libcros: Watch for display brightness changes.

chromeos_brightness.cc

Index: chromeos_brightness.cc
diff --git a/chromeos_brightness.cc b/chromeos_brightness.cc
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+++ b/chromeos_brightness.cc
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+// Copyright (c) 2010 The Chromium OS 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 "chromeos_brightness.h"
+
+#include <string>
+
+#include <dbus/dbus-glib-lowlevel.h>
+
+#include "base/logging.h"
+#include "base/stringprintf.h"
+#include "chromeos/dbus/dbus.h"
+#include "chromeos/dbus/service_constants.h"
+
+using std::string;
+
+namespace {
+
+// Returns a string matching the D-Bus messages that we want to listen for.
+string GetDBusMatchString() {
+  return StringPrintf("type='signal', interface='%s', member='%s'",
+                      power_manager::kPowerManagerInterface,
+                      power_manager::kBrightnessChangedSignal);
+}
+
+}  // namespace
+
+namespace chromeos {
+
+class OpaqueBrightnessConnection {
+ public:
+  OpaqueBrightnessConnection(const BrightnessMonitorFunction& monitor_function,
+                             void* object)
+     : monitor_function_(monitor_function),
+       object_(object) {
+  }
+
+  // A D-Bus message filter to receive signals.
+  static DBusHandlerResult FilterDBusMessage(DBusConnection* dbus_conn,
+                                             DBusMessage* message,
+                                             void* data) {
+    BrightnessConnection self = static_cast<BrightnessConnection>(data);
+    if (dbus_message_is_signal(message,
+                               power_manager::kPowerManagerInterface,
+                               power_manager::kBrightnessChangedSignal)) {
+      DBusError error;
+      dbus_error_init(&error);
+      int brightness_level = 0;
+      if (dbus_message_get_args(message, &error,
+                                DBUS_TYPE_INT32, &brightness_level,
+                                DBUS_TYPE_INVALID)) {
+        self->monitor_function_(self->object_, brightness_level);
+      } else {
+        LOG(WARNING) << "Unable to read brightness level from "
+                     << power_manager::kBrightnessChangedSignal << " signal";
+      }
+      return DBUS_HANDLER_RESULT_HANDLED;
+    } else {
+      return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+    }
+  }
+
+ private:
+  // Function within Chrome that we invoke when the brightness changes.
+  BrightnessMonitorFunction monitor_function_;
+
+  // Opaque pointer supplied to ChromeOSMonitorBrightness() that we pass back
+  // via |monitor_function_|.
+  void* object_;
+};
+
+extern "C"
+BrightnessConnection ChromeOSMonitorBrightness(
+    BrightnessMonitorFunction monitor_function, void* object) {
+  BrightnessConnection connection =
+      new OpaqueBrightnessConnection(monitor_function, object);
+
+  // Snoop on D-Bus messages so we can get notified about brightness changes.
+  DBusConnection* dbus_conn =
+      dbus_g_connection_get_connection(
+          dbus::GetSystemBusConnection().g_connection());
+  DCHECK(dbus_conn);
+
+  DBusError error;
+  dbus_error_init(&error);
+  dbus_bus_add_match(dbus_conn, GetDBusMatchString().c_str(), &error);
+  if (dbus_error_is_set(&error)) {
+    LOG(DFATAL) << "Got error while adding D-Bus match rule: " << error.name
+                << " (" << error.message << ")";
+  }
+
+  if (!dbus_connection_add_filter(
+           dbus_conn,
+           &OpaqueBrightnessConnection::FilterDBusMessage,
+           connection,  // user_data
+           NULL)) {     // free_data_function
+    LOG(DFATAL) << "Unable to add D-Bus filter";
+  }
+
+  return connection;
+}
+
+extern "C"
+void ChromeOSDisconnectBrightness(BrightnessConnection connection) {
+  DCHECK(connection);
+
+  DBusConnection* dbus_conn =
+      dbus_g_connection_get_connection(
+          dbus::GetSystemBusConnection().g_connection());
+  DCHECK(dbus_conn);
+
+  dbus_connection_remove_filter(
+      dbus_conn,
+      &OpaqueBrightnessConnection::FilterDBusMessage,
+      connection);
+  delete connection;
+
+  DBusError error;
+  dbus_error_init(&error);
+  dbus_bus_remove_match(dbus_conn, GetDBusMatchString().c_str(), &error);
+  if (dbus_error_is_set(&error)) {
+    LOG(DFATAL) << "Got error while removing D-Bus match rule: " << error.name
+                << " (" << error.message << ")";
+  }
+}
+
+}  // namespace chromeos