bus.h

// Copyright (c) 2012 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 DBUS_BUS_H_
#define DBUS_BUS_H_

#include <dbus/dbus.h>
#include <stdint.h>

#include <map>
#include <set>
#include <string>
#include <utility>
#include <vector>

#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/waitable_event.h"
#include "base/threading/platform_thread.h"
#include "dbus/dbus_export.h"
#include "dbus/object_path.h"

namespace base {
class SequencedTaskRunner;
class TaskRunner;
}

namespace dbus {

class ExportedObject;
class ObjectManager;
class ObjectProxy;

// Bus is used to establish a connection with D-Bus, create object
// proxies, and export objects.
//
// For asynchronous operations such as an asynchronous method call, the
// bus object will use a task runner to monitor the underlying file
// descriptor used for D-Bus communication. By default, the bus will use
// the current thread's task runner. If |dbus_task_runner| option is
// specified, the bus will use that task runner instead.
//
// THREADING
//
// In the D-Bus library, we use the two threads:
//
// - The origin thread: the thread that created the Bus object.
// - The D-Bus thread: the thread servicing |dbus_task_runner|.
//
// The origin thread is usually Chrome's UI thread. The D-Bus thread is
// usually a dedicated thread for the D-Bus library.
//
// BLOCKING CALLS
//
// Functions that issue blocking calls are marked "BLOCKING CALL" and
// these functions should be called in the D-Bus thread (if
// supplied). AssertOnDBusThread() is placed in these functions.
//
// Note that it's hard to tell if a libdbus function is actually blocking
// or not (ex. dbus_bus_request_name() internally calls
// dbus_connection_send_with_reply_and_block(), which is a blocking
// call). To err on the safe side, we consider all libdbus functions that
// deal with the connection to dbus-daemon to be blocking.
//
// SHUTDOWN
//
// The Bus object must be shut down manually by ShutdownAndBlock() and
// friends. We require the manual shutdown to make the operation explicit
// rather than doing it silently in the destructor.
//
// EXAMPLE USAGE:
//
// Synchronous method call:
//
//   dbus::Bus::Options options;
//   // Set up the bus options here.
//   ...
//   dbus::Bus bus(options);
//
//   dbus::ObjectProxy* object_proxy =
//       bus.GetObjectProxy(service_name, object_path);
//
//   dbus::MethodCall method_call(interface_name, method_name);
//   std::unique_ptr<dbus::Response> response(
//       object_proxy.CallMethodAndBlock(&method_call, timeout_ms));
//   if (response.get() != nullptr) {  // Success.
//     ...
//   }
//
// Asynchronous method call:
//
//   void OnResponse(dbus::Response* response) {
//     // response is NULL if the method call failed.
//     if (!response)
//       return;
//   }
//
//   ...
//   object_proxy.CallMethod(&method_call, timeout_ms,
//                           base::Bind(&OnResponse));
//
// Exporting a method:
//
//   void Echo(dbus::MethodCall* method_call,
//             dbus::ExportedObject::ResponseSender response_sender) {
//     // Do something with method_call.
//     Response* response = Response::FromMethodCall(method_call);
//     // Build response here.
//     // Can send an immediate response here to implement a synchronous service
//     // or store the response_sender and send a response later to implement an
//     // asynchronous service.
//     response_sender.Run(response);
//   }
//
//   void OnExported(const std::string& interface_name,
//                   const ObjectPath& object_path,
//                   bool success) {
//     // success is true if the method was exported successfully.
//   }
//
//   ...
//   dbus::ExportedObject* exported_object =
//       bus.GetExportedObject(service_name, object_path);
//   exported_object.ExportMethod(interface_name, method_name,
//                                base::Bind(&Echo),
//                                base::Bind(&OnExported));
//
// WHY IS THIS A REF COUNTED OBJECT?
//
// Bus is a ref counted object, to ensure that |this| of the object is
// alive when callbacks referencing |this| are called. However, after the
// bus is shut down, |connection_| can be NULL. Hence, callbacks should
// not rely on that |connection_| is alive.
class CHROME_DBUS_EXPORT Bus : public base::RefCountedThreadSafe<Bus> {
 public:
  // Specifies the bus type. SESSION is used to communicate with per-user
  // services like GNOME applications. SYSTEM is used to communicate with
  // system-wide services like NetworkManager. CUSTOM_ADDRESS is used to
  // communicate with an user specified address.
  enum BusType {
    SESSION = DBUS_BUS_SESSION,
    SYSTEM = DBUS_BUS_SYSTEM,
    CUSTOM_ADDRESS,
  };

