Question

How do I best capture the HTML (in my instance, for logging) rendered by an aspx-page?

I dont want to have to write back to the page using Response.Write, since it messes up my site layout.

Using the Response.OutputStream or Response.Output’s stream results in an ArgumentException ({System.ArgumentException: Stream was not readable.)

Answer 1

Good question, i had to try out and see if i could create a HttpModule to do what you are describing.

I didnt have any luck trying to read from the responsestream, but using the ResponseFilter gave me a way to capture the content.

The following code seems to work pretty good, and i figured maybe you could use the code as a base. But remember this is just something i threw together fast, it has not been tested in any way. So dont use it in any production environment without proper reviewing/testing and such. Feel free to comment on it though 😉

public class ResponseLoggerModule : IHttpModule {     private class ResponseCaptureStream : Stream     {         private readonly Stream _streamToCapture;         private readonly Encoding _responseEncoding;          private string _streamContent;         public string StreamContent         {             get { return _streamContent; }             private set             {                 _streamContent = value;             }         }          public ResponseCaptureStream(Stream streamToCapture, Encoding responseEncoding)         {             _responseEncoding = responseEncoding;             _streamToCapture = streamToCapture;          }          public override bool CanRead         {             get { return _streamToCapture.CanRead; }         }          public override bool CanSeek         {             get { return _streamToCapture.CanSeek; }         }          public override bool CanWrite         {             get { return _streamToCapture.CanWrite; }         }          public override void Flush()         {             _streamToCapture.Flush();         }          public override long Length         {             get { return _streamToCapture.Length; }         }          public override long Position         {             get             {                 return _streamToCapture.Position;             }             set             {                 _streamToCapture.Position = value;             }         }          public override int Read(byte[] buffer, int offset, int count)         {             return _streamToCapture.Read(buffer, offset, count);         }          public override long Seek(long offset, SeekOrigin origin)         {             return _streamToCapture.Seek(offset, origin);         }          public override void SetLength(long value)         {             _streamToCapture.SetLength(value);         }          public override void Write(byte[] buffer, int offset, int count)         {             _streamContent += _responseEncoding.GetString(buffer);             _streamToCapture.Write(buffer, offset, count);         }          public override void Close()         {             _streamToCapture.Close();             base.Close();         }     }      #region IHttpModule Members      private HttpApplication _context;     public void Dispose()     {      }      public void Init(HttpApplication context)     {         _context = context;          context.PreRequestHandlerExecute += new EventHandler(context_PreRequestHandlerExecute);         context.PreSendRequestContent += new EventHandler(context_PreSendRequestContent);     }      void context_PreRequestHandlerExecute(object sender, EventArgs e)     {         _context.Response.Filter = new ResponseCaptureStream(_context.Response.Filter, _context.Response.ContentEncoding);     }      void context_PreSendRequestContent(object sender, EventArgs e)     {         ResponseCaptureStream filter = _context.Response.Filter as ResponseCaptureStream;          if (filter != null)         {             string responseText = filter.StreamContent;              // Logging logic here         }     }      #endregion }