[fsp] Introduce BufferingFileStreamReader to read files in bigger chunks.

chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h

+// Copyright 2014 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_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BUFFERING_FILE_STREAM_READER_H_
+#define CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BUFFERING_FILE_STREAM_READER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "webkit/browser/blob/file_stream_reader.h"
+
+namespace net {
+class IOBuffer;
+}  // namespace net
+
+namespace chromeos {
+namespace file_system_provider {
+
+// Wraps the file stream reader implementation with a prefetching buffer.
+// Reads data from the internal file stream reader in chunks of size at least
+// |buffer_size| bytes (or less for the last chunk, because of EOF).
+//
+// The underlying inner file stream reader *must not* return any values
+// synchronously. Instead, results must be returned by a callback, including
+// errors.
+class BufferingFileStreamReader : public webkit_blob::FileStreamReader {
+ public:
+  BufferingFileStreamReader(
+      scoped_ptr<webkit_blob::FileStreamReader> file_stream_reader,
+      int buffer_size);
+
+  virtual ~BufferingFileStreamReader();
+
+  // webkit_blob::FileStreamReader overrides.
+  virtual int Read(net::IOBuffer* buf,
+                   int buf_len,
+                   const net::CompletionCallback& callback) OVERRIDE;
+  virtual int64 GetLength(
+      const net::Int64CompletionCallback& callback) OVERRIDE;
+
+ private:
+  // Copies data from the preloading buffer and updates the internal iterator.
+  // Returns number of bytes successfully copied.
+  int CopyFromPreloadingBuffer(scoped_refptr<net::IOBuffer> buffer,
+                               int buffer_length);
+
+  // Preloads data from the internal stream reader and calls the |callback|.
+  void Preload(const net::CompletionCallback& callback);
+
+  // Called when preloading of a buffer chunk is finished. Updates state of the
+  // preloading buffer and copied requested data to the |buffer|.
+  void OnPreloadCompleted(scoped_refptr<net::IOBuffer> buffer,
+                          int buffer_length,
+                          const net::CompletionCallback& callback,
+                          int result);
+
+  scoped_ptr<webkit_blob::FileStreamReader> file_stream_reader_;
+  int buffer_size_;
+  scoped_refptr<net::IOBuffer> preloading_buffer_;
+  int preloading_buffer_offset_;
+  int buffered_bytes_;
+
+  base::WeakPtrFactory<BufferingFileStreamReader> weak_ptr_factory_;
+  DISALLOW_COPY_AND_ASSIGN(BufferingFileStreamReader);
+};
+
+}  // namespace file_system_provider
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BUFFERING_FILE_STREAM_READER_H_