTOBUF_PROTOC}
+      ARGS --grpc_out "${CMAKE_CURRENT_BINARY_DIR}"
+        --cpp_out "${CMAKE_CURRENT_BINARY_DIR}"
+        -I "${hw_proto_path}"
+        --plugin=protoc-gen-grpc="${_GRPC_CPP_PLUGIN_EXECUTABLE}"
+        "${hw_proto}"
+      DEPENDS "${hw_proto}")
+
+# Include generated *.pb.h files
+include_directories("${CMAKE_CURRENT_BINARY_DIR}")
+
+# hw_grpc_proto
+add_library(hw_grpc_proto
+  ${hw_grpc_srcs}
+  ${hw_grpc_hdrs}
+  ${hw_proto_srcs}
+  ${hw_proto_hdrs})
+target_link_libraries(hw_grpc_proto
+  ${_REFLECTION}
+  ${_GRPC_GRPCPP}
+  ${_PROTOBUF_LIBPROTOBUF})
+
+# Targets greeter_[async_](client|server)
+foreach(_target
+  greeter_callback_client greeter_callback_server
+  add_executable(${_target} "${_target}.cc")
+  target_link_libraries(${_target}
+    hw_grpc_proto
+    absl::flags
+    absl::flags_parse
+    ${_REFLECTION}
+    ${_GRPC_GRPCPP}
+    ${_PROTOBUF_LIBPROTOBUF})
+endforeach()

examples/cpp/keepalive/README.md

@@ -0,0 +1,27 @@
+# gRPC C++ Keepalive Example
+
+The keepalive example builds on the [Hello World Example](https://github.com/grpc/grpc/tree/master/examples/cpp/helloworld) and changes the gRPC client and server to show a sample way of configuring keepalive pings on the client and on the server.
+
+For more information on keepalive pings in gRPC, please refer to -
+* [keepalive guide](https://github.com/grpc/grpc/blob/master/doc/keepalive.md)
+* [A8: Client-side Keepalive](https://github.com/grpc/proposal/blob/master/A8-client-side-keepalive.md)
+* [A9: Server-side Connection Management](https://github.com/grpc/proposal/blob/master/A9-server-side-conn-mgt.md)
+
+## Running the example
+
+To run the server -
+
+```
+$ tools/bazel run examples/cpp/keepalive:greeter_callback_server
+```
+
+To run the client -
+
+```
+$ tools/bazel run examples/cpp/keepalive:greeter_callback_client
+```
+
+You can find a complete set of instructions for building gRPC and running the
+Hello World app in the [C++ Quick Start][].
+
+[C++ Quick Start]: https://grpc.io/docs/languages/cpp/quickstart

examples/cpp/keepalive/greeter_callback_client.cc

@@ -0,0 +1,121 @@
+/*
+ *
+ * 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 <condition_variable>
+#include <iostream>
+#include <memory>
+#include <mutex>
+#include <string>
+#include <thread>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.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::Channel;
+using grpc::ClientContext;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+class GreeterClient {
+ public:
+  GreeterClient(std::shared_ptr<Channel> channel)
+      : stub_(Greeter::NewStub(channel)) {}
+
+  // Assembles the client's payload, sends it and presents the response back
+  // from the server.
+  std::string SayHello(const std::string& user) {
+    // Data we are sending to the server.
+    HelloRequest request;
+    request.set_name(user);
+
+    // Container for the data we expect from the server.
+    HelloReply reply;
+
+    // Context for the client. It could be used to convey extra information to
+    // the server and/or tweak certain RPC behaviors.
+    ClientContext context;
+
+    // The actual RPC.
+    std::mutex mu;
+    std::condition_variable cv;
+    bool done = false;
+    Status status;
+    stub_->async()->SayHello(&context, &request, &reply,
+                             [&mu, &cv, &done, &status](Status s) {
+                               status = std::move(s);
+                               std::lock_guard<std::mutex> lock(mu);
+                               done = true;
+                               cv.notify_one();
+                             });
+
+    std::unique_lock<std::mutex> lock(mu);
+    while (!done) {
+      cv.wait(lock);
+    }
+
+    // Act upon its status.
+    if (status.ok()) {
+      return reply.message();
+    } else {
+      std::cout << status.error_code() << ": " << status.error_message()
+                << std::endl;
+      return "RPC failed";
+    }
+  }
+
+ private:
+  std::unique_ptr<Greeter::Stub> stub_;
+};
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  // Instantiate the client. It requires a channel, out of which the actual RPCs
+  // are created. This channel models a connection to an endpoint specified by
+  // the argument "--target=" which is the only expected argument.
+  std::string target_str = absl::GetFlag(FLAGS_target);
+  grpc::ChannelArguments args;
+  // Sample way of setting keepalive arguments on the client channel. Here we
+  // are configuring a keepalive time period of 20 seconds, with a timeout of 10
+  // seconds. Additionally, pings will be sent even if there are no calls in
+  // flight on an active connection.
+  args.SetInt(GRPC_ARG_KEEPALIVE_TIME_MS, 20 * 1000 /*20 sec*/);
+  args.SetInt(GRPC_ARG_KEEPALIVE_TIMEOUT_MS, 10 * 1000 /*10 sec*/);
+  args.SetInt(GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS, 1);
+  for (auto i = 0; i < 10; ++i) {
+    GreeterClient greeter(grpc::CreateCustomChannel(
+        target_str, grpc::InsecureChannelCredentials(), args));
+    std::string user("world");
+    std::string reply = greeter.SayHello(user);
+    std::cout << "Greeter received: " << reply << std::endl;
+    std::this_thread::sleep_for(std::chrono::seconds(10));
+  }
+
+  return 0;
+}

examples/cpp/keepalive/greeter_callback_server.cc

@@ -0,0 +1,100 @@
+/*
+ *
+ * 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 <iostream>
+#include <memory>
+#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");
+
+using grpc::CallbackServerContext;
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerUnaryReactor;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public Greeter::CallbackService {
+  ServerUnaryReactor* SayHello(CallbackServerContext* context,
+                               const HelloRequest* request,
+                               HelloReply* reply) override {
+    std::string prefix("Hello ");
+    reply->set_message(prefix + request->name());
+
+    ServerUnaryReactor* reactor = context->DefaultReactor();
+    reactor->Finish(Status::OK);
+    return reactor;
+  }
+};
+
+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();
+  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);
+  // Sample way of setting keepalive arguments on the server. Here, we are
+  // configuring the server to send keepalive pings at a period of 10 minutes
+  // with a timeout of 20 seconds. Additionally, pings will be sent even if
+  // there are no calls in flight on an active HTTP2 connection. When receiving
+  // pings, the server will permit pings at an interval of 10 seconds.
+  builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIME_MS,
+                             10 * 60 * 1000 /*10 min*/);
+  builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIMEOUT_MS,
+                             20 * 1000 /*20 sec*/);
+  builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS, 1);
+  builder.AddChannelArgument(
+      GRPC_ARG_HTTP2_MIN_RECV_PING_INTERVAL_WITHOUT_DATA_MS,
+      10 * 1000 /*10 sec*/);
+  // Finally assemble the server.
+  std::unique_ptr<Server> 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;
+}