Add control to use If-Range header for range request.

content/browser/download/parallel_download_job.cc

 // Copyright 2017 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 "content/browser/download/parallel_download_job.h"
 
 #include "base/memory/ptr_util.h"
 #include "content/browser/download/download_create_info.h"
 #include "content/browser/download/parallel_download_utils.h"
 #include "content/public/browser/browser_context.h"
@@ skipping 170 matching lines @@
                                 storage_partition->GetURLRequestContext()));
   download_params->set_file_path(download_item_->GetFullPath());
   download_params->set_last_modified(download_item_->GetLastModifiedTime());
   download_params->set_etag(download_item_->GetETag());
   download_params->set_offset(offset);
 
   // Setting the length will result in range request to fetch a slice of the
   // file.
   download_params->set_length(length);
 
+  // Subsequent range requests don't need the "If-Range" header.
+  download_params->set_use_if_range(false);

[qinmin, 2017/03/30 05:21:43]

still need this?

[xingliu, 2017/03/30 17:16:46]

Yes, I think so.

Precondition failed for initial request and subsequent requests are different.
The initial request will handle the full content returned with http 200 but
subsequent requests need to drop it.

We previously distinguish initial request and subsequent requests based on their
length cap. But subsequent requests now can also be half opened.

Another option is to check the length difference in worker layer, which is not
ideal according to previous review. I guess the main reason is we'd better use
http protocol instead of relying on length checking in worker layer.

+
   // Subsequent range requests have the same referrer URL as the original
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),
                                          blink::WebReferrerPolicyAlways));
   // Send the request.
   worker->SendRequest(std::move(download_params));
   DCHECK(workers_.find(offset) == workers_.end());
   workers_[offset] = std::move(worker);
 }
 
 }  // namespace content