How to send the 'Connection' header using HttpListenerResponse

Shmuel Zang

Hello all.

While trying to implement a web-socket handshake, I encountered a weird behavior. It looks like the HttpListenerResponse class doesn't send the 'Connection' header.

Here is an example for explaining what I mean:

public void TestWebSocketHttpHandshake()
{
int port = 9444;
ManualResetEvent serverStartedEvent = new ManualResetEvent(false);
ManualResetEvent clientClosedEvent = new ManualResetEvent(false);

// HTTP server that gets a web-socket handshake request and,
// send back a web-socket handshake response.
async Task RunHttpServer()
{
    HttpListener hl = new HttpListener();
    hl.Prefixes.Add($"http://+:{port}/");
    hl.Start();
    serverStartedEvent.Set();
    HttpListenerContext hlc = await hl.GetContextAsync();

    string secWebSocketKeyHeader = hlc.Request.Headers\["Sec-WebSocket-Key"\]?.Trim();
    string secWebSocketAcceptHeader = Convert.ToBase64String(
        System.Security.Cryptography.SHA1.Create().ComputeHash(
            Encoding.UTF8.GetBytes(secWebSocketKeyHeader + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11")
        )
    );

    hlc.Response.StatusCode = (int)HttpStatusCode.SwitchingProtocols; // 101
    hlc.Response.StatusDescription = "Switching Protocols";
    hlc.Response.ProtocolVersion = new Version("1.1");
    hlc.Response.AddHeader("Upgrade", "websocket");
    **hlc.Response.AddHeader("Connection", "Upgrade");**
    hlc.Response.AddHeader("Sec-WebSocket-Accept", secWebSocketAcceptHeader);

    hlc.Response.Close();

    // Wait for the client to close.
    clientClosedEvent.WaitOne();
    hl.Stop();
}

// Tcp Client that sends a web-socket handshake request and,
// writes the received web-socket handshake response.
async Task RunTcpClient()
{
    const string eol = "\\r\\n"; // HTTP/1.1 defines the sequence CR LF as the end-of-line marker

    // Wait for the server to start.
    serverStartedEvent.WaitOne();

    using (TcpClient tc = new TcpClient())
    {
        tc.Connect("localhost", port);

        using (NetworkStream ns = tc.GetStream())
        {
            string wsRequest =
                $"GET /chat HTTP/1.1{eol}Host: localhost:{port}{eol}"+ 
                $"Upgrad