Implement Bus and ObjectProxy classes for our D-Bus library.

dbus/exported_object.cc

+// Copyright (c) 2011 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 "dbus/exported_object.h"
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop.h"
+#include "base/threading/thread_restrictions.h"
+#include "dbus/bus.h"
+#include "dbus/error.h"
+#include "dbus/message.h"
+
+namespace dbus {
+
+namespace {
+
+// Gets the absolute method name by concatenating the interface name and
+// the method name. Used for building keys for method_table_ in
+// ExportedObject.
+std::string GetAbsoluteMethodName(
+    const std::string& interface_name,
+    const std::string& method_name) {
+  return interface_name + "." + method_name;
+}
+
+}  // namespace
+
+ExportedObject::ExportedObject(Bus* bus,
+                               const std::string& service_name,
+                               const std::string& object_path)
+    : bus_(bus),
+      service_name_(service_name),
+      object_path_(object_path),
+      object_is_registered_(false),
+      method_is_called_(false),
+      response_from_method_(NULL),
+      on_method_is_called_(&method_is_called_lock_) {
+}
+
+ExportedObject::~ExportedObject() {
+  DCHECK(!object_is_registered_);
+}
+
+bool ExportedObject::ExportMethodAndBlock(
+    const std::string& interface_name,
+    const std::string& method_name,
+    MethodCallCallback method_call_callback) {
+  bus_->AssertOnDBusThread();
+
+  if (!bus_->Connect())
+    return false;
+  if (!bus_->SetUpAsyncOperations())
+    return false;
+  if (!bus_->RequestOwnership(service_name_))
+    return false;
+  if (!Register())
+    return false;
+
+  const std::string absolute_method_name =
+      GetAbsoluteMethodName(interface_name, method_name);
+  if (method_table_.find(absolute_method_name) != method_table_.end()) {
+    LOG(ERROR) << absolute_method_name << " is already exported";

[stevenjb, 2011/08/15 21:42:04]

Should we do this check earlier, i.e. before Register(), possibly other calls?
Lookup is relatively quick.

[satorux1, 2011/08/16 22:25:37]

I think it's slightly easier to read to keep this near
method_table_[absolute_method_name] = ... below.

If an method is already exported, all initialization like Connect() and
Register() has been done, so calls above almost do nothing.

[stevenjb, 2011/08/16 22:53:29]

OK, it looks like Register() just returns true if already registered, so that's
fine.

+    return false;
+  }
+  method_table_[absolute_method_name] = method_call_callback;
+
+  return true;
+}
+
+void ExportedObject::ExportMethod(const std::string& interface_name,
+                                  const std::string& method_name,
+                                  MethodCallCallback method_call_callback,
+                                  OnExportedCallback on_exported_calback) {
+  bus_->AssertOnOriginThread();
+
+  base::Closure task = base::Bind(&ExportedObject::ExportMethodInternal,
+                                  this,
+                                  interface_name,
+                                  method_name,
+                                  method_call_callback,
+                                  on_exported_calback);
+  bus_->PostTaskToDBusThread(FROM_HERE, task);
+}
+
+void ExportedObject::Unregister() {
+  bus_->AssertOnDBusThread();
+
+  if (!object_is_registered_)
+    return;
+
+  bus_->UnregisterObjectPath(object_path_);
+  object_is_registered_ = false;
+}
+
+void ExportedObject::ExportMethodInternal(
+    const std::string& interface_name,
+    const std::string& method_name,
+    MethodCallCallback method_call_callback,
+    OnExportedCallback on_exported_calback) {
+  bus_->AssertOnDBusThread();
+
+  const bool success = ExportMethodAndBlock(interface_name,
+                                            method_name,
+                                            method_call_callback);
+  bus_->PostTaskToOriginThread(FROM_HERE,
+                               base::Bind(&ExportedObject::OnExported,
+                                          this,
+                                          on_exported_calback,
+                                          interface_name,
+                                          method_name,
+                                          success));
+}
+
+void ExportedObject::OnExported(OnExportedCallback on_exported_callback,
+                                const std::string& interface_name,
+                                const std::string& method_name,
+                                bool success) {
+  bus_->AssertOnOriginThread();
+
+  on_exported_callback.Run(interface_name, method_name, success);
+}
+
+bool ExportedObject::Register() {
+  bus_->AssertOnDBusThread();
+
+  if (object_is_registered_)
+    return true;
+
+  ScopedDBusError error;
+
+  DBusObjectPathVTable vtable = {};
+  vtable.message_function = &ExportedObject::HandleMessageThunk;
+  vtable.unregister_function = &ExportedObject::OnUnregisteredThunk;
+  const bool success = bus_->TryRegisterObjectPath(object_path_,
+                                                   &vtable,
+                                                   this,
+                                                   error.get());
+  if (!success) {
+    LOG(ERROR) << "Failed to regiser the object: " << object_path_ << ": "
+               << (error.is_set() ? error.message() : "");
+    return false;
+  }
+
+  object_is_registered_ = true;
+  return true;
+}
+
+DBusHandlerResult ExportedObject::HandleMessage(
+    DBusConnection* connection,
+    DBusMessage* raw_message) {
+  bus_->AssertOnDBusThread();
+  DCHECK_EQ(DBUS_MESSAGE_TYPE_METHOD_CALL, dbus_message_get_type(raw_message));
+
+  // raw_message will be unrefed on exit of the function. Increment the
+  // reference so we can use it in MethodCall.
+  dbus_message_ref(raw_message);
+  scoped_ptr<MethodCall> method_call(
+      MethodCall::FromRawMessage(raw_message));
+  const std::string interface = method_call->GetInterface();
+  const std::string member = method_call->GetMember();
+
+  if (interface.empty()) {
+    // We don't support method calls without interface.
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+  }
+
+  // Check if we know about the method.
+  const std::string absolute_method_name = GetAbsoluteMethodName(
+      interface, member);
+  MethodTable::const_iterator iter = method_table_.find(absolute_method_name);
+  if (iter == method_table_.end()) {
+    // Don't know about the method.
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+  }
+
+  Response* response = NULL;
+  if (bus_->has_dbus_thread()) {
+    response_from_method_ = NULL;
+    method_is_called_ = false;
+    // Post a task to run the method in the origin thread.
+    bus_->PostTaskToOriginThread(FROM_HERE,
+                                 base::Bind(&ExportedObject::RunMethod,
+                                            this,
+                                            iter->second,
+                                            method_call.get()));
+    // Wait until the method call is done. Blocking is not desirable but we
+    // should return the response to the dbus-daemon in the function, so we
+    // don't have a choice. We wait in the D-Bus thread, so it should be ok.
+    {
+      base::AutoLock auto_lock(method_is_called_lock_);
+      while (!method_is_called_)
+        on_method_is_called_.Wait();

[stevenjb, 2011/08/15 21:42:04]

Does this have a built-in timeout? If not, should we add one? It could be
difficult to debug if the DBus thread gets stuck causing other valid requests to
timeout or fail.  Apologies if I already asked this :)

[stevenjb, 2011/08/16 22:53:29]

Looking at this more closely, if the callback (iter->second) gets stuck waiting
or in an infinite loop, then on_method_call_.Signal() will never get called, and
this will be stuck in an infinite loop on a background thread. These types of
errors can be very difficult to debug, so I think we need a timeout here.
Fortunately ConditionVariable has a TimedWait() function that we can use:

const TimeDelta delta_time(TimeDelta::FromSeconds(10));
Time start_time = Time::Now();
while (!method_is_called_) {
  on_method_is_called_.TimedWait(delta_time);
  CHECK(Time::Now() - start_time < delta_time);
}

[satorux1, 2011/08/16 23:19:40]

My bad, I missed the original comment. You are absolutely right that infinite
blocking should be avoided. Changed accordingly.

+    }
+    response = response_from_method_;
+  } else {
+    // If the D-Bus thread is not used, just call the method directly. We
+    // don't need the complicated logic to wait for the method call to be
+    // complete.
+    response = iter->second.Run(method_call.get());
+  }
+
+  if (!response) {
+    // Something bad happend in the method call.
+    scoped_ptr<dbus::ErrorResponse> error_response(
+        ErrorResponse::FromMethodCall(method_call.get(),
+                                      DBUS_ERROR_FAILED,
+                                      "error occurred in " + member));
+    dbus_connection_send(connection, error_response->raw_message(), NULL);
+    return DBUS_HANDLER_RESULT_HANDLED;
+  }
+
+  // The method call was successful.
+  dbus_connection_send(connection, response->raw_message(), NULL);
+  delete response;
+
+  return DBUS_HANDLER_RESULT_HANDLED;
+}
+
+void ExportedObject::RunMethod(MethodCallCallback method_call_callback,
+                               MethodCall* method_call) {
+  bus_->AssertOnOriginThread();
+
+  base::AutoLock auto_lock(method_is_called_lock_);
+  response_from_method_ = method_call_callback.Run(method_call);
+  method_is_called_ = true;
+  on_method_is_called_.Signal();
+}
+
+void ExportedObject::OnUnregistered(DBusConnection* connection) {
+}
+
+DBusHandlerResult ExportedObject::HandleMessageThunk(
+    DBusConnection* connection,
+    DBusMessage* raw_message,
+    void* user_data) {
+  ExportedObject* self = reinterpret_cast<ExportedObject*>(user_data);
+  return self->HandleMessage(connection, raw_message);
+}
+
+void ExportedObject::OnUnregisteredThunk(DBusConnection *connection,
+                                         void* user_data) {
+  ExportedObject* self = reinterpret_cast<ExportedObject*>(user_data);
+  return self->OnUnregistered(connection);
+}
+
+}  // namespace dbus