  // Specifies the connection type. PRIVATE should usually be used unless
  // you are sure that SHARED is safe for you, which is unlikely the case
  // in Chrome.
  //
  // PRIVATE gives you a private connection, that won't be shared with
  // other Bus objects.
  //
  // SHARED gives you a connection shared among other Bus objects, which
  // is unsafe if the connection is shared with multiple threads.
  enum ConnectionType {
    PRIVATE,
    SHARED,
  };

  // Specifies whether the GetServiceOwnerAndBlock call should report or
  // suppress errors.
  enum GetServiceOwnerOption {
    REPORT_ERRORS,
    SUPPRESS_ERRORS,
  };

  // Specifies service ownership options.
  //
  // REQUIRE_PRIMARY indicates that you require primary ownership of the
  // service name.
  //
  // ALLOW_REPLACEMENT indicates that you'll allow another connection to
  // steal ownership of this service name from you.
  //
  // REQUIRE_PRIMARY_ALLOW_REPLACEMENT does the obvious.
  enum ServiceOwnershipOptions {
    REQUIRE_PRIMARY = (DBUS_NAME_FLAG_DO_NOT_QUEUE |
                       DBUS_NAME_FLAG_REPLACE_EXISTING),
    REQUIRE_PRIMARY_ALLOW_REPLACEMENT = (REQUIRE_PRIMARY |
                                         DBUS_NAME_FLAG_ALLOW_REPLACEMENT),
  };

  // Options used to create a Bus object.
  struct CHROME_DBUS_EXPORT Options {
    Options();
    ~Options();

    BusType bus_type;  // SESSION by default.
    ConnectionType connection_type;  // PRIVATE by default.
    // If dbus_task_runner is set, the bus object will use that
    // task runner to process asynchronous operations.
    //
    // The thread servicing the task runner should meet the following
    // requirements:
    // 1) Already running.
    // 2) Has a MessageLoopForIO.
    scoped_refptr<base::SequencedTaskRunner> dbus_task_runner;

    // Specifies the server addresses to be connected. If you want to
    // communicate with non dbus-daemon such as ibus-daemon, set |bus_type| to
    // CUSTOM_ADDRESS, and |address| to the D-Bus server address you want to
    // connect to. The format of this address value is the dbus address style
    // which is described in
    // http://dbus.freedesktop.org/doc/dbus-specification.html#addresses
    //
    // EXAMPLE USAGE:
    //   dbus::Bus::Options options;
    //   options.bus_type = CUSTOM_ADDRESS;
    //   options.address.assign("unix:path=/tmp/dbus-XXXXXXX");
    //   // Set up other options
    //   dbus::Bus bus(options);
    //
    //   // Do something.
    //
    std::string address;
  };

  // Creates a Bus object. The actual connection will be established when
  // Connect() is called.
  explicit Bus(const Options& options);

  // Called when an ownership request is complete.
  // Parameters:
  // - the requested service name.
  // - whether ownership has been obtained or not.
  typedef base::Callback<void (const std::string&, bool)> OnOwnershipCallback;

  // Called when GetServiceOwner() completes.
  // |service_owner| is the return value from GetServiceOwnerAndBlock().
  typedef base::Callback<void (const std::string& service_owner)>
      GetServiceOwnerCallback;

  // TODO(satorux): Remove the service name parameter as the caller of
  // RequestOwnership() knows the service name.

