StreamWriter won't flush to NetworkStream

问题

Using a StreamWriter to write to a NetworkStream, and a StreamReader to read the response. The app is sending commands and reading responses to a news server.

Simplified code (sans error handling, etc.):

tcpClient = new TcpClient();
tcpClient.Connect(Name, Port);

networkStream = tcpClient.GetStream();
serverReader = new StreamReader(networkStream, Encoding.Default);
serverWriter = new StreamWriter(networkStream, Encoding.ASCII) {
                     AutoFlush = true
                   };

// reads the server's response to the connect:  "200 news.newsserver.com"
// commenting out these lines doesn't solve the problem
while (serverReader.Peek() > -1) {
    serverReader.ReadLine();
}

serverWriter.WriteLine("authinfo user username");

// expect response "381 more authentication required", but code just blocks
string response = serverReader.ReadLine();

The code blocks at that last line, presumably waiting for the network stream to send a response.

I can avoid hanging the app by setting a timeout loop using serverReader.Peek(), but I will always timeout; I never get a response.

If I telnet to the server and port directly and enter the commands, I get an immediate response.

If I call serverWriter.Flush() explicitly, instead of using the AutoFlush property, I still block and never get a response.

Any ideas why I'm not getting a response to the server using this approach?

Thanks!

Resolved:

The above code does work for me, so I went back and built upon that code to the code that wouldn't work.

In the code that hangs, I was still using the timeout loop with serverReader.Peek(). Peek() always returns -1, even though there is data in the buffer to read!! Replacing the Peek() loop with a blocking call to ReadLine() solves my problem.

I put the timeout loop in originally because the app is multi-threaded, and I didn't want to block. I will have to revisit this issue and see how I can resolve the thread timing without using Peek().

Thanks all, good answers!

回答1:

I doubt that it's the StreamWriter that's the problem... but there's a simple way to find out. Download WireShark and see what's actually coming and going on the network. That's by far the simplest way of finding out what's going on.

回答2:

Try "authinfo user username\r\n". The RFC says NNTP command lines must be terminated by a CR-LF.

回答3:

The above code does work for me, so I went back and built upon that code to the code that wouldn't work.

In the code that hangs, I was still using the timeout loop with serverReader.Peek(). Peek() always returns -1, even though there is data in the buffer to read!! Replacing the Peek() loop with a blocking call to ReadLine() solves my problem.

I put the timeout loop in originally because the app is multi-threaded, and I didn't want to block. I will have to revisit this issue and see how I can resolve the thread timing without using Peek().

Thanks all, good answers!

来源：https://stackoverflow.com/questions/1412852/streamwriter-wont-flush-to-networkstream