Merge pull request moby#3142 from thaJeztah/simplify_resolvconf

executor/oci: GetResolvConf(): simplify handling of resolv.conf

Author: tonistiigi

executor/oci/resolvconf.go

@@ -16,7 +16,7 @@ var notFirstRun bool
 var lastNotEmpty bool
 
 // overridden by tests
-var resolvconfGet = resolvconf.Get
+var resolvconfPath = resolvconf.Path
 
 type DNSConfig struct {
 	Nameservers   []string
@@ -39,7 +39,7 @@ func GetResolvConf(ctx context.Context, stateDir string, idmap *idtools.Identity
 				generate = true
 			}
 			if !generate {
-				fiMain, err := os.Stat(resolvconf.Path())
+				fiMain, err := os.Stat(resolvconfPath())
 				if err != nil {
 					if !errors.Is(err, os.ErrNotExist) {
 						return nil, err
@@ -60,33 +60,30 @@ func GetResolvConf(ctx context.Context, stateDir string, idmap *idtools.Identity
 			return "", nil
 		}
 
-		var dt []byte
-		f, err := resolvconfGet()
-		if err != nil {
-			if !errors.Is(err, os.ErrNotExist) {
-				return "", err
-			}
-		} else {
-			dt = f.Content
+		dt, err := os.ReadFile(resolvconfPath())
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
+			return "", err
 		}
 
+		var f *resolvconf.File
+		tmpPath := p + ".tmp"
 		if dns != nil {
 			var (
-				dnsNameservers   = resolvconf.GetNameservers(dt, resolvconf.IP)
-				dnsSearchDomains = resolvconf.GetSearchDomains(dt)
-				dnsOptions       = resolvconf.GetOptions(dt)
+				dnsNameservers   = dns.Nameservers
+				dnsSearchDomains = dns.SearchDomains
+				dnsOptions       = dns.Options
 			)
-			if len(dns.Nameservers) > 0 {
-				dnsNameservers = dns.Nameservers
+			if len(dns.Nameservers) == 0 {
+				dnsNameservers = resolvconf.GetNameservers(dt, resolvconf.IP)
 			}
-			if len(dns.SearchDomains) > 0 {
-				dnsSearchDomains = dns.SearchDomains
+			if len(dns.SearchDomains) == 0 {
+				dnsSearchDomains = resolvconf.GetSearchDomains(dt)
 			}
-			if len(dns.Options) > 0 {
-				dnsOptions = dns.Options
+			if len(dns.Options) == 0 {
+				dnsOptions = resolvconf.GetOptions(dt)
 			}
 
-			f, err = resolvconf.Build(p+".tmp", dnsNameservers, dnsSearchDomains, dnsOptions)
+			f, err = resolvconf.Build(tmpPath, dnsNameservers, dnsSearchDomains, dnsOptions)
 			if err != nil {
 				return "", err
 			}
@@ -98,7 +95,6 @@ func GetResolvConf(ctx context.Context, stateDir string, idmap *idtools.Identity
 			return "", err
 		}
 
-		tmpPath := p + ".tmp"
 		if err := os.WriteFile(tmpPath, f.Content, 0644); err != nil {
 			return "", err
 		}

executor/oci/resolvconf_test.go

@@ -5,19 +5,18 @@ import (
 	"os"
 	"testing"
 
-	"github.com/docker/docker/libnetwork/resolvconf"
 	"github.com/stretchr/testify/require"
 )
 
 // TestResolvConfNotExist modifies a global variable
 // It must not run in parallel.
 func TestResolvConfNotExist(t *testing.T) {
-	oldResolvconfGet := resolvconfGet
-	defer func() {
-		resolvconfGet = oldResolvconfGet
-	}()
-	resolvconfGet = func() (*resolvconf.File, error) {
-		return nil, os.ErrNotExist
+	oldResolvconfPath := resolvconfPath
+	t.Cleanup(func() {
+		resolvconfPath = oldResolvconfPath
+	})
+	resolvconfPath = func() string {
+		return "no-such-file"
 	}
 
 	defaultResolvConf := `