This is the IPC and bits of the browser backend for FileWriter. The rest of...

chrome/browser/file_system/file_system_dispatcher_host.cc

 // Copyright (c) 2010 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/file_system/file_system_dispatcher_host.h"
 
 #include "base/file_path.h"
 #include "base/thread.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
@@ skipping 97 matching lines @@
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP_EX(FileSystemDispatcherHost, message, *message_was_ok)
     IPC_MESSAGE_HANDLER(ViewHostMsg_OpenFileSystemRequest, OnOpenFileSystem)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Move, OnMove)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Copy, OnCopy)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Remove, OnRemove)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_ReadMetadata, OnReadMetadata)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Create, OnCreate)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Exists, OnExists)
     IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_ReadDirectory, OnReadDirectory)
+    IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Write, OnWrite)
+    IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_Truncate, OnTruncate)
+    IPC_MESSAGE_HANDLER(ViewHostMsg_FileSystem_CancelWrite, OnCancel)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP_EX()
   return handled;
 }
 
 void FileSystemDispatcherHost::OnOpenFileSystem(
     const ViewHostMsg_OpenFileSystemRequest_Params& params) {
 
   // TODO(kinuko): hook up ContentSettings cookies type checks.
 
@@ skipping 71 matching lines @@
     GetNewOperation(request_id)->FileExists(path);
 }
 
 void FileSystemDispatcherHost::OnReadDirectory(
     int request_id, const FilePath& path) {
   if (!CheckValidFileSystemPath(path, request_id))
     return;
   GetNewOperation(request_id)->ReadDirectory(path);
 }
 
+void FileSystemDispatcherHost::OnWrite(
+    int request_id,
+    const FilePath& path,
+    const GURL& blob_url,
+    int64 offset) {
+  if (!CheckValidFileSystemPath(path, request_id))
+    return;
+  GetNewOperation(request_id)->Write(path, blob_url, offset);
+}
+
+void FileSystemDispatcherHost::OnTruncate(
+    int request_id,
+    const FilePath& path,
+    int64 length) {
+  if (!CheckValidFileSystemPath(path, request_id))
+    return;
+  GetNewOperation(request_id)->Truncate(path, length);
+}
+
+void FileSystemDispatcherHost::OnCancel(
+    int request_id,
+    int request_id_to_cancel) {
+  fileapi::FileSystemOperation* write =
+      operations_.Lookup(request_id_to_cancel);
+  if (write) {
+    write->Cancel();
+    Send(new ViewMsg_FileSystem_DidSucceed(request_id));
+  } else {
+    Send(new ViewMsg_FileSystem_DidFail(
+        request_id, base::PLATFORM_FILE_ERROR_INVALID_OPERATION));
+  }
+}
+
 void FileSystemDispatcherHost::Send(IPC::Message* message) {
   DCHECK(ChromeThread::CurrentlyOn(ChromeThread::IO));
   if (!shutdown_ && message_sender_)
     message_sender_->Send(message);
   else
     delete message;
 }
 
 bool FileSystemDispatcherHost::CheckValidFileSystemPath(
     const FilePath& path, int request_id) {
@@ skipping 15 matching lines @@
       dispatcher,
       ChromeThread::GetMessageLoopProxyForThread(ChromeThread::FILE));
   operations_.AddWithID(operation, request_id);
   return operation;
 }
 
 void FileSystemDispatcherHost::RemoveCompletedOperation(int request_id) {
   DCHECK(operations_.Lookup(request_id));
   operations_.Remove(request_id);
 }