implement gRPC demo

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.20)
+
+project(gRPCTest C CXX)
+
+# Options to build certain parts of the application
+option(BUILD_CLIENT "Build the gRPC client." ON)
+option(BUILD_SERVER "Build the gRPC server." ON)
+
+# If you do not have gRPC isntalled through a package manager, you can set the custom install location here
+# so CMake can find the libraries
+set(GRPC_INSTALL_LOCATION "" CACHE PATH "Custom gRPC installation location.")
+cmake_path(ABSOLUTE_PATH GRPC_INSTALL_LOCATION)
+
+# set required C++ version
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")
+add_compile_options(-Wall
+        -Wextra
+        -Wconversion-null
+        -Wmissing-declarations
+        -Woverlength-strings)
+add_compile_options(
+        -Wpointer-arith
+        -Wunused-local-typedefs
+        -Wunused-result
+        -Wvarargs
+        -Wvla
+        -Wwrite-strings
+        -Wformat-security
+        -Wundef)
+add_compile_options(-O2)
+
+# Find the protoc protobuffer compiler
+find_program(_PROTOBUF_PROTOC protoc)
+
+# Find the required gRPC libraries
+# Since we have the option to link dynamically, we have to be explicit
+find_library(
+    _PROTOBUF_LIBPROTOBUF 
+    protobuf 
+    HINTS ${GRPC_INSTALL_LOCATION}/lib/
+    REQUIRED
+)
+find_library(
+    _GRPC_GRPCPP_REFLECTION
+    grpc++_reflection
+    HINTS ${GRPC_INSTALL_LOCATION}/lib/
+    REQUIRED
+)
+find_library(
+    _GRPC_GRPCPP
+    grpc++
+    HINTS ${GRPC_INSTALL_LOCATION}/lib/
+    REQUIRED
+)
+find_library(
+    _GRPC_GRPC
+    grpc
+    HINTS ${GRPC_INSTALL_LOCATION}/lib/
+    REQUIRED
+)
+find_library(
+    _GRPC_GPR
+    gpr
+    HINTS ${GRPC_INSTALL_LOCATION}/lib/
+    REQUIRED
+)
+
+# Configure the location of the gRPC protoc plugin
+find_program(_GRPC_CPP_PLUGIN_EXECUTABLE grpc_cpp_plugin)
+
+# gRPC uses the Abseil package
+find_package(absl REQUIRED)
+
+# Include the protobuffers
+add_subdirectory(buffers)
+
+# Include the client
+if(BUILD_CLIENT)
+    add_subdirectory(client)
+endif(BUILD_CLIENT)
+
+# Include the controller server
+if(BUILD_SERVER)
+    add_subdirectory(controller)
+endif(BUILD_SERVER)

buffers/CMakeLists.txt

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+# Generate the source files from the protobuf files.
+# These will be bundled into a statically linked library and
+# linked into the applications.
+
+# library name
+set(PROTOBUFFER_LIB "grpc_proto_buffers")
+set(PROTOBUFFER_LIB ${PROTOBUFFER_LIB} PARENT_SCOPE)
+
+# protoc needs the folder in which all the buffer files reside 
+# in case there is an import
+set(protobuf_src_folder ".")
+cmake_path(ABSOLUTE_PATH protobuf_src_folder)
+
+# Grab all the protobuffer files
+file(
+    GLOB BUFFER_SRCS
+    "*.proto"
+)
+
+# Initialize the lists of generated files
+set(proto_srcs)
+set(proto_hdrs)
+set(grpc_srcs)
+set(grpc_hdrs)
+
+# Generate all headers and buffer sources
+foreach(buffer_src ${BUFFER_SRCS})
+    # Get the name stem of the file
+    cmake_path(GET buffer_src STEM buffer_name)
+    
+    # Set the names for all generated files
+    set(buffer_proto_src "${CMAKE_CURRENT_BINARY_DIR}/${buffer_name}.pb.cc")
+    set(buffer_proto_hdr "${CMAKE_CURRENT_BINARY_DIR}/${buffer_name}.pb.h")
+    set(buffer_grpc_src "${CMAKE_CURRENT_BINARY_DIR}/${buffer_name}.grpc.pb.cc")
+    set(buffer_grpc_hdr "${CMAKE_CURRENT_BINARY_DIR}/${buffer_name}.grpc.pb.h")
+
+    # Generate
+    add_custom_command(
+        OUTPUT "${buffer_proto_src}" "${buffer_proto_hdr}" "${buffer_grpc_src}" "${buffer_grpc_hdr}"
+        COMMAND ${_PROTOBUF_PROTOC}
+        ARGS    --grpc_out "${CMAKE_CURRENT_BINARY_DIR}"
+                --cpp_out "${CMAKE_CURRENT_BINARY_DIR}"
+                -I "${protobuf_src_folder}"
+                --plugin=protoc-gen-grpc="${_GRPC_CPP_PLUGIN_EXECUTABLE}"
+                "${buffer_src}"
+        DEPENDS "${buffer_src}"
+    )
+
+    # Add the files to the list of generated files
+    list(APPEND proto_srcs ${buffer_proto_src})
+    list(APPEND proto_hdrs ${buffer_proto_hdr})
+    list(APPEND grpc_srcs ${buffer_grpc_src})
+    list(APPEND grpc_hdrs ${buffer_grpc_hdr})
+endforeach(buffer_src)
+
+# Include the generated headers
+include_directories(${CMAKE_CURRENT_BINARY_DIR})
+
+# Build the library
+add_library(
+    ${PROTOBUFFER_LIB}
+    ${proto_srcs}
+    ${proto_hdrs}
+    ${grpc_srcs}
+    ${grpc_hdrs}
+)
+
+target_link_libraries(
+    ${PROTOBUFFER_LIB}
+    absl::check
+    ${_GRPC_GRPCPP_REFLECTION}
+    ${_GRPC_GRPCPP}
+    ${_PROTOBUF_LIBPROTOBUF}
+)
+
+# Make the headers available to other parts of the program
+set(PROTOBUFFER_HDRS_DIR "${CMAKE_CURRENT_BINARY_DIR}" PARENT_SCOPE)

buffers/hello_world.proto

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+service Greeter {
+    rpc SayHello (HelloRequest) returns (HelloReply);
+}
+
+message HelloRequest {
+    required string name = 1;
+}
+
+message HelloReply {
+    required string message = 1;
+}

client/CMakeLists.txt

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+
+# Include the headers generated by the protobuffers
+include_directories(${PROTOBUFFER_HDRS_DIR}/)
+
+file(
+    GLOB CLIENT_SRCS
+    "*.cpp"
+)
+
+# Add the main executable
+add_executable(
+    ${PROJECT_NAME}
+    ${CLIENT_SRCS}
+)
+
+target_link_libraries(${PROJECT_NAME}
+    ${PROTOBUFFER_LIB}
+    absl::check
+    absl::flags
+    absl::flags_parse
+    absl::log
+    ${_GRPC_GRPC}
+    ${_GRPC_GRPCPP}
+    ${_GRPC_GRPCPP_REFLECTION}
+    ${_PROTOBUF_LIBPROTOBUF}
+    ${_GRPC_GPR}
+)

client/greeter_client.cpp

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+/*
+ *
+ * Copyright 2015 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 "hello_world.pb.h"
+
+#include <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "hello_world.grpc.pb.h"
+#endif
+
+ABSL_FLAG(std::string, target, "localhost:50051", "Server address");
+
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Status;
+
+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.
+    Status status = stub_->SayHello(&context, request, &reply);
+
+    // 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);
+  // We indicate that the channel isn't authenticated (use of
+  // InsecureChannelCredentials()).
+  GreeterClient greeter(
+      grpc::CreateChannel(target_str, grpc::InsecureChannelCredentials()));
+  std::string user("world");
+  std::string reply = greeter.SayHello(user);
+  std::cout << "Greeter received: " << reply << std::endl;
+
+  return 0;
+}

controller/CMakeLists.txt

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+
+# Include the headers generated by the protobuffers
+include_directories(${PROTOBUFFER_HDRS_DIR})
+
+file(
+    GLOB CONTROLLER_SRCS
+    "*.cpp"
+)
+
+
+# Add the main executable
+add_executable(
+    ${PROJECT_NAME}_controller
+    ${CONTROLLER_SRCS}
+)
+
+target_link_libraries(${PROJECT_NAME}_controller
+    ${PROTOBUFFER_LIB}
+    absl::check
+    absl::flags
+    absl::flags_parse
+    absl::log
+    ${_GRPC_GRPC}
+    ${_GRPC_GRPCPP}
+    ${_GRPC_GRPCPP_REFLECTION}
+    ${_PROTOBUF_LIBPROTOBUF}
+    ${_GRPC_GPR}
+)

controller/greeter_server.cpp

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+/*
+ *
+ * Copyright 2015 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 "hello_world.pb.h"
+
+#include <grpcpp/server_context.h>
+#include <grpcpp/support/server_callback.h>
+#include <grpcpp/support/status.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 "hello_world.grpc.pb.h"
+#endif
+
+void RunServer(uint16_t port);
+
+using grpc::Server;
+using grpc::ServerBuilder;
+
+ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");
+
+// This is the implementation of the actual service;
+// We elect to implement this as a callback server (preferred implementation)
+class GreeterServiceImpl final : public Greeter::CallbackService {
+
+public:
+  // We only reply with a single message back, thus we use a unary reactor
+  grpc::ServerUnaryReactor *
+  SayHello([[maybe_unused]] grpc::CallbackServerContext *context,
+           const HelloRequest *request, HelloReply *reply) override {
+
+    // To be able to handle more fancy things, we elect to implement our own
+    // reactor
+    class HelloReactor : public grpc::ServerUnaryReactor {
+    public:
+      HelloReactor(const HelloRequest &request, const std::string &prefix,
+                   HelloReply *reply) {
+        reply->set_message(prefix + request.name());
+        Finish(grpc::Status::OK);
+      }
+
+    private:
+      void OnDone() override {
+        std::cout << "RPC completed." << std::endl;
+        delete this;
+      }
+
+      void OnCancel() override { std::cerr << "RPC cancelled." << std::endl; }
+    };
+
+    return new HelloReactor(*request, "Hello ", reply);
+  }
+};
+
+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);
+  // 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;
+}