dbus: add ObjectPath type

Rather than use std::string for object paths, add a dbus::ObjectPath type
that wraps one while allowing more type-safety. This solves all sorts of
issues with confusing object paths for strings, and allows us to do
Properties code using templates disambiguating them from strings.

BUG=chromium:109194
TEST=built and run tests

Change-Id: Icaf6f19daea4af23a9d2ec0ed76d2cbd379d680e


Review URL: http://codereview.chromium.org/9378039

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@121920 0039d316-1c4b-4281-b951-d872f2087c98

22 files changed, 205 insertions, 112 deletions

diff --git a/dbus/bus.cc b/dbus/bus.cc
index 0c6a421..3b2f059 100644
--- a/dbus/bus.cc
+++ b/dbus/bus.cc
@@ -16,6 +16,7 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "dbus/exported_object.h"
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "dbus/scoped_dbus_error.h"
 
@@ -207,18 +208,19 @@ Bus::~Bus() {
 }
 
 ObjectProxy* Bus::GetObjectProxy(const std::string& service_name,
-                                 const std::string& object_path) {
+                                 const ObjectPath& object_path) {
   return GetObjectProxyWithOptions(service_name, object_path,
                                    ObjectProxy::DEFAULT_OPTIONS);
 }
 
 ObjectProxy* Bus::GetObjectProxyWithOptions(const std::string& service_name,
-                                            const std::string& object_path,
+                                            const dbus::ObjectPath& object_path,
                                             int options) {
   AssertOnOriginThread();
 
   // Check if we already have the requested object proxy.
-  const ObjectProxyTable::key_type key(service_name + object_path, options);
+  const ObjectProxyTable::key_type key(service_name + object_path.value(),
+                                       options);
   ObjectProxyTable::iterator iter = object_proxy_table_.find(key);
   if (iter != object_proxy_table_.end()) {
     return iter->second;
@@ -232,11 +234,11 @@ ObjectProxy* Bus::GetObjectProxyWithOptions(const std::string& service_name,
 }
 
 ExportedObject* Bus::GetExportedObject(const std::string& service_name,
-                                       const std::string& object_path) {
+                                       const ObjectPath& object_path) {
   AssertOnOriginThread();
 
   // Check if we already have the requested exported object.
-  const std::string key = service_name + object_path;
+  const std::string key = service_name + object_path.value();
   ExportedObjectTable::iterator iter = exported_object_table_.find(key);
   if (iter != exported_object_table_.end()) {
     return iter->second;
@@ -521,7 +523,7 @@ void Bus::RemoveMatch(const std::string& match_rule, DBusError* error) {
   match_rules_added_.erase(match_rule);
 }
 
-bool Bus::TryRegisterObjectPath(const std::string& object_path,
+bool Bus::TryRegisterObjectPath(const ObjectPath& object_path,
                                 const DBusObjectPathVTable* vtable,
                                 void* user_data,
                                 DBusError* error) {
@@ -530,13 +532,13 @@ bool Bus::TryRegisterObjectPath(const std::string& object_path,
 
   if (registered_object_paths_.find(object_path) !=
       registered_object_paths_.end()) {
-    LOG(ERROR) << "Object path already registered: " << object_path;
+    LOG(ERROR) << "Object path already registered: " << object_path.value();
     return false;
   }
 
   const bool success = dbus_connection_try_register_object_path(
       connection_,
-      object_path.c_str(),
+      object_path.value().c_str(),
       vtable,
       user_data,
       error);
@@ -545,20 +547,20 @@ bool Bus::TryRegisterObjectPath(const std::string& object_path,
   return success;
 }
 
-void Bus::UnregisterObjectPath(const std::string& object_path) {
+void Bus::UnregisterObjectPath(const ObjectPath& object_path) {
   DCHECK(connection_);
   AssertOnDBusThread();
 
   if (registered_object_paths_.find(object_path) ==
       registered_object_paths_.end()) {
     LOG(ERROR) << "Requested to unregister an unknown object path: "
-               << object_path;
+               << object_path.value();
     return;
   }
 
   const bool success = dbus_connection_unregister_object_path(
       connection_,
-      object_path.c_str());
+      object_path.value().c_str());
   CHECK(success) << "Unable to allocate memory";
   registered_object_paths_.erase(object_path);
 }
diff --git a/dbus/bus.h b/dbus/bus.h
index 22c2218..e045386 100644
--- a/dbus/bus.h
+++ b/dbus/bus.h
@@ -17,6 +17,7 @@
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "base/tracked_objects.h"
+#include "dbus/object_path.h"
 
 class MessageLoop;
 
@@ -112,7 +113,7 @@ class ObjectProxy;
 //   }
 //
 //   void OnExported(const std::string& interface_name,
-//                   const std::string& object_path,
+//                   const ObjectPath& object_path,
 //                   bool success) {
 //     // success is true if the method was exported successfully.
 //   }
@@ -194,13 +195,13 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   //
   // Must be called in the origin thread.
   virtual ObjectProxy* GetObjectProxy(const std::string& service_name,
-                                      const std::string& object_path);
+                                      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 std::string& object_path,
+      const ObjectPath& object_path,
       int options);
 
   // Gets the exported object for the given service name and the object
@@ -219,7 +220,7 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   //
   // Must be called in the origin thread.
   virtual ExportedObject* GetExportedObject(const std::string& service_name,
-                                            const std::string& object_path);
+                                            const ObjectPath& object_path);
 