  // Gets the object proxy for the given service name and the object path.
  // The caller must not delete the returned object.
  //
  // Returns an existing object proxy if the bus object already owns the
  // object proxy for the given service name and the object path.
  // Never returns NULL.
  //
  // The bus will own all object proxies created by the bus, to ensure
  // that the object proxies are detached from remote objects at the
  // shutdown time of the bus.
  //
  // The object proxy is used to call methods of remote objects, and
  // receive signals from them.
  //
  // |service_name| looks like "org.freedesktop.NetworkManager", and
  // |object_path| looks like "/org/freedesktop/NetworkManager/Devices/0".
  //
  // Must be called in the origin thread.
  virtual ObjectProxy* GetObjectProxy(const std::string& service_name,
                                      const ObjectPath& object_path);

  // Same as above, but also takes a bitfield of ObjectProxy::Options.
  // See object_proxy.h for available options.
  virtual ObjectProxy* GetObjectProxyWithOptions(
      const std::string& service_name,
      const ObjectPath& object_path,
      int options);

  // Removes the previously created object proxy for the given service
  // name and the object path and releases its memory.
  //
  // If and object proxy for the given service name and object was
  // created with GetObjectProxy, this function removes it from the
  // bus object and detaches the ObjectProxy, invalidating any pointer
  // previously acquired for it with GetObjectProxy. A subsequent call
  // to GetObjectProxy will return a new object.
  //
  // All the object proxies are detached from remote objects at the
  // shutdown time of the bus, but they can be detached early to reduce
  // memory footprint and used match rules for the bus connection.
  //
  // |service_name| looks like "org.freedesktop.NetworkManager", and
  // |object_path| looks like "/org/freedesktop/NetworkManager/Devices/0".
  // |callback| is called when the object proxy is successfully removed and
  // detached.
  //
  // The function returns true when there is an object proxy matching the
  // |service_name| and |object_path| to remove, and calls |callback| when it
  // is removed. Otherwise, it returns false and the |callback| function is
  // never called. The |callback| argument must not be null.
  //
  // Must be called in the origin thread.
  virtual bool RemoveObjectProxy(const std::string& service_name,
                                 const ObjectPath& object_path,
                                 const base::Closure& callback);

  // Same as above, but also takes a bitfield of ObjectProxy::Options.
  // See object_proxy.h for available options.
  virtual bool RemoveObjectProxyWithOptions(
      const std::string& service_name,
      const ObjectPath& object_path,
      int options,
      const base::Closure& callback);

  // Gets the exported object for the given object path.
  // The caller must not delete the returned object.
  //
  // Returns an existing exported object if the bus object already owns
  // the exported object for the given object path. Never returns NULL.
  //
  // The bus will own all exported objects created by the bus, to ensure
  // that the exported objects are unregistered at the shutdown time of
  // the bus.
  //
  // The exported object is used to export methods of local objects, and
  // send signal from them.
  //
  // Must be called in the origin thread.
  virtual ExportedObject* GetExportedObject(const ObjectPath& object_path);

  // Unregisters the exported object for the given object path |object_path|.
  //
  // Getting an exported object for the same object path after this call
  // will return a new object, method calls on any remaining copies of the
  // previous object will not be called.
  //
  // Must be called in the origin thread.
  virtual void UnregisterExportedObject(const ObjectPath& object_path);


  // Gets an object manager for the given remote object path |object_path|
  // exported by the service |service_name|.
  //
  // Returns an existing object manager if the bus object already owns a
  // matching object manager, never returns NULL.
  //
  // The caller must not delete the returned object, the bus retains ownership
  // of all object managers.
  //
  // Must be called in the origin thread.
  virtual ObjectManager* GetObjectManager(const std::string& service_name,
                                          const ObjectPath& object_path);

  // Unregisters the object manager for the given remote object path
  // |object_path| exported by the srevice |service_name|.
  //
  // Getting an object manager for the same remote object after this call
  // will return a new object, method calls on any remaining copies of the
  // previous object are not permitted.
  //
  // This method will asynchronously clean up any match rules that have been
  // added for the object manager and invoke |callback| when the operation is
  // complete. If this method returns false, then |callback| is never called.
  // The |callback| argument must not be null.
  //
  // Must be called in the origin thread.
  virtual bool RemoveObjectManager(const std::string& service_name,
                                   const ObjectPath& object_path,
                                   const base::Closure& callback);

