How to view contents of HTMLTextWriter?

Question

I have an HtmlTextWriter object (theWriter) being passed into a method. This method is in the middle tier. I'd like to read the contents of the theWriter in debug mode. The method is:

protected override void Render (HtmlTextWriter theWriter) {...}

which inherits from Panel:WebControl.

I've tried

theWriter.Flush();
theWriter.InnerWriter.ToString();

but that only outputs the object type: "System.Web.HttpWriter". I've seen some examples use methods on the Response object. But I don't have access to Response in this layer. Any ideas?

Answer 1

The InnerWriter is a TextWriter-derived class, which writes to a stream. You will have to open that stream and read data from it. Whether you can open and read from that stream is an open question, and depends very much on what type of stream it is.

So to use your example, theWriter.InnerWriter is an object derived from TextWriter. But you don't know what kind, and TextWriter itself doesn't expose the underlying stream.

Now, if InnerWriter is a StreamWriter, then you might be able to write:

var sWriter = theWriter.InnerWriter as StreamWriter;
var stream = sWriter.BaseStream;
var savePosition = stream.Position;
stream.Position = 0;
// now, you can read the stream
// when you're done reading the stream, be sure to reset its position
stream.Position = savePosition;

You have to be very careful, though. If you get the base stream and then open it with a StreamReader, closing the StreamReaderwill close the underlying stream. Then your HtmlTextWriter will throw an exception the next time you try to write to it.

It's also possible that you won't be able to read the stream. If the base stream is a NetworkStream, for example, you can't read it. Or it could be a FileStream that was open for write only. There's no good general way to do this, as it entirely depends not only on the specific TextWriter-derived class, but also on the stream that the TextWriter is writing to.

For example, the HtmlTextWriter could be writing to a StreamWriter, which is connected to a BufferedStream connected to a GZipStream, which finally writes to a MemoryStream.

So, in general, I'd recommend that you look for some other solution to your problem. Unless you know for sure what the underlying stream is, and that you can read it ... and that things won't change on you unexpectedly.