2nd try: separate FileStream related code out of BlobURLRequest

The original change I had tried to submit was:
http://codereview.chromium.org/9651032
The change was reverted because FileStream cannot be created on other
threads than on IO thread on Windows, and therefore broke
the ExtensionPageCaptureApiTest.SaveAsMHTML browser test.

BUG=114999
TEST=test_shell_tests:BlobURLRequestJobTest.*, browser_tests:ExtensionPageCaptureApiTest.SaveAsMHTML


Review URL: http://codereview.chromium.org/10029008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@131791 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 381 insertions, 123 deletions

diff --git a/webkit/blob/blob_url_request_job.cc b/webkit/blob/blob_url_request_job.cc
index d6be8a5..1a360f1 100644
--- a/webkit/blob/blob_url_request_job.cc
+++ b/webkit/blob/blob_url_request_job.cc
@@ -6,14 +6,11 @@
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
-#include "base/file_path.h"
-#include "base/file_util.h"
 #include "base/file_util_proxy.h"
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
+#include "base/stl_util.h"
 #include "base/string_number_conversions.h"
-#include "base/threading/thread_restrictions.h"
-#include "net/base/file_stream.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_request_headers.h"
@@ -23,6 +20,7 @@
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_error_job.h"
 #include "net/url_request/url_request_status.h"
+#include "webkit/blob/local_file_reader.h"
 
 namespace webkit_blob {
 
@@ -71,9 +69,7 @@ BlobURLRequestJob::BlobURLRequestJob(
 }
 
 BlobURLRequestJob::~BlobURLRequestJob() {
-  // FileStream's destructor won't close it for us because we passed in our own
-  // file handle.
-  CloseFileStream();
+  STLDeleteValues(&index_to_reader_);
 }
 
 void BlobURLRequestJob::Start() {
@@ -84,7 +80,7 @@ void BlobURLRequestJob::Start() {
 }
 
 void BlobURLRequestJob::Kill() {
-  CloseFileStream();
+  DeleteCurrentFileReader();
 
   net::URLRequestJob::Kill();
   weak_factory_.InvalidateWeakPtrs();
@@ -185,9 +181,8 @@ void BlobURLRequestJob::CountSize() {
     const BlobData::Item& item = blob_data_->items().at(i);
     if (item.type == BlobData::TYPE_FILE) {
       ++pending_get_file_info_count_;
-      base::FileUtilProxy::GetFileInfo(
-          file_thread_proxy_, item.file_path,
-          base::Bind(&BlobURLRequestJob::DidGetFileItemInfo,
+      GetFileReader(i)->GetLength(
+          base::Bind(&BlobURLRequestJob::DidGetFileItemLength,
                      weak_factory_.GetWeakPtr(), i));
       continue;
     }
@@ -227,41 +222,28 @@ void BlobURLRequestJob::DidCountSize(int error) {
   NotifySuccess();
 }
 
-void BlobURLRequestJob::DidGetFileItemInfo(
-    size_t index,
-    base::PlatformFileError rv,
-    const base::PlatformFileInfo& file_info) {
+void BlobURLRequestJob::DidGetFileItemLength(size_t index, int result) {
   // Do nothing if we have encountered an error.
   if (error_)
     return;
 
-  if (rv == base::PLATFORM_FILE_ERROR_NOT_FOUND) {
+  if (result == net::ERR_UPLOAD_FILE_CHANGED) {
     NotifyFailure(net::ERR_FILE_NOT_FOUND);
     return;
-  } else if (rv != base::PLATFORM_FILE_OK) {
-    NotifyFailure(net::ERR_FAILED);
+  } else if (result < 0) {
+    NotifyFailure(result);
     return;
   }
 
-  // Validate the expected modification time.
-  // Note that the expected modification time from WebKit is based on
-  // time_t precision. So we have to convert both to time_t to compare.
   DCHECK_LT(index, blob_data_->items().size());
   const BlobData::Item& item = blob_data_->items().at(index);
   DCHECK(item.type == BlobData::TYPE_FILE);
 