  // Shuts down the bus and blocks until it's done. More specifically, this
  // function does the following:
  //
  // - Unregisters the object paths
  // - Releases the service names
  // - Closes the connection to dbus-daemon.
  //
  // This function can be called multiple times and it is no-op for the 2nd time
  // calling.
  //
  // BLOCKING CALL.
  virtual void ShutdownAndBlock();

  // Similar to ShutdownAndBlock(), but this function is used to
  // synchronously shut down the bus that uses the D-Bus thread. This
  // function is intended to be used at the very end of the browser
  // shutdown, where it makes more sense to shut down the bus
  // synchronously, than trying to make it asynchronous.
  //
  // BLOCKING CALL, but must be called in the origin thread.
  virtual void ShutdownOnDBusThreadAndBlock();

  // Returns true if the shutdown has been completed.
  bool shutdown_completed() { return shutdown_completed_; }

  //
  // The public functions below are not intended to be used in client
  // code. These are used to implement ObjectProxy and ExportedObject.
  //

  // Connects the bus to the dbus-daemon.
  // Returns true on success, or the bus is already connected.
  //
  // BLOCKING CALL.
  virtual bool Connect();

  // Disconnects the bus from the dbus-daemon.
  // Safe to call multiple times and no operation after the first call.
  // Do not call for shared connection it will be released by libdbus.
  //
  // BLOCKING CALL.
  virtual void ClosePrivateConnection();

  // Requests the ownership of the service name given by |service_name|.
  // See also RequestOwnershipAndBlock().
  //
  // |on_ownership_callback| is called when the service name is obtained
  // or failed to be obtained, in the origin thread.
  //
  // Must be called in the origin thread.
  virtual void RequestOwnership(const std::string& service_name,
                                ServiceOwnershipOptions options,
                                OnOwnershipCallback on_ownership_callback);

  // Requests the ownership of the given service name.
  // Returns true on success, or the the service name is already obtained.
  //
  // Note that it's important to expose methods before requesting a service
  // name with this method.  See also ExportedObject::ExportMethodAndBlock()
  // for details.
  //
  // BLOCKING CALL.
  virtual bool RequestOwnershipAndBlock(const std::string& service_name,
                                        ServiceOwnershipOptions options);

  // Releases the ownership of the given service name.
  // Returns true on success.
  //
  // BLOCKING CALL.
  virtual bool ReleaseOwnership(const std::string& service_name);

  // Sets up async operations.
  // Returns true on success, or it's already set up.
  // This function needs to be called before starting async operations.
  //
  // BLOCKING CALL.
  virtual bool SetUpAsyncOperations();

  // Sends a message to the bus and blocks until the response is
  // received. Used to implement synchronous method calls.
  //
  // BLOCKING CALL.
  virtual DBusMessage* SendWithReplyAndBlock(DBusMessage* request,
                                             int timeout_ms,
                                             DBusError* error);

  // Requests to send a message to the bus. The reply is handled with
  // |pending_call| at a later time.
  //
  // BLOCKING CALL.
  virtual void SendWithReply(DBusMessage* request,
                             DBusPendingCall** pending_call,
                             int timeout_ms);

  // Requests to send a message to the bus. The message serial number will
  // be stored in |serial|.
  //
  // BLOCKING CALL.
  virtual void Send(DBusMessage* request, uint32_t* serial);

  // Adds the message filter function. |filter_function| will be called
  // when incoming messages are received.
  //
  // When a new incoming message arrives, filter functions are called in
  // the order that they were added until the the incoming message is
  // handled by a filter function.
  //
  // The same filter function associated with the same user data cannot be
  // added more than once.
  //
  // BLOCKING CALL.
  virtual void AddFilterFunction(DBusHandleMessageFunction filter_function,
                                 void* user_data);

  // Removes the message filter previously added by AddFilterFunction().
  //
  // BLOCKING CALL.
  virtual void RemoveFilterFunction(DBusHandleMessageFunction filter_function,
                                    void* user_data);

  // Adds the match rule. Messages that match the rule will be processed
  // by the filter functions added by AddFilterFunction().
  //
  // You cannot specify which filter function to use for a match rule.
  // Instead, you should check if an incoming message is what you are
  // interested in, in the filter functions.
  //
  // The same match rule can be added more than once and should be removed
  // as many times as it was added.
  //
  // The match rule looks like:
  // "type='signal', interface='org.chromium.SomeInterface'".
  //
  // See "Message Bus Message Routing" section in the D-Bus specification
  // for details about match rules:
  // http://dbus.freedesktop.org/doc/dbus-specification.html#message-bus-routing
  //
  // BLOCKING CALL.
  virtual void AddMatch(const std::string& match_rule, DBusError* error);

  // Removes the match rule previously added by AddMatch().
  // Returns false if the requested match rule is unknown or has already been
  // removed. Otherwise, returns true and sets |error| accordingly.
  //
  // BLOCKING CALL.
  virtual bool RemoveMatch(const std::string& match_rule, DBusError* error);

  // Tries to register the object path. Returns true on success.
  // Returns false if the object path is already registered.
  //
  // |message_function| in |vtable| will be called every time when a new
  // |message sent to the object path arrives.
  //
  // The same object path must not be added more than once.
  //
  // See also documentation of |dbus_connection_try_register_object_path| at
  // http://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html
  //
  // BLOCKING CALL.
  virtual bool TryRegisterObjectPath(const ObjectPath& object_path,
                                     const DBusObjectPathVTable* vtable,
                                     void* user_data,
                                     DBusError* error);

  // Tries to register the object path and its sub paths.
  // Returns true on success.
  // Returns false if the object path is already registered.
  //
  // |message_function| in |vtable| will be called every time when a new
  // message sent to the object path (or hierarchically below) arrives.
  //
  // The same object path must not be added more than once.
  //
  // See also documentation of |dbus_connection_try_register_fallback| at
  // http://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html
  //
  // BLOCKING CALL.
  virtual bool TryRegisterFallback(const ObjectPath& object_path,
                                   const DBusObjectPathVTable* vtable,
                                   void* user_data,
                                   DBusError* error);

  // Unregister the object path.
  //
  // BLOCKING CALL.
  virtual void UnregisterObjectPath(const ObjectPath& object_path);

  // Returns the task runner of the D-Bus thread.
  virtual base::TaskRunner* GetDBusTaskRunner();

  // Returns the task runner of the thread that created the bus.
  virtual base::TaskRunner* GetOriginTaskRunner();

  // Returns true if the bus has the D-Bus thread.
  virtual bool HasDBusThread();

  // Check whether the current thread is on the origin thread (the thread
  // that created the bus). If not, DCHECK will fail.
  virtual void AssertOnOriginThread();

  // Check whether the current thread is on the D-Bus thread. If not,
  // DCHECK will fail. If the D-Bus thread is not supplied, it calls
  // AssertOnOriginThread().
  virtual void AssertOnDBusThread();

  // Gets the owner for |service_name| via org.freedesktop.DBus.GetNameOwner.
  // Returns the owner name, if any, or an empty string on failure.
  // |options| specifies where to printing error messages or not.
  //
  // BLOCKING CALL.
  virtual std::string GetServiceOwnerAndBlock(const std::string& service_name,
                                              GetServiceOwnerOption options);

  // A non-blocking version of GetServiceOwnerAndBlock().
  // Must be called in the origin thread.
  virtual void GetServiceOwner(const std::string& service_name,
                               const GetServiceOwnerCallback& callback);

  // Whenever the owner for |service_name| changes, run |callback| with the
  // name of the new owner. If the owner goes away, then |callback| receives
  // an empty string.
  //
  // Any unique (service_name, callback) can be used. Duplicate are ignored.
  // |service_name| must not be empty and |callback| must not be null.
  //
  // Must be called in the origin thread.
  virtual void ListenForServiceOwnerChange(
      const std::string& service_name,
      const GetServiceOwnerCallback& callback);

  // Stop listening for |service_name| owner changes for |callback|.
  // Any unique (service_name, callback) can be used. Non-registered callbacks
  // for a given service name are ignored.
  // |service_name| must not be empty and |callback| must not be null.
  //
  // Must be called in the origin thread.
  virtual void UnlistenForServiceOwnerChange(
      const std::string& service_name,
      const GetServiceOwnerCallback& callback);

  // Return the unique name of the bus connnection if it is connected to
  // D-BUS. Otherwise, return an empty string.
  std::string GetConnectionName();

  // Returns true if the bus is connected to D-Bus.
  virtual bool IsConnected();

 protected:
  // This is protected, so we can define sub classes.
  virtual ~Bus();

 private:
  using TryRegisterObjectPathFunction =
      dbus_bool_t(DBusConnection* connection,
                  const char* object_path,
                  const DBusObjectPathVTable* vtable,
                  void* user_data,
                  DBusError* error);

  friend class base::RefCountedThreadSafe<Bus>;

  bool TryRegisterObjectPathInternal(
      const ObjectPath& object_path,
      const DBusObjectPathVTable* vtable,
      void* user_data,
      DBusError* error,
      TryRegisterObjectPathFunction* register_function);

  // Helper function used for RemoveObjectProxy().
  void RemoveObjectProxyInternal(scoped_refptr<dbus::ObjectProxy> object_proxy,
                                 const base::Closure& callback);

  // Helper functions used for RemoveObjectManager().
  void RemoveObjectManagerInternal(
      scoped_refptr<dbus::ObjectManager> object_manager,
      const base::Closure& callback);
  void RemoveObjectManagerInternalHelper(
      scoped_refptr<dbus::ObjectManager> object_manager,
      const base::Closure& callback);

  // Helper function used for UnregisterExportedObject().
  void UnregisterExportedObjectInternal(
      scoped_refptr<dbus::ExportedObject> exported_object);

  // Helper function used for ShutdownOnDBusThreadAndBlock().
  void ShutdownOnDBusThreadAndBlockInternal();

  // Helper function used for RequestOwnership().
  void RequestOwnershipInternal(const std::string& service_name,
                                ServiceOwnershipOptions options,
                                OnOwnershipCallback on_ownership_callback);

  // Helper function used for GetServiceOwner().
  void GetServiceOwnerInternal(const std::string& service_name,
                               const GetServiceOwnerCallback& callback);

  // Helper function used for ListenForServiceOwnerChange().
  void ListenForServiceOwnerChangeInternal(
      const std::string& service_name,
      const GetServiceOwnerCallback& callback);

  // Helper function used for UnListenForServiceOwnerChange().
  void UnlistenForServiceOwnerChangeInternal(
      const std::string& service_name,
      const GetServiceOwnerCallback& callback);

  // Processes the all incoming data to the connection, if any.
  //
  // BLOCKING CALL.
  void ProcessAllIncomingDataIfAny();

  // Called when a watch object is added. Used to start monitoring the
  // file descriptor used for D-Bus communication.
  dbus_bool_t OnAddWatch(DBusWatch* raw_watch);

  // Called when a watch object is removed.
  void OnRemoveWatch(DBusWatch* raw_watch);

  // Called when the "enabled" status of |raw_watch| is toggled.
  void OnToggleWatch(DBusWatch* raw_watch);

  // Called when a timeout object is added. Used to start monitoring
  // timeout for method calls.
  dbus_bool_t OnAddTimeout(DBusTimeout* raw_timeout);

  // Called when a timeout object is removed.
  void OnRemoveTimeout(DBusTimeout* raw_timeout);

  // Called when the "enabled" status of |raw_timeout| is toggled.
  void OnToggleTimeout(DBusTimeout* raw_timeout);

  // Called when the dispatch status (i.e. if any incoming data is
  // available) is changed.
  void OnDispatchStatusChanged(DBusConnection* connection,
                               DBusDispatchStatus status);

  // Called when a service owner change occurs.
  void OnServiceOwnerChanged(DBusMessage* message);

