Created a blocking copy to temporary file function.

mojo/data_pipe_utils/data_pipe_file_utils.cc

 // Copyright 2014 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 "mojo/data_pipe_utils/data_pipe_utils.h"
 
 #include <stdio.h>
 
 #include <limits>
 
@@ skipping 297 matching lines @@
                          base::Bind(&CopyFromFileHandler::OnHandleReady,
                                     base::Unretained(this), result));
 }
 
 size_t CopyToFileHelper(FILE* fp, const void* buffer, uint32_t num_bytes) {
   return fwrite(buffer, 1, num_bytes, fp);
 }
 
 }  // namespace
 
-bool BlockingCopyToFile(ScopedDataPipeConsumerHandle source,
-                        const base::FilePath& destination) {
-  TRACE_EVENT1("data_pipe_utils", "BlockingCopyToFile", "dest",
-               destination.MaybeAsASCII());
-  base::ScopedFILE fp(base::OpenFile(destination, "wb"));
+base::ScopedFILE BlockingCopyToTempFile(ScopedDataPipeConsumerHandle source) {
+  base::FilePath path;
+  base::ScopedFILE fp(CreateAndOpenTemporaryFile(&path));
   if (!fp) {
-    LOG(ERROR) << "OpenFile('" << destination.value()
-               << "'failed in BlockingCopyToFile";
-    return false;
+    LOG(ERROR) << "CreateAndOpenTemporaryFile failed in"
+               << "BlockingCopyToTempFile";
+    return NULL;

[jamesr, 2015/09/02 23:29:31]

s/NULL/nullptr/.  Only use NULL in code that has to compile as C

[Sean Klein, 2015/09/02 23:35:35]

Whoops! Sorry, a bit new to C++, and old habits die hard apparently.

   }
-  return BlockingCopyHelper(source.Pass(),
-                            base::Bind(&CopyToFileHelper, fp.get()));
+  if (unlink(path.value().c_str())) {
+    LOG(ERROR) << "Failed to unlink temporary file";
+    return NULL;
+  }
+  if (!BlockingCopyHelper(source.Pass(),
+                          base::Bind(&CopyToFileHelper, fp.get()))) {
+    LOG(ERROR) << "Could not copy source to temporary file";
+    return NULL;

[jamesr, 2015/09/02 23:29:31]

ditto

[Sean Klein, 2015/09/02 23:35:35]

Done.

+  }
+  return fp;
 }
 
 void CopyToFile(ScopedDataPipeConsumerHandle source,
                 const base::FilePath& destination,
                 base::TaskRunner* task_runner,
                 const base::Callback<void(bool)>& callback) {
   new CopyToFileHandler(source.Pass(), destination, task_runner, callback);
 }
 
 void CopyFromFile(const base::FilePath& source,
                   ScopedDataPipeProducerHandle destination,
                   uint32_t skip,
                   base::TaskRunner* task_runner,
                   const base::Callback<void(bool)>& callback) {
   new CopyFromFileHandler(source, destination.Pass(), skip, task_runner,
                           callback);
 }
 
 }  // namespace common
 }  // namespace mojo