IIRF UrlRewrite PostBack地址有关问题

namespace DOTA.Browser {    public class FormRewriterControlAdapter :            System.Web.UI.Adapters.ControlAdapter {        protected override void Render(HtmlTextWriter writer) {            base.Render(new RewriteFormHtmlTextWriter(writer));        }    }    public class RewriteFormHtmlTextWriter : HtmlTextWriter {        public RewriteFormHtmlTextWriter(HtmlTextWriter writer)            : base(writer) {            this.InnerWriter = writer.InnerWriter;        }        public RewriteFormHtmlTextWriter(TextWriter writer)            : base(writer) {            this.InnerWriter = writer;        }        public override void WriteAttribute(string name, string value, bool fEncode) {            if (name == "action") {                HttpContext context = HttpContext.Current;                if (context.Items["ActionAlreadyWritten"] == null) {                    value = context.Request.ServerVariables["HTTP_X_REWRITE_URL"] ?? context.Request.RawUrl;                    context.Response.Write(value);  //这里执行了，源代码里有,是Request.RawUrl的值。 HTTP_X_REWRITE_URL 这个是空的.                    context.Items["ActionAlreadyWritten"] = true;                }            }            base.WriteAttribute(name, value, fEncode);        }    }}

<browser refID="Default">        <controlAdapters>            <adapter controlType="System.Web.UI.HtmlControls.HtmlForm"                     adapterType="DOTA.Browser.FormRewriterControlAdapter" />        </controlAdapters>    </browser>