   // Shuts down the bus and blocks until it's done. More specifically, this
   // function does the following:
@@ -353,7 +354,7 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   // http://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html
   //
   // BLOCKING CALL.
-  virtual bool TryRegisterObjectPath(const std::string& object_path,
+  virtual bool TryRegisterObjectPath(const ObjectPath& object_path,
                                      const DBusObjectPathVTable* vtable,
                                      void* user_data,
                                      DBusError* error);
@@ -361,7 +362,7 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   // Unregister the object path.
   //
   // BLOCKING CALL.
-  virtual void UnregisterObjectPath(const std::string& object_path);
+  virtual void UnregisterObjectPath(const ObjectPath& object_path);
 
   // Posts the task to the message loop of the thread that created the bus.
   virtual void PostTaskToOriginThread(
@@ -461,7 +462,7 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   // The following sets are used to check if rules/object_paths/filters
   // are properly cleaned up before destruction of the bus object.
   std::set<std::string> match_rules_added_;
-  std::set<std::string> registered_object_paths_;
+  std::set<ObjectPath> registered_object_paths_;
   std::set<std::pair<DBusHandleMessageFunction, void*> >
       filter_functions_added_;
 
diff --git a/dbus/bus_unittest.cc b/dbus/bus_unittest.cc
index c21044b..c66a05b 100644
--- a/dbus/bus_unittest.cc
+++ b/dbus/bus_unittest.cc
@@ -9,6 +9,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread.h"
 #include "dbus/exported_object.h"
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
@@ -30,20 +31,21 @@ TEST(BusTest, GetObjectProxy) {
 
   dbus::ObjectProxy* object_proxy1 =
       bus->GetObjectProxy("org.chromium.TestService",
-                          "/org/chromium/TestObject");
+                          dbus::ObjectPath("/org/chromium/TestObject"));
   ASSERT_TRUE(object_proxy1);
 
   // This should return the same object.
   dbus::ObjectProxy* object_proxy2 =
       bus->GetObjectProxy("org.chromium.TestService",
-                          "/org/chromium/TestObject");
+                          dbus::ObjectPath("/org/chromium/TestObject"));
   ASSERT_TRUE(object_proxy2);
   EXPECT_EQ(object_proxy1, object_proxy2);
 
   // This should not.
   dbus::ObjectProxy* object_proxy3 =
-      bus->GetObjectProxy("org.chromium.TestService",
-                          "/org/chromium/DifferentTestObject");
+      bus->GetObjectProxy(
+          "org.chromium.TestService",
+          dbus::ObjectPath("/org/chromium/DifferentTestObject"));
   ASSERT_TRUE(object_proxy3);
   EXPECT_NE(object_proxy1, object_proxy3);
 
@@ -57,7 +59,7 @@ TEST(BusTest, GetObjectProxyIgnoreUnknownService) {
   dbus::ObjectProxy* object_proxy1 =
       bus->GetObjectProxyWithOptions(
           "org.chromium.TestService",
-          "/org/chromium/TestObject",
+          dbus::ObjectPath("/org/chromium/TestObject"),
           dbus::ObjectProxy::IGNORE_SERVICE_UNKNOWN_ERRORS);
   ASSERT_TRUE(object_proxy1);
 
@@ -65,7 +67,7 @@ TEST(BusTest, GetObjectProxyIgnoreUnknownService) {
   dbus::ObjectProxy* object_proxy2 =
       bus->GetObjectProxyWithOptions(
           "org.chromium.TestService",
-          "/org/chromium/TestObject",
+          dbus::ObjectPath("/org/chromium/TestObject"),
           dbus::ObjectProxy::IGNORE_SERVICE_UNKNOWN_ERRORS);
   ASSERT_TRUE(object_proxy2);
   EXPECT_EQ(object_proxy1, object_proxy2);
@@ -74,7 +76,7 @@ TEST(BusTest, GetObjectProxyIgnoreUnknownService) {
   dbus::ObjectProxy* object_proxy3 =
       bus->GetObjectProxyWithOptions(
           "org.chromium.TestService",
-          "/org/chromium/DifferentTestObject",
+          dbus::ObjectPath("/org/chromium/DifferentTestObject"),
           dbus::ObjectProxy::IGNORE_SERVICE_UNKNOWN_ERRORS);
   ASSERT_TRUE(object_proxy3);
   EXPECT_NE(object_proxy1, object_proxy3);
@@ -88,20 +90,21 @@ TEST(BusTest, GetExportedObject) {
 
   dbus::ExportedObject* object_proxy1 =
       bus->GetExportedObject("org.chromium.TestService",
-                             "/org/chromium/TestObject");
+                             dbus::ObjectPath("/org/chromium/TestObject"));
   ASSERT_TRUE(object_proxy1);
 
   // This should return the same object.
   dbus::ExportedObject* object_proxy2 =
       bus->GetExportedObject("org.chromium.TestService",
-                             "/org/chromium/TestObject");
+                             dbus::ObjectPath("/org/chromium/TestObject"));
   ASSERT_TRUE(object_proxy2);
   EXPECT_EQ(object_proxy1, object_proxy2);
 
