Implement SandboxFileWriter and rewrite FileWriterDelegate to use it

webkit/fileapi/file_writer.h

 // 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.
 
 #ifndef WEBKIT_FILEAPI_FILE_WRITER_H_
 #define WEBKIT_FILEAPI_FILE_WRITER_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "net/base/completion_callback.h"
 
 namespace net {
 class IOBuffer;
 }
 
 namespace fileapi {
 
 // A generic interface for writing to a file-like object.
+//
+// Note: this does not directly correspond to FileWriter in File API (which
+// is implemented by WebCore::FileWriter), though this class is used to
+// implement a part of it.  FileWriterDelegate is NOT a delegate of this
+// class either.
+// TODO(kinuko): Consider better naming.
 class FileWriter {
  public:
   // Closes the file. If there's an in-flight operation, it is canceled (i.e.,
   // the callback function associated with the operation is not called).
   virtual ~FileWriter() {}
 
   // Writes to the current cursor position asynchronously.
   //
   // Up to buf_len bytes will be written.  (In other words, partial
   // writes are allowed.) If the write completed synchronously, it returns
   // the number of bytes written. If the operation could not be performed, it
   // returns an error code. Otherwise, net::ERR_IO_PENDING is returned, and the
   // callback will be run on the thread where Write() was called when the write
   // has completed.
   //
+  // This errors out (either synchronously or via callback) with:
+  //   net::ERR_FILE_NOT_FOUND: When the target file is not found.
+  //   net::ERR_ACCESS_DENIED: When the target file is a directory or
+  //      the writer has no permission on the file.
+  //   net::ERR_FILE_NO_SPACE: When the write will result in out of quota
+  //      or there is not enough room left on the disk.
+  //
   // It is invalid to call Write while there is an in-flight async operation.
   virtual int Write(net::IOBuffer* buf, int buf_len,
                     const net::CompletionCallback& callback) = 0;
 
   // Cancels an in-flight async operation.
   //
   // If the cancel is finished synchronously, it returns net::OK. If the
   // cancel could not be performed, it returns an error code. Especially when
   // there is no in-flight operation, net::ERR_UNEXPECTED is returned.
   // Otherwise, net::ERR_IO_PENDING is returned, and the callback will be run on
   // the thread where Cancel() was called when the cancel has completed. It is
   // invalid to call Cancel() more than once on the same async operation.
   //
   // In either case, the callback function passed to the in-flight async
   // operation is dismissed immediately when Cancel() is called, and thus
   // will never be called.
   virtual int Cancel(const net::CompletionCallback& callback) = 0;
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_FILEAPI_FILE_WRITER_H_
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