Merge pull request #9648 from estesp/9202-update-resolvconf

Update container resolv.conf when host network changes /etc/resolv.conf

networkfs/resolvconf/resolvconf.go

@@ -5,13 +5,25 @@ import (
 	"io/ioutil"
 	"regexp"
 	"strings"
+	"sync"
+
+	log "github.com/Sirupsen/logrus"
+	"github.com/docker/docker/utils"
 )
 
 var (
-	nsRegexp     = regexp.MustCompile(`^\s*nameserver\s*(([0-9]+\.){3}([0-9]+))\s*$`)
+	defaultDns      = []string{"8.8.8.8", "8.8.4.4"}
-	searchRegexp = regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`)
+	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 {
@@ -20,6 +32,57 @@ func Get() ([]byte, error) {
 	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"))

networkfs/resolvconf/resolvconf_test.go

@@ -156,3 +156,34 @@ func TestBuildWithZeroLengthDomainSearch(t *testing.T) {
 		t.Fatalf("Expected to not find '%s' got '%s'", notExpected, content)
 	}
 }
+
+func TestRemoveReplaceLocalDns(t *testing.T) {
+	ns0 := "nameserver 10.16.60.14\nnameserver 10.16.60.21\n"
+
+	if result, _ := RemoveReplaceLocalDns([]byte(ns0)); result != nil {
+		if ns0 != string(result) {
+			t.Fatalf("Failed No Localhost: expected \n<%s> got \n<%s>", ns0, string(result))
+		}
+	}
+
+	ns1 := "nameserver 10.16.60.14\nnameserver 10.16.60.21\nnameserver 127.0.0.1\n"
+	if result, _ := RemoveReplaceLocalDns([]byte(ns1)); result != nil {
+		if ns0 != string(result) {
+			t.Fatalf("Failed Localhost: expected \n<%s> got \n<%s>", ns0, string(result))
+		}
+	}
+
+	ns1 = "nameserver 10.16.60.14\nnameserver 127.0.0.1\nnameserver 10.16.60.21\n"
+	if result, _ := RemoveReplaceLocalDns([]byte(ns1)); result != nil {
+		if ns0 != string(result) {
+			t.Fatalf("Failed Localhost: expected \n<%s> got \n<%s>", ns0, string(result))
+		}
+	}
+
+	ns1 = "nameserver 127.0.1.1\nnameserver 10.16.60.14\nnameserver 10.16.60.21\n"
+	if result, _ := RemoveReplaceLocalDns([]byte(ns1)); result != nil {
+		if ns0 != string(result) {
+			t.Fatalf("Failed Localhost: expected \n<%s> got \n<%s>", ns0, string(result))
+		}
+	}
+}