Add a simple network client / server example

Issue: #77

CMakeLists.txt

@@ -286,5 +286,6 @@ if(CPPDAP_BUILD_EXAMPLES)
     endfunction(build_example)
 
     build_example(hello_debugger)
+    build_example(simple_net_client_server)
 
 endif(CPPDAP_BUILD_EXAMPLES)

examples/simple_net_client_server.cpp

@@ -0,0 +1,104 @@
+// Copyright 2022 Google LLC
+//
+// 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
+//
+//     https://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.
+
+// simple_net_client_server demonstrates a minimal DAP network connection
+// between a server and client.
+
+#include "dap/io.h"
+#include "dap/network.h"
+#include "dap/protocol.h"
+#include "dap/session.h"
+
+#include <condition_variable>
+#include <mutex>
+
+int main(int, char*[]) {
+  constexpr int kPort = 19021;
+
+  // Callback handler for a socket connection to the server
+  auto onClientConnected =
+      [&](const std::shared_ptr<dap::ReaderWriter>& socket) {
+        auto session = dap::Session::create();
+        session->bind(socket);
+
+        // The Initialize request is the first message sent from the client and
+        // the response reports debugger capabilities.
+        // https://microsoft.github.io/debug-adapter-protocol/specification#Requests_Initialize
+        session->registerHandler([&](const dap::InitializeRequest&) {
+          dap::InitializeResponse response;
+          printf("Server received initialize request from client\n");
+          return response;
+        });
+
+        // Signal used to terminate the server session when a DisconnectRequest
+        // is made by the client.
+        bool terminate = false;
+        std::condition_variable cv;
+        std::mutex mutex;  // guards 'terminate'
+
+        // The Disconnect request is made by the client before it disconnects
+        // from the server.
+        // https://microsoft.github.io/debug-adapter-protocol/specification#Requests_Disconnect
+        session->registerHandler([&](const dap::DisconnectRequest&) {
+          // Client wants to disconnect. Set terminate to true, and signal the
+          // condition variable to unblock the server thread.
+          std::unique_lock<std::mutex> lock(mutex);
+          terminate = true;
+          cv.notify_one();
+          return dap::DisconnectResponse{};
+        });
+
+        // Wait for the client to disconnect (or reach a 5 second timeout)
+        // before releasing the session and disconnecting the socket to the
+        // client.
+        std::unique_lock<std::mutex> lock(mutex);
+        cv.wait_for(lock, std::chrono::seconds(5), [&] { return terminate; });
+        printf("Server closing connection\n");
+      };
+
+  // Error handler
+  auto onError = [&](const char* msg) { printf("Server error: %s\n", msg); };
+
+  // Create the network server
+  auto server = dap::net::Server::create();
+  // Start listening on kPort.
+  // onClientConnected will be called when a client wants to connect.
+  // onError will be called on any connection errors.
+  server->start(kPort, onClientConnected, onError);
+
+  // Create a socket to the server. This will be used for the client side of the
+  // connection.
+  auto client = dap::net::connect("localhost", kPort);
+  if (!client) {
+    printf("Couldn't connect to server\n");
+    return 1;
+  }
+
+  // Attach a session to the client socket.
+  auto session = dap::Session::create();
+  session->bind(client);
+
+  // Set an initialize request to the server.
+  auto future = session->send(dap::InitializeRequest{});
+  printf("Client sent initialize request to server\n");
+  printf("Waiting for response from server...\n");
+  // Wait on the response.
+  auto response = future.get();
+  printf("Response received from server\n");
+  printf("Disconnecting...\n");
+  // Disconnect.
+  session->send(dap::DisconnectRequest{});
+
+  return 0;
+}