  // Callback helper functions. Redirects to the corresponding member function.
  static dbus_bool_t OnAddWatchThunk(DBusWatch* raw_watch, void* data);
  static void OnRemoveWatchThunk(DBusWatch* raw_watch, void* data);
  static void OnToggleWatchThunk(DBusWatch* raw_watch, void* data);
  static dbus_bool_t OnAddTimeoutThunk(DBusTimeout* raw_timeout, void* data);
  static void OnRemoveTimeoutThunk(DBusTimeout* raw_timeout, void* data);
  static void OnToggleTimeoutThunk(DBusTimeout* raw_timeout, void* data);
  static void OnDispatchStatusChangedThunk(DBusConnection* connection,
                                           DBusDispatchStatus status,
                                           void* data);

  // Calls OnConnectionDisconnected if the Disconnected signal is received.
  static DBusHandlerResult OnConnectionDisconnectedFilter(
      DBusConnection* connection,
      DBusMessage* message,
      void* user_data);

  // Calls OnServiceOwnerChanged for a NameOwnerChanged signal.
  static DBusHandlerResult OnServiceOwnerChangedFilter(
      DBusConnection* connection,
      DBusMessage* message,
      void* user_data);

  const BusType bus_type_;
  const ConnectionType connection_type_;
  scoped_refptr<base::SequencedTaskRunner> dbus_task_runner_;
  base::WaitableEvent on_shutdown_;
  DBusConnection* connection_;

  base::PlatformThreadId origin_thread_id_;
  scoped_refptr<base::SequencedTaskRunner> origin_task_runner_;

  std::set<std::string> owned_service_names_;
  // The following sets are used to check if rules/object_paths/filters
  // are properly cleaned up before destruction of the bus object.
  // Since it's not an error to add the same match rule twice, the repeated
  // match rules are counted in a map.
  std::map<std::string, int> match_rules_added_;
  std::set<ObjectPath> registered_object_paths_;
  std::set<std::pair<DBusHandleMessageFunction, void*>> filter_functions_added_;

  // ObjectProxyTable is used to hold the object proxies created by the
  // bus object. Key is a pair; the first part is a concatenated string of
  // service name + object path, like
  // "org.chromium.TestService/org/chromium/TestObject".
  // The second part is the ObjectProxy::Options for the proxy.
  typedef std::map<std::pair<std::string, int>,
                   scoped_refptr<dbus::ObjectProxy>> ObjectProxyTable;
  ObjectProxyTable object_proxy_table_;

  // ExportedObjectTable is used to hold the exported objects created by
  // the bus object. Key is a concatenated string of service name +
  // object path, like "org.chromium.TestService/org/chromium/TestObject".
  typedef std::map<const dbus::ObjectPath,
                   scoped_refptr<dbus::ExportedObject>> ExportedObjectTable;
  ExportedObjectTable exported_object_table_;

  // ObjectManagerTable is used to hold the object managers created by the
  // bus object. Key is a concatenated string of service name + object path,
  // like "org.chromium.TestService/org/chromium/TestObject".
  typedef std::map<std::string,
                   scoped_refptr<dbus::ObjectManager>> ObjectManagerTable;
  ObjectManagerTable object_manager_table_;

  // A map of NameOwnerChanged signals to listen for and the callbacks to run
  // on the origin thread when the owner changes.
  // Only accessed on the DBus thread.
  // Key: Service name
  // Value: Vector of callbacks. Unique and expected to be small. Not using
  //        std::set here because base::Callbacks don't have a '<' operator.
  typedef std::map<std::string, std::vector<GetServiceOwnerCallback>>
      ServiceOwnerChangedListenerMap;
  ServiceOwnerChangedListenerMap service_owner_changed_listener_map_;

  bool async_operations_set_up_;
  bool shutdown_completed_;

  // Counters to make sure that OnAddWatch()/OnRemoveWatch() and
  // OnAddTimeout()/OnRemoveTimeou() are balanced.
  int num_pending_watches_;
  int num_pending_timeouts_;

  std::string address_;

  DISALLOW_COPY_AND_ASSIGN(Bus);
};

}  // namespace dbus

#endif  // DBUS_BUS_H_