SocketException - WebResponse Issue

microsoft.public.dotnet.framework

30 Mar 2007 7:03 PM

Al Tenhundfeld

I just discovered the solution to a problem that took me many hours to
debug. I'm going to document it here in case anyone else has a similar
problem.

I have a simple app that performs on-demand data transformations between two
systems. During this process, it has to download N number of documents from
a specific website. I accomplished this using the WebRequest and WebResponse
classes.

My code looked something like this:

foreach (Document doc in documentList)
{

    WebRequest request;
    WebResponse response;
    Stream responseStream = null;

    try
    {
        request = WebRequest.Create(doc.URI);
        response = request.GetResponse();
        responseStream = response.GetResponseStream();
        ...
        code to read stream & process document
        ...
    }
    finally
    {
        if (responseStream != null)
        {
            responseStream.Close();
        }
    }
}

I was sporadically encountering the following error:

SocketException {"An existing connection was forcibly closed by the remote
host"}

"   at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32
size, SocketFlags socketFlags)\r\n
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32
size)"

After some troubleshooting, I determined that the exception was being thrown
when the app tried to read from a new response stream after reading more
than 20 MB from other response streams. For example, it needs to process
four documents that are each 7 MB. It would process the first three fine and
then fail on the first call to responseStream.Read for the fourth document.
The issue may be related to this KB article:
http://support.microsoft.com/default.aspx?scid=kb;en-us;826756. I have no
control over the webserver.

I finally resolved this issue by explicitly closing the WebResponse. For
some reason, I was under the impression that closing the response stream was
sufficient. After I added the following code to the finally block, my app
works without problem. I realize that calling response.Close should close
the responseStream as well, but when I'm having issues with code, I like to
be explicit.

finally
{
        if (responseStream != null)
        {
            responseStream.Close();
        }

        if (response != null)
        {
            response.Close();
        }
}

I hope this helps somebody else save a few hours.
Search Keywords: ConnectStream, HttpWebRequest, HttpWebResponse,
System.IO.IOException: Unable to read data from the transport connection: