mirror of https://github.com/tailscale/tailscale/
net/dns/resolvconffile: unify three /etc/resolv.conf parsers into new package
Change-Id: I2120893ca802d12f1bd0407d49077d3672627d33 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>pull/3947/head
Brad Fitzpatrick
2 years ago
committed by
Brad Fitzpatrick
parent
1dc4151f8b
commit
c988bd6ed1
@ -0,0 +1,120 @@
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// Copyright (c) 2022 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 resolvconffile parses & serializes /etc/resolv.conf-style files.
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//
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// It's a leaf package so both net/dns and net/dns/resolver can depend
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// on it and we can unify a handful of implementations.
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//
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// The package is verbosely named to disambiguate it from resolvconf
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// the daemon, which Tailscale also supports.
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package resolvconffile
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"os"
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"strings"
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"inet.af/netaddr"
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"tailscale.com/util/dnsname"
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)
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// Path is the canonical location of resolv.conf.
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const Path = "/etc/resolv.conf"
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// Config represents a resolv.conf(5) file.
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type Config struct {
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// Nameservers are the IP addresses of the nameservers to use.
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Nameservers []netaddr.IP
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// SearchDomains are the domain suffixes to use when expanding
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// single-label name queries. SearchDomains is additive to
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// whatever non-Tailscale search domains the OS has.
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SearchDomains []dnsname.FQDN
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}
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// Write writes c to w. It does so in one Write call.
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func (c *Config) Write(w io.Writer) error {
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buf := new(bytes.Buffer)
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io.WriteString(buf, "# resolv.conf(5) file generated by tailscale\n")
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io.WriteString(buf, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
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for _, ns := range c.Nameservers {
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io.WriteString(buf, "nameserver ")
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io.WriteString(buf, ns.String())
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io.WriteString(buf, "\n")
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}
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if len(c.SearchDomains) > 0 {
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io.WriteString(buf, "search")
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for _, domain := range c.SearchDomains {
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io.WriteString(buf, " ")
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io.WriteString(buf, domain.WithoutTrailingDot())
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}
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io.WriteString(buf, "\n")
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}
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_, err := w.Write(buf.Bytes())
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return err
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}
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// Parse parses a resolv.conf file from r.
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func Parse(r io.Reader) (*Config, error) {
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config := new(Config)
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scanner := bufio.NewScanner(r)
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for scanner.Scan() {
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line := scanner.Text()
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i := strings.IndexByte(line, '#')
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if i >= 0 {
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line = line[:i]
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}
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line = strings.TrimSpace(line)
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if strings.HasPrefix(line, "nameserver") {
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s := strings.TrimPrefix(line, "nameserver")
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nameserver := strings.TrimSpace(s)
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if len(nameserver) == len(s) {
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return nil, fmt.Errorf("missing space after \"nameserver\" in %q", line)
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}
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ip, err := netaddr.ParseIP(nameserver)
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if err != nil {
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return nil, err
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}
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config.Nameservers = append(config.Nameservers, ip)
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continue
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}
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if strings.HasPrefix(line, "search") {
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s := strings.TrimPrefix(line, "search")
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domain := strings.TrimSpace(s)
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if len(domain) == len(s) {
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// No leading space?!
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return nil, fmt.Errorf("missing space after \"domain\" in %q", line)
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}
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fqdn, err := dnsname.ToFQDN(domain)
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if err != nil {
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return nil, fmt.Errorf("parsing search domains %q: %w", line, err)
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}
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config.SearchDomains = append(config.SearchDomains, fqdn)
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continue
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}
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}
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return config, nil
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}
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// ParseFile parses the named resolv.conf file.
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func ParseFile(name string) (*Config, error) {
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fi, err := os.Stat(name)
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if err != nil {
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return nil, err
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}
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if n := fi.Size(); n > 10<<10 {
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return nil, fmt.Errorf("unexpectedly large %q file: %d bytes", name, n)
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}
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all, err := os.ReadFile(name)
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if err != nil {
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return nil, err
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}
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return Parse(bytes.NewReader(all))
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}
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@ -0,0 +1,79 @@
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// Copyright (c) 2022 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 resolvconffile
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import (
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"reflect"
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"strings"
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"testing"
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"inet.af/netaddr"
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"tailscale.com/util/dnsname"
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)
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func TestParse(t *testing.T) {
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tests := []struct {
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in string
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want *Config
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wantErr bool
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}{
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{in: `nameserver 192.168.0.100`,
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want: &Config{
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Nameservers: []netaddr.IP{
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netaddr.MustParseIP("192.168.0.100"),
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},
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},
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},
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{in: `nameserver 192.168.0.100 # comment`,
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want: &Config{
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Nameservers: []netaddr.IP{
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netaddr.MustParseIP("192.168.0.100"),
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},
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},
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},
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{in: `nameserver 192.168.0.100#`,
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want: &Config{
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Nameservers: []netaddr.IP{
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netaddr.MustParseIP("192.168.0.100"),
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},
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},
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},
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{in: `nameserver #192.168.0.100`, wantErr: true},
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{in: `nameserver`, wantErr: true},
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{in: `# nameserver 192.168.0.100`, want: &Config{}},
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{in: `nameserver192.168.0.100`, wantErr: true},
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{in: `search tailsacle.com`,
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want: &Config{
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SearchDomains: []dnsname.FQDN{"tailsacle.com."},
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},
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},
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{in: `search tailsacle.com # typo`,
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want: &Config{
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SearchDomains: []dnsname.FQDN{"tailsacle.com."},
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},
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},
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{in: `searchtailsacle.com`, wantErr: true},
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{in: `search`, wantErr: true},
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}
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for _, tt := range tests {
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cfg, err := Parse(strings.NewReader(tt.in))
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if tt.wantErr {
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if err != nil {
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continue
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}
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t.Errorf("missing error for %q", tt.in)
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continue
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}
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if err != nil {
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t.Errorf("unexpected error for %q: %v", tt.in, err)
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continue
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}
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if !reflect.DeepEqual(cfg, tt.want) {
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t.Errorf("got: %v\nwant: %v\n", cfg, tt.want)
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}
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}
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}
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