-  if (!item.expected_modification_time.is_null() &&
-      item.expected_modification_time.ToTimeT() !=
-          file_info.last_modified.ToTimeT()) {
-    NotifyFailure(net::ERR_FILE_NOT_FOUND);
-    return;
-  }
-
   // If item length is -1, we need to use the file size being resolved
   // in the real time.
   int64 item_length = static_cast<int64>(item.length);
   if (item_length == -1)
-    item_length = file_info.size;
+    item_length = result;
 
   // Cache the size and add it to the total size.
   DCHECK_LT(index, item_length_list_.size());
@@ -283,6 +265,20 @@ void BlobURLRequestJob::Seek(int64 offset) {
 
   // Set the offset that need to jump to for the first item in the range.
   current_item_offset_ = offset;
+
+  if (offset == 0)
+    return;
+
+  // Adjust the offset of the first stream if it is of file type.
+  const BlobData::Item& item = blob_data_->items().at(current_item_index_);
+  if (item.type == BlobData::TYPE_FILE) {
+    DeleteCurrentFileReader();
+    index_to_reader_[current_item_index_] = new LocalFileReader(
+        file_thread_proxy_,
+        item.file_path,
+        item.offset + offset,
+        item.expected_modification_time);
+  }
 }
 
 bool BlobURLRequestJob::ReadItem() {
@@ -312,7 +308,7 @@ bool BlobURLRequestJob::ReadItem() {
     case BlobData::TYPE_DATA:
       return ReadBytesItem(item, bytes_to_read);
     case BlobData::TYPE_FILE:
-      return ReadFileItem(item, bytes_to_read);
+      return ReadFileItem(GetFileReader(current_item_index_), bytes_to_read);
     default:
       DCHECK(false);
       return false;
@@ -320,8 +316,8 @@ bool BlobURLRequestJob::ReadItem() {
 }
 
 void BlobURLRequestJob::AdvanceItem() {
-  // Close the stream if the current item is a file.
-  CloseFileStream();
+  // Close the file if the current item is a file.
+  DeleteCurrentFileReader();
 
   // Advance to the next item.
   current_item_index_++;
@@ -357,79 +353,24 @@ bool BlobURLRequestJob::ReadBytesItem(const BlobData::Item& item,
   return true;
 }
 
-bool BlobURLRequestJob::ReadFileItem(const BlobData::Item& item,
+bool BlobURLRequestJob::ReadFileItem(LocalFileReader* reader,
                                      int bytes_to_read) {
-  // If the stream already exists, keep reading from it.
-  if (stream_ != NULL)
-    return ReadFileStream(bytes_to_read);
-
-  base::FileUtilProxy::CreateOrOpen(
-      file_thread_proxy_, item.file_path, kFileOpenFlags,
-      base::Bind(&BlobURLRequestJob::DidOpenFile,
-                 weak_factory_.GetWeakPtr(), bytes_to_read));
-  SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
-  return false;
-}
-
-void BlobURLRequestJob::DidOpenFile(int bytes_to_read,
-                                    base::PlatformFileError rv,
-                                    base::PassPlatformFile file,
-                                    bool created) {
-  if (rv != base::PLATFORM_FILE_OK) {
-    NotifyFailure(net::ERR_FAILED);
-    return;
-  }
-
-  DCHECK(!stream_.get());
-  stream_.reset(new net::FileStream(file.ReleaseValue(), kFileOpenFlags, NULL));
-
-  const BlobData::Item& item = blob_data_->items().at(current_item_index_);
-  {
-    // stream_.SeekSync() blocks the IO thread, see http://crbug.com/75548.
-    base::ThreadRestrictions::ScopedAllowIO allow_io;
-    int64 offset = current_item_offset_ + static_cast<int64>(item.offset);
-    if (offset > 0 && offset != stream_->SeekSync(net::FROM_BEGIN, offset)) {
-      NotifyFailure(net::ERR_FAILED);
-      return;
-    }
-  }
-
-  ReadFileStream(bytes_to_read);
-}
-
-bool BlobURLRequestJob::ReadFileStream(int bytes_to_read) {
-  DCHECK(stream_.get());
-  DCHECK(stream_->IsOpen());
   DCHECK_GE(read_buf_->BytesRemaining(), bytes_to_read);
-
-  // Start the asynchronous reading.
-  int rv = stream_->Read(read_buf_,
-                         bytes_to_read,
-                         base::Bind(&BlobURLRequestJob::DidReadFileStream,
-                                    base::Unretained(this)));
-
-  // If I/O pending error is returned, we just need to wait.
-  if (rv == net::ERR_IO_PENDING) {
-    SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
-    return false;
-  }
-
-  // For all other errors (and for unexpected EOF case), bail out.
-  if (rv <= 0) {
-    NotifyFailure(net::ERR_FAILED);
+  DCHECK(reader);
+  const int result = reader->Read(
+      read_buf_, bytes_to_read,
+      base::Bind(&BlobURLRequestJob::DidReadFile,
+                 base::Unretained(this)));
+  if (result != net::ERR_IO_PENDING) {
+    DCHECK(result != net::OK);
+    NotifyFailure(result);
     return false;
   }
-
-  // Otherwise, data is immediately available.
-  if (GetStatus().is_io_pending())
-    DidReadFileStream(rv);
-  else
-    AdvanceBytesRead(rv);
-
-  return true;
+  SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
+  return false;
 }
 
