AU: No need to calculate SHA-256 on the payload twice for delta updates.

download_action.cc

 // Copyright (c) 2010 The Chromium OS 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 "update_engine/download_action.h"
 #include <errno.h>
 #include <algorithm>
 #include <string>
 #include <vector>
 #include <glib.h>
@@ skipping 105 matching lines @@
                                    int length) {
   bytes_received_ += length;
   if (delegate_)
     delegate_->BytesReceived(bytes_received_, install_plan_.size);
   if (writer_ && writer_->Write(bytes, length) < 0) {
     LOG(ERROR) << "Write error -- terminating processing.";
     TerminateProcessing();
     processor_->ActionComplete(this, kActionCodeDownloadWriteError);
     return;
   }
-  omaha_hash_calculator_.Update(bytes, length);
+  // DeltaPerformer checks the hashes for delta updates.
+  if (install_plan_.is_full_update) {
+    omaha_hash_calculator_.Update(bytes, length);
+  }
 }
 
 namespace {
 void FlushLinuxCaches() {
   vector<string> command;
   command.push_back("/bin/sync");
   int rc;
   LOG(INFO) << "FlushLinuxCaches-sync...";
   Subprocess::SynchronousExec(command, &rc);
   LOG(INFO) << "FlushLinuxCaches-drop_caches...";
@@ skipping 48 matching lines @@
 
   FlushLinuxCaches();
 
   // Write the path to the output pipe if we're successful.
   if (code == kActionCodeSuccess && HasOutputPipe())
     SetOutputObject(GetInputObject());
   processor_->ActionComplete(this, code);
 }
 
 };  // namespace {}