"Invalid use of response filter" when compressing response from an IHttpHandler

Question

I have an IHttpHandler returning a file. When the response stream is compressed, either automatically using Telerik RadCompression or by explicitly setting a filter using

context.Response.Filter = new GZipStream(context.Response.Filter, CompressionMode.Compress);

the response returned to the browser is correct but at the end of the response is some HTML. The HTML contains the exception:

[HttpException (0x80004005): Invalid use of response filter]
   System.Web.HttpResponseStreamFilterSink.VerifyState() +3928894
   System.Web.HttpResponseStreamFilterSink.Write(Byte[] buffer, Int32 offset, Int32 count) +28
   System.IO.Compression.DeflateStream.Dispose(Boolean disposing) +363
   System.IO.Stream.Close() +28
   System.IO.Compression.GZipStream.Dispose(Boolean disposing) +63
   System.IO.Stream.Close() +28
   System.IO.Compression.DeflateStream.Dispose(Boolean disposing) +595
   System.IO.Stream.Close() +28
   System.IO.Compression.GZipStream.Dispose(Boolean disposing) +63
   System.IO.Stream.Close() +28
   System.Web.HttpWriter.FilterIntegrated(Boolean finalFiltering, IIS7WorkerRequest wr) +754
   System.Web.HttpResponse.FilterOutput() +121
   System.Web.CallFilterExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +174

If I make sure the response is NOT compressed, the response contains no exception.

What's up with that?

Answer 1

Make sure you're not preventing buffering. Apparently, to compress the response, you have to allow it to be buffered.

I.e., one of the following two lines needs to be removed:

context.Response.BufferOutput = false;
context.Response.Filter = new GZipStream(context.Response.Filter, CompressionMode.Compress);