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

net/url_request/url_request_simple_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 "net/url_request/url_request_simple_job.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
+#include "base/memory/ref_counted_memory.h"
 #include "base/message_loop/message_loop.h"
 #include "base/profiler/scoped_tracker.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_util.h"
 #include "net/url_request/url_request_status.h"
 
 namespace net {
 
@@ skipping 22 matching lines @@
 }
 
 URLRequestSimpleJob::~URLRequestSimpleJob() {}
 
 bool URLRequestSimpleJob::ReadRawData(IOBuffer* buf, int buf_size,
                                       int* bytes_read) {
   DCHECK(bytes_read);
   int remaining = byte_range_.last_byte_position() - data_offset_ + 1;
   if (buf_size > remaining)
     buf_size = remaining;
-  memcpy(buf->data(), data_.data() + data_offset_, buf_size);
+  memcpy(buf->data(), data_->front() + data_offset_, buf_size);
   data_offset_ += buf_size;
   *bytes_read = buf_size;
   return true;
 }
 
+int URLRequestSimpleJob::GetData(std::string* mime_type,
+                                 std::string* charset,
+                                 std::string* data,
+                                 const CompletionCallback& callback) const {
+  NOTREACHED();
+  return ERR_UNEXPECTED;
+}
+
+int URLRequestSimpleJob::GetRefCountedData(
+    std::string* mime_type,
+    std::string* charset,
+    scoped_refptr<base::RefCountedMemory>* data,
+    const CompletionCallback& callback) const {
+  scoped_refptr<base::RefCountedString> str_data(new base::RefCountedString());

[mmenke, 2014/11/17 15:54:10]

Do we get anything from using a temporary here?

[Jeffrey Yasskin, 2014/11/17 17:16:23]

Yeah, I have to use the subclass's member functions to fill in the string in or
after the GetData() call. The temporary lets me delay the upcast long enough to
do that. I'd make the temporary a std::string, but RefCountedString() doesn't
have a constructor taking a string, so I'd still need the temporary
scoped_refptr<RefCountedString>.

+  int result = GetData(mime_type, charset, &str_data->data(), callback);
+  *data = str_data;
+  return result;
+}
+
 void URLRequestSimpleJob::StartAsync() {
   if (!request_)
     return;
 
   if (ranges().size() > 1) {
     // TODO(vadimt): Remove ScopedTracker below once crbug.com/422489 is fixed.
     tracked_objects::ScopedTracker tracking_profile(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "422489 URLRequestSimpleJob::StartAsync 1"));
 
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED,
                                 ERR_REQUEST_RANGE_NOT_SATISFIABLE));
     return;
   }
 
   if (!ranges().empty() && range_parse_result() == OK)
     byte_range_ = ranges().front();
 
   int result;
   {
     // TODO(vadimt): Remove ScopedTracker below once crbug.com/422489 is fixed.
     // Remove the block and assign 'result' in its declaration.
     tracked_objects::ScopedTracker tracking_profile(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "422489 URLRequestSimpleJob::StartAsync 2"));
 
-    result = GetData(&mime_type_,
-                     &charset_,
-                     &data_,
-                     base::Bind(&URLRequestSimpleJob::OnGetDataCompleted,
-                                weak_factory_.GetWeakPtr()));
+    result =
+        GetRefCountedData(&mime_type_, &charset_, &data_,
+                          base::Bind(&URLRequestSimpleJob::OnGetDataCompleted,
+                                     weak_factory_.GetWeakPtr()));
   }
 
   if (result != ERR_IO_PENDING) {
     // TODO(vadimt): Remove ScopedTracker below once crbug.com/422489 is fixed.
     tracked_objects::ScopedTracker tracking_profile(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "422489 URLRequestSimpleJob::StartAsync 3"));
 
     OnGetDataCompleted(result);
   }
 }
 
 void URLRequestSimpleJob::OnGetDataCompleted(int result) {
   // TODO(vadimt): Remove ScopedTracker below once crbug.com/422489 is fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "422489 URLRequestSimpleJob::OnGetDataCompleted"));
 
   if (result == OK) {
     // Notify that the headers are complete
-    if (!byte_range_.ComputeBounds(data_.size())) {
+    if (!byte_range_.ComputeBounds(data_->size())) {
       NotifyDone(URLRequestStatus(URLRequestStatus::FAILED,
                  ERR_REQUEST_RANGE_NOT_SATISFIABLE));
       return;
     }
 
     data_offset_ = byte_range_.first_byte_position();
     int remaining_bytes = byte_range_.last_byte_position() -
         byte_range_.first_byte_position() + 1;
     set_expected_content_size(remaining_bytes);
     NotifyHeadersComplete();
   } else {
     NotifyStartError(URLRequestStatus(URLRequestStatus::FAILED, result));
   }
 }
 
 }  // namespace net