闲置一段时间后，如何使Go的http.Server退出？

Question

I am writing a web server in Go using the standard library net/http package that makes use of systemd socket activation.

I have the basics working such that the server is started the first time a connection is made to the listening socket, and I can perform a graceful shutdown when signalled (i.e. so systemctl stop will work without cutting off active requests).

What I would like is for the server to automatically exit when it has been idle for some period of time. Something like the following:

1. when the last active request completes, start a timer for say 30 seconds.
2. if any new request arrives during that period, stop the timer.
3. if the timer expires, perform a graceful shutdown.

The idea being to release the resources the server was using, in the knowledge that systemd will start us again when a new client turns up.

It's parts (1) and (2) that I'm not sure about. Ideally I'd like a solution that doesn't involve modifying all the registered handlers too.

Answer 1

Using @CeriseLimón's suggestion, the following helper type seems to do the trick:

type IdleTracker struct {
    mu     sync.Mutex
    active map[net.Conn]bool
    idle   time.Duration
    timer  *time.Timer
}

func NewIdleTracker(idle time.Duration) *IdleTracker {
    return &IdleTracker{
        active: make(map[net.Conn]bool),
        idle:   idle,
        timer:  time.NewTimer(idle),
    }
}

func (t *IdleTracker) ConnState(conn net.Conn, state http.ConnState) {
    t.mu.Lock()
    defer t.mu.Unlock()

    oldActive := len(t.active)
    switch state {
    case http.StateNew, http.StateActive, http.StateHijacked:
        t.active[conn] = true
        // stop the timer if we transitioned to idle
        if oldActive == 0 {
            t.timer.Stop()
        }
    case http.StateIdle, http.StateClosed:
        delete(t.active, conn)
        // Restart the timer if we've become idle
        if oldActive > 0 && len(t.active) == 0 {
            t.timer.Reset(t.idle)
        }
    }
}

func (t *IdleTracker) Done() <-chan time.Time {
    return t.timer.C
}

Assigning its ConnState method to the server's ConnState member will track whether the server is busy, and signal us when we've been idle for the requested amount of time:

idle := NewIdleTracker(5 * time.Second)
server.ConnState = idle.ConnState

go func() {
    <-idle.Done()
    if err := server.Shutdown(context.Background()); err != nil {
        log.Fatalf("error shutting down: %v
", err)
    }
}()