-void BlobURLRequestJob::DidReadFileStream(int result) {
+void BlobURLRequestJob::DidReadFile(int result) {
   if (result <= 0) {
     NotifyFailure(net::ERR_FAILED);
     return;
@@ -451,12 +392,11 @@ void BlobURLRequestJob::DidReadFileStream(int result) {
     NotifyReadComplete(bytes_read);
 }
 
-void BlobURLRequestJob::CloseFileStream() {
-  if (stream_ != NULL) {
-    // stream_.Close() blocks the IO thread, see http://crbug.com/75548.
-    base::ThreadRestrictions::ScopedAllowIO allow_io;
-    stream_->CloseSync();
-    stream_.reset(NULL);
+void BlobURLRequestJob::DeleteCurrentFileReader() {
+  IndexToReaderMap::iterator found = index_to_reader_.find(current_item_index_);
+  if (found != index_to_reader_.end() && found->second) {
+    delete found->second;
+    index_to_reader_.erase(found);
   }
 }
 
@@ -578,4 +518,20 @@ void BlobURLRequestJob::HeadersCompleted(int status_code,
   NotifyHeadersComplete();
 }
 
+LocalFileReader* BlobURLRequestJob::GetFileReader(size_t index) {
+  DCHECK_LT(index, blob_data_->items().size());
+  const BlobData::Item& item = blob_data_->items().at(index);
+  if (item.type != BlobData::TYPE_FILE)
+    return NULL;
+  if (index_to_reader_.find(index) == index_to_reader_.end()) {
+    index_to_reader_[index] = new LocalFileReader(
+        file_thread_proxy_,
+        item.file_path,
+        item.offset,
+        item.expected_modification_time);
+  }
+  DCHECK(index_to_reader_[index]);
+  return index_to_reader_[index];
+}
+
 }  // namespace webkit_blob
diff --git a/webkit/blob/blob_url_request_job.h b/webkit/blob/blob_url_request_job.h
index e242aff..86a5f31 100644
--- a/webkit/blob/blob_url_request_job.h
+++ b/webkit/blob/blob_url_request_job.h
@@ -26,6 +26,8 @@ class IOBuffer;
 
 namespace webkit_blob {
 
+class LocalFileReader;
+
 // A request job that handles reading blob URLs.
 class BLOB_EXPORT BlobURLRequestJob : public net::URLRequestJob {
  public:
@@ -47,13 +49,13 @@ class BLOB_EXPORT BlobURLRequestJob : public net::URLRequestJob {
       const net::HttpRequestHeaders& headers) OVERRIDE;
 
  private:
+  typedef std::map<size_t, LocalFileReader*> IndexToReaderMap;
+
   // For preparing for read: get the size, apply the range and perform seek.
   void DidStart();
   void CountSize();
   void DidCountSize(int error);
-  void DidGetFileItemInfo(size_t index,
-                          base::PlatformFileError error,
-                          const base::PlatformFileInfo& file_info);
+  void DidGetFileItemLength(size_t index, int result);
   void Seek(int64 offset);
 
