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moby--moby/pkg/networkfs/resolvconf/resolvconf.go
Phil Estes 63a7ccdd23 Update container resolv.conf when host network changes /etc/resolv.conf
Only modifies non-running containers resolv.conf bind mount, and only if
the container has an unmodified resolv.conf compared to its contents at
container start time (so we don't overwrite manual/automated changes
within the container runtime). For containers which are running when
the host resolv.conf changes, the update will only be applied to the
container version of resolv.conf when the container is "bounced" down
and back up (e.g. stop/start or restart)

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
2015-01-08 14:15:13 -05:00

155 lines
4.6 KiB
Go

package resolvconf
import (
"bytes"
"io/ioutil"
"regexp"
"strings"
"sync"
log "github.com/Sirupsen/logrus"
"github.com/docker/docker/utils"
)
var (
defaultDns = []string{"8.8.8.8", "8.8.4.4"}
localHostRegexp = regexp.MustCompile(`(?m)^nameserver 127[^\n]+\n*`)
nsRegexp = regexp.MustCompile(`^\s*nameserver\s*(([0-9]+\.){3}([0-9]+))\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
}
// RemoveReplaceLocalDns looks for localhost (127.*) 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
// It also returns a boolean to notify the caller if changes were made at all
func RemoveReplaceLocalDns(resolvConf []byte) ([]byte, bool) {
changed := false
cleanedResolvConf := localHostRegexp.ReplaceAll(resolvConf, []byte{})
// if the resulting resolvConf is empty, use defaultDns
if !bytes.Contains(cleanedResolvConf, []byte("nameserver")) {
log.Infof("No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : %v", defaultDns)
cleanedResolvConf = append(cleanedResolvConf, []byte("\nnameserver "+strings.Join(defaultDns, "\nnameserver "))...)
}
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
}
// 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)
}