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

net/url_request/url_request_simple_job.cc

Index: net/url_request/url_request_simple_job.cc
diff --git a/net/url_request/url_request_simple_job.cc b/net/url_request/url_request_simple_job.cc
index b855932d577824997d390d3c32dd0661415f6737..55a0f8842710743a61364492bf630d20d755af5f 100644
--- a/net/url_request/url_request_simple_job.cc
+++ b/net/url_request/url_request_simple_job.cc
@@ -8,6 +8,7 @@
 
 #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"
@@ -50,12 +51,31 @@ bool URLRequestSimpleJob::ReadRawData(IOBuffer* buf, int buf_size,
   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;
@@ -82,11 +102,10 @@ void URLRequestSimpleJob::StartAsync() {
         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) {
@@ -107,7 +126,7 @@ void URLRequestSimpleJob::OnGetDataCompleted(int result) {
 
   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;