   // This should not.
   dbus::ExportedObject* object_proxy3 =
-      bus->GetExportedObject("org.chromium.TestService",
-                             "/org/chromium/DifferentTestObject");
+      bus->GetExportedObject(
+          "org.chromium.TestService",
+          dbus::ObjectPath("/org/chromium/DifferentTestObject"));
   ASSERT_TRUE(object_proxy3);
   EXPECT_NE(object_proxy1, object_proxy3);
 
diff --git a/dbus/dbus.gyp b/dbus/dbus.gyp
index 2dc8fee..8a3cb22 100644
--- a/dbus/dbus.gyp
+++ b/dbus/dbus.gyp
@@ -25,6 +25,8 @@
         'exported_object.h',
         'message.cc',
         'message.h',
+        'object_path.cc',
+        'object_path.h',
         'object_proxy.cc',
         'object_proxy.h',
         'scoped_dbus_error.h',
diff --git a/dbus/end_to_end_async_unittest.cc b/dbus/end_to_end_async_unittest.cc
index 150ed29..9a88b42 100644
--- a/dbus/end_to_end_async_unittest.cc
+++ b/dbus/end_to_end_async_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -15,6 +15,7 @@
 #include "base/threading/thread_restrictions.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "dbus/test_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -51,8 +52,9 @@ class EndToEndAsyncTest : public testing::Test {
     bus_options.dbus_thread_message_loop_proxy =
         dbus_thread_->message_loop_proxy();
     bus_ = new dbus::Bus(bus_options);
-    object_proxy_ = bus_->GetObjectProxy("org.chromium.TestService",
-                                         "/org/chromium/TestObject");
+    object_proxy_ = bus_->GetObjectProxy(
+        "org.chromium.TestService",
+        dbus::ObjectPath("/org/chromium/TestObject"));
     ASSERT_TRUE(bus_->HasDBusThread());
 
     // Connect to the "Test" signal of "org.chromium.TestInterface" from
diff --git a/dbus/end_to_end_sync_unittest.cc b/dbus/end_to_end_sync_unittest.cc
index c338809..26a9011 100644
--- a/dbus/end_to_end_sync_unittest.cc
+++ b/dbus/end_to_end_sync_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -6,6 +6,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "dbus/test_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -31,8 +32,9 @@ class EndToEndSyncTest : public testing::Test {
     client_bus_options.bus_type = dbus::Bus::SESSION;
     client_bus_options.connection_type = dbus::Bus::PRIVATE;
     client_bus_ = new dbus::Bus(client_bus_options);
-    object_proxy_ = client_bus_->GetObjectProxy("org.chromium.TestService",
-                                                "/org/chromium/TestObject");
+    object_proxy_ = client_bus_->GetObjectProxy(
+        "org.chromium.TestService",
+        dbus::ObjectPath("/org/chromium/TestObject"));
     ASSERT_FALSE(client_bus_->HasDBusThread());
   }
 
diff --git a/dbus/exported_object.cc b/dbus/exported_object.cc
index de25168..730c98b 100644
--- a/dbus/exported_object.cc
+++ b/dbus/exported_object.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -13,6 +13,7 @@
 #include "base/time.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
+#include "dbus/object_path.h"
 #include "dbus/scoped_dbus_error.h"
 
 namespace dbus {
@@ -35,7 +36,7 @@ std::string GetAbsoluteMethodName(
 
 ExportedObject::ExportedObject(Bus* bus,
                                const std::string& service_name,
-                               const std::string& object_path)
+                               const ObjectPath& object_path)
     : bus_(bus),
       service_name_(service_name),
       object_path_(object_path),
@@ -175,8 +176,8 @@ bool ExportedObject::Register() {
                                                    this,
                                                    error.get());
   if (!success) {
-    LOG(ERROR) << "Failed to register the object: " << object_path_ << ": "
-               << (error.is_set() ? error.message() : "");
+    LOG(ERROR) << "Failed to register the object: " << object_path_.value()
+               << ": " << (error.is_set() ? error.message() : "");
     return false;
   }
 
diff --git a/dbus/exported_object.h b/dbus/exported_object.h
index 7ac2f88..24db66e 100644
--- a/dbus/exported_object.h
+++ b/dbus/exported_object.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -17,6 +17,7 @@
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
+#include "dbus/object_path.h"
 
 namespace dbus {
 
@@ -36,7 +37,7 @@ class ExportedObject : public base::RefCountedThreadSafe<ExportedObject> {
   // constructor.
   ExportedObject(Bus* bus,
                  const std::string& service_name,
-                 const std::string& object_path);
+                 const ObjectPath& object_path);
 
   // Called to send a response from an exported method. Response* is the
   // response message. Callers should pass a NULL Response* in the event
@@ -157,7 +158,7 @@ class ExportedObject : public base::RefCountedThreadSafe<ExportedObject> {
 
   scoped_refptr<Bus> bus_;
   std::string service_name_;
-  std::string object_path_;
+  ObjectPath object_path_;
   bool object_is_registered_;
 
   // The method table where keys are absolute method names (i.e. interface
diff --git a/dbus/message.cc b/dbus/message.cc
index 4a94b54..486538a 100644
--- a/dbus/message.cc
+++ b/dbus/message.cc
@@ -10,6 +10,7 @@
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/stringprintf.h"
+#include "dbus/object_path.h"
 #include "third_party/protobuf/src/google/protobuf/message_lite.h"
 
 namespace {
@@ -157,10 +158,10 @@ std::string Message::ToStringInternal(const std::string& indent,
         break;
       }
       case OBJECT_PATH: {
-        std::string value;
+        ObjectPath value;
         if (!reader->PopObjectPath(&value))
           return kBrokenMessage;
-        output += indent + "object_path \"" + value + "\"\n";
+        output += indent + "object_path \"" + value.value() + "\"\n";
         break;
       }
       case ARRAY: {
@@ -224,7 +225,7 @@ std::string Message::ToString() {
   std::string headers;
   AppendStringHeader("message_type", GetMessageTypeAsString(), &headers);
   AppendStringHeader("destination", GetDestination(), &headers);
-  AppendStringHeader("path", GetPath(), &headers);
+  AppendStringHeader("path", GetPath().value(), &headers);
   AppendStringHeader("interface", GetInterface(), &headers);
   AppendStringHeader("member", GetMember(), &headers);
   AppendStringHeader("error_name", GetErrorName(), &headers);
@@ -244,9 +245,9 @@ void Message::SetDestination(const std::string& destination) {
   CHECK(success) << "Unable to allocate memory";
 }
 
