diff --git a/payload_state.h b/payload_state.h
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+// Copyright (c) 2012 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.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_PAYLOAD_STATE_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_PAYLOAD_STATE_H__
+
+#include "base/file_path.h"
+
+#include "update_engine/action_processor.h"
+#include "update_engine/prefs_interface.h"
+
+namespace chromeos_update_engine {
+
+// Forward declaration here because we get a circular dependency if
+// we include omaha_request_action.h directly.
+struct OmahaResponse;
+
+// Encapsulates all the payload state required for download. This includes the
+// state necessary for handling multiple URLs in Omaha response, the back-off
+// state, etc. All state is persisted so that we use the most recently saved
+// value when resuming the update_engine process. All state is also cached in
+// memory so that we ensure we always make progress based on last known good
+// state even when there's any issue in reading/writing from the file system.
+class PayloadState {
+ public:
+
+  PayloadState() : prefs_(NULL), num_urls_(0), url_index_(0) {}
+
+  // Initializes a payload state object using |prefs| for storing the
+  // persisted state. It also performs the initial loading of all persisted
+  // state into memory and dumps the initial state for debugging purposes.
+  // Note: the other methods should be called only after calling Initialize
+  // on this object.
+  bool Initialize(PrefsInterface* prefs);
+
+  // Logs the current payload state.
+  void LogPayloadState();
+
+  // Sets the internal payload state based on the given Omaha response. This
+  // response could be the same or different from the one for which we've stored
+  // the internal state. If it's different, then this method resets all the
+  // internal state corresponding to the old response. Since the Omaha response
+  // has a lot of fields that are not related to payload state, it uses only
+  // a subset of the fields in the Omaha response to compare equality.
+  void SetResponse(const OmahaResponse& response);
+
+  // Updates the payload state when the current update attempt has failed.
+  void UpdateFailed(ActionExitCode error);
+
+  // Returns the internally stored subset of the response state as a string.
+  // This is logically a private method, but exposed here for unit tests.
+  std::string GetResponse() {
+    return response_;
+  }
+
+  // Returns the current URL index.
+  uint32_t GetUrlIndex() {
+    return url_index_;
+  }
+
+ private:
+  // Sets the stored response_ value from the currently persisted value for
+  // the response. Returns the same value.
+  std::string LoadResponse();
+
+  // Sets the url_index_ value from the currently persisted value for
+  // URL index. Returns the same value.
+  uint32_t LoadUrlIndex();
+
+  // Sets the current URL index.
+  void SetUrlIndex(uint32_t url_index);
+
+  // Interface object with which we read/write persisted state. This must
+  // be set by calling the Initialize method before calling any other method.
+  PrefsInterface* prefs_;
+
+  // Cached value of the latest subset of the Omaha response with which we're
+  // working off currently. This value is persisted so we load it off the next
+  // time when update_engine restarts. The rest of the state in this class will
+  // be cleared when we set a new  response.
+  std::string response_;
+
+  // The number of urls in the current response. Not persisted.
+  uint32_t num_urls_;
+
+  // Cached value of the index of the current URL, to be used in case we are
+  // unable to read from the persisted store for any reason. This type is
+  // different from the one in the accessor methods because PrefsInterface
+  // supports only int64_t but we want to provide a stronger abstraction of
+  // uint32_t.
+  int64_t url_index_;
+
+  DISALLOW_COPY_AND_ASSIGN(PayloadState);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_PAYLOAD_STATE_H__