   // For reading the blob.
@@ -62,15 +64,10 @@ class BLOB_EXPORT BlobURLRequestJob : public net::URLRequestJob {
   void AdvanceItem();
   void AdvanceBytesRead(int result);
   bool ReadBytesItem(const BlobData::Item& item, int bytes_to_read);
-  bool ReadFileItem(const BlobData::Item& item, int bytes_to_read);
+  bool ReadFileItem(LocalFileReader* reader, int bytes_to_read);
 
-  void DidOpenFile(int bytes_to_read,
-                   base::PlatformFileError rv,
-                   base::PassPlatformFile file,
-                   bool created);
-  bool ReadFileStream(int bytes_to_read);
-  void DidReadFileStream(int result);
-  void CloseFileStream();
+  void DidReadFile(int result);
+  void DeleteCurrentFileReader();
 
   int ComputeBytesToRead() const;
   int BytesReadCompleted();
@@ -79,6 +76,10 @@ class BLOB_EXPORT BlobURLRequestJob : public net::URLRequestJob {
   void NotifyFailure(int);
   void HeadersCompleted(int status_code, const std::string& status_txt);
 
+  // Returns a LocalFileReader for a blob item at |index|.
+  // If the item at |index| is not of TYPE_FILE this returns NULL.
+  LocalFileReader* GetFileReader(size_t index);
+
   base::WeakPtrFactory<BlobURLRequestJob> weak_factory_;
   scoped_refptr<BlobData> blob_data_;
   scoped_refptr<base::MessageLoopProxy> file_thread_proxy_;
@@ -86,7 +87,7 @@ class BLOB_EXPORT BlobURLRequestJob : public net::URLRequestJob {
   int64 total_size_;
   int64 remaining_bytes_;
   int pending_get_file_info_count_;
-  scoped_ptr<net::FileStream> stream_;
+  IndexToReaderMap index_to_reader_;
   size_t current_item_index_;
   int64 current_item_offset_;
   scoped_refptr<net::DrainableIOBuffer> read_buf_;
diff --git a/webkit/blob/blob_url_request_job_unittest.cc b/webkit/blob/blob_url_request_job_unittest.cc
index 12a0cb7..515574a 100644
--- a/webkit/blob/blob_url_request_job_unittest.cc
+++ b/webkit/blob/blob_url_request_job_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -259,10 +259,10 @@ class BlobURLRequestJobTest : public testing::Test {
 
   void VerifyResponse() {
     EXPECT_TRUE(request_->status().is_success());
-    EXPECT_EQ(request_->response_headers()->response_code(),
-              expected_status_code_);
-    EXPECT_STREQ(url_request_delegate_->response_data().c_str(),
-                 expected_response_.c_str());
+    EXPECT_EQ(expected_status_code_,
+              request_->response_headers()->response_code());
+    EXPECT_STREQ(expected_response_.c_str(),
+                 url_request_delegate_->response_data().c_str());
     TestFinished();
   }
 