-void Message::SetPath(const std::string& path) {
+void Message::SetPath(const ObjectPath& path) {
   const bool success = dbus_message_set_path(raw_message_,
-                                             path.c_str());
+                                             path.value().c_str());
   CHECK(success) << "Unable to allocate memory";
 }
 
@@ -287,9 +288,9 @@ std::string Message::GetDestination() {
   return destination ? destination : "";
 }
 
-std::string Message::GetPath() {
+ObjectPath Message::GetPath() {
   const char* path = dbus_message_get_path(raw_message_);
-  return path ? path : "";
+  return ObjectPath(path ? path : "");
 }
 
 std::string Message::GetInterface() {
@@ -490,8 +491,8 @@ void MessageWriter::AppendString(const std::string& value) {
   // bool AppendStringWithErrorChecking().
 }
 
-void MessageWriter::AppendObjectPath(const std::string& value) {
-  const char* pointer = value.c_str();
+void MessageWriter::AppendObjectPath(const ObjectPath& value) {
+  const char* pointer = value.value().c_str();
   AppendBasic(DBUS_TYPE_OBJECT_PATH, &pointer);
 }
 
@@ -587,7 +588,7 @@ void MessageWriter::AppendArrayOfStrings(
 }
 
 void MessageWriter::AppendArrayOfObjectPaths(
-    const std::vector<std::string>& object_paths) {
+    const std::vector<ObjectPath>& object_paths) {
   DCHECK(!container_is_open_);
   MessageWriter array_writer(message_);
   OpenArray("o", &array_writer);
@@ -652,8 +653,8 @@ void MessageWriter::AppendVariantOfString(const std::string& value) {
   AppendVariantOfBasic(DBUS_TYPE_STRING, &pointer);
 }
 
-void MessageWriter::AppendVariantOfObjectPath(const std::string& value) {
-  const char* pointer = value.c_str();
+void MessageWriter::AppendVariantOfObjectPath(const ObjectPath& value) {
+  const char* pointer = value.value().c_str();
   AppendVariantOfBasic(DBUS_TYPE_OBJECT_PATH, &pointer);
 }
 
@@ -746,11 +747,11 @@ bool MessageReader::PopString(std::string* value) {
   return success;
 }
 
-bool MessageReader::PopObjectPath(std::string* value) {
+bool MessageReader::PopObjectPath(ObjectPath* value) {
   char* tmp_value = NULL;
   const bool success = PopBasic(DBUS_TYPE_OBJECT_PATH, &tmp_value);
   if (success)
-    value->assign(tmp_value);
+    *value = ObjectPath(tmp_value);
   return success;
 }
 
@@ -805,12 +806,12 @@ bool MessageReader::PopArrayOfStrings(
 }
 
 bool MessageReader::PopArrayOfObjectPaths(
-    std::vector<std::string> *object_paths) {
+    std::vector<ObjectPath> *object_paths) {
   MessageReader array_reader(message_);
   if (!PopArray(&array_reader))
       return false;
   while (array_reader.HasMoreData()) {
-    std::string object_path;
+    ObjectPath object_path;
     if (!array_reader.PopObjectPath(&object_path))
       return false;
     object_paths->push_back(object_path);
@@ -882,11 +883,11 @@ bool MessageReader::PopVariantOfString(std::string* value) {
   return success;
 }
 
-bool MessageReader::PopVariantOfObjectPath(std::string* value) {
+bool MessageReader::PopVariantOfObjectPath(ObjectPath* value) {
   char* tmp_value = NULL;
   const bool success = PopVariantOfBasic(DBUS_TYPE_OBJECT_PATH, &tmp_value);
   if (success)
-    value->assign(tmp_value);
+    *value = ObjectPath(tmp_value);
   return success;
 }
 
diff --git a/dbus/message.h b/dbus/message.h
index 54227a0..4683abe 100644
--- a/dbus/message.h
+++ b/dbus/message.h
@@ -11,6 +11,7 @@
 #include <dbus/dbus.h>
 
 #include "base/basictypes.h"
+#include "dbus/object_path.h"
 
 namespace google {
 namespace protobuf {
@@ -80,7 +81,7 @@ class Message {
 
   // Sets the destination, the path, the interface, the member, etc.
   void SetDestination(const std::string& destination);
-  void SetPath(const std::string& path);
+  void SetPath(const ObjectPath& path);
   void SetInterface(const std::string& interface);
   void SetMember(const std::string& member);
   void SetErrorName(const std::string& error_name);
@@ -92,7 +93,7 @@ class Message {
   // Gets the destination, the path, the interface, the member, etc.
   // If not set, an empty string is returned.
   std::string GetDestination();
-  std::string GetPath();
+  ObjectPath GetPath();
   std::string GetInterface();
   std::string GetMember();
   std::string GetErrorName();
@@ -265,7 +266,7 @@ class MessageWriter {
   void AppendUint64(uint64 value);
   void AppendDouble(double value);
   void AppendString(const std::string& value);
-  void AppendObjectPath(const std::string& value);
+  void AppendObjectPath(const ObjectPath& value);
 
