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

mojo/shell/dbus_service_loader_linux.cc

Index: mojo/shell/dbus_service_loader_linux.cc
diff --git a/mojo/shell/dbus_service_loader_linux.cc b/mojo/shell/dbus_service_loader_linux.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a476d251b32242eba435247a30dc763b5655e2da
--- /dev/null
+++ b/mojo/shell/dbus_service_loader_linux.cc
@@ -0,0 +1,185 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/shell/dbus_service_loader_linux.h"
+
+#include <string>
+
+#include "base/command_line.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/task_runner_util.h"
+#include "base/threading/thread_restrictions.h"
+#include "dbus/bus.h"
+#include "dbus/file_descriptor.h"
+#include "dbus/message.h"
+#include "dbus/object_path.h"
+#include "dbus/object_proxy.h"
+#include "mojo/common/channel_init.h"
+#include "mojo/embedder/platform_channel_pair.h"
+#include "mojo/public/cpp/bindings/allocation_scope.h"
+#include "mojo/public/cpp/bindings/interface.h"
+#include "mojo/public/cpp/bindings/remote_ptr.h"
+#include "mojo/shell/context.h"
+#include "mojo/shell/external_service.mojom.h"
+#include "mojo/shell/keep_alive.h"
+
+namespace mojo {
+namespace shell {
+
+// Manages the connection to a single externally-running service.
+class DBusServiceLoader::LoadContext : public mojo::ExternalServiceHost {
+ public:
+  // Kicks off the attempt to bootstrap a connection to the externally-running
+  // service specified by url_.
+  // Creates a MessagePipe and passes one end over DBus to the service. Then,
+  // calls ExternalService::Activate(ShellHandle) over the now-shared pipe.
+  LoadContext(DBusServiceLoader* loader,
+              const scoped_refptr<dbus::Bus>& bus,
+              const GURL& url,
+              ScopedShellHandle shell_handle)
+      : loader_(loader),
+        bus_(bus),
+        service_dbus_proxy_(NULL),
+        url_(url),
+        shell_handle_(shell_handle.Pass()),
+        keep_alive_(loader->context_) {
+    base::PostTaskAndReplyWithResult(
+        loader_->context_->task_runners()->io_runner(),
+        FROM_HERE,
+        base::Bind(&LoadContext::CreateChannelOnIOThread,
+                   base::Unretained(this)),
+        base::Bind(&LoadContext::ConnectChannel, base::Unretained(this)));
+  }
+
+  virtual ~LoadContext() {
+  }
+
+ private:
+  // Sets up a pipe to share with the externally-running service and returns
+  // the endpoint that should be sent over DBus.
+  // The FD for the endpoint must be validated on an IO thread.
+  scoped_ptr<dbus::FileDescriptor> CreateChannelOnIOThread() {
+    base::ThreadRestrictions::AssertIOAllowed();
+    CHECK(bus_->Connect());
+    CHECK(bus_->SetUpAsyncOperations());
+
+    embedder::PlatformChannelPair channel_pair;
+    channel_init_.reset(new common::ChannelInit);
+    mojo::ScopedMessagePipeHandle bootstrap_message_pipe =
+        channel_init_->Init(channel_pair.PassServerHandle().release().fd,
+                            loader_->context_->task_runners()->io_runner());
+    CHECK(bootstrap_message_pipe.is_valid());
+
+    external_service_.reset(
+        mojo::ScopedExternalServiceHandle::From(bootstrap_message_pipe.Pass()),
+        this);
+
+    scoped_ptr<dbus::FileDescriptor> client_fd(new dbus::FileDescriptor);
+    client_fd->PutValue(channel_pair.PassClientHandle().release().fd);
+    client_fd->CheckValidity();  // Must be run on an IO thread.
+    return client_fd.Pass();
+  }
+
+  // Sends client_fd over to the externally-running service. If that
+  // attempt is successful, the service will then be "activated" by
+  // sending it a ShellHandle.
