| package resolvconf |
| |
| import ( |
| "bytes" |
| "io/ioutil" |
| "regexp" |
| "strings" |
| "sync" |
| |
| log "github.com/Sirupsen/logrus" |
| "github.com/docker/docker/utils" |
| ) |
| |
| var ( |
| // Note: the default IPv4 & IPv6 resolvers are set to Google's Public DNS |
| defaultIPv4Dns = []string{"nameserver 8.8.8.8", "nameserver 8.8.4.4"} |
| defaultIPv6Dns = []string{"nameserver 2001:4860:4860::8888", "nameserver 2001:4860:4860::8844"} |
| ipv4NumBlock = `(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)` |
| ipv4Address = `(` + ipv4NumBlock + `\.){3}` + ipv4NumBlock |
| // This is not an IPv6 address verifier as it will accept a super-set of IPv6, and also |
| // will *not match* IPv4-Embedded IPv6 Addresses (RFC6052), but that and other variants |
| // -- e.g. other link-local types -- either won't work in containers or are unnecessary. |
| // For readability and sufficiency for Docker purposes this seemed more reasonable than a |
| // 1000+ character regexp with exact and complete IPv6 validation |
| ipv6Address = `([0-9A-Fa-f]{0,4}:){2,7}([0-9A-Fa-f]{0,4})` |
| ipLocalhost = `((127\.([0-9]{1,3}.){2}[0-9]{1,3})|(::1))` |
| |
| localhostIPRegexp = regexp.MustCompile(ipLocalhost) |
| localhostNSRegexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipLocalhost + `\s*\n*`) |
| nsIPv6Regexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipv6Address + `\s*\n*`) |
| nsRegexp = regexp.MustCompile(`^\s*nameserver\s*((` + ipv4Address + `)|(` + ipv6Address + `))\s*$`) |
| searchRegexp = regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`) |
| ) |
| |
| var lastModified struct { |
| sync.Mutex |
| sha256 string |
| contents []byte |
| } |
| |
| func Get() ([]byte, error) { |
| resolv, err := ioutil.ReadFile("/etc/resolv.conf") |
| if err != nil { |
| return nil, err |
| } |
| return resolv, nil |
| } |
| |
| // Retrieves the host /etc/resolv.conf file, checks against the last hash |
| // and, if modified since last check, returns the bytes and new hash. |
| // This feature is used by the resolv.conf updater for containers |
| func GetIfChanged() ([]byte, string, error) { |
| lastModified.Lock() |
| defer lastModified.Unlock() |
| |
| resolv, err := ioutil.ReadFile("/etc/resolv.conf") |
| if err != nil { |
| return nil, "", err |
| } |
| newHash, err := utils.HashData(bytes.NewReader(resolv)) |
| if err != nil { |
| return nil, "", err |
| } |
| if lastModified.sha256 != newHash { |
| lastModified.sha256 = newHash |
| lastModified.contents = resolv |
| return resolv, newHash, nil |
| } |
| // nothing changed, so return no data |
| return nil, "", nil |
| } |
| |
| // retrieve the last used contents and hash of the host resolv.conf |
| // Used by containers updating on restart |
| func GetLastModified() ([]byte, string) { |
| lastModified.Lock() |
| defer lastModified.Unlock() |
| |
| return lastModified.contents, lastModified.sha256 |
| } |
| |
| // FilterResolvDns has two main jobs: |
| // 1. It looks for localhost (127.*|::1) entries in the provided |
| // resolv.conf, removing local nameserver entries, and, if the resulting |
| // cleaned config has no defined nameservers left, adds default DNS entries |
| // 2. Given the caller provides the enable/disable state of IPv6, the filter |
| // code will remove all IPv6 nameservers if it is not enabled for containers |
| // |
| // It also returns a boolean to notify the caller if changes were made at all |
| func FilterResolvDns(resolvConf []byte, ipv6Enabled bool) ([]byte, bool) { |
| changed := false |
| cleanedResolvConf := localhostNSRegexp.ReplaceAll(resolvConf, []byte{}) |
| // if IPv6 is not enabled, also clean out any IPv6 address nameserver |
| if !ipv6Enabled { |
| cleanedResolvConf = nsIPv6Regexp.ReplaceAll(cleanedResolvConf, []byte{}) |
| } |
| // if the resulting resolvConf has no more nameservers defined, add appropriate |
| // default DNS servers for IPv4 and (optionally) IPv6 |
| if len(GetNameservers(cleanedResolvConf)) == 0 { |
| log.Infof("No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : %v", defaultIPv4Dns) |
| dns := defaultIPv4Dns |
| if ipv6Enabled { |
| log.Infof("IPv6 enabled; Adding default IPv6 external servers : %v", defaultIPv6Dns) |
| dns = append(dns, defaultIPv6Dns...) |
| } |
| cleanedResolvConf = append(cleanedResolvConf, []byte("\n"+strings.Join(dns, "\n"))...) |
| } |
| if !bytes.Equal(resolvConf, cleanedResolvConf) { |
| changed = true |
| } |
| return cleanedResolvConf, changed |
| } |
| |
| // 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 |
| } |
| |
| // returns true if the IP string matches the localhost IP regular expression. |
| // Used for determining if nameserver settings are being passed which are |
| // localhost addresses |
| func IsLocalhost(ip string) bool { |
| return localhostIPRegexp.MatchString(ip) |
| } |
| |
| // GetNameservers returns nameservers (if any) listed in /etc/resolv.conf |
| func GetNameservers(resolvConf []byte) []string { |
| nameservers := []string{} |
| for _, line := range getLines(resolvConf, []byte("#")) { |
| var ns = nsRegexp.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 { |
| domains := []string{} |
| for _, line := range getLines(resolvConf, []byte("#")) { |
| match := searchRegexp.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 searchString := strings.Join(dnsSearch, " "); strings.Trim(searchString, " ") != "." { |
| if _, err := content.WriteString("search " + searchString + "\n"); err != nil { |
| return err |
| } |
| } |
| } |
| |
| return ioutil.WriteFile(path, content.Bytes(), 0644) |
| } |