   // Opens an array. The array contents can be added to the array with
   // |sub_writer|. The client code must close the array with
@@ -302,7 +303,7 @@ class MessageWriter {
   // Appends the array of object paths. Arrays of object paths are often
   // used when exchanging object paths, hence it's worth having a
   // specialized function.
-  void AppendArrayOfObjectPaths(const std::vector<std::string>& object_paths);
+  void AppendArrayOfObjectPaths(const std::vector<ObjectPath>& object_paths);
 
   // Appends the protocol buffer as an array of bytes. The buffer is serialized
   // into an array of bytes before communication, since protocol buffers are not
@@ -326,7 +327,7 @@ class MessageWriter {
   void AppendVariantOfUint64(uint64 value);
   void AppendVariantOfDouble(double value);
   void AppendVariantOfString(const std::string& value);
-  void AppendVariantOfObjectPath(const std::string& value);
+  void AppendVariantOfObjectPath(const ObjectPath& value);
 
  private:
   // Helper function used to implement AppendByte etc.
@@ -374,7 +375,7 @@ class MessageReader {
   bool PopUint64(uint64* value);
   bool PopDouble(double* value);
   bool PopString(std::string* value);
-  bool PopObjectPath(std::string* value);
+  bool PopObjectPath(ObjectPath* value);
 
   // Sets up the given message reader to read an array at the current
   // iterator position.
@@ -409,7 +410,7 @@ class MessageReader {
   // Arrays of object paths are often used to communicate with D-Bus
   // services like NetworkManager, hence it's worth having a specialized
   // function.
-  bool PopArrayOfObjectPaths(std::vector<std::string>* object_paths);
+  bool PopArrayOfObjectPaths(std::vector<ObjectPath>* object_paths);
 
   // Gets the array of bytes at the current iterator position. It then parses
   // this binary blob into the protocol buffer supplied.
@@ -436,7 +437,7 @@ class MessageReader {
   bool PopVariantOfUint64(uint64* value);
   bool PopVariantOfDouble(double* value);
   bool PopVariantOfString(std::string* value);
-  bool PopVariantOfObjectPath(std::string* value);
+  bool PopVariantOfObjectPath(ObjectPath* value);
 
   // Get the data type of the value at the current iterator
   // position. INVALID_DATA will be returned if the iterator points to the
diff --git a/dbus/message_unittest.cc b/dbus/message_unittest.cc
index 1e6d668..a40ba0aa 100644
--- a/dbus/message_unittest.cc
+++ b/dbus/message_unittest.cc
@@ -7,6 +7,7 @@
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "dbus/object_path.h"
 #include "dbus/test_proto.pb.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -50,7 +51,7 @@ TEST(MessageTest, AppendAndPopBasicDataTypes) {
   writer.AppendUint64(7);
   writer.AppendDouble(8.0);
   writer.AppendString("string");
-  writer.AppendObjectPath("/object/path");
+  writer.AppendObjectPath(dbus::ObjectPath("/object/path"));
 
   uint8 byte_value = 0;
   bool bool_value = false;
@@ -62,7 +63,7 @@ TEST(MessageTest, AppendAndPopBasicDataTypes) {
   uint64 uint64_value = 0;
   double double_value = 0;
   std::string string_value;
-  std::string object_path_value;
+  dbus::ObjectPath object_path_value;
 
   dbus::MessageReader reader(message.get());
   ASSERT_TRUE(reader.HasMoreData());
@@ -90,7 +91,7 @@ TEST(MessageTest, AppendAndPopBasicDataTypes) {
   EXPECT_EQ(7U, uint64_value);
   EXPECT_DOUBLE_EQ(8.0, double_value);
   EXPECT_EQ("string", string_value);
-  EXPECT_EQ("/object/path", object_path_value);
+  EXPECT_EQ(dbus::ObjectPath("/object/path"), object_path_value);
 }
 
 // Check all variant types can be properly written and read.
@@ -109,7 +110,7 @@ TEST(MessageTest, AppendAndPopVariantDataTypes) {
   writer.AppendVariantOfUint64(7);
   writer.AppendVariantOfDouble(8.0);
   writer.AppendVariantOfString("string");
-  writer.AppendVariantOfObjectPath("/object/path");
+  writer.AppendVariantOfObjectPath(dbus::ObjectPath("/object/path"));
 
   uint8 byte_value = 0;
   bool bool_value = false;
@@ -121,7 +122,7 @@ TEST(MessageTest, AppendAndPopVariantDataTypes) {
   uint64 uint64_value = 0;
   double double_value = 0;
   std::string string_value;
-  std::string object_path_value;
+  dbus::ObjectPath object_path_value;
 
   dbus::MessageReader reader(message.get());
   ASSERT_TRUE(reader.HasMoreData());
@@ -149,7 +150,7 @@ TEST(MessageTest, AppendAndPopVariantDataTypes) {
   EXPECT_EQ(7U, uint64_value);
   EXPECT_DOUBLE_EQ(8.0, double_value);
   EXPECT_EQ("string", string_value);
-  EXPECT_EQ("/object/path", object_path_value);
+  EXPECT_EQ(dbus::ObjectPath("/object/path"), object_path_value);
 }
 
