device/bluetooth: Update GATT descriptor value D-Bus bindings.

This CL updates the Chrome D-Bus bindings and modifies the device/bluetooth
GATT Chrome OS code to use the new bindings defined in crbug.com/378182 for
descriptor value reads and writes.

BUG=378182
TEST=device_unittests; manual tests using custom bluetoothd

Review URL: https://codereview.chromium.org/309623002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275718 0039d316-1c4b-4281-b951-d872f2087c98

10 files changed, 255 insertions, 123 deletions

diff --git a/chromeos/dbus/bluetooth_gatt_descriptor_client.cc b/chromeos/dbus/bluetooth_gatt_descriptor_client.cc
index 9ec73e7..850b228 100644
--- a/chromeos/dbus/bluetooth_gatt_descriptor_client.cc
+++ b/chromeos/dbus/bluetooth_gatt_descriptor_client.cc
@@ -13,6 +13,13 @@
 
 namespace chromeos {
 
+// static
+const char BluetoothGattDescriptorClient::kNoResponseError[] =
+    "org.chromium.Error.NoResponse";
+// static
+const char BluetoothGattDescriptorClient::kUnknownDescriptorError[] =
+    "org.chromium.Error.UnknownDescriptor";
+
 BluetoothGattDescriptorClient::Properties::Properties(
     dbus::ObjectProxy* object_proxy,
     const std::string& interface_name,
@@ -21,7 +28,6 @@ BluetoothGattDescriptorClient::Properties::Properties(
   RegisterProperty(bluetooth_gatt_descriptor::kUUIDProperty, &uuid);
   RegisterProperty(bluetooth_gatt_descriptor::kCharacteristicProperty,
                    &characteristic);
-  RegisterProperty(bluetooth_gatt_descriptor::kValueProperty, &value);
 }
 
 BluetoothGattDescriptorClient::Properties::~Properties() {
@@ -73,6 +79,61 @@ class BluetoothGattDescriptorClientImpl
             bluetooth_gatt_descriptor::kBluetoothGattDescriptorInterface));
   }
 
+  // BluetoothGattDescriptorClientImpl override.
+  virtual void ReadValue(const dbus::ObjectPath& object_path,
+                         const ValueCallback& callback,
+                         const ErrorCallback& error_callback) OVERRIDE {
+    dbus::ObjectProxy* object_proxy =
+        object_manager_->GetObjectProxy(object_path);
+    if (!object_proxy) {
+      error_callback.Run(kUnknownDescriptorError, "");
+      return;
+    }
+
+    dbus::MethodCall method_call(
+        bluetooth_gatt_descriptor::kBluetoothGattDescriptorInterface,
+        bluetooth_gatt_descriptor::kReadValue);
+
+    object_proxy->CallMethodWithErrorCallback(
+        &method_call,
+        dbus::ObjectProxy::TIMEOUT_USE_DEFAULT,
+        base::Bind(&BluetoothGattDescriptorClientImpl::OnValueSuccess,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   callback),
+        base::Bind(&BluetoothGattDescriptorClientImpl::OnError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback));
+  }
+
+  // BluetoothGattDescriptorClientImpl override.
+  virtual void WriteValue(const dbus::ObjectPath& object_path,
+                          const std::vector<uint8>& value,
+                          const base::Closure& callback,
+                          const ErrorCallback& error_callback) OVERRIDE {
+    dbus::ObjectProxy* object_proxy =
+        object_manager_->GetObjectProxy(object_path);
+    if (!object_proxy) {
+      error_callback.Run(kUnknownDescriptorError, "");
+      return;
+    }
+
+    dbus::MethodCall method_call(
+        bluetooth_gatt_descriptor::kBluetoothGattDescriptorInterface,
+        bluetooth_gatt_descriptor::kWriteValue);
+    dbus::MessageWriter writer(&method_call);
+    writer.AppendArrayOfBytes(value.data(), value.size());
+
+    object_proxy->CallMethodWithErrorCallback(
+        &method_call,
+        dbus::ObjectProxy::TIMEOUT_USE_DEFAULT,
+        base::Bind(&BluetoothGattDescriptorClientImpl::OnSuccess,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   callback),
+        base::Bind(&BluetoothGattDescriptorClientImpl::OnError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback));
+  }
+
   // dbus::ObjectManager::Interface override.
   virtual dbus::PropertySet* CreateProperties(
       dbus::ObjectProxy *object_proxy,
@@ -128,6 +189,49 @@ class BluetoothGattDescriptorClientImpl
                                                     property_name));
   }
 
