/// <summary>

        /// Copies all headers and content (except the URL) from an incoming to an outgoing

        /// request.

        /// </summary>

        /// <param name="source">The request to copy from</param>

        /// <param name="destination">The request to copy to</param>

        public static void CopyTo(this System.Web.HttpRequestBase source, HttpWebRequest destination)

        {

            Contract.Requires(source != null && destination != null);

            //注意：HttpWebRequire.Method默认为Get，

            //在写入请求前必须把HttpWebRequire.Method设置为Post,

            //否则在使用BeginGetRequireStream获取请求数据流的时候，系统就会发出“无法发送具有此谓词类型的内容正文”的异常。

            destination.Method = source.HttpMethod;

            // Copy unrestricted headers (including cookies, if any)

            foreach (var headerKey in source.Headers.AllKeys)

            {

                switch (headerKey)

                {

                    case "Connection":

                    case "Content-Length":

                    case "Date":

                    case "Expect":

                    case "Host":

                    case "If-Modified-Since":

                    case "Range":

                    case "Transfer-Encoding":

                    case "Proxy-Connection":

                        // Let IIS handle these

                        break;

                    case "Accept":

                    case "Content-Type":

                    case "Referer":

                    case "User-Agent":

                        // Restricted - copied below

                        break;

                    default:

                        destination.Headers[headerKey] = source.Headers[headerKey];

                        break;

                }

            }

            // Copy restricted headers

            if (!source.AcceptTypes.IsNullOrEmpty())

            {

                destination.Accept = string.Join(",", source.AcceptTypes);

            }

            destination.ContentType = source.ContentType;

            if (source.UrlReferrer != null)

            {

                destination.Referer = source.UrlReferrer.AbsoluteUri;

            }

            destination.UserAgent = source.UserAgent;

            destination.ContentLength = source.ContentLength;

            destination.ContentType = source.ContentType;

            destination.KeepAlive = source.Headers["Connection"] != "close";

            DateTime ifModifiedSince;

            if (DateTime.TryParse(source.Headers["If-Modified-Since"], out ifModifiedSince))

            {

                destination.IfModifiedSince = ifModifiedSince;

            }

            string transferEncoding = source.Headers["Transfer-Encoding"];

            if (transferEncoding != null)

            {

                destination.SendChunked = true;

                destination.TransferEncoding = transferEncoding;

            }

            // Copy content (if content body is allowed)

            if (source.HttpMethod != WebRequestMethods.Http.Get && source.HttpMethod != WebRequestMethods.Http.Head && source.ContentLength > )

            {

                var destinationStream = destination.GetRequestStream();

                source.InputStream.FixedCopyTo(destinationStream, source.ContentLength);

                destinationStream.Close();

            }

        }