 TEST(MessageTest, ArrayOfBytes) {
@@ -211,20 +212,20 @@ TEST(MessageTest, ArrayOfStrings) {
 TEST(MessageTest, ArrayOfObjectPaths) {
   scoped_ptr<dbus::Response> message(dbus::Response::CreateEmpty());
   dbus::MessageWriter writer(message.get());
-  std::vector<std::string> object_paths;
-  object_paths.push_back("/object/path/1");
-  object_paths.push_back("/object/path/2");
-  object_paths.push_back("/object/path/3");
+  std::vector<dbus::ObjectPath> object_paths;
+  object_paths.push_back(dbus::ObjectPath("/object/path/1"));
+  object_paths.push_back(dbus::ObjectPath("/object/path/2"));
+  object_paths.push_back(dbus::ObjectPath("/object/path/3"));
   writer.AppendArrayOfObjectPaths(object_paths);
 
   dbus::MessageReader reader(message.get());
-  std::vector<std::string> output_object_paths;
+  std::vector<dbus::ObjectPath> output_object_paths;
   ASSERT_TRUE(reader.PopArrayOfObjectPaths(&output_object_paths));
   ASSERT_FALSE(reader.HasMoreData());
   ASSERT_EQ(3U, output_object_paths.size());
-  EXPECT_EQ("/object/path/1", output_object_paths[0]);
-  EXPECT_EQ("/object/path/2", output_object_paths[1]);
-  EXPECT_EQ("/object/path/3", output_object_paths[2]);
+  EXPECT_EQ(dbus::ObjectPath("/object/path/1"), output_object_paths[0]);
+  EXPECT_EQ(dbus::ObjectPath("/object/path/2"), output_object_paths[1]);
+  EXPECT_EQ(dbus::ObjectPath("/object/path/3"), output_object_paths[2]);
 }
 
 TEST(MessageTest, ProtoBuf) {
@@ -408,7 +409,7 @@ TEST(MessageTest, MethodCall) {
   EXPECT_EQ(dbus::Message::MESSAGE_METHOD_CALL, method_call.GetMessageType());
   EXPECT_EQ("MESSAGE_METHOD_CALL", method_call.GetMessageTypeAsString());
   method_call.SetDestination("com.example.Service");
-  method_call.SetPath("/com/example/Object");
+  method_call.SetPath(dbus::ObjectPath("/com/example/Object"));
 
   dbus::MessageWriter writer(&method_call);
   writer.AppendString("payload");
@@ -440,7 +441,7 @@ TEST(MessageTest, Signal) {
   EXPECT_TRUE(signal.raw_message() != NULL);
   EXPECT_EQ(dbus::Message::MESSAGE_SIGNAL, signal.GetMessageType());
   EXPECT_EQ("MESSAGE_SIGNAL", signal.GetMessageTypeAsString());
-  signal.SetPath("/com/example/Object");
+  signal.SetPath(dbus::ObjectPath("/com/example/Object"));
 
   dbus::MessageWriter writer(&signal);
   writer.AppendString("payload");
@@ -513,7 +514,7 @@ TEST(MessageTest, GetAndSetHeaders) {
   scoped_ptr<dbus::Response> message(dbus::Response::CreateEmpty());
 
   EXPECT_EQ("", message->GetDestination());
-  EXPECT_EQ("", message->GetPath());
+  EXPECT_EQ(dbus::ObjectPath(""), message->GetPath());
   EXPECT_EQ("", message->GetInterface());
   EXPECT_EQ("", message->GetMember());
   EXPECT_EQ("", message->GetErrorName());
@@ -522,7 +523,7 @@ TEST(MessageTest, GetAndSetHeaders) {
   EXPECT_EQ(0U, message->GetReplySerial());
 
   message->SetDestination("org.chromium.destination");
-  message->SetPath("/org/chromium/path");
+  message->SetPath(dbus::ObjectPath("/org/chromium/path"));
   message->SetInterface("org.chromium.interface");
   message->SetMember("member");
   message->SetErrorName("org.chromium.error");
@@ -531,7 +532,7 @@ TEST(MessageTest, GetAndSetHeaders) {
   message->SetReplySerial(456);
 
   EXPECT_EQ("org.chromium.destination", message->GetDestination());
-  EXPECT_EQ("/org/chromium/path", message->GetPath());
+  EXPECT_EQ(dbus::ObjectPath("/org/chromium/path"), message->GetPath());
   EXPECT_EQ("org.chromium.interface", message->GetInterface());
   EXPECT_EQ("member", message->GetMember());
   EXPECT_EQ("org.chromium.error", message->GetErrorName());
diff --git a/dbus/mock_bus.h b/dbus/mock_bus.h
index 31c1349..463790a 100644
--- a/dbus/mock_bus.h
+++ b/dbus/mock_bus.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "dbus/bus.h"
+#include "dbus/object_path.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 namespace dbus {
@@ -20,14 +21,14 @@ class MockBus : public Bus {
   virtual ~MockBus();
 
   MOCK_METHOD2(GetObjectProxy, ObjectProxy*(const std::string& service_name,
-                                            const std::string& object_path));
+                                            const ObjectPath& object_path));
   MOCK_METHOD3(GetObjectProxyWithOptions,
                ObjectProxy*(const std::string& service_name,
-                            const std::string& object_path,
+                            const ObjectPath& object_path,
                             int options));
   MOCK_METHOD2(GetExportedObject, ExportedObject*(
       const std::string& service_name,
-      const std::string& object_path));
+      const ObjectPath& object_path));
   MOCK_METHOD0(ShutdownAndBlock, void());
   MOCK_METHOD0(ShutdownOnDBusThreadAndBlock, void());
   MOCK_METHOD0(Connect, bool());
@@ -50,11 +51,11 @@ class MockBus : public Bus {
                               DBusError* error));
   MOCK_METHOD2(RemoveMatch, void(const std::string& match_rule,
                                  DBusError* error));
-  MOCK_METHOD4(TryRegisterObjectPath, bool(const std::string& object_path,
+  MOCK_METHOD4(TryRegisterObjectPath, bool(const ObjectPath& object_path,
                                            const DBusObjectPathVTable* vtable,
                                            void* user_data,
                                            DBusError* error));
-  MOCK_METHOD1(UnregisterObjectPath, void(const std::string& object_path));
+  MOCK_METHOD1(UnregisterObjectPath, void(const ObjectPath& object_path));
   MOCK_METHOD2(PostTaskToOriginThread, void(
       const tracked_objects::Location& from_here,
       const base::Closure& task));
diff --git a/dbus/mock_exported_object.cc b/dbus/mock_exported_object.cc
index 0fd4f2e..f49cd3d 100644
--- a/dbus/mock_exported_object.cc
+++ b/dbus/mock_exported_object.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -8,7 +8,7 @@ namespace dbus {
 
 MockExportedObject::MockExportedObject(Bus* bus,
                                        const std::string& service_name,
-                                       const std::string& object_path)
+                                       const ObjectPath& object_path)
     : ExportedObject(bus, service_name, object_path) {
 }
 
diff --git a/dbus/mock_exported_object.h b/dbus/mock_exported_object.h
index 17a36d0..7deb111 100644
--- a/dbus/mock_exported_object.h
+++ b/dbus/mock_exported_object.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "dbus/exported_object.h"
+#include "dbus/object_path.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 namespace dbus {
@@ -18,7 +19,7 @@ class MockExportedObject : public ExportedObject {
  public:
   MockExportedObject(Bus* bus,
                      const std::string& service_name,
-                     const std::string& object_path);
+                     const ObjectPath& object_path);
   virtual ~MockExportedObject();
 
   MOCK_METHOD3(ExportMethodAndBlock,
diff --git a/dbus/mock_object_proxy.cc b/dbus/mock_object_proxy.cc
index a7186bb..7e26f01 100644
--- a/dbus/mock_object_proxy.cc
+++ b/dbus/mock_object_proxy.cc
@@ -8,7 +8,7 @@ namespace dbus {
 
 MockObjectProxy::MockObjectProxy(Bus* bus,
                                  const std::string& service_name,
-                                 const std::string& object_path)
+                                 const ObjectPath& object_path)
     : ObjectProxy(bus, service_name, object_path, DEFAULT_OPTIONS) {
 }
 
diff --git a/dbus/mock_object_proxy.h b/dbus/mock_object_proxy.h
index b5d4477..a8a5791 100644
--- a/dbus/mock_object_proxy.h
+++ b/dbus/mock_object_proxy.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -8,6 +8,7 @@
 
 #include <string>
 
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
@@ -18,7 +19,7 @@ class MockObjectProxy : public ObjectProxy {
  public:
   MockObjectProxy(Bus* bus,
                   const std::string& service_name,
-                  const std::string& object_path);
+                  const ObjectPath& object_path);
   virtual ~MockObjectProxy();
 
   MOCK_METHOD2(CallMethodAndBlock, Response*(MethodCall* method_call,
diff --git a/dbus/mock_unittest.cc b/dbus/mock_unittest.cc
index 022b03d..cf644df 100644
--- a/dbus/mock_unittest.cc
+++ b/dbus/mock_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -11,6 +11,7 @@
 #include "dbus/mock_bus.h"
 #include "dbus/mock_object_proxy.h"
 #include "dbus/mock_exported_object.h"
+#include "dbus/object_path.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -31,9 +32,10 @@ class MockTest : public testing::Test {
     mock_bus_ = new dbus::MockBus(options);
 
     // Create a mock proxy.
-    mock_proxy_ = new dbus::MockObjectProxy(mock_bus_.get(),
-                                            "org.chromium.TestService",
-                                            "/org/chromium/TestObject");
+    mock_proxy_ = new dbus::MockObjectProxy(
+        mock_bus_.get(),
+        "org.chromium.TestService",
+        dbus::ObjectPath("/org/chromium/TestObject"));
 
     // Set an expectation so mock_proxy's CallMethodAndBlock() will use
     // CreateMockProxyResponse() to return responses.
@@ -49,8 +51,9 @@ class MockTest : public testing::Test {
 
     // Set an expectation so mock_bus's GetObjectProxy() for the given
     // service name and the object path will return mock_proxy_.
-    EXPECT_CALL(*mock_bus_, GetObjectProxy("org.chromium.TestService",
-                                          "/org/chromium/TestObject"))
+    EXPECT_CALL(*mock_bus_, GetObjectProxy(
+        "org.chromium.TestService",
+        dbus::ObjectPath("/org/chromium/TestObject")))
         .WillOnce(Return(mock_proxy_.get()));
 
     // ShutdownAndBlock() will be called in TearDown().
@@ -130,7 +133,7 @@ TEST_F(MockTest, CallMethodAndBlock) {
   // Get an object proxy from the mock bus.
   dbus::ObjectProxy* proxy = mock_bus_->GetObjectProxy(
       "org.chromium.TestService",
-      "/org/chromium/TestObject");
+      dbus::ObjectPath("/org/chromium/TestObject"));
 
