Implement a trivial Mojo EchoService that can be connected to over DBus

mojo/services/dbus_echo/dbus_echo_service.cc

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.

[viettrungluu, 2014/04/23 20:07:24]

Nit: There's no "(c)" in the current copyright notice.

[Chris Masone, 2014/04/23 22:31:00]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/at_exit.h"
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/message_loop/message_loop.h"
+#include "base/message_loop/message_loop_proxy.h"
+#include "base/run_loop.h"
+#include "dbus/bus.h"
+#include "dbus/exported_object.h"
+#include "dbus/file_descriptor.h"
+#include "dbus/message.h"
+#include "dbus/object_path.h"
+#include "mojo/common/mojo_channel_init.h"
+#include "mojo/embedder/embedder.h"
+#include "mojo/public/cpp/bindings/interface.h"
+#include "mojo/public/cpp/bindings/remote_ptr.h"
+#include "mojo/public/cpp/environment/environment.h"
+#include "mojo/public/cpp/shell/application.h"
+#include "mojo/public/interfaces/shell/shell.mojom.h"
+#include "mojo/services/dbus_echo/echo.mojom.h"
+#include "mojo/shell/external_service.mojom.h"
+
+class EchoServiceImpl : public mojo::ServiceConnection<mojo::EchoService,
+                                                       EchoServiceImpl> {
+ public:
+  EchoServiceImpl() {}
+  virtual ~EchoServiceImpl() {}
+
+ protected:
+  virtual void Echo(
+      const mojo::String& in_to_echo,
+      const mojo::Callback<void(mojo::String)>& callback) OVERRIDE {
+    DVLOG(1) << "Asked to echo " << in_to_echo.To<std::string>();
+    callback.Run(in_to_echo);
+  }
+};
+
+
+class DBusEchoService : public mojo::ExternalService {
+ public:
+  static const char kMojoImplPath[];
+  static const char kMojoInterface[];
+  static const char kServiceName[];
+
+  DBusEchoService() : exported_object_(NULL) {
+  }
+  ~DBusEchoService() {}
+
+  void Start() {
+    InitializeDBus();
+    ExportMethods();
+    TakeDBusServiceOwnership();
+    DVLOG(1) << "Echo service started";
+  }
+
+ private:
+  // TODO(cmasone): Use a Delegate pattern to allow the ConnectChannel
+  // code to be shared among all Mojo services that wish to be
+  // connected to over DBus.
+  virtual void Activate(mojo::ScopedMessagePipeHandle client_handle) OVERRIDE {
+    mojo::ScopedShellHandle shell_handle(
+        mojo::ShellHandle(client_handle.release().value()));
+    app_.reset(new mojo::Application(shell_handle.Pass()));
+    app_->AddServiceConnector(new mojo::ServiceConnector<EchoServiceImpl>());
+  }
+
+  // Implementation of org.chromium.Mojo.ConnectChannel, exported over DBus.
+  // Takes a file descriptor and uses it to create a MessagePipe that is then
+  // hooked to a RemotePtr<mojo::ExternalServiceHost>.
+  void ConnectChannel(dbus::MethodCall* method_call,
+                      dbus::ExportedObject::ResponseSender sender) {
+    dbus::MessageReader reader(method_call);
+    dbus::FileDescriptor wrapped_fd;
+    if (!reader.PopFileDescriptor(&wrapped_fd)) {
+      sender.Run(
+          dbus::ErrorResponse::FromMethodCall(
+              method_call,
+              "org.chromium.Mojo.BadHandle",
+              "Invalid FD.").PassAs<dbus::Response>());
+      return;
+    }
+    wrapped_fd.CheckValidity();
+    channel_init_.reset(new mojo::common::MojoChannelInit);
+    channel_init_->Init(wrapped_fd.TakeValue(),
+                        base::MessageLoopProxy::current());
+    CHECK(channel_init_->is_handle_valid());
+
+    // TODO(cmasone): Figure out how to correctly clean up the channel when
+    // the peer disappears. Passing an ErrorHandler when constructing the
+    // RemotePtr<> below didn't seem to work. OnError wasn't called.
+    mojo::ScopedExternalServiceHostHandle client_handle(
+        mojo::ExternalServiceHostHandle(
+            channel_init_->bootstrap_message_pipe().release().value()));
+    external_service_host_.reset(client_handle.Pass(), this);
+
+    sender.Run(dbus::Response::FromMethodCall(method_call));
+  }
+
+  void ExportMethods() {
+    CHECK(exported_object_);
+    CHECK(exported_object_->ExportMethodAndBlock(
+        kMojoInterface, "ConnectChannel",
+        base::Bind(&DBusEchoService::ConnectChannel,
+                   base::Unretained(this))));
+  }
+
+  void InitializeDBus() {
+    CHECK(!bus_);
+    dbus::Bus::Options options;
+    options.bus_type = dbus::Bus::SESSION;
+    bus_ = new dbus::Bus(options);
+    CHECK(bus_->Connect());
+    CHECK(bus_->SetUpAsyncOperations());
+
+    exported_object_ = bus_->GetExportedObject(dbus::ObjectPath(kMojoImplPath));
+  }
+
+  void TakeDBusServiceOwnership() {
+    CHECK(bus_->RequestOwnershipAndBlock(
+        kServiceName,
+        dbus::Bus::REQUIRE_PRIMARY_ALLOW_REPLACEMENT))
+        << "Unable to take ownership of " << kServiceName;
+  }
+
+  scoped_refptr<dbus::Bus> bus_;
+  dbus::ExportedObject* exported_object_;  // Owned by bus_;
+  scoped_ptr<mojo::common::MojoChannelInit> channel_init_;
+  mojo::RemotePtr<mojo::ExternalServiceHost> external_service_host_;
+  scoped_ptr<mojo::Application> app_;
+};
+
+// TODO(cmasone): Figure out where these "well-known" names should be defined
+// so they can be shared with DBusServiceLoader and such.
+const char DBusEchoService::kMojoImplPath[] = "/org/chromium/MojoImpl";
+const char DBusEchoService::kMojoInterface[] = "org.chromium.Mojo";
+const char DBusEchoService::kServiceName[] = "org.chromium.EchoService";
+
+int main(int argc, char** argv) {
+  base::AtExitManager exit_manager;
+  CommandLine::Init(argc, argv);
+
+  logging::LoggingSettings settings;
+  settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
+  logging::InitLogging(settings);
+  logging::SetLogItems(false,    // Process ID
+                       false,    // Thread ID
+                       false,    // Timestamp
+                       false);   // Tick count
+
+  mojo::Environment env;
+  mojo::embedder::Init();
+
+  base::MessageLoopForIO message_loop;
+  base::RunLoop run_loop;
+
+  DBusEchoService echo_service;
+  echo_service.Start();
+
+  run_loop.Run();
+}

[viettrungluu, 2014/04/23 20:07:24]

nit: Presumably, this never actually quits, and the C++ standard actually carves
out a special rule for main() (defining the return value of main() to be 0 if
there's no return), but I hate this special rule.

[Chris Masone, 2014/04/23 22:31:00]

Done.