+  void ConnectChannel(scoped_ptr<dbus::FileDescriptor> client_fd) {
+    size_t first_slash = url_.path().find_first_of('/');
+    DCHECK_NE(first_slash, std::string::npos);
+
+    const std::string service_name = url_.path().substr(0, first_slash);
+    const std::string object_path =  url_.path().substr(first_slash);
+    service_dbus_proxy_ =
+        bus_->GetObjectProxy(service_name, dbus::ObjectPath(object_path));
+
+    dbus::MethodCall call("org.chromium.Mojo", "ConnectChannel");
+    dbus::MessageWriter writer(&call);
+    writer.AppendFileDescriptor(*client_fd.get());
+
+    // TODO(cmasone): handle errors!
+    service_dbus_proxy_->CallMethod(
+        &call,
+        dbus::ObjectProxy::TIMEOUT_USE_DEFAULT,
+        base::Bind(&LoadContext::ActivateService, base::Unretained(this)));
+  }
+
+  // Sends a ShellHandle over to the now-connected externally-running service,
+  // using the Mojo ExternalService API.
+  void ActivateService(dbus::Response* response) {
+    mojo::AllocationScope scope;
+    external_service_->Activate(
+        mojo::ScopedMessagePipeHandle(
+            mojo::MessagePipeHandle(shell_handle_.release().value())));
+  }
+
+  // Should the ExternalService disappear completely, destroy connection state.
+  // NB: This triggers off of the service disappearing from
+  // DBus. Perhaps there's a way to watch at the Mojo layer instead,
+  // and that would be superior?
+  void HandleNameOwnerChanged(const std::string& old_owner,
+                              const std::string& new_owner) {
+    DCHECK(loader_->context_->task_runners()->ui_runner()->
+           BelongsToCurrentThread());
+
+    if (new_owner.empty()) {
+      loader_->context_->task_runners()->ui_runner()->PostTask(
+          FROM_HERE,
+          base::Bind(&DBusServiceLoader::ForgetService,
+                     base::Unretained(loader_), url_));
+    }
+  }
+
+  DBusServiceLoader* const loader_;
+  scoped_refptr<dbus::Bus> bus_;
+  dbus::ObjectProxy* service_dbus_proxy_;  // Owned by bus_;
+  const GURL url_;
+  ScopedShellHandle shell_handle_;
+  KeepAlive keep_alive_;
+  scoped_ptr<common::ChannelInit> channel_init_;
+  mojo::RemotePtr<mojo::ExternalService> external_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoadContext);
+};
+
+DBusServiceLoader::DBusServiceLoader(Context* context) : context_(context) {
+  dbus::Bus::Options options;
+  options.bus_type = dbus::Bus::SESSION;
+  options.dbus_task_runner = context_->task_runners()->io_runner();
+  bus_ = new dbus::Bus(options);
+}
+
+DBusServiceLoader::~DBusServiceLoader() {
+  DCHECK(url_to_load_context_.empty());
+}
+
+void DBusServiceLoader::LoadService(ServiceManager* manager,
+                                    const GURL& url,
+                                    ScopedShellHandle service_handle) {
+  DCHECK(url.SchemeIs("dbus"));
+  DCHECK(url_to_load_context_.find(url) == url_to_load_context_.end());
+  url_to_load_context_[url] =
+      new LoadContext(this, bus_, url, service_handle.Pass());
+}
+
+void DBusServiceLoader::OnServiceError(ServiceManager* manager,
+                                       const GURL& url) {
+  // TODO(cmasone): Anything at all in this method here.
+}
+
+void DBusServiceLoader::ForgetService(const GURL& url) {
+  DCHECK(context_->task_runners()->ui_runner()->BelongsToCurrentThread());
+  DVLOG(2) << "Forgetting service (url: " << url << ")";
+
+  LoadContextMap::iterator it = url_to_load_context_.find(url);
+  DCHECK(it != url_to_load_context_.end()) << url;
+
+  LoadContext* doomed = it->second;
+  url_to_load_context_.erase(it);
+
+  delete doomed;
+}
+
+}  // namespace shell
+}  // namespace mojo