   // Create a method call.
   dbus::MethodCall method_call("org.chromium.TestInterface", "Echo");
@@ -159,7 +162,7 @@ TEST_F(MockTest, CallMethod) {
   // Get an object proxy from the mock bus.
   dbus::ObjectProxy* proxy = mock_bus_->GetObjectProxy(
       "org.chromium.TestService",
-      "/org/chromium/TestObject");
+      dbus::ObjectPath("/org/chromium/TestObject"));
 
   // Create a method call.
   dbus::MethodCall method_call("org.chromium.TestInterface", "Echo");
diff --git a/dbus/object_path.cc b/dbus/object_path.cc
new file mode 100644
index 0000000..2dda466
--- /dev/null
+++ b/dbus/object_path.cc
@@ -0,0 +1,21 @@
+// 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.
+
+#include "dbus/object_path.h"
+
+namespace dbus {
+
+bool ObjectPath::operator<(const ObjectPath& that) const {
+  return value_ < that.value_;
+}
+
+bool ObjectPath::operator==(const ObjectPath& that) const {
+  return value_ == that.value_;
+}
+
+bool ObjectPath::operator!=(const ObjectPath& that) const {
+  return value_ != that.value_;
+}
+
+} // namespace dbus
diff --git a/dbus/object_path.h b/dbus/object_path.h
new file mode 100644
index 0000000..59071da
--- /dev/null
+++ b/dbus/object_path.h
@@ -0,0 +1,46 @@
+// 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_OBJECT_PATH_H_
+#define DBUS_OBJECT_PATH_H_
+#pragma once
+
+#include <string>
+
+namespace dbus {
+
+// ObjectPath is a type used to distinguish D-Bus object paths from simple
+// strings, especially since normal practice is that these should be only
+// initialized from static constants or obtained from remote objects and no
+// assumptions about their value made.
+class ObjectPath {
+ public:
+  // Permit initialization without a value for passing to
+  // dbus::MessageReader::PopObjectPath to fill in and from std::string
+  // objects.
+  //
+  // The compiler synthesised copy constructor and assignment operator are
+  // sufficient for our needs, as is implicit initialization of a std::string
+  // from a string constant.
+  ObjectPath() {}
+  explicit ObjectPath(const std::string& value) : value_(value) {}
+
+  // Retrieves value as a std::string.
+  const std::string& value() const { return value_; }
+
+  // Permit sufficient comparison to allow an ObjectPath to be used as a
+  // key in a std::map.
+  bool operator<(const ObjectPath&) const;
+
+  // Permit testing for equality, required for mocks to work and useful for
+  // observers.
+  bool operator==(const ObjectPath&) const;
+  bool operator!=(const ObjectPath&) const;
+ private:
+  std::string value_;
+};
+
+}  // namespace dbus
+
+#endif  // DBUS_OBJECT_PATH_H_
diff --git a/dbus/object_proxy.cc b/dbus/object_proxy.cc
index 58d679c..32f6a60 100644
--- a/dbus/object_proxy.cc
+++ b/dbus/object_proxy.cc
@@ -13,6 +13,7 @@
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "dbus/message.h"
+#include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "dbus/scoped_dbus_error.h"
 
@@ -42,7 +43,7 @@ namespace dbus {
 
 ObjectProxy::ObjectProxy(Bus* bus,
                          const std::string& service_name,
-                         const std::string& object_path,
+                         const ObjectPath& object_path,
                          int options)
     : bus_(bus),
       service_name_(service_name),
diff --git a/dbus/object_proxy.h b/dbus/object_proxy.h
index 3da4e9b..3a9fab1 100644
--- a/dbus/object_proxy.h
+++ b/dbus/object_proxy.h
@@ -16,6 +16,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/string_piece.h"
 #include "base/time.h"
+#include "dbus/object_path.h"
 
 namespace dbus {
 
@@ -35,7 +36,7 @@ class ObjectProxy : public base::RefCountedThreadSafe<ObjectProxy> {
   // Bus::GetObjectProxyWithOptions() instead of this constructor.
   ObjectProxy(Bus* bus,
               const std::string& service_name,
-              const std::string& object_path,
+              const ObjectPath& object_path,
               int options);
 
   // Options to be OR-ed together when calling Bus::GetObjectProxyWithOptions().
@@ -196,7 +197,7 @@ class ObjectProxy : public base::RefCountedThreadSafe<ObjectProxy> {
 
   scoped_refptr<Bus> bus_;
   std::string service_name_;
-  std::string object_path_;
+  ObjectPath object_path_;
 
   // True if the message filter was added.
   bool filter_added_;
diff --git a/dbus/test_service.cc b/dbus/test_service.cc
index 714c09b..6454bb5 100644
--- a/dbus/test_service.cc
+++ b/dbus/test_service.cc
@@ -10,6 +10,7 @@
 #include "dbus/bus.h"
 #include "dbus/exported_object.h"
 #include "dbus/message.h"
+#include "dbus/object_path.h"
 
 namespace dbus {
 
@@ -96,7 +97,7 @@ void TestService::SendTestSignalFromRootInternal(const std::string& message) {
   // Use "/" just like dbus-send does.
   ExportedObject* root_object =
       bus_->GetExportedObject("org.chromium.TestService",
-                              "/");
+                              dbus::ObjectPath("/"));
   root_object->SendSignal(&signal);
 }
 
@@ -125,7 +126,7 @@ void TestService::Run(MessageLoop* message_loop) {
 
   exported_object_ = bus_->GetExportedObject(
       "org.chromium.TestService",
-      "/org/chromium/TestObject");
+      dbus::ObjectPath("/org/chromium/TestObject"));
 
   int num_methods = 0;
   exported_object_->ExportMethod(