golang TCPConn.SetWriteDeadline doesn't seem to work as expected

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问题内容

I'm trying to detect sending failures by inspecting the error returned by golang TCPConn.Write, but it's nil. I also tried using TCPConn.SetWriteDeadline without success.

That's how things happen:

1. the server starts
2. a client connects
3. the server sends a message and the client receives it
4. the client shuts down
5. the server sends one more message: no error
6. the server sends the third message: only now the error appears

Question : why only the second message to a non-existing client results in an error? How should the case be handled properly?

The code follows:

package main

import (
    "net"
    "os"
    "bufio"
    "fmt"
    "time"
)

func AcceptConnections(listener net.Listener, console 
The server console looks like this:
listening on 127.0.0.1:6666
client connected
hi there!
read from console: hi there!
msg sent: hi there!
this one should fail
read from console: this one should fail
msg sent: this one should fail
this one actually fails
read from console: this one actually fails
failed sending a message to network: write tcp 127.0.0.1:51194: broken pipe

The client looks like this:
package main

import (
    "net"
    "os"
    "io"
    //"bufio"
    //"fmt"
)

func cp(dst io.Writer, src io.Reader, errc chan
EDIT : Following JimB's suggestion I came up with a working example.
Messages don't get lost any more and are re-sent in a new connection. I'm not
quite sure though how safe is it to use a shared variable (connWrap.IsFaulted)
between different go routines.
package main

import (
    "net"
    "os"
    "bufio"
    "fmt"
)

type Connection struct {
    IsFaulted bool
    Conn net.Conn
}

func StartWritingToNetwork(connWrap * Connection, errChannel chan 

    正确答案

This isn't Go specific, and is a artifact of the underlying TCP socket showing
through.
A decent diagram of the TCP termination steps is at the bottom of this page:
http://www.tcpipguide.com/free/t_TCPConnectionTermination-2.htm
The simple version is that when the client closes its socket, it sends a FIN,
and receives an ACK from the server. It then waits for the server to do the
same. Instead of sending a FIN though, you're sending more data, which is
discarded, and the client socket now assumes that any more data coming from
you is invalid, so the next time you send you get an RST, which is what
bubbles up into the error you see.
Going back to your program, you need to handle this somehow. Generally you can
think of whomever is in charge of initiating a send, is also in charge of
initiating termination, hence your server should assume that it can continue
to send until it closes the connection, or encounters an error. If you need
to more reliably detect the client closing, you need to have some sort of
client response in the protocol. That way recv can be called on the socket and
return 0, which alerts you to the closed connection.
In go, this will return an EOF error from the connection's Read method (or
from within the Copy in your case). SetWriteDeadline doesn't work because a
small write will go though and get dropped silently, or the client will
eventually respond with an RST, giving you an error.
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