A simple xml-rpc endpoint in .NET

k10n
Jim Klopfenstein's Radio Weblog

A simple xml-rpc endpoint in .NET

It's easy to bypass the entire ASP.NET infrastructure on a .NET framework/IIS system to receive and respond to HTTP post requests. All you have to do is create a C# class library that implements the (single-method) IHttpHandler interface, put the executable in the right place, and reference it in a web.config file.

Here's the simple class I wrote (or more accurately, modified from the Microsoft sample) to log rss.xml file change notifications. (You can register for these notifications by sending a separate xml-rpc message to Userland's xmlStorageSystem, as described on this page).

 using System;
using System.Web;
using System.IO;
 namespace HandlerExample
{
   public class MyHttpHandler : IHttpHandler
   {
      private void logMessage(string header,string message)
      {
         FileStream fs = new FileStream("c:\\logs\\log.txt",FileMode.Append,FileAccess.Write);
         StreamWriter w = new StreamWriter(fs);
         w.WriteLine("--- " + header);
         w.WriteLine(message);
         w.Flush();
         w.Close();
      }
       // Override the ProcessRequest method.
      public void ProcessRequest(HttpContext context)
      {
         StreamReader r = new StreamReader(context.Request.InputStream);
         logMessage("xml-rpc request",r.ReadToEnd());
         r.Close();
          String successResponse = "<?xml version=\"1.0"?>n";
         successResponse += "<methodResponse>\n";
         successResponse += "<params>\n";
         successResponse += "<param>\n";
         successResponse += "<value><boolean>1</boolean></value>\n";
         successResponse += "</param>\n";
         successResponse += "</params>\n";
         successResponse += "</methodResponse>\n";
          context.Response.ContentType = "text/xml";
         context.Response.Write(successResponse);      
      }
       // Override the IsReusable property.
      public bool IsReusable
      {
         get { return true; }
      }
   }
}

The lone method in the interface is ProcessRequest. Its one parameter, an HttpContext object, is stocked with everything you need to read and respond to the HTTP request. I use the Request property of the HttpContext to get the "post" data, and the Response property to return my xml-rpc response message.

To build this class, just run the command:

csc /t:library /r:System.Web.dll HandlerTest.cs

This will create a file called HandlerTest.dll in the same directory.

To hook it up, just copy the dll into inetpubwwwrootbin (you might have to create it; I did). Then create another subdirectory under inetpubwwwroot (I called mine HandlerDir) and create a file in it called web.config. Here's what it should contain:

<configuration>
   <system.web>
      <httpHandlers>
         <add verb="*" path="handler.aspx" type="HandlerExample.MyHttpHandler,HandlerTest"/>
      </httpHandlers>
   </system.web>
</configuration>

Once this is set up, any HTTP requests to /HandlerDir/handler.aspx will go to your class instead of to ASP.NET. You can test this in a browser. I created this HTML file in the HandlerDir directory (I called it test.html):

<html>
 <body>
  <form action="handler.aspx" method="POST">
   <input name="data" type="text">
   <input type="submit">
  </form>
 </body>
</html>

When I browse to it and click "Submit", I see the xml-rpc response in the browser and get the "data=" message in my log file.

That's all there is to it. Set it up and your .NET system talks (a very, very basic) xml-rpc.

Coming soon: an article showing the code I used to register my callback with xmlStorageSystem.