MTP Streaming: Optimize block reading

chrome/browser/media_galleries/linux/mtp_device_task_helper.h

 // Copyright 2013 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 CHROME_BROWSER_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 14 matching lines @@
 // MTPDeviceTaskHelper lives on the UI thread. MTPDeviceTaskHelperMapService
 // owns the MTPDeviceTaskHelper objects. MTPDeviceTaskHelper is instantiated per
 // MTP device storage.
 class MTPDeviceTaskHelper {
  public:
   typedef base::Callback<void(bool succeeded)> OpenStorageCallback;
 
   typedef MTPDeviceAsyncDelegate::GetFileInfoSuccessCallback
       GetFileInfoSuccessCallback;
 
+  typedef base::Callback<void(int)> ReadBytesSuccessCallback;
+
   typedef base::Callback<void(const fileapi::AsyncFileUtil::EntryList&)>
       ReadDirectorySuccessCallback;
 
   typedef MTPDeviceAsyncDelegate::ErrorCallback ErrorCallback;
 
   MTPDeviceTaskHelper();
   ~MTPDeviceTaskHelper();
 
   // Dispatches the request to the MediaTransferProtocolManager to open the MTP
   // storage for communication.
@@ skipping 37 matching lines @@
   // object.
   //
   // |request_info| specifies the snapshot file request params.
   // |snapshot_file_info| specifies the metadata of the snapshot file.
   void WriteDataIntoSnapshotFile(
       const SnapshotRequestInfo& request_info,
       const base::File::Info& snapshot_file_info);
 
   // Dispatches the read bytes request to the MediaTransferProtocolManager.
   //
-  // |request| contains details about the byte request including the file path,
-  // byte range, and the callbacks. The callbacks specified within |request| are
-  // called on the IO thread to notify the caller about success or failure.
-  void ReadBytes(const MTPDeviceAsyncDelegate::ReadBytesRequest& request);
+  // |success_callback| is invoked on the IO thread to notify the caller about
+  // the number of bytes read.
+  //
+  // If there is an error, |error_callback| is invoked on the IO thread to
+  // notify the caller about the file error.
+  void ReadBytes(const std::string& device_file_relative_path,
+                 net::IOBuffer* buf, int64 offset, int buf_len,
+                 const ReadBytesSuccessCallback& success_callback,
+                 const ErrorCallback& error_callback);
 
   // Dispatches the CloseStorage request to the MediaTransferProtocolManager.
   void CloseStorage() const;
 
  private:
   // Query callback for OpenStorage() to run |callback| on the IO thread.
   //
   // If OpenStorage request succeeds, |error| is set to false and
   // |device_handle| contains the handle to communicate with the MTP device.
   //
@@ skipping 26 matching lines @@
   // If there is an error, |error| is set to true, |file_entries| is empty
   // and |error_callback| is invoked on the IO thread to notify the caller.
   void OnDidReadDirectoryByPath(
       const ReadDirectorySuccessCallback& success_callback,
       const ErrorCallback& error_callback,
       const std::vector<MtpFileEntry>& file_entries,
       bool error) const;
 
   // Query callback for ReadBytes();
   //
-  // If there is no error, |error| is set to false, the buffer within |request|
-  // is written to, and the success callback within |request| is invoked on the
-  // IO thread to notify the caller.
+  // If there is no error, |error| is set to false, the buffer |buf| is written
+  // to, and |success_callback| is invoked on the IO thread to notify the
+  // caller.
   //
-  // If there is an error, |error| is set to true, the buffer within |request|
-  // is untouched, and the error callback within |request| is invoked on the
-  // IO thread to notify the caller.
+  // If there is an error, |error| is set to true, |buf| is untouched, and
+  // |error_callback| is invoked on the IO thread to notify the caller.
   void OnDidReadBytes(
-      const MTPDeviceAsyncDelegate::ReadBytesRequest& request,
+      net::IOBuffer* buf, int buf_len,
+      const ReadBytesSuccessCallback& success_callback,
+      const ErrorCallback& error_callback,
       const std::string& data,
       bool error) const;
 
   // Called when the device is uninitialized.
   //
   // Runs |error_callback| on the IO thread to notify the caller about the
   // device |error|.
   void HandleDeviceError(const ErrorCallback& error_callback,
                          base::File::Error error) const;
 
   // Handle to communicate with the MTP device.
   std::string device_handle_;
 
   // Used to handle WriteDataInfoSnapshotFile request.
   scoped_ptr<MTPReadFileWorker> read_file_worker_;
 
   // For callbacks that may run after destruction.
   base::WeakPtrFactory<MTPDeviceTaskHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MTPDeviceTaskHelper);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_