MTP Streaming: Optimize block reading

device/media_transfer_protocol/media_transfer_protocol_daemon_client.cc

 // 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 "device/media_transfer_protocol/media_transfer_protocol_daemon_client.h"
 
 #include "base/bind.h"
 #include "base/memory/weak_ptr.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
 #include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
 #include "device/media_transfer_protocol/mtp_file_entry.pb.h"
 #include "device/media_transfer_protocol/mtp_storage_info.pb.h"
 #include "third_party/cros_system_api/dbus/service_constants.h"
 
 namespace device {
 
 namespace {
 
 const char kInvalidResponseMsg[] = "Invalid Response: ";
+uint32 kMaxChunkSize = 1024*1024;  // D-Bus has message size limits.
 
 // The MediaTransferProtocolDaemonClient implementation.
 class MediaTransferProtocolDaemonClientImpl
     : public MediaTransferProtocolDaemonClient {
  public:
   explicit MediaTransferProtocolDaemonClientImpl(dbus::Bus* bus)
       : proxy_(bus->GetObjectProxy(
           mtpd::kMtpdServiceName,
           dbus::ObjectPath(mtpd::kMtpdServicePath))),
         listen_for_changes_called_(false),
@@ skipping 101 matching lines @@
   }
 
   // MediaTransferProtocolDaemonClient override.
   virtual void ReadFileChunkByPath(
       const std::string& handle,
       const std::string& path,
       uint32 offset,
       uint32 bytes_to_read,
       const ReadFileCallback& callback,
       const ErrorCallback& error_callback) OVERRIDE {
+    DCHECK_LE(bytes_to_read, kMaxChunkSize);
     dbus::MethodCall method_call(mtpd::kMtpdInterface,
                                  mtpd::kReadFileChunkByPath);
     dbus::MessageWriter writer(&method_call);
     writer.AppendString(handle);
     writer.AppendString(path);
     writer.AppendUint32(offset);
     writer.AppendUint32(bytes_to_read);
     proxy_->CallMethod(
         &method_call, dbus::ObjectProxy::TIMEOUT_USE_DEFAULT,
         base::Bind(&MediaTransferProtocolDaemonClientImpl::OnReadFile,
                    weak_ptr_factory_.GetWeakPtr(),
                    callback,
                    error_callback));
   }
 
   // MediaTransferProtocolDaemonClient override.
   virtual void ReadFileChunkById(const std::string& handle,
                                  uint32 file_id,
                                  uint32 offset,
                                  uint32 bytes_to_read,
                                  const ReadFileCallback& callback,
                                  const ErrorCallback& error_callback) OVERRIDE {
+    DCHECK_LE(bytes_to_read, kMaxChunkSize);
     dbus::MethodCall method_call(mtpd::kMtpdInterface,
                                  mtpd::kReadFileChunkById);
     dbus::MessageWriter writer(&method_call);
     writer.AppendString(handle);
     writer.AppendUint32(file_id);
     writer.AppendUint32(offset);
     writer.AppendUint32(bytes_to_read);
     proxy_->CallMethod(
         &method_call, dbus::ObjectProxy::TIMEOUT_USE_DEFAULT,
         base::Bind(&MediaTransferProtocolDaemonClientImpl::OnReadFile,
@@ skipping 248 matching lines @@
 
 MediaTransferProtocolDaemonClient::~MediaTransferProtocolDaemonClient() {}
 
 // static
 MediaTransferProtocolDaemonClient* MediaTransferProtocolDaemonClient::Create(
     dbus::Bus* bus) {
   return new MediaTransferProtocolDaemonClientImpl(bus);
 }
 
 }  // namespace device