Question

I need to locally test some code that uses a WebClient object for communicating with an http server. For that purpose, I decided to write an incredibly simplistic mock server that reads some bytes from a binary file and sends them to the client. Here is the relevant server’s code:

public void Listen()
{
    TcpClient client;
    NetworkStream netStream;
    listener.Start();

    try
    {
        client = listener.AcceptTcpClient();
        netStream = client.GetStream();
        ReadData(netStream);
        Console.WriteLine("Writing data, sequence 1");
        WriteData(netStream, 1);
        netStream.Close();
        client.Close();

        client = listener.AcceptTcpClient();
        netStream = client.GetStream();
        ReadData(netStream);
        Console.WriteLine("Writing data, sequence 2");
        WriteData(netStream, 2);
        netStream.Close();
        client.Close();
    }
    catch(Exception e)
    {
    }
}

private void WriteData(NetworkStream netStream, int sequence)
{
    byte[] bytes = PrepareResponse(sequence);    //get data from a file
    netStream.Write(bytes, 0, bytes.Length);
}

With WebClient I use UploadString:

string response = client.UploadString(address + link, data);

So, the thing is, the WebClient apparently receives all the sent data, but throws a System.IO.Exception (“Unable to read data from the transport connection: The connection was closed.”) when I close the stream server-side. If I don’t close the stream, WebClient blocks and waits for the transfer to finish, despite all the data being received. I tried to substitute WebClient with WebRequest, and it also either throws an exception if the socket was closed server-side or blocks on stream.Read after reading all the data. What I find strange is that the first block of data I send to WebClient is an http 302 “Moved” response, which causes the WebClient to immediately send a GET request. Despite the fact that I send data identically two times, WebClient throws an exception only on the second response.

So – I need a way to correctly send the data and close the connection so it works with WebClient, and I would also like to know why does WebClient correctly handle the 302 response and throw an exception on the second response.

Thank you.

Answer 1

The answer was actually quite trivial – the second http response had “Transfer-Encoding: chunked” set in its headers, and I didn’t actually send the terminating zero-length chunk at the end of the response, thus WebClient was waiting for more data.