Tcp connections hang on CLOSE_WAIT status

Question

Client close the socket first, when there is not much data from server, tcp connection shutdown is okay like:

FIN -->
   <-- ACK
   <-- FIN, ACK
ACK -->

When the server is busying sending data:

FIN -->
    <-- ACK,PSH
RST -->

And the server connection comes to CLOSE_WAIT state and hang on there for a long time.

What's the problem here? client related or server related? This happens on Redhat5 for local sockets.

This article talk about why "RST" is sent, but I do not know why the server connection stuck on CLOSE_WAIT, and do not send a FIN out.

[EDIT]I ignored the most important information, this happens on qemu's slirp network emulation. It seems to be a problem of slirp bug for dealing with close connection.

Solution 1

This a known defect for qemu.

Solution 2

This means that there is unread data left in in the stream, that the client hasn't finished reading.

You can force it off by using the SO_LINGER option. Here's relevant documentation for Linux (also see the option itself, here), and [here's the matching function2] for Win32.

It's the server side that is remaining open, so it's on the server side you can try disabling SO_LINGER.

Comments

[Sam Liao]

It seems that the SO_LINGER only influence the close() call, but the server hang on write() call instead?

[Len Holgate]

If the server's hanging on a write call then you've probably filled the TCP window and the stack is waiting for ACKs from the client before it can accept more data to send...

[Sam Liao]

The problem is that the server is hung on write call, and I can not detect error.