Question

I have an ISAPI filter for IIS 6 which does some custom processing using the bytes-sent field of the response. I’d like to update that for IIS 7, but I’m running into a problem. None of the IIS 7 events seem to have access to the content-length, bytes sent, or any data which would let me calculate the content-length or bytes sent. (I know the content-length header and bytes sent are not the same, but either will work for this purpose.)

From what I can tell, the content-length header is added by HTTP.SYS after the managed modules have finished executing. Right now I have an event handler which runs on EndRequest. If I could get at the output stream I could calculate what I need myself but the managed pipeline doesn’t seem to have access to that either.

Is there some way of getting the content-length or bytes sent in the managed pipeline? Failing that, is there some way I can calculate content-length or bytes sent from objects available in the managed pipeline?

Answer 1

To get at the bytes sent you can use the HttpResponse.Filter property. As the MSDN docs say this property gets or sets a wrapping filter object that is used to modify the HTTP entity body before transmission.

You can create a new System.IO.Stream that wraps the existing HttpResponse.Filter stream and counts the bytes passed in to the Write method before passing them on. For example:

public class ContentLengthModule : IHttpModule {     public void Init(HttpApplication context)     {         context.BeginRequest += OnBeginRequest;         context.EndRequest += OnEndRequest;     }      void OnBeginRequest(object sender, EventArgs e)     {         var application = (HttpApplication) sender;         application.Response.Filter = new ContentLengthFilter(application.Response.Filter);     }      void OnEndRequest(object sender, EventArgs e)     {         var application = (HttpApplication) sender;         var contentLengthFilter = (ContentLengthFilter) application.Response.Filter;         var contentLength = contentLengthFilter.BytesWritten;     }      public void Dispose()     {     } }  public class ContentLengthFilter : Stream {     private readonly Stream _responseFilter;      public int BytesWritten { get; set; }      public ContentLengthFilter(Stream responseFilter)     {         _responseFilter = responseFilter;     }      public override void Flush()     {         _responseFilter.Flush();     }      public override long Seek(long offset, SeekOrigin origin)     {         return _responseFilter.Seek(offset, origin);     }      public override void SetLength(long value)     {         _responseFilter.SetLength(value);     }      public override int Read(byte[] buffer, int offset, int count)     {         return _responseFilter.Read(buffer, offset, count);     }      public override void Write(byte[] buffer, int offset, int count)     {         BytesWritten += count;         _responseFilter.Write(buffer, offset, count);     }      public override bool CanRead     {         get { return _responseFilter.CanRead; }     }      public override bool CanSeek     {         get { return _responseFilter.CanSeek; }     }      public override bool CanWrite     {         get { return _responseFilter.CanWrite; }     }      public override long Length     {         get { return _responseFilter.Length; }     }      public override long Position     {         get { return _responseFilter.Position; }         set { _responseFilter.Position = value; }     } }