tailscale/health/health.go

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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package health is a registry for other packages to report & check
// overall health status of the node.
package health
import (
"sync"
)
var (
mu sync.Mutex
m = map[string]error{} // error key => err (or nil for no error)
watchers = map[*watchHandle]func(string, error){} // opt func to run if error state changes
)
type watchHandle byte
// RegisterWatcher adds a function that will be called if an
// error changes state either to unhealthy or from unhealthy. It is
// not called on transition from unknown to healthy. It must be non-nil
// and is run in its own goroutine. The returned func unregisters it.
func RegisterWatcher(cb func(errKey string, err error)) (unregister func()) {
mu.Lock()
defer mu.Unlock()
handle := new(watchHandle)
watchers[handle] = cb
return func() {
mu.Lock()
defer mu.Unlock()
delete(watchers, handle)
}
}
// SetRouter sets the state of the wgengine/router.Router.
func SetRouterHealth(err error) { set("router", err) }
// RouterHealth returns the wgengine/router.Router error state.
func RouterHealth() error { return get("router") }
func get(key string) error {
mu.Lock()
defer mu.Unlock()
return m[key]
}
func set(key string, err error) {
mu.Lock()
defer mu.Unlock()
old, ok := m[key]
if !ok && err == nil {
// Initial happy path.
m[key] = nil
return
}
if ok && (old == nil) == (err == nil) {
// No change in overall error status (nil-vs-not), so
// don't run callbacks, but exact error might've
// changed, so note it.
if err != nil {
m[key] = err
}
return
}
m[key] = err
for _, cb := range watchers {
go cb(key, err)
}
}