DNS: dnscontext doesn't restore resolv.conf (#1342)

* new solution for resolv.conf restoring Signed-off-by: Nikita Skrynnik <[email protected]> * cleanup Signed-off-by: Nikita Skrynnik <[email protected]> * resolve linter issues Signed-off-by: Nikita Skrynnik <[email protected]> * fix tests Signed-off-by: Nikita Skrynnik <[email protected]> * fix linter issues Signed-off-by: Nikita Skrynnik <[email protected]> * use dns library to check that we have commented resolv config Signed-off-by: Nikita Skrynnik <[email protected]> * fix Test_DNSContextClient_Usecases test Signed-off-by: Nikita Skrynnik <[email protected]> * cleanup Signed-off-by: Nikita Skrynnik <[email protected]> * apply review comments Signed-off-by: Nikita Skrynnik <[email protected]> * rerun CI Signed-off-by: Nikita Skrynnik <[email protected]> Signed-off-by: Nikita Skrynnik <[email protected]>
networkservicemesh · Sep 23, 2022 · 143843a · 143843a
1 parent 4056e30
commit 143843a
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Showing 4 changed files with 62 additions and 31 deletions.
diff --git a/pkg/networkservice/connectioncontext/dnscontext/client.go b/pkg/networkservice/connectioncontext/dnscontext/client.go
@@ -21,8 +21,10 @@ package dnscontext
 import (
 	"context"
 	"os"
+	"strings"
 
 	"github.com/golang/protobuf/ptypes/empty"
+	"github.com/miekg/dns"
 	"github.com/networkservicemesh/api/pkg/api/networkservice"
 	"google.golang.org/grpc"
 
@@ -33,12 +35,11 @@ import (
 )
 
 type dnsContextClient struct {
-	chainContext           context.Context
-	resolveConfigPath      string
-	storedResolvConfigPath string
-	defaultNameServerIP    string
-	resolvconfDNSConfig    *networkservice.DNSConfig
-	dnsConfigsMap          *dnsconfig.Map
+	chainContext        context.Context
+	resolveConfigPath   string
+	defaultNameServerIP string
+	resolvconfDNSConfig *networkservice.DNSConfig
+	dnsConfigsMap       *dnsconfig.Map
 }
 
 // NewClient creates a new DNS client chain component. Setups all DNS traffic to the localhost. Monitors DNS configs from connections.
@@ -52,7 +53,6 @@ func NewClient(options ...DNSOption) networkservice.NetworkServiceClient {
 		o.apply(c)
 	}
 
-	c.storedResolvConfigPath = c.resolveConfigPath + ".restore"
 	c.initialize()
 
 	return c
@@ -96,22 +96,51 @@ func (c *dnsContextClient) Close(ctx context.Context, conn *networkservice.Conne
 }
 
 func (c *dnsContextClient) restoreResolvConf() {
-	originalResolvConf, err := os.ReadFile(c.storedResolvConfigPath)
-	if err != nil || len(originalResolvConf) == 0 {
+	bytes, err := os.ReadFile(c.resolveConfigPath)
+	if err != nil {
 		return
 	}
-	_ = os.WriteFile(c.resolveConfigPath, originalResolvConf, os.ModePerm)
+
+	commentLines := make([]string, 0)
+	for _, line := range strings.Split(string(bytes), "\n") {
+		if strings.HasPrefix(line, "#") {
+			commentLines = append(commentLines, line[1:])
+		}
+	}
+
+	commentedPart := strings.Join(commentLines, "\n")
+	parsedConfig, _ := dns.ClientConfigFromReader(strings.NewReader(commentedPart))
+
+	if len(parsedConfig.Servers) == 0 {
+		return
+	}
+
+	_ = os.WriteFile(c.resolveConfigPath, []byte(commentedPart), os.ModePerm)
 }
 
 func (c *dnsContextClient) storeOriginalResolvConf() {
-	if _, err := os.Stat(c.storedResolvConfigPath); err == nil {
+	bytes, err := os.ReadFile(c.resolveConfigPath)
+	if err != nil {
 		return
 	}
-	originalResolvConf, err := os.ReadFile(c.resolveConfigPath)
+	originalResolvConfig := string(bytes)
+
+	lines := strings.Split(originalResolvConfig, "\n")
+	for i := range lines {
+		lines[i] = "#" + lines[i]
+	}
+
+	_ = os.WriteFile(c.resolveConfigPath, []byte(strings.Join(lines, "\n")+"\n\n"), os.ModePerm)
+}
+
+func (c *dnsContextClient) appendResolvConf(resolvConf string) error {
+	bytes, err := os.ReadFile(c.resolveConfigPath)
 	if err != nil {
-		return
+		return err
 	}
-	_ = os.WriteFile(c.storedResolvConfigPath, originalResolvConf, os.ModePerm)
+	originalResolvConfig := string(bytes)
+
+	return os.WriteFile(c.resolveConfigPath, []byte(originalResolvConfig+resolvConf), os.ModePerm)
 }
 
