mirror of
https://github.com/tailscale/tailscale.git
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69 lines
1.5 KiB
Go
69 lines
1.5 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"context"
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"encoding/json"
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"expvar"
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"log"
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"net"
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"net/http"
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"strings"
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"time"
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"tailscale.com/syncs"
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)
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var dnsCache syncs.AtomicValue[[]byte]
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var bootstrapDNSRequests = expvar.NewInt("counter_bootstrap_dns_requests")
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func refreshBootstrapDNSLoop() {
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if *bootstrapDNS == "" {
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return
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}
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for {
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refreshBootstrapDNS()
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time.Sleep(10 * time.Minute)
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}
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}
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func refreshBootstrapDNS() {
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if *bootstrapDNS == "" {
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return
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}
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dnsEntries := make(map[string][]net.IP)
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ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
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defer cancel()
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names := strings.Split(*bootstrapDNS, ",")
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var r net.Resolver
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for _, name := range names {
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addrs, err := r.LookupIP(ctx, "ip", name)
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if err != nil {
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log.Printf("bootstrap DNS lookup %q: %v", name, err)
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continue
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}
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dnsEntries[name] = addrs
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}
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j, err := json.MarshalIndent(dnsEntries, "", "\t")
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if err != nil {
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// leave the old values in place
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return
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}
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dnsCache.Store(j)
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}
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func handleBootstrapDNS(w http.ResponseWriter, r *http.Request) {
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bootstrapDNSRequests.Add(1)
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w.Header().Set("Content-Type", "application/json")
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j := dnsCache.Load()
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// Bootstrap DNS requests occur cross-regions,
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// and are randomized per request,
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// so keeping a connection open is pointlessly expensive.
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w.Header().Set("Connection", "close")
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w.Write(j)
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}
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