125 lines
3.4 KiB
Go
125 lines
3.4 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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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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"net/netip"
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"os"
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"strings"
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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 []netip.Addr
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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, "# For more info, see https://tailscale.com/s/resolvconf-overwrite\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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line, _, _ = strings.Cut(line, "#") // remove any comments
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line = strings.TrimSpace(line)
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if s, ok := strings.CutPrefix(line, "nameserver"); ok {
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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 := netip.ParseAddr(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 s, ok := strings.CutPrefix(line, "search"); ok {
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domains := strings.TrimSpace(s)
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if len(domains) == len(s) {
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// No leading space?!
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return nil, fmt.Errorf("missing space after \"search\" in %q", line)
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}
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for len(domains) > 0 {
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domain := domains
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i := strings.IndexAny(domain, " \t")
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if i != -1 {
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domain = domain[:i]
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domains = strings.TrimSpace(domains[i+1:])
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} else {
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domains = ""
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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 domain %q in %q: %w", domain, line, err)
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}
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config.SearchDomains = append(config.SearchDomains, fqdn)
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}
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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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