Avoid a string copy in URLRequestResourceBundleJob::GetData().

net/url_request/url_request_simple_job.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 NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_
 #define NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_
 
 #include <string>
 
 #include "base/memory/weak_ptr.h"
+#include "base/strings/string_piece.h"
 #include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 #include "net/url_request/url_range_request_job.h"
 
 namespace net {
 
 class URLRequest;
 
 class NET_EXPORT URLRequestSimpleJob : public URLRangeRequestJob {
  public:
@@ skipping 13 matching lines @@
   //  - ERR_IO_PENDING if async processing is needed to finish obtaining data.
   //    This is the only case when |callback| should be called after
   //    completion of the operation. In other situations |callback| should
   //    never be called;
   //  - any other ERR_* code to indicate an error. This code will be used
   //    as the error code in the URLRequestStatus when the URLRequest
   //    is finished.
   virtual int GetData(std::string* mime_type,
                       std::string* charset,
                       std::string* data,
-                      const CompletionCallback& callback) const = 0;
+                      const CompletionCallback& callback) const;
+  // Similar to GetData(), except the subclass must ensure that the characters
+  // referred to by *data live at least as long as *this.
+  virtual int GetStringPieceData(std::string* mime_type,
+                                 std::string* charset,
+                                 base::StringPiece* data,
+                                 const CompletionCallback& callback);

[mmenke, 2014/11/14 22:46:40]

Could be instead take a base::RefCountedMemory?  See
ResourceBundle::LoadDataResourceBytes[ForScale]?

That may allow other cases of dynamically created data to avoid a copy, too.

[Jeffrey Yasskin, 2014/11/15 02:34:20]

Ah, that's definitely better; thanks! I'm inclined to switch the rest of the
implementations of GetData() over to RefCountedMemory too, but to do that in a
separate patch after we've seen that this patch fixes the problem.

 
  protected:
   void StartAsync();
 
  private:
   void OnGetDataCompleted(int result);
 
   HttpByteRange byte_range_;
   std::string mime_type_;
   std::string charset_;
-  std::string data_;
+  std::string data_storage_;
+  base::StringPiece data_;
   int data_offset_;
   base::WeakPtrFactory<URLRequestSimpleJob> weak_factory_;
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_