如何在Go中禁用HTTP警报

Question

I have a problem with the following error when calling http.ListenAndServe:

http: Accept error: *ip* accept tcp too many open files; retrying in 10ms

How I can disable this? ulimit -n is 1024 and I can't change it.

Answer 1

The problem is that you cannot open anymore file descriptors and therefore you cannot accept more connections. If you can't change the fact you have three possible options to deal with this problem:

1. Leave it as it is: The standard library uses an exponential backoff to wait for a time when there are file descriptors again. This is generally a good practice and gives future clients a chance to get a slot. In fact, the http package does this for every temporary network error that occurs.
2. Close the connection when a temporary error like this occurs. This can be achieved by wrapping the net.Listener returned by net.Listen and modify it's Accept() method to drop the connection on temporary errors.
3. Ignore the message. If the message is the only thing that bothers you, you can simply set the log.Output() to ioutil.Discard. (While this is an option, I don't see the use of that. You will end up ignoring important error messages and wonder why your service does not work.)

I would prefer the first but there may be a case where you want the second, so here is an example of a connection dropping listener (on play):

type DroppingListener struct {
    net.Listener
}

func (d DroppingListener) Accept() (net.Conn, error) {
    for {
        conn, err := d.Listener.Accept()

        if err != nil {
            if ne, ok := err.(net.Error); ok && ne.Temporary() {
                log.Println("Dropping connection because:", ne)
                continue
            }
        }

        return conn, err
    }
}

func ListenAndServe(addr string, handler http.Handler) error {
    srv := &http.Server{Addr: addr, Handler: handler}

    l, e := net.Listen("tcp", addr)
    if e != nil {
        return e
    }

    l = &DroppingListener{l}

    return srv.Serve(l)
}

With this DroppingListener, the Accept method will return a connection as soon as there is no more temporary error.