Add testutil daemon.WithResolvConf

Signed-off-by: Rob Murray <rob.murray@docker.com>

integration/internal/network/dns.go

@@ -2,7 +2,6 @@ package network
 
 import (
 	"net"
-	"os"
 	"testing"
 
 	"github.com/miekg/dns"
@@ -11,22 +10,10 @@ import (
 
 const DNSRespAddr = "10.11.12.13"
 
-// WriteTempResolvConf writes a resolv.conf that only contains a single
-// nameserver line, with address addr.
-// It returns the name of the temp file. The temp file will be deleted
-// automatically by a t.Cleanup().
-func WriteTempResolvConf(t *testing.T, addr string) string {
-	t.Helper()
-	// Not using t.TempDir() here because in rootless mode, while the temporary
-	// directory gets mode 0777, it's a subdir of an 0700 directory owned by root.
-	// So, it's not accessible by the daemon.
-	f, err := os.CreateTemp("", "resolv.conf")
-	assert.NilError(t, err)
-	t.Cleanup(func() { os.Remove(f.Name()) })
-	err = f.Chmod(0o644)
-	assert.NilError(t, err)
-	f.Write([]byte("nameserver " + addr + "\n"))
-	return f.Name()
+// GenResolvConf generates a resolv.conf that only contains a single
+// nameserver line, with address addr, and returns the file content.
+func GenResolvConf(addr string) string {
+	return "nameserver " + addr + "\n"
 }
 
 // StartDaftDNS starts and returns a really, really daft DNS server that only

integration/network/dns_test.go

@@ -102,8 +102,10 @@ func TestExtDNSInIPv6OnlyNw(t *testing.T) {
 	network.StartDaftDNS(t, "127.0.0.1")
 
 	// Set up a temp resolv.conf pointing at that DNS server, and a daemon using it.
-	tmpFileName := network.WriteTempResolvConf(t, "127.0.0.1")
-	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName), daemon.WithExperimental())
+	d := daemon.New(t,
+		daemon.WithResolvConf(network.GenResolvConf("127.0.0.1")),
+		daemon.WithExperimental(),
+	)
 	d.StartWithBusybox(ctx, t)
 	defer d.Stop(t)
 

integration/network/ipvlan/ipvlan_test.go

@@ -569,8 +569,7 @@ func TestIPVlanDNS(t *testing.T) {
 
 	net.StartDaftDNS(t, "127.0.0.1")
 
-	tmpFileName := net.WriteTempResolvConf(t, "127.0.0.1")
-	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
+	d := daemon.New(t, daemon.WithResolvConf(net.GenResolvConf("127.0.0.1")))
 	d.StartWithBusybox(ctx, t)
 	t.Cleanup(func() { d.Stop(t) })
 	c := d.NewClientT(t)

integration/network/macvlan/macvlan_test.go

@@ -566,8 +566,7 @@ func TestMACVlanDNS(t *testing.T) {
 
 	net.StartDaftDNS(t, "127.0.0.1")
 
-	tmpFileName := net.WriteTempResolvConf(t, "127.0.0.1")
-	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
+	d := daemon.New(t, daemon.WithResolvConf(net.GenResolvConf("127.0.0.1")))
 	d.StartWithBusybox(ctx, t)
 	t.Cleanup(func() { d.Stop(t) })
 	c := