package resolvconf import ( "bytes" "io/ioutil" "regexp" "strings" ) func Get() ([]byte, error) { resolv, err := ioutil.ReadFile("/etc/resolv.conf") if err != nil { return nil, err } return resolv, nil } // getLines parses input into lines and strips away comments. func getLines(input []byte, commentMarker []byte) [][]byte { lines := bytes.Split(input, []byte("\n")) var output [][]byte for _, currentLine := range lines { var commentIndex = bytes.Index(currentLine, commentMarker) if commentIndex == -1 { output = append(output, currentLine) } else { output = append(output, currentLine[:commentIndex]) } } return output } // GetNameservers returns nameservers (if any) listed in /etc/resolv.conf func GetNameservers(resolvConf []byte) []string { nameservers := []string{} re := regexp.MustCompile(`^\s*nameserver\s*(([0-9]+\.){3}([0-9]+))\s*$`) for _, line := range getLines(resolvConf, []byte("#")) { var ns = re.FindSubmatch(line) if len(ns) > 0 { nameservers = append(nameservers, string(ns[1])) } } return nameservers } // GetNameserversAsCIDR returns nameservers (if any) listed in // /etc/resolv.conf as CIDR blocks (e.g., "1.2.3.4/32") // This function's output is intended for net.ParseCIDR func GetNameserversAsCIDR(resolvConf []byte) []string { nameservers := []string{} for _, nameserver := range GetNameservers(resolvConf) { nameservers = append(nameservers, nameserver+"/32") } return nameservers } // GetSearchDomains returns search domains (if any) listed in /etc/resolv.conf // If more than one search line is encountered, only the contents of the last // one is returned. func GetSearchDomains(resolvConf []byte) []string { re := regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`) domains := []string{} for _, line := range getLines(resolvConf, []byte("#")) { match := re.FindSubmatch(line) if match == nil { continue } domains = strings.Fields(string(match[1])) } return domains } func Build(path string, dns, dnsSearch []string) error { content := bytes.NewBuffer(nil) for _, dns := range dns { if _, err := content.WriteString("nameserver " + dns + "\n"); err != nil { return err } } if len(dnsSearch) > 0 { if _, err := content.WriteString("search " + strings.Join(dnsSearch, " ") + "\n"); err != nil { return err } } return ioutil.WriteFile(path, content.Bytes(), 0644) }