+  // Called when a response for a successful method call is received.
+  void OnSuccess(const base::Closure& callback, dbus::Response* response) {
+    DCHECK(response);
+    callback.Run();
+  }
+
+  // Called when a descriptor value response for a successful method call is
+  // received.
+  void OnValueSuccess(const ValueCallback& callback, dbus::Response* response) {
+    DCHECK(response);
+    dbus::MessageReader reader(response);
+
+    const uint8* bytes = NULL;
+    size_t length = 0;
+
+    if (!reader.PopArrayOfBytes(&bytes, &length))
+      VLOG(2) << "Error reading array of bytes in ValueCallback";
+
+    std::vector<uint8> value;
+
+    if (bytes)
+      value.assign(bytes, bytes + length);
+
+    callback.Run(value);
+  }
+
+  // Called when a response for a failed method call is received.
+  void OnError(const ErrorCallback& error_callback,
+               dbus::ErrorResponse* response) {
+    // Error response has optional error message argument.
+    std::string error_name;
+    std::string error_message;
+    if (response) {
+      dbus::MessageReader reader(response);
+      error_name = response->GetErrorName();
+      reader.PopString(&error_message);
+    } else {
+      error_name = kNoResponseError;
+      error_message = "";
+    }
+    error_callback.Run(error_name, error_message);
+  }
+
   dbus::ObjectManager* object_manager_;
 
   // List of observers interested in event notifications from us.
diff --git a/chromeos/dbus/bluetooth_gatt_descriptor_client.h b/chromeos/dbus/bluetooth_gatt_descriptor_client.h
index 3a7a26f..c3f24ac 100644
--- a/chromeos/dbus/bluetooth_gatt_descriptor_client.h
+++ b/chromeos/dbus/bluetooth_gatt_descriptor_client.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "chromeos/chromeos_export.h"
 #include "chromeos/dbus/dbus_client.h"
 #include "dbus/object_path.h"
@@ -28,11 +29,6 @@ class CHROMEOS_EXPORT BluetoothGattDescriptorClient : public DBusClient {
     // [read-only]
     dbus::Property<dbus::ObjectPath> characteristic;
 
-    // Raw characteristic descriptor value read from the remote Bluetooth
-    // device. Setting the value sends a write request to the remote device.
-    // [read-write]
-    dbus::Property<std::vector<uint8> > value;
-
     Properties(dbus::ObjectProxy* object_proxy,
                const std::string& interface_name,
                const PropertyChangedCallback& callback);
@@ -60,6 +56,11 @@ class CHROMEOS_EXPORT BluetoothGattDescriptorClient : public DBusClient {
         const std::string& property_name) {}
   };
 
+  // Callbacks used to report the result of asynchronous methods.
+  typedef base::Callback<void(const std::string& error_name,
+                              const std::string& error_message)> ErrorCallback;
+  typedef base::Callback<void(const std::vector<uint8>& value)> ValueCallback;
+
   virtual ~BluetoothGattDescriptorClient();
 
   // Adds and removes observers for events on all remote GATT descriptors. Check
@@ -75,9 +76,28 @@ class CHROMEOS_EXPORT BluetoothGattDescriptorClient : public DBusClient {
   // |object_path|. Values should be copied if needed.
   virtual Properties* GetProperties(const dbus::ObjectPath& object_path) = 0;
 
+  // Issues a request to read the value of GATT descriptor with object path
+  // |object_path| and returns the value in |callback| on success. On error,
+  // invokes |error_callback|.
+  virtual void ReadValue(const dbus::ObjectPath& object_path,
+                         const ValueCallback& callback,
+                         const ErrorCallback& error_callback) = 0;
+
+  // Issues a request to write the value of GATT descriptor with object path
+  // |object_path| with value |value|. Invokes |callback| on success and
+  // |error_callback| on failure.
+  virtual void WriteValue(const dbus::ObjectPath& object_path,
+                          const std::vector<uint8>& value,
+                          const base::Closure& callback,
+                          const ErrorCallback& error_callback) = 0;
+
   // Creates the instance.
   static BluetoothGattDescriptorClient* Create();
 
+  // Constants used to indicate exceptional error conditions.
+  static const char kNoResponseError[];
+  static const char kUnknownDescriptorError[];
+
  protected:
   BluetoothGattDescriptorClient();
 
diff --git a/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.cc b/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.cc
index 4bb5255..a39a160 100644
--- a/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.cc
+++ b/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.cc
@@ -42,19 +42,13 @@ void FakeBluetoothGattDescriptorClient::Properties::Set(
     dbus::PropertyBase* property,
     dbus::PropertySet::SetCallback callback) {
   VLOG(1) << "Set " << property->name();
-  if (property->name() != value.name()) {
-    callback.Run(false);
-    return;
-  }
+  callback.Run(false);
+}
 
-  // TODO(armansito): Setting the "Value" property should be allowed based
-  // on permissions.
-  if (uuid.value() != kClientCharacteristicConfigurationUUID) {
-    callback.Run(false);
-    return;
-  }
-  callback.Run(true);
-  property->ReplaceValueWithSetValue();
+FakeBluetoothGattDescriptorClient::DescriptorData::DescriptorData() {
+}
+
+FakeBluetoothGattDescriptorClient::DescriptorData::~DescriptorData() {
 }
 
 FakeBluetoothGattDescriptorClient::FakeBluetoothGattDescriptorClient()
@@ -91,7 +85,37 @@ FakeBluetoothGattDescriptorClient::GetProperties(
   PropertiesMap::const_iterator iter = properties_.find(object_path);
   if (iter == properties_.end())
     return NULL;
-  return iter->second;
+  return iter->second->properties.get();
+}
+
+void FakeBluetoothGattDescriptorClient::ReadValue(
+    const dbus::ObjectPath& object_path,
+    const ValueCallback& callback,
+    const ErrorCallback& error_callback) {
+  PropertiesMap::iterator iter = properties_.find(object_path);
+  if (iter == properties_.end()) {
+    error_callback.Run(kUnknownDescriptorError, "");
+    return;
+  }
+
+  callback.Run(iter->second->value);
+}
+
+void FakeBluetoothGattDescriptorClient::WriteValue(
+    const dbus::ObjectPath& object_path,
+    const std::vector<uint8>& value,
+    const base::Closure& callback,
+    const ErrorCallback& error_callback) {
+  if (properties_.find(object_path) == properties_.end()) {
+    error_callback.Run(kUnknownDescriptorError, "");
+    return;
+  }
+
+  // Since the only fake descriptor is "Client Characteristic Configuration"
+  // and BlueZ doesn't allow writing to it, return failure.
+  error_callback.Run("org.bluez.Error.Failed",
+                     "Writing to the Client Characteristic Configuration "
+                     "descriptor not allowed");
 }
 
 dbus::ObjectPath FakeBluetoothGattDescriptorClient::ExposeDescriptor(
@@ -118,14 +142,16 @@ dbus::ObjectPath FakeBluetoothGattDescriptorClient::ExposeDescriptor(
       &FakeBluetoothGattDescriptorClient::OnPropertyChanged,
       weak_ptr_factory_.GetWeakPtr(),
       object_path));
-  properties_[object_path] = properties;
   properties->uuid.ReplaceValue(uuid);
   properties->characteristic.ReplaceValue(characteristic_path);
 
-  std::vector<uint8> value;
-  value.push_back(0);  // Notifications/Indications disabled.
-  value.push_back(0);
-  properties->value.ReplaceValue(value);
+  DescriptorData* data = new DescriptorData();
+  data->properties.reset(properties);
+
+  data->value.push_back(1);  // Notifications enabled.
+  data->value.push_back(0);
+
+  properties_[object_path] = data;
 
