AU: Try delta updates first, then full updates

src/platform/update_engine/omaha_response_handler_action.cc

 // Copyright (c) 2009 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 "update_engine/omaha_response_handler_action.h"
 #include <string>
 #include "update_engine/utils.h"
 
 using std::string;
 
 namespace chromeos_update_engine {
 
 namespace {
 // If the file part of the download URL contains kFullUpdateTag, then and
 // only then do we assume it's a full update. Otherwise, we assume it's a
 // delta update.
 const string kFullUpdateTag = "_FULL_";
 }  // namespace
 
 void OmahaResponseHandlerAction::PerformAction() {
   CHECK(HasInputObject());
   ScopedActionCompleter completer(processor_, this);
   const UpdateCheckResponse& response = GetInputObject();
   if (!response.update_exists) {
+    got_no_update_response_ = true;
     LOG(INFO) << "There are no updates. Aborting.";
     return;
   }
   InstallPlan install_plan;
   install_plan.download_url = response.codebase;
   install_plan.download_hash = response.hash;
   TEST_AND_RETURN(GetInstallDev(
       (!boot_device_.empty() ? boot_device_ : utils::BootDevice()),
       &install_plan.install_path));
 
   // Get the filename part of the url. Assume that if it has kFullUpdateTag
   // in the name, it's a full update.
   string::size_type last_slash = response.codebase.rfind('/');
   string filename;
   if (last_slash == string::npos)
     filename = response.codebase;
   else
     filename = response.codebase.substr(last_slash + 1);
   install_plan.is_full_update = (filename.find(kFullUpdateTag) != string::npos);
 
   if (filename.size() > 255) {
     // Very long name. Let's shorten it
     filename.resize(255);
   }
   // TODO(adlr): come up with a better place to download to:
-  install_plan.download_path = utils::kStatefulPartition + "/" + filename;
+  install_plan.download_path = string(utils::kStatefulPartition) + "/" +
+      filename;
   if (HasOutputPipe())
     SetOutputObject(install_plan);
   LOG(INFO) << "Using this install plan:";
   install_plan.Dump();
   completer.set_success(true);
 }
 
 bool OmahaResponseHandlerAction::GetInstallDev(const std::string& boot_dev,
                                                std::string* install_dev) {
   TEST_AND_RETURN_FALSE(!boot_dev.empty());
   string ret(boot_dev);
   char last_char = *ret.rbegin();
   TEST_AND_RETURN_FALSE((last_char >= '0') && (last_char <= '9'));
   // Chop off last char
   ret.resize(ret.size() - 1);
   // If last_char is odd (1 or 3), increase it, otherwise decrease
   if (last_char % 2)
     last_char++;
   else
     last_char--;
   ret += last_char;
   *install_dev = ret;
   return true;
 }
 
 }  // namespace chromeos_update_engine