diff --git a/update_check_action.h b/update_check_action.h
new file mode 100644
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--- /dev/null
+++ b/update_check_action.h
@@ -0,0 +1,142 @@
+// Copyright (c) 2009 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 UPDATE_ENGINE_UPDATE_CHECK_ACTION_H__
+#define UPDATE_ENGINE_UPDATE_CHECK_ACTION_H__
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include <string>
+
+#include <curl/curl.h>
+
+#include "base/scoped_ptr.h"
+#include "action.h"
+#include "http_fetcher.h"
+
+// The Update Check action makes an update check request to Omaha and
+// can output the response on the output ActionPipe.
+
+using std::string;
+
+namespace chromeos_update_engine {
+
+// Encodes XML entities in a given string with libxml2. input must be
+// UTF-8 formatted. Output will be UTF-8 formatted.
+std::string XmlEncode(const std::string& input);
+
+// This struct encapsulates the data Omaha gets for the update check.
+// These strings in this struct should not be XML escaped.
+struct UpdateCheckParams {
+  UpdateCheckParams()
+      : os_platform(kOsPlatform), os_version(kOsVersion), app_id(kAppId) {}
+  UpdateCheckParams(const std::string& in_machine_id,
+                    const std::string& in_user_id,
+                    const std::string& in_os_platform,
+                    const std::string& in_os_version,
+                    const std::string& in_os_sp,
+                    const std::string& in_app_id,
+                    const std::string& in_app_version,
+                    const std::string& in_app_lang,
+                    const std::string& in_app_track)
+      : machine_id(in_machine_id),
+        user_id(in_user_id),
+        os_platform(in_os_platform),
+        os_version(in_os_version),
+        os_sp(in_os_sp),
+        app_id(in_app_id),
+        app_version(in_app_version),
+        app_lang(in_app_lang),
+        app_track(in_app_track) {}
+
+    std::string machine_id;
+    std::string user_id;
+    std::string os_platform;
+    std::string os_version;
+    std::string os_sp;
+    std::string app_id;
+    std::string app_version;
+    std::string app_lang;
+    std::string app_track;
+
+  // Suggested defaults
+  static const char* const kAppId;
+  static const char* const kOsPlatform;
+  static const char* const kOsVersion;
+};
+
+// This struct encapsulates the data Omaha returns for the update check.
+// These strings in this struct are not XML escaped.
+struct UpdateCheckResponse {
+  UpdateCheckResponse()
+      : update_exists(false), size(0), needs_admin(false), prompt(false) {}
+  // True iff there is an update to be downloaded.
+  bool update_exists;
+
+  // These are only valid if update_exists is true:
+  std::string display_version;
+  std::string codebase;
+  std::string more_info_url;
+  std::string hash;
+  off_t size;
+  bool needs_admin;
+  bool prompt;
+};
+COMPILE_ASSERT(sizeof(off_t) == 8, off_t_not_64bit);
+
+class UpdateCheckAction;
+class NoneType;
+
+template<>
+class ActionTraits<UpdateCheckAction> {
+ public:
+  // Does not take an object for input
+  typedef NoneType InputObjectType;
+  // On success, puts the output path on output
+  typedef UpdateCheckResponse OutputObjectType;
+};
+
+class UpdateCheckAction : public Action<UpdateCheckAction>,
+                          public HttpFetcherDelegate {
+ public:
+  // The ctor takes in all the parameters that will be used for
+  // making the request to Omaha. For some of them we have constants
+  // that should be used.
+  // Takes ownership of the passed in HttpFetcher. Useful for testing.
+  // A good calling pattern is:
+  // UpdateCheckAction(..., new WhateverHttpFetcher);
+  UpdateCheckAction(const UpdateCheckParams& params,
+                    HttpFetcher* http_fetcher);
+  virtual ~UpdateCheckAction();
+  typedef ActionTraits<UpdateCheckAction>::InputObjectType InputObjectType;
+  typedef ActionTraits<UpdateCheckAction>::OutputObjectType OutputObjectType;
+  void PerformAction();
+  void TerminateProcessing();
+
+  // Debugging/logging
+  std::string Type() const { return "UpdateCheckAction"; }
+
+  // Delegate methods (see http_fetcher.h)
+  virtual void ReceivedBytes(HttpFetcher *fetcher,
+                             const char* bytes, int length);
+  virtual void TransferComplete(HttpFetcher *fetcher, bool successful);
+
+ private:
+  // These are data that are passed in the request to the Omaha server
+  UpdateCheckParams params_;
+
+  // pointer to the HttpFetcher that does the http work
+  scoped_ptr<HttpFetcher> http_fetcher_;
+
+  // Stores the response from the omaha server
+  std::vector<char> response_buffer_;
+
+  DISALLOW_COPY_AND_ASSIGN(UpdateCheckAction);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_UPDATE_CHECK_ACTION_H__