diff --git a/webkit/blob/local_file_reader.cc b/webkit/blob/local_file_reader.cc
new file mode 100644
index 0000000..54493c1
--- /dev/null
+++ b/webkit/blob/local_file_reader.cc
@@ -0,0 +1,216 @@
+// 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.
+
+#include "webkit/blob/local_file_reader.h"
+
+#include "base/file_util.h"
+#include "base/file_util_proxy.h"
+#include "base/logging.h"
+#include "base/message_loop_proxy.h"
+#include "base/platform_file.h"
+#include "net/base/file_stream.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_errors.h"
+
+namespace webkit_blob {
+
+namespace {
+
+const int kOpenFlagsForRead = base::PLATFORM_FILE_OPEN |
+                              base::PLATFORM_FILE_READ |
+                              base::PLATFORM_FILE_ASYNC;
+
+int PlatformFileErrorToNetError(base::PlatformFileError file_error) {
+  switch (file_error) {
+    case base::PLATFORM_FILE_OK:
+      return net::OK;
+    case base::PLATFORM_FILE_ERROR_NOT_FOUND:
+      return net::ERR_FILE_NOT_FOUND;
+    case base::PLATFORM_FILE_ERROR_ACCESS_DENIED:
+      return net::ERR_ACCESS_DENIED;
+    default:
+      return net::ERR_FAILED;
+  }
+}
+
+// Verify if the underlying file has not been modified.
+bool VerifySnapshotTime(const base::Time& expected_modification_time,
+                        const base::PlatformFileInfo& file_info) {
+  return expected_modification_time.is_null() ||
+         expected_modification_time.ToTimeT() ==
+             file_info.last_modified.ToTimeT();
+}
+
+void DidGetFileInfoForGetLength(const net::CompletionCallback& callback,
+                                const base::Time& expected_modification_time,
+                                int64 initial_offset,
+                                base::PlatformFileError error,
+                                const base::PlatformFileInfo& file_info) {
+  if (file_info.is_directory) {
+    callback.Run(net::ERR_FILE_NOT_FOUND);
+    return;
+  }
+  if (error != base::PLATFORM_FILE_OK) {
+    callback.Run(PlatformFileErrorToNetError(error));
+    return;
+  }
+  if (!VerifySnapshotTime(expected_modification_time, file_info)) {
+    callback.Run(net::ERR_UPLOAD_FILE_CHANGED);
+    return;
+  }
+  callback.Run(file_info.size - initial_offset);
+}
+
+void DidSeekFile(const LocalFileReader::OpenFileStreamCallback& callback,
+                 scoped_ptr<net::FileStream> stream_impl,
+                 int64 initial_offset,
+                 int64 new_offset) {
+  int result = net::OK;
+  if (new_offset < 0)
+    result = static_cast<int>(new_offset);
+  else if (new_offset != initial_offset)
+    result = net::ERR_FAILED;
+  callback.Run(result, stream_impl.Pass());
+}
+
+void EmptyCompletionCallback(int) {}
+
+}  // namespace
+
+// A helper class to open, verify and seek a file stream for a given path.
+class LocalFileReader::OpenFileStreamHelper {
+ public:
+  OpenFileStreamHelper(base::MessageLoopProxy* file_thread_proxy)
+      : file_thread_proxy_(file_thread_proxy),
+        file_handle_(base::kInvalidPlatformFileValue),
+        result_(net::OK) {}
+  ~OpenFileStreamHelper() {
+    if (file_handle_ != base::kInvalidPlatformFileValue) {
+      file_thread_proxy_->PostTask(
+          FROM_HERE,
+          base::Bind(base::IgnoreResult(&base::ClosePlatformFile),
+                     file_handle_));
+    }
+  }
+
+  void OpenAndVerifyOnFileThread(const FilePath& file_path,
+                                 const base::Time& expected_modification_time) {
+    base::PlatformFileError file_error = base::PLATFORM_FILE_OK;
+    file_handle_ = base::CreatePlatformFile(
+        file_path, kOpenFlagsForRead, NULL, &file_error);
+    if (file_error != base::PLATFORM_FILE_OK) {
+      result_ = PlatformFileErrorToNetError(file_error);
+      return;
+    }
+    DCHECK_NE(base::kInvalidPlatformFileValue, file_handle_);
