Getting form data from HttpListenerRequest

Odd that an accepted answer with full source code + a link to download a working demo would result in a negative score and votes to be deleted. If I were the kind of person who cared about my score I'd have deleted this answer, and then nobody would have benefited. Psychology, eh :)

I found a few examples of web servers for MonoTouch but none of them parsed the data sent in a POST request. I looked around the web and was unable to find any examples of how to achieve this. So now that I’ve written it myself I’ve decided to share my own implementation. This includes not only the code for processing the form post data but also for registering request handlers etc.

Here is an example of how you would use the web server 

 public BookUploadViewController() 
   : base("BookUploadViewController", null)
 {
   RequestHandler = new DefaultRequestHandler();
   var defaultActionHandlerFactory = new DefaultActionHandlerFactory();
   RegisterActionHandlers(defaultActionHandlerFactory);
   RequestHandler.AddActionHandlerFactory(defaultActionHandlerFactory);

   WebServer = new EmbeddedWebServer(RequestHandler);
 }

 void RegisterActionHandlers(DefaultActionHandlerFactory factory)
 {
   factory.RegisterHandler(
     request => request.RawUrl == "/",
     request => new IndexActionHandler(request)
     );
   factory.RegisterHandler(
     request => 
       string.Compare(request.RawUrl, "/Upload", true) == 0 && 
       string.Compare(request.HttpMethod, "POST", true) == 0,
     request => new UploadActionHandler(request)
     );
 }

 public override void ViewDidAppear(bool animated)
 {
   base.ViewDidAppear(animated);
   StatusLabel.Text = string.Format("Server listening on\r\nhttp://{0}:8080", GetIPAddress ());
   WebServer.Start(8080);
 }

 public override void ViewDidDisappear (bool animated)
 {
   base.ViewDidDisappear(animated);
   WebServer.Stop();
 }

And here are two app specific examples of request handlers

 class IndexActionHandler : DefaultActionHandler
 {
   public IndexActionHandler(HttpListenerRequest request)
     : base(request)
   {
   }

   public override ActionResult Execute()
   {
     var result = new HtmlResult();
     result.AppendLine("<html>");
     result.AppendLine("<body>");
     result.AppendLine("<h1>Upload an image</h1>");
     result.AppendLine("<form action='/Upload' enctype='multipart/form-data' method='post'>");
     result.AppendLine ("<input name='Image' type='file'/><br/>");
     result.AppendLine("<input name='Upload' type='submit' text='Upload'/>");
     result.AppendLine("</form>");
     result.AppendLine("</body>");
     result.AppendLine("</html>");
     return result;
   }
 }

 class UploadActionHandler : DefaultActionHandler
 {
   public UploadActionHandler(HttpListenerRequest request)
     : base(request)
   {
   }

   public override ActionResult Execute()
   {
     string errorMessage = null;
     var file = FormData.GetFile("Image");
     if (file == null 
       || file.FileData == null 
       || file.FileData.Length == 0 
       || string.IsNullOrEmpty(file.FileName))
       errorMessage = "No image uploaded";

     if (errorMessage == null)
       ProcessFile(file);

     var result = new HtmlResult();
     result.AppendLine("<html>");
     result.AppendLine("<body>");
     if (errorMessage == null)
       result.AppendLine("<h1>File uploaded successfully</h1>");
     else
     {
       result.AppendLine("<h1>Error</h1>");
       result.AppendLine("<h2>" + errorMessage + "</h2>");
     }
     result.AppendLine("</body>");
     result.AppendLine("</html>");
     return result;
   }

   void ProcessFile(MultiPartStreamFileValue postedFile)
   {
     string fileName = "Where to save the file";
     using (var fileStream = 
       new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None))
     {
       fileStream.Write(postedFile.FileData, 0, postedFile.FileData.Length);
     }
   }
 }

You can download the source code here https://sites.google.com/site/mrpmorris/EmbeddedWebServerMT.zip


The main thing to understand is that HttpListener is a low level tool to work with http requests. All post data is in HttpListenerRequest.InputStream stream. Suppose we have a form like that:

<form method=\"post\" enctype=\"multipart/form-data\"><input id=\"fileUp\" name=\"fileUpload\" type=\"file\" /><input type=\"submit\" /></form>

Now we want to see the post data. Lets implement a method to do this:

public static string GetRequestPostData(HttpListenerRequest request)
{
  if (!request.HasEntityBody)
  {
    return null;
  }
  using (System.IO.Stream body = request.InputStream) // here we have data
  {
    using (var reader = new System.IO.StreamReader(body, request.ContentEncoding))
    {
      return reader.ReadToEnd();
    }
  }
}

upload some file and see result:

Content-Disposition: form-data; name="somename"; filename="D:\Test.bmp" 
Content-Type: image/bmp
...here is the raw file data...

Next suppose we have simple form without uploading files:

<form method=\"post\">First name: <input type=\"text\" name=\"firstname\" /><br />Last name: <input type=\"text\" name=\"lastname\" /><input type=\"submit\" value=\"Submit\" /></form>

Let's see the output:

firstname=MyName&lastname=MyLastName

Combined form result:

Content-Disposition: form-data; name="firstname"
My Name
Content-Disposition: form-data; name="somename"; filename="D:\test.xls"
Content-Type: application/octet-stream
...raw file data...

As you can see in case of simple form you can just read InputStream to string and parse post values. If there is a more complex form - you need to perform more complex parsing but it's still can be done. Hope this examples will save your time. Note, that is not always the case to read all stream as a string.

Tags:

C#

Forms

Http Post

Httplistenerrequest

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