[fsp] Improve performance for reading small chunks of data.

storage/browser/blob/blob_url_request_job.cc

 // 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 "storage/browser/blob/blob_url_request_job.h"
 
+#include <algorithm>
 #include <limits>
+#include <string>
+#include <vector>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_util_proxy.h"
 #include "base/format_macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/numerics/safe_conversions.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_response_info.h"
 #include "net/http/http_util.h"
 #include "net/url_request/url_request.h"
@@ skipping 190 matching lines @@
     NotifyFailure(error);
     return;
   }
 
   // Apply the range requirement.
   if (!byte_range_.ComputeBounds(total_size_)) {
     NotifyFailure(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE);
     return;
   }
 
-  remaining_bytes_ = byte_range_.last_byte_position() -
-                     byte_range_.first_byte_position() + 1;
+  remaining_bytes_ = base::checked_cast<int64>(
+      byte_range_.last_byte_position() - byte_range_.first_byte_position() + 1);
   DCHECK_GE(remaining_bytes_, 0);
 
   // Do the seek at the beginning of the request.
   if (byte_range_.first_byte_position())
     Seek(byte_range_.first_byte_position());
 
   NotifySuccess();
 }
 
 void BlobURLRequestJob::DidGetFileItemLength(size_t index, int64 result) {
@@ skipping 17 matching lines @@
   uint64 item_offset = item.offset();
   uint64 item_length = item.length();
 
   if (item_offset > file_length) {
     NotifyFailure(net::ERR_FILE_NOT_FOUND);
     return;
   }
 
   uint64 max_length = file_length - item_offset;
 
-  // If item length is -1, we need to use the file size being resolved
-  // in the real time.
-  if (item_length == static_cast<uint64>(-1)) {
+  // If item length is undefined, then we need to use the file size being
+  // resolved in the real time.
+  if (item_length == std::numeric_limits<uint64>::max()) {
     item_length = max_length;
   } else if (item_length > max_length) {
     NotifyFailure(net::ERR_FILE_NOT_FOUND);
     return;
   }
 
   if (!AddItemLength(index, item_length))
     return;
 
   if (--pending_get_file_info_count_ == 0)
@@ skipping 287 matching lines @@
   FileStreamReader* reader = NULL;
   switch (item.type()) {
     case BlobData::Item::TYPE_FILE:
       reader = FileStreamReader::CreateForLocalFile(
           file_thread_proxy_.get(),
           item.path(),
           item.offset() + additional_offset,
           item.expected_modification_time());
       break;
     case BlobData::Item::TYPE_FILE_FILESYSTEM:
-      reader = file_system_context_->CreateFileStreamReader(
-                                         storage::FileSystemURL(
-                                             file_system_context_->CrackURL(
-                                                 item.filesystem_url())),
-                                         item.offset() + additional_offset,
-                                         item.expected_modification_time())
+      reader = file_system_context_
+                   ->CreateFileStreamReader(
+                         storage::FileSystemURL(file_system_context_->CrackURL(
+                             item.filesystem_url())),
+                         item.offset() + additional_offset,
+                         item.length() == std::numeric_limits<uint64>::max()
+                             ? storage::kMaximumLength
+                             : item.length() - additional_offset,

[jianli, 2014/09/11 17:45:51]

Should this be item.length() - item.offset() - additional_offset?

[mtomasz, 2014/09/16 08:58:22]

I don't think so. item.offset() is the start position in bytes, and
item.length() length of the item from the offset.

+                         item.expected_modification_time())
                    .release();
       break;
     default:
       NOTREACHED();
   }
   DCHECK(reader);
   index_to_reader_[index] = reader;
 }
 
 }  // namespace storage