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

mojo/shell/dbus_service_loader.h

Index: mojo/shell/dbus_service_loader.h
diff --git a/mojo/shell/dbus_service_loader.h b/mojo/shell/dbus_service_loader.h
new file mode 100644
index 0000000000000000000000000000000000000000..bc5464d0c061bc64ae6cc106330f83719fd69e54
--- /dev/null
+++ b/mojo/shell/dbus_service_loader.h
@@ -0,0 +1,90 @@
+// 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.
+
+#ifndef MOJO_SHELL_DBUS_SERVICE_LOADER_H_
+#define MOJO_SHELL_DBUS_SERVICE_LOADER_H_
+
+#include <map>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "mojo/public/cpp/system/core.h"
+#include "mojo/public/interfaces/shell/shell.mojom.h"
+#include "mojo/service_manager/service_loader.h"
+#include "mojo/shell/keep_alive.h"
+#include "url/gurl.h"
+
+namespace dbus {
+class Bus;
+}  // namespace dbus
+
+namespace mojo {
+namespace shell {
+
+class Context;
+
+// An implementation of ServiceLoader that contacts a system service
+// and bootstraps a Mojo connection to it over DBus.
+//
+// In order to allow the externally-running service to accept connections from
+// a Mojo shell, we need to get it a ShellHandle. This class creates a
+// dedicated MessagePipe, passes a handle to one end to the desired service
+// over DBus, and then passes the ShellHandle over that pipe.
+//
+// This class assumes the following:
+// 1) Your service is already running,
+// 2) Your service implements the Mojo ExternalService API
+//    (from external_service.mojom).
+// 3) Your service exports an object that implements the org.chromium.Mojo DBus
+//    interface:
+//    <interface name="org.chromium.Mojo">
+//      <method name="ConnectChannel">
+//        <arg type="h" name="file_descriptor" direction="in" />
+//      </method>
+//    </interface>
+class DBusServiceLoader : public ServiceLoader {
+ public:
+  DBusServiceLoader(Context* context);
+  virtual ~DBusServiceLoader();
+
+  // URL for DBus services are of the following format:
+  // dbus:tld.domain.ServiceName/path/to/DBusObject
+  //
+  // This is simply the scheme (dbus:) and then the DBus service name followed
+  // by the DBus object path of an object that implements the org.chromium.Mojo
+  // interface as discussed above.
+  //
+  // Example:
+  //   dbus:org.chromium.EchoService/org/chromium/MojoImpl
+  //
+  // This will tell DBusServiceLoader to reach out to a service with
+  // the name "org.chromium.EchoService" and invoke the method
+  // "org.chromium.Mojo.ConnectChannel" on the object exported at
+  // "/org/chromium/MojoImpl".
+  virtual void LoadService(ServiceManager* manager,
+                           const GURL& url,
+                           ScopedShellHandle service_handle) OVERRIDE;
+
+  virtual void OnServiceError(ServiceManager* manager, const GURL& url)
+      OVERRIDE;
+
+ private:
+  class LoadContext;
+
+  // Tosses out connection-related state to service at given URL.
+  void ForgetService(const GURL& url);
+
+  Context* const context_;
+  scoped_refptr<dbus::Bus> bus_;
+
+  typedef std::map<GURL, LoadContext*> LoadContextMap;
+  LoadContextMap url_to_load_context_;
+
+  DISALLOW_COPY_AND_ASSIGN(DBusServiceLoader);
+};
+
+}  // namespace shell
+}  // namespace mojo
+
+#endif  // MOJO_SHELL_DBUS_SERVICE_LOADER_H_