+    base::PlatformFileInfo file_info;
+    if (!base::GetPlatformFileInfo(file_handle_, &file_info)) {
+      result_ = net::ERR_FAILED;
+      return;
+    }
+    if (!VerifySnapshotTime(expected_modification_time, file_info)) {
+      result_ = net::ERR_UPLOAD_FILE_CHANGED;
+      return;
+    }
+    result_ = net::OK;
+  }
+
+  void OpenStreamOnCallingThread(int64 initial_offset,
+                                 const OpenFileStreamCallback& callback) {
+    DCHECK(!callback.is_null());
+    scoped_ptr<net::FileStream> stream_impl;
+    if (result_ != net::OK) {
+      callback.Run(result_, stream_impl.Pass());
+      return;
+    }
+    stream_impl.reset(
+        new net::FileStream(file_handle_, kOpenFlagsForRead, NULL));
+    file_handle_ = base::kInvalidPlatformFileValue;
+    result_ = stream_impl->Seek(net::FROM_BEGIN, initial_offset,
+                                base::Bind(&DidSeekFile, callback,
+                                           base::Passed(&stream_impl),
+                                           initial_offset));
+    if (result_ != net::ERR_IO_PENDING)
+      callback.Run(result_, stream_impl.Pass());
+  }
+
+ private:
+  scoped_refptr<base::MessageLoopProxy> file_thread_proxy_;
+  base::PlatformFile file_handle_;
+  int result_;
+  DISALLOW_COPY_AND_ASSIGN(OpenFileStreamHelper);
+};
+
+LocalFileReader::LocalFileReader(
+    base::MessageLoopProxy* file_thread_proxy,
+    const FilePath& file_path,
+    int64 initial_offset,
+    const base::Time& expected_modification_time)
+    : file_thread_proxy_(file_thread_proxy),
+      file_path_(file_path),
+      initial_offset_(initial_offset),
+      expected_modification_time_(expected_modification_time),
+      has_pending_open_(false),
+      weak_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {}
+
+LocalFileReader::~LocalFileReader() {
+  if (!stream_impl_.get())
+    return;
+  stream_impl_->Close(base::Bind(&EmptyCompletionCallback));
+}
+
+int LocalFileReader::Read(net::IOBuffer* buf, int buf_len,
+                          const net::CompletionCallback& callback) {
+  DCHECK(!has_pending_open_);
+  if (stream_impl_.get())
+    return stream_impl_->Read(buf, buf_len, callback);
+  return Open(base::Bind(&LocalFileReader::DidOpen, weak_factory_.GetWeakPtr(),
+                         make_scoped_refptr(buf), buf_len, callback));
+}
+
+int LocalFileReader::GetLength(const net::CompletionCallback& callback) {
+  const bool posted = base::FileUtilProxy::GetFileInfo(
+      file_thread_proxy_, file_path_,
+      base::Bind(&DidGetFileInfoForGetLength, callback,
+                 expected_modification_time_, initial_offset_));
+  DCHECK(posted);
+  return net::ERR_IO_PENDING;
+}
+
+int LocalFileReader::Open(const OpenFileStreamCallback& callback) {
+  DCHECK(!has_pending_open_);
+  DCHECK(!stream_impl_.get());
+  has_pending_open_ = true;
+  OpenFileStreamHelper* helper = new OpenFileStreamHelper(file_thread_proxy_);
+  const bool posted = file_thread_proxy_->PostTaskAndReply(
+      FROM_HERE,
+      base::Bind(&OpenFileStreamHelper::OpenAndVerifyOnFileThread,
+                 base::Unretained(helper), file_path_,
+                 expected_modification_time_),
+      base::Bind(&OpenFileStreamHelper::OpenStreamOnCallingThread,
+                 base::Owned(helper), initial_offset_, callback));
+  DCHECK(posted);
+  return net::ERR_IO_PENDING;
+}
+
+void LocalFileReader::DidOpen(net::IOBuffer* buf,
+                              int buf_len,
+                              const net::CompletionCallback& callback,
+                              int open_error,
+                              scoped_ptr<net::FileStream> stream_impl) {
+  DCHECK(has_pending_open_);
+  DCHECK(!stream_impl_.get());
+  has_pending_open_ = false;
+  if (open_error != net::OK) {
+    callback.Run(open_error);
+    return;
+  }
