如何判断服务器或客户端关闭的连接？

I have a server which handle receiving data like this:

func handleRecv(conn *net.TCPConn) {
    header := make([]byte, 2)
    for {
        /**block until recieve len(header)**/
        n, err := io.ReadFull(conn, header)
        if err != nil {
             log.Error(err)
              break
        }
     }
 }

I would like to know which the connnection is closed by ? server or client according to err ?

First of all, if you're closing the connection locally, you should know about it in your code. Otherwise, receiving an io.EOF generally signals that the remote side initiated a close.

If Close() was called on the local side, you get a *net.OpError with the message use of closed network connection. You may want to just check for the net.Error interface, since that would theoretically cover more error conditions.

        if err, ok := err.(net.Error); ok {
            fmt.Error("not an io.EOF")
            fmt.Error(err.Error())
        }

This doesn't work however if CloseRead() was called on the local connection (which isn't very likely, but it has its uses). That will return an io.EOF, and is why you still need to know what's happening to the connection locally.

If the connection was closed due to a timeout, you will get a net.Error indicating the timeout:

        if err, ok := err.(net.Error); ok && err.Timeout() {
            fmt.Error("timeout error")
        }

Finally, if you are concerned about the error returned, you may not want to use io.Readfull, which doesn't return io.EOF after a short read. Just read into your buffer and check the number of bytes read and the error yourself.