   NotifyDescriptorAdded(object_path);
 
@@ -154,9 +180,6 @@ void FakeBluetoothGattDescriptorClient::OnPropertyChanged(
 
   FOR_EACH_OBSERVER(BluetoothGattDescriptorClient::Observer, observers_,
                     GattDescriptorPropertyChanged(object_path, property_name));
-
-  // TODO(armansito): Implement CCC behavior (enable/disable notifications
-  // or indications characteristics).
 }
 
 void FakeBluetoothGattDescriptorClient::NotifyDescriptorAdded(
diff --git a/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.h b/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.h
index 3676983..ce3f2d4 100644
--- a/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.h
+++ b/chromeos/dbus/fake_bluetooth_gatt_descriptor_client.h
@@ -46,6 +46,13 @@ class CHROMEOS_EXPORT FakeBluetoothGattDescriptorClient
   virtual std::vector<dbus::ObjectPath> GetDescriptors() OVERRIDE;
   virtual Properties* GetProperties(const dbus::ObjectPath& object_path)
       OVERRIDE;
+  virtual void ReadValue(const dbus::ObjectPath& object_path,
+                         const ValueCallback& callback,
+                         const ErrorCallback& error_callback) OVERRIDE;
+  virtual void WriteValue(const dbus::ObjectPath& object_path,
+                          const std::vector<uint8>& value,
+                          const base::Closure& callback,
+                          const ErrorCallback& error_callback) OVERRIDE;
 
   // Makes the descriptor with the UUID |uuid| visible under the characteristic
   // with object path |characteristic_path|. Descriptor object paths are
@@ -71,7 +78,14 @@ class CHROMEOS_EXPORT FakeBluetoothGattDescriptorClient
   void NotifyDescriptorRemoved(const dbus::ObjectPath& object_path);
 
   // Mapping from object paths to Properties structures.
-  typedef std::map<dbus::ObjectPath, Properties*> PropertiesMap;
+  struct DescriptorData {
+    DescriptorData();
+    ~DescriptorData();
+
+    scoped_ptr<Properties> properties;
+    std::vector<uint8> value;
+  };
+  typedef std::map<dbus::ObjectPath, DescriptorData*> PropertiesMap;
   PropertiesMap properties_;
 
   // List of observers interested in event notifications from us.
diff --git a/device/bluetooth/bluetooth_gatt_chromeos_unittest.cc b/device/bluetooth/bluetooth_gatt_chromeos_unittest.cc
index 814b163..235cc72 100644
--- a/device/bluetooth/bluetooth_gatt_chromeos_unittest.cc
+++ b/device/bluetooth/bluetooth_gatt_chromeos_unittest.cc
@@ -944,15 +944,19 @@ TEST_F(BluetoothGattChromeOSTest, GattDescriptorValue) {
             descriptor->GetUUID());
 
   std::vector<uint8> desc_value;
+  desc_value.push_back(1);
   desc_value.push_back(0);
-  desc_value.push_back(0);
-  EXPECT_TRUE(ValuesEqual(desc_value, descriptor->GetValue()));
+
+  /* The cached value will be empty until the first read request */
+  EXPECT_FALSE(ValuesEqual(desc_value, descriptor->GetValue()));
+  EXPECT_TRUE(descriptor->GetValue().empty());
 
   EXPECT_EQ(0, success_callback_count_);
   EXPECT_EQ(0, error_callback_count_);
   EXPECT_TRUE(last_read_value_.empty());
 
-  // Read value.
+  // Read value. GattDescriptorValueChanged event will be sent after a
+  // successful read.
   descriptor->ReadRemoteDescriptor(
       base::Bind(&BluetoothGattChromeOSTest::ValueCallback,
                  base::Unretained(this)),
@@ -961,10 +965,11 @@ TEST_F(BluetoothGattChromeOSTest, GattDescriptorValue) {
   EXPECT_EQ(1, success_callback_count_);
   EXPECT_EQ(0, error_callback_count_);
   EXPECT_TRUE(ValuesEqual(last_read_value_, descriptor->GetValue()));
+  EXPECT_TRUE(ValuesEqual(desc_value, descriptor->GetValue()));
   EXPECT_EQ(4, service_observer.gatt_service_changed_count_);
-  EXPECT_EQ(0, service_observer.gatt_descriptor_value_changed_count_);
+  EXPECT_EQ(1, service_observer.gatt_descriptor_value_changed_count_);
 