 func (c *dnsContextClient) initialize() {
@@ -136,8 +165,8 @@ func (c *dnsContextClient) initialize() {
 	r.SetValue(nameserverProperty, c.defaultNameServerIP)
 	r.SetValue(searchProperty, []string{}...)
 
-	if err = r.Save(); err != nil {
-		log.FromContext(c.chainContext).Errorf("An error during save resolve config: %v", err.Error())
+	if err = c.appendResolvConf(r.String()); err != nil {
+		log.FromContext(c.chainContext).Errorf("An error during appending resolve config: %v", err.Error())
 		return
 	}
 }

diff --git a/pkg/networkservice/connectioncontext/dnscontext/client_test.go b/pkg/networkservice/connectioncontext/dnscontext/client_test.go
@@ -55,7 +55,12 @@ func Test_DNSContextClient_Usecases(t *testing.T) {
 		),
 	)
 
-	const expectedResolvconfFile = `nameserver 127.0.0.1`
+	const expectedResolvconfFile = `#nameserver 8.8.4.4
+#search example.com
+#
+
+nameserver 127.0.0.1`
+
 	requireFileChanged(ctx, t, resolveConfigPath, expectedResolvconfFile)
 
 	request := &networkservice.NetworkServiceRequest{

diff --git a/pkg/networkservice/connectioncontext/dnscontext/resolvconf.go b/pkg/networkservice/connectioncontext/dnscontext/resolvconf.go
@@ -19,7 +19,7 @@
 package dnscontext
 
 import (
-	"os"
+	"io/ioutil"
 	"strings"
 )
 
@@ -42,14 +42,16 @@ func openResolveConfig(p string) (*resolveConfig, error) {
 }
 
 func (r *resolveConfig) readProperties() error {
-	b, err := os.ReadFile(r.path)
+	b, err := ioutil.ReadFile(r.path)
 	if err != nil {
 		return err
 	}
 	for _, l := range strings.Split(string(b), "\n") {
-		words := strings.Split(l, " ")
-		if len(words) > 1 {
-			r.properties[words[0]] = words[1:]
+		if !strings.HasPrefix(l, "#") {
+			words := strings.Split(l, " ")
+			if len(words) > 1 {
+				r.properties[words[0]] = words[1:]
+			}
 		}
 	}
 	return nil
@@ -69,8 +71,8 @@ func (r *resolveConfig) SetValue(k string, values ...string) {
 	}
 }
 
-// Save saves resolve config file
-func (r *resolveConfig) Save() error {
+// String serializes resolve config
+func (r *resolveConfig) String() string {
 	var sb strings.Builder
 	var index int
 	for k, v := range r.properties {
@@ -80,7 +82,7 @@ func (r *resolveConfig) Save() error {
 			_, _ = sb.WriteRune('\n')
 		}
 	}
-	return os.WriteFile(r.path, []byte(sb.String()), os.ModePerm)
+	return sb.String()
 }
 
 const (

diff --git a/pkg/networkservice/connectioncontext/dnscontext/resolvconf_test.go b/pkg/networkservice/connectioncontext/dnscontext/resolvconf_test.go
@@ -19,7 +19,6 @@ package dnscontext
 import (
 	"os"
 	"path"
-	"path/filepath"
 	"strings"
 	"testing"
 
@@ -71,11 +70,7 @@ options ndots:5`
 	config.SetValue(searchProperty, "default.svc.cluster.local", "svc.cluster.local", "cluster.local")
 	config.SetValue(optionsProperty, "ndots:5")
 	config.SetValue("my_property")
-	err = config.Save()
-	require.Nil(t, err)
-	bytes, err := os.ReadFile(filepath.Clean(p))
-	require.Nil(t, err)
-	actual := string(bytes)
+	actual := config.String()
 	require.Len(t, actual, len(sample))
 	for _, l := range strings.Split(actual, "\n") {
 		require.Contains(t, sample, l)