arc: Implement ArcContentFileSystemFileStreamReader::Read/GetLength

chrome/browser/chromeos/arc/fileapi/arc_content_file_system_backend_delegate.cc

 // Copyright 2016 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/arc/fileapi/arc_content_file_system_backend_delegate.h"
 
+#include "base/memory/ptr_util.h"
 #include "chrome/browser/chromeos/arc/fileapi/arc_content_file_system_async_file_util.h"
 #include "chrome/browser/chromeos/arc/fileapi/arc_content_file_system_file_stream_reader.h"
+#include "chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "storage/browser/fileapi/file_stream_writer.h"
 #include "storage/browser/fileapi/file_system_url.h"
 
 namespace arc {
 
 ArcContentFileSystemBackendDelegate::ArcContentFileSystemBackendDelegate()
     : async_file_util_(new ArcContentFileSystemAsyncFileUtil()) {}
 
 ArcContentFileSystemBackendDelegate::~ArcContentFileSystemBackendDelegate() =
     default;
 
 storage::AsyncFileUtil* ArcContentFileSystemBackendDelegate::GetAsyncFileUtil(
     storage::FileSystemType type) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeArcContent, type);
   return async_file_util_.get();
 }
 
 std::unique_ptr<storage::FileStreamReader>
 ArcContentFileSystemBackendDelegate::CreateFileStreamReader(
     const storage::FileSystemURL& url,
     int64_t offset,
     int64_t max_bytes_to_read,
     const base::Time& expected_modification_time,
     storage::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeArcContent, url.type());
-  return std::unique_ptr<storage::FileStreamReader>(
-      new ArcContentFileSystemFileStreamReader(url, offset, max_bytes_to_read));
+  GURL arc_url = FileSystemUrlToArcUrl(url);
+  return base::MakeUnique<ArcContentFileSystemFileStreamReader>(arc_url,

[hidehiko, 2016/11/10 07:07:06]

max_bytes_to_read gets ignored now.

According to:
https://cs.chromium.org/chromium/src/storage/browser/fileapi/file_system_back...

it needs to be supported?

[hashimoto, 2016/11/11 22:30:17]

IIUC implementations MAY use max_bytes_to_read to avoid downloading unneeded
contents.
In many parts, existing code is ignoring this value.
https://cs.chromium.org/chromium/src/storage/browser/fileapi/isolated_file_sy...

Because AFAIK there is no way to benefit from this argument with Android's
ContentResolver, I'm just ignoring it here.

[hidehiko, 2016/11/14 17:46:34]

Good to know. Thanks.

+                                                                offset);
 }
 
 std::unique_ptr<storage::FileStreamWriter>
 ArcContentFileSystemBackendDelegate::CreateFileStreamWriter(
     const storage::FileSystemURL& url,
     int64_t offset,
     storage::FileSystemContext* context) {
   NOTIMPLEMENTED();
   return std::unique_ptr<storage::FileStreamWriter>();
 }
 
 storage::WatcherManager* ArcContentFileSystemBackendDelegate::GetWatcherManager(
     storage::FileSystemType type) {
   NOTIMPLEMENTED();
   return nullptr;
 }
 
 void ArcContentFileSystemBackendDelegate::GetRedirectURLForContents(
     const storage::FileSystemURL& url,
     const storage::URLCallback& callback) {
   NOTIMPLEMENTED();
 }
 
 }  // namespace arc