-  // Write value.
+  // Write value. Writes to this descriptor will fail.
   desc_value[0] = 0x03;
   descriptor->WriteRemoteDescriptor(
       desc_value,
@@ -972,10 +977,10 @@ TEST_F(BluetoothGattChromeOSTest, GattDescriptorValue) {
                  base::Unretained(this)),
       base::Bind(&BluetoothGattChromeOSTest::ErrorCallback,
                  base::Unretained(this)));
-  EXPECT_EQ(2, success_callback_count_);
-  EXPECT_EQ(0, error_callback_count_);
-  EXPECT_FALSE(ValuesEqual(last_read_value_, descriptor->GetValue()));
-  EXPECT_TRUE(ValuesEqual(desc_value, descriptor->GetValue()));
+  EXPECT_EQ(1, success_callback_count_);
+  EXPECT_EQ(1, error_callback_count_);
+  EXPECT_TRUE(ValuesEqual(last_read_value_, descriptor->GetValue()));
+  EXPECT_FALSE(ValuesEqual(desc_value, descriptor->GetValue()));
   EXPECT_EQ(4, service_observer.gatt_service_changed_count_);
   EXPECT_EQ(1, service_observer.gatt_descriptor_value_changed_count_);
 
@@ -985,12 +990,12 @@ TEST_F(BluetoothGattChromeOSTest, GattDescriptorValue) {
                  base::Unretained(this)),
       base::Bind(&BluetoothGattChromeOSTest::ErrorCallback,
                  base::Unretained(this)));
-  EXPECT_EQ(3, success_callback_count_);
-  EXPECT_EQ(0, error_callback_count_);
+  EXPECT_EQ(2, success_callback_count_);
+  EXPECT_EQ(1, error_callback_count_);
   EXPECT_TRUE(ValuesEqual(last_read_value_, descriptor->GetValue()));
-  EXPECT_TRUE(ValuesEqual(desc_value, descriptor->GetValue()));
+  EXPECT_FALSE(ValuesEqual(desc_value, descriptor->GetValue()));
   EXPECT_EQ(4, service_observer.gatt_service_changed_count_);
-  EXPECT_EQ(1, service_observer.gatt_descriptor_value_changed_count_);
+  EXPECT_EQ(2, service_observer.gatt_descriptor_value_changed_count_);
 }
 
 }  // namespace chromeos
diff --git a/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.cc b/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.cc
index 0a8a225..e3de615 100644
--- a/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.cc
+++ b/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.cc
@@ -268,30 +268,6 @@ void BluetoothRemoteGattCharacteristicChromeOS::GattDescriptorRemoved(
   service_->NotifyServiceChanged();
 }
 
-void BluetoothRemoteGattCharacteristicChromeOS::GattDescriptorPropertyChanged(
-    const dbus::ObjectPath& object_path,
-    const std::string& property_name) {
-  DescriptorMap::const_iterator iter = descriptors_.find(object_path);
-  if (iter == descriptors_.end())
-    return;
-
-  // Ignore all property changes except for "Value".
-  BluetoothGattDescriptorClient::Properties* properties =
-      DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->
-          GetProperties(object_path);
-  DCHECK(properties);
-  if (property_name != properties->value.name())
-    return;
-
-  VLOG(1) << "GATT descriptor property changed: " << object_path.value()
-          << ", property: " << property_name;
-
-  DCHECK(service_);
-
-  service_->NotifyDescriptorValueChanged(
-      this, iter->second, properties->value.value());
-}
-
 void BluetoothRemoteGattCharacteristicChromeOS::OnValueSuccess(
     const ValueCallback& callback,
     const std::vector<uint8>& value) {
diff --git a/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.h b/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.h
index 91c3f62..35a0884 100644
--- a/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.h
+++ b/device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.h
@@ -80,9 +80,6 @@ class BluetoothRemoteGattCharacteristicChromeOS
       const dbus::ObjectPath& object_path) OVERRIDE;
   virtual void GattDescriptorRemoved(
       const dbus::ObjectPath& object_path) OVERRIDE;
-  virtual void GattDescriptorPropertyChanged(
-      const dbus::ObjectPath& object_path,
-      const std::string& property_name) OVERRIDE;
 
