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tailscale/cmd/derper/bootstrap_dns.go

68 lines
1.5 KiB
Go

// 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 main
import (
"context"
"encoding/json"
"expvar"
"log"
"net"
"net/http"
"strings"
"sync/atomic"
"time"
)
var dnsCache atomic.Value // of []byte
var bootstrapDNSRequests = expvar.NewInt("counter_bootstrap_dns_requests")
func refreshBootstrapDNSLoop() {
if *bootstrapDNS == "" {
return
}
for {
refreshBootstrapDNS()
time.Sleep(10 * time.Minute)
}
}
func refreshBootstrapDNS() {
if *bootstrapDNS == "" {
return
}
dnsEntries := make(map[string][]net.IP)
ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
defer cancel()
names := strings.Split(*bootstrapDNS, ",")
var r net.Resolver
for _, name := range names {
addrs, err := r.LookupIP(ctx, "ip", name)
if err != nil {
log.Printf("bootstrap DNS lookup %q: %v", name, err)
continue
}
dnsEntries[name] = addrs
}
j, err := json.MarshalIndent(dnsEntries, "", "\t")
if err != nil {
// leave the old values in place
return
}
dnsCache.Store(j)
}
func handleBootstrapDNS(w http.ResponseWriter, r *http.Request) {
bootstrapDNSRequests.Add(1)
w.Header().Set("Content-Type", "application/json")
j, _ := dnsCache.Load().([]byte)
// Bootstrap DNS requests occur cross-regions,
// and are randomized per request,
// so keeping a connection open is pointlessly expensive.
w.Header().Set("Connection", "close")
w.Write(j)
}