tailscale/wgengine/monitor/polling.go

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// Copyright (c) 2020 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.
//go:build !freebsd && !windows && !darwin
// +build !freebsd,!windows,!darwin
package monitor
import (
"bytes"
"errors"
"os"
"runtime"
"sync"
"time"
"tailscale.com/net/interfaces"
"tailscale.com/types/logger"
)
func newPollingMon(logf logger.Logf, m *Mon) (osMon, error) {
return &pollingMon{
logf: logf,
m: m,
stop: make(chan struct{}),
}, nil
}
// pollingMon is a bad but portable implementation of the link monitor
// that works by polling the interface state every 10 seconds, in lieu
// of anything to subscribe to.
type pollingMon struct {
logf logger.Logf
m *Mon
closeOnce sync.Once
stop chan struct{}
}
func (pm *pollingMon) Close() error {
pm.closeOnce.Do(func() {
close(pm.stop)
})
return nil
}
func (pm *pollingMon) isCloudRun() bool {
// https: //cloud.google.com/run/docs/reference/container-contract#env-vars
if os.Getenv("K_REVISION") == "" || os.Getenv("K_CONFIGURATION") == "" ||
os.Getenv("K_SERVICE") == "" || os.Getenv("PORT") == "" {
return false
}
vers, err := os.ReadFile("/proc/version")
if err != nil {
pm.logf("Failed to read /proc/version: %v", err)
return false
}
return string(bytes.TrimSpace(vers)) == "Linux version 4.4.0 #1 SMP Sun Jan 10 15:06:54 PST 2016"
}
func (pm *pollingMon) Receive() (message, error) {
d := 10 * time.Second
if runtime.GOOS == "android" {
// We'll have Android notify the link monitor to wake up earlier,
// so this can go very slowly there, to save battery.
// https://github.com/tailscale/tailscale/issues/1427
d = 10 * time.Minute
}
if pm.isCloudRun() {
// Cloud Run routes never change at runtime. the containers are killed within
// 15 minutes by default, set the interval long enough to be effectively infinite.
pm.logf("monitor polling: Cloud Run detected, reduce polling interval to 24h")
d = 24 * time.Hour
}
ticker := time.NewTicker(d)
defer ticker.Stop()
base := pm.m.InterfaceState()
for {
if cur, err := pm.m.interfaceStateUncached(); err == nil && !cur.EqualFiltered(base, interfaces.FilterInteresting) {
return unspecifiedMessage{}, nil
}
select {
case <-ticker.C:
case <-pm.stop:
return nil, errors.New("stopped")
}
}
}