   // Called by dbus:: on successful completion of a request to read
   // the characteristic value.
diff --git a/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.cc b/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.cc
index 0027173..8978cc5 100644
--- a/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.cc
+++ b/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.cc
@@ -10,6 +10,7 @@
 #include "chromeos/dbus/bluetooth_gatt_descriptor_client.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "device/bluetooth/bluetooth_remote_gatt_characteristic_chromeos.h"
+#include "device/bluetooth/bluetooth_remote_gatt_service_chromeos.h"
 
 namespace chromeos {
 
@@ -59,11 +60,7 @@ bool BluetoothRemoteGattDescriptorChromeOS::IsLocal() const {
 
 const std::vector<uint8>&
 BluetoothRemoteGattDescriptorChromeOS::GetValue() const {
-  BluetoothGattDescriptorClient::Properties* properties =
-      DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->
-          GetProperties(object_path_);
-  DCHECK(properties);
-  return properties->value.value();
+  return cached_value_;
 }
 
 device::BluetoothGattCharacteristic*
@@ -84,14 +81,15 @@ void BluetoothRemoteGattDescriptorChromeOS::ReadRemoteDescriptor(
   VLOG(1) << "Sending GATT characteristic descriptor read request to "
           << "descriptor: " << GetIdentifier() << ", UUID: "
           << GetUUID().canonical_value();
-  BluetoothGattDescriptorClient::Properties* properties =
-      DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->
-          GetProperties(object_path_);
-  DCHECK(properties);
-  properties->value.Get(
-      base::Bind(&BluetoothRemoteGattDescriptorChromeOS::OnGetValue,
+
+  DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->ReadValue(
+      object_path_,
+      base::Bind(&BluetoothRemoteGattDescriptorChromeOS::OnValueSuccess,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 callback),
+      base::Bind(&BluetoothRemoteGattDescriptorChromeOS::OnError,
                  weak_ptr_factory_.GetWeakPtr(),
-                 callback, error_callback));
+                 error_callback));
 }
 
 void BluetoothRemoteGattDescriptorChromeOS::WriteRemoteDescriptor(
@@ -102,47 +100,38 @@ void BluetoothRemoteGattDescriptorChromeOS::WriteRemoteDescriptor(
           << "characteristic: " << GetIdentifier() << ", UUID: "
           << GetUUID().canonical_value() << ", with value: "
           << new_value << ".";
-  BluetoothGattDescriptorClient::Properties* properties =
-      DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->
-          GetProperties(object_path_);
-  DCHECK(properties);
-  properties->value.Set(
+
+  DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->WriteValue(
+      object_path_,
       new_value,
-      base::Bind(&BluetoothRemoteGattDescriptorChromeOS::OnSetValue,
+      callback,
+      base::Bind(&BluetoothRemoteGattDescriptorChromeOS::OnError,
                  weak_ptr_factory_.GetWeakPtr(),
-                 callback, error_callback));
+                 error_callback));
 }
 
-void BluetoothRemoteGattDescriptorChromeOS::OnGetValue(
+void BluetoothRemoteGattDescriptorChromeOS::OnValueSuccess(
     const ValueCallback& callback,
-    const ErrorCallback& error_callback,
-    bool success) {
-  if (!success) {
-    VLOG(1) << "Failed to read the value from the remote descriptor.";
-    error_callback.Run();
-    return;
-  }
-
-  VLOG(1) << "Read value of remote descriptor.";
-  BluetoothGattDescriptorClient::Properties* properties =
-      DBusThreadManager::Get()->GetBluetoothGattDescriptorClient()->
-          GetProperties(object_path_);
-  DCHECK(properties);
-  callback.Run(properties->value.value());
+    const std::vector<uint8>& value) {
+  VLOG(1) << "Descriptor value read: " << value;
+  cached_value_ = value;
+
+  DCHECK(characteristic_);
+  BluetoothRemoteGattServiceChromeOS* service =
+      static_cast<BluetoothRemoteGattServiceChromeOS*>(
+          characteristic_->GetService());
+  DCHECK(service);
+  service->NotifyDescriptorValueChanged(characteristic_, this, value);
+  callback.Run(value);
 }
 
-void BluetoothRemoteGattDescriptorChromeOS::OnSetValue(
-    const base::Closure& callback,
+void BluetoothRemoteGattDescriptorChromeOS::OnError(
     const ErrorCallback& error_callback,
-    bool success) {
-  if (!success) {
-    VLOG(1) << "Failed to write the value of remote descriptor.";
-    error_callback.Run();
-    return;
-  }
-
-  VLOG(1) << "Wrote value of remote descriptor.";
-  callback.Run();
+    const std::string& error_name,
+    const std::string& error_message) {
+  VLOG(1) << "Operation failed: " << error_name
+          << ", message: " << error_message;
+  error_callback.Run();
 }
 
 }  // namespace chromeos
diff --git a/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.h b/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.h
index 129daea..d4ea1e6 100644
--- a/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.h
+++ b/device/bluetooth/bluetooth_remote_gatt_descriptor_chromeos.h
@@ -57,15 +57,16 @@ class BluetoothRemoteGattDescriptorChromeOS
       const dbus::ObjectPath& object_path);
   virtual ~BluetoothRemoteGattDescriptorChromeOS();
 
-  // Called by dbus:: on completion of the request to get the descriptor value.
-  void OnGetValue(const ValueCallback& callback,
-                  const ErrorCallback& error_callback,
-                  bool success);
+  // Called by dbus:: on successful completion of a request to read
+  // the descriptor value.
+  void OnValueSuccess(const ValueCallback& callback,
+                      const std::vector<uint8>& value);
 
-  // Called by dbus:: on completion of the request to set the descriptor value.
-  void OnSetValue(const base::Closure& callback,
-                  const ErrorCallback& error_callback,
-                  bool success);
+  // Called by dbus:: on unsuccessful completion of a request to read or write
+  // the descriptor value.
+  void OnError(const ErrorCallback& error_callback,
+               const std::string& error_name,
+               const std::string& error_message);
 
   // Object path of the D-Bus descriptor object.
   dbus::ObjectPath object_path_;
@@ -73,6 +74,9 @@ class BluetoothRemoteGattDescriptorChromeOS
   // The GATT characteristic this descriptor belongs to.
   BluetoothRemoteGattCharacteristicChromeOS* characteristic_;
 
+  // The cached characteristic value based on the most recent read request.
+  std::vector<uint8> cached_value_;
+
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<BluetoothRemoteGattDescriptorChromeOS> weak_ptr_factory_;
diff --git a/device/bluetooth/bluetooth_remote_gatt_service_chromeos.h b/device/bluetooth/bluetooth_remote_gatt_service_chromeos.h
index db42ecf..e490ffc 100644
--- a/device/bluetooth/bluetooth_remote_gatt_service_chromeos.h
+++ b/device/bluetooth/bluetooth_remote_gatt_service_chromeos.h
@@ -89,8 +89,8 @@ class BluetoothRemoteGattServiceChromeOS
       bool added);
 
   // Notifies its observers that the value of a descriptor has changed. Called
-  // by BluetoothRemoteGattCharacteristicChromeOS instances to notify service
-  // observers when the value of one of their descriptors gets updated.
+  // by BluetoothRemoteGattDescriptorChromeOS instances to notify service
+  // observers when their cached value gets updated after a read request.
   void NotifyDescriptorValueChanged(
       BluetoothRemoteGattCharacteristicChromeOS* characteristic,
       BluetoothRemoteGattDescriptorChromeOS* descriptor,