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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
//go:build linux
package dns
import (
"context"
"fmt"
"net/netip"
"os"
"path/filepath"
"testing"
"testing/synctest"
"github.com/illarion/gonotify/v3"
"tailscale.com/util/dnsname"
"tailscale.com/util/eventbus/eventbustest"
)
func TestDNSTrampleRecovery(t *testing.T) {
HookWatchFile.Set(watchFile)
synctest.Test(t, func(t *testing.T) {
tmp := t.TempDir()
if err := os.MkdirAll(filepath.Join(tmp, "etc"), 0700); err != nil {
t.Fatal(err)
}
const resolvPath = "/etc/resolv.conf"
fs := directFS{prefix: tmp}
readFile := func(t *testing.T, path string) string {
t.Helper()
b, err := fs.ReadFile(path)
if err != nil {
t.Errorf("Reading DNS config: %v", err)
}
return string(b)
}
bus := eventbustest.NewBus(t)
eventbustest.LogAllEvents(t, bus)
m := newDirectManagerOnFS(t.Logf, nil, bus, fs)
defer m.Close()
if err := m.SetDNS(OSConfig{
Nameservers: []netip.Addr{netip.MustParseAddr("8.8.8.8"), netip.MustParseAddr("8.8.4.4")},
SearchDomains: []dnsname.FQDN{"ts.net.", "ts-dns.test."},
MatchDomains: []dnsname.FQDN{"ignored."},
}); err != nil {
t.Fatal(err)
}
const want = `# resolv.conf(5) file generated by tailscale
# For more info, see https://tailscale.com/s/resolvconf-overwrite
# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN
nameserver 8.8.8.8
nameserver 8.8.4.4
search ts.net ts-dns.test
`
if got := readFile(t, resolvPath); got != want {
t.Fatalf("resolv.conf:\n%s, want:\n%s", got, want)
}
tw := eventbustest.NewWatcher(t, bus)
const trample = "Hvem er det som tramper på min bro?"
if err := fs.WriteFile(resolvPath, []byte(trample), 0644); err != nil {
t.Fatal(err)
}
synctest.Wait()
if err := eventbustest.Expect(tw, eventbustest.Type[TrampleDNS]()); err != nil {
t.Errorf("did not see trample event: %s", err)
}
})
}
// watchFile is generally copied from linuxtrample, but cancels the context
// after the first call to cb() after the first trample to end the test.
func watchFile(ctx context.Context, dir, filename string, cb func()) error {
ctx, cancel := context.WithCancel(ctx)
defer cancel()
const events = gonotify.IN_ATTRIB |
gonotify.IN_CLOSE_WRITE |
gonotify.IN_CREATE |
gonotify.IN_DELETE |
gonotify.IN_MODIFY |
gonotify.IN_MOVE
watcher, err := gonotify.NewDirWatcher(ctx, events, dir)
if err != nil {
return fmt.Errorf("NewDirWatcher: %w", err)
}
for {
select {
case event := <-watcher.C:
if event.Name == filename {
cb()
cancel()
}
case <-ctx.Done():
return ctx.Err()
}
}
}
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