diff --git a/common/http_common.h b/common/http_common.h
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+//
+// Copyright (C) 2009 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// This file contains general definitions used in implementing, testing and
+// emulating communication over HTTP.
+
+#ifndef UPDATE_ENGINE_COMMON_HTTP_COMMON_H_
+#define UPDATE_ENGINE_COMMON_HTTP_COMMON_H_
+
+#include <cstdlib>
+
+namespace chromeos_update_engine {
+
+// Enumeration type for HTTP response codes.
+enum HttpResponseCode {
+  kHttpResponseUndefined           = 0,
+  kHttpResponseOk                  = 200,
+  kHttpResponseCreated             = 201,
+  kHttpResponseAccepted            = 202,
+  kHttpResponseNonAuthInfo         = 203,
+  kHttpResponseNoContent           = 204,
+  kHttpResponseResetContent        = 205,
+  kHttpResponsePartialContent      = 206,
+  kHttpResponseMultipleChoices     = 300,
+  kHttpResponseMovedPermanently    = 301,
+  kHttpResponseFound               = 302,
+  kHttpResponseSeeOther            = 303,
+  kHttpResponseNotModified         = 304,
+  kHttpResponseUseProxy            = 305,
+  kHttpResponseTempRedirect        = 307,
+  kHttpResponseBadRequest          = 400,
+  kHttpResponseUnauth              = 401,
+  kHttpResponseForbidden           = 403,
+  kHttpResponseNotFound            = 404,
+  kHttpResponseRequestTimeout      = 408,
+  kHttpResponseReqRangeNotSat      = 416,
+  kHttpResponseInternalServerError = 500,
+  kHttpResponseNotImplemented      = 501,
+  kHttpResponseServiceUnavailable  = 503,
+  kHttpResponseVersionNotSupported = 505,
+};
+
+// Returns a standard HTTP status line string for a given response code.
+const char *GetHttpResponseDescription(HttpResponseCode code);
+
+// Converts a string beginning with an HTTP error code into numerical value.
+HttpResponseCode StringToHttpResponseCode(const char *s);
+
+
+// Enumeration type for HTTP Content-Type.
+enum HttpContentType {
+  kHttpContentTypeUnspecified = 0,
+  kHttpContentTypeTextXml,
+};
+
+// Returns a standard HTTP Content-Type string.
+const char *GetHttpContentTypeString(HttpContentType type);
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_HTTP_COMMON_H_