+  DCHECK(stream_impl.get());
+  stream_impl_ = stream_impl.Pass();
+  const int read_error = stream_impl_->Read(buf, buf_len, callback);
+  if (read_error != net::ERR_IO_PENDING)
+    callback.Run(read_error);
+}
+
+}  // namespace webkit_blob
diff --git a/webkit/blob/local_file_reader.h b/webkit/blob/local_file_reader.h
new file mode 100644
index 0000000..fd87dd4
--- /dev/null
+++ b/webkit/blob/local_file_reader.h
@@ -0,0 +1,83 @@
+// 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_BLOB_LOCAL_FILE_READER_H_
+#define WEBKIT_BLOB_LOCAL_FILE_READER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/file_path.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time.h"
+#include "net/base/completion_callback.h"
+#include "webkit/blob/blob_export.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace net {
+class FileStream;
+class IOBuffer;
+}
+
+namespace webkit_blob {
+
+// A thin wrapper of net::FileStream with range support for sliced file
+// handling.
+class BLOB_EXPORT LocalFileReader {
+ public:
+  typedef base::Callback<void(int error, scoped_ptr<net::FileStream> stream)>
+      OpenFileStreamCallback;
+
+  // Creates a new FileReader for a local file |file_path|.
+  // |initial_offset| specifies the offset in the file where the first read
+  // should start.
+  // |expected_modification_time| specifies the expected last modification
+  // If the value is non-null, the reader will check the underlying file's
+  // actual modification time to see if the file has been modified, and if
+  // it does any succeeding read operations should fail with
+  // ERR_UPLOAD_FILE_CHANGED error.
+  LocalFileReader(base::MessageLoopProxy* file_thread_proxy,
+                  const FilePath& file_path,
+                  int64 initial_offset,
+                  const base::Time& expected_modification_time);
+
+  ~LocalFileReader();
+
+  // Reads from the current cursor position asynchronously.
+  // This works mostly same as how net::FileStream::Read() works except that
+  // it internally opens (and seeks) the file if it is not opened yet.
+  // It is invalid to call Read while there is an in-flight Read operation.
+  int Read(net::IOBuffer* buf, int buf_len,
+           const net::CompletionCallback& callback);
+
+  // Returns the number of bytes available to read from the beginning of
+  // the file (or initial_offset) until the end of the file (rv >= 0 cases).
+  // Otherwise, a negative error code is returned (rv < 0 cases).
+  int GetLength(const net::CompletionCallback& callback);
+
+ private:
+  class OpenFileStreamHelper;
+
+  int Open(const OpenFileStreamCallback& callback);
+  void DidOpen(net::IOBuffer* buf,
+               int buf_len,
+               const net::CompletionCallback& callback,
+               int open_error,
+               scoped_ptr<net::FileStream> stream);
+
+  scoped_refptr<base::MessageLoopProxy> file_thread_proxy_;
+  scoped_ptr<net::FileStream> stream_impl_;
+  const FilePath file_path_;
+  const int64 initial_offset_;
+  const base::Time expected_modification_time_;
+  bool has_pending_open_;
+  base::WeakPtrFactory<LocalFileReader> weak_factory_;
+};
+
+}  // namespace webkit_blob
+
+#endif  // WEBKIT_BLOB_LOCAL_FILE_READER_H_
diff --git a/webkit/blob/webkit_blob.gypi b/webkit/blob/webkit_blob.gypi
index bb07019..196c3fb 100644
--- a/webkit/blob/webkit_blob.gypi
+++ b/webkit/blob/webkit_blob.gypi
@@ -1,4 +1,4 @@
-# Copyright (c) 2011 The Chromium Authors. All rights reserved.
+# 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.
 
@@ -37,6 +37,8 @@
         'blob_url_request_job.h',
         'blob_url_request_job_factory.cc',
         'blob_url_request_job_factory.h',
+        'local_file_reader.cc',
+        'local_file_reader.h',
         'shareable_file_reference.cc',
         'shareable_file_reference.h',
         'view_blob_internals_job.cc',