Extract several packages to form a public API

framework/hooks/hooks.go

@@ -0,0 +1,62 @@
+package hooks
+
+import "sync"
+
+type Event int
+
+const (
+	// EventShutdown is triggered when the server process is about to stop.
+	EventShutdown Event = iota
+
+	// EventReload is triggered when the server process receives the SIGUSR2
+	// signal (on POSIX platforms) and indicates the request to reload the
+	// server configuration from persistent storage.
+	//
+	// Since it is by design problematic to reload the modules configuration,
+	// this event only applies to secondary files such as aliases mapping and
+	// TLS certificates.
+	EventReload
+
+	// EventLogRotate is triggered when the server process receives the SIGUSR1
+	// signal (on POSIX platforms) and indicates the request to reopen used log
+	// files since they might have rotated.
+	EventLogRotate
+)
+
+var (
+	hooks    = make(map[Event][]func())
+	hooksLck sync.Mutex
+)
+
+func hooksToRun(eventName Event) []func() {
+	hooksLck.Lock()
+	defer hooksLck.Unlock()
+	hooksEv := hooks[eventName]
+	if hooksEv == nil {
+		return nil
+	}
+
+	// The slice is copied so hooks can be run without holding the lock what
+	// might be important since they are likely to do a lot of I/O.
+	hooksEvCpy := make([]func(), 0, len(hooksEv))
+	hooksEvCpy = append(hooksEvCpy, hooksEv...)
+
+	return hooksEvCpy
+}
+
+// RunHooks runs the hooks installed for the specified eventName in the reverse
+// order.
+func RunHooks(eventName Event) {
+	hooks := hooksToRun(eventName)
+	for i := len(hooks) - 1; i >= 0; i-- {
+		hooks[i]()
+	}
+}
+
+// AddHook installs the hook to be executed when certain event occurs.
+func AddHook(eventName Event, f func()) {
+	hooksLck.Lock()
+	defer hooksLck.Unlock()
+
+	hooks[eventName] = append(hooks[eventName], f)
+}