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

chrome/browser/chromeos/file_system_provider/fileapi/backend_delegate.cc

 // 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.
 
 #include "chrome/browser/chromeos/file_system_provider/fileapi/backend_delegate.h"
 
 #include "base/memory/scoped_ptr.h"
+#include "chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h"
 #include "chrome/browser/chromeos/file_system_provider/fileapi/file_stream_reader.h"
 #include "chrome/browser/chromeos/file_system_provider/fileapi/provider_async_file_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "webkit/browser/blob/file_stream_reader.h"
 #include "webkit/browser/fileapi/file_stream_writer.h"
 #include "webkit/browser/fileapi/file_system_url.h"
 
 using content::BrowserThread;
 
 namespace chromeos {
 namespace file_system_provider {
+namespace {
+
+// Size of the stream reader internal buffer. At most this number of bytes will
+// be read ahead of the requested data.
+const int kBufferSize = 512 * 1024;  // 512KB.

[hashimoto, 2014/06/05 03:18:36]

nit: kBufferSize sounds too general. How about something like kReaderBufferSize?

[mtomasz, 2014/06/05 09:22:27]

Done.

+
+}  // namespace
 
 BackendDelegate::BackendDelegate()
     : async_file_util_(new internal::ProviderAsyncFileUtil) {}
 
 BackendDelegate::~BackendDelegate() {}
 
 fileapi::AsyncFileUtil* BackendDelegate::GetAsyncFileUtil(
     fileapi::FileSystemType type) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, type);
   return async_file_util_.get();
 }
 
 scoped_ptr<webkit_blob::FileStreamReader>
 BackendDelegate::CreateFileStreamReader(
     const fileapi::FileSystemURL& url,
     int64 offset,
     const base::Time& expected_modification_time,
     fileapi::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, url.type());
 
   return scoped_ptr<webkit_blob::FileStreamReader>(
-      new FileStreamReader(context, url, offset, expected_modification_time));
+      new BufferingFileStreamReader(
+          scoped_ptr<webkit_blob::FileStreamReader>(new FileStreamReader(
+              context, url, offset, expected_modification_time)),
+          kBufferSize));
 }
 
 scoped_ptr<fileapi::FileStreamWriter> BackendDelegate::CreateFileStreamWriter(
     const fileapi::FileSystemURL& url,
     int64 offset,
     fileapi::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, url.type());
   NOTIMPLEMENTED();
   return scoped_ptr<fileapi::FileStreamWriter>();
 }
 
 }  // namespace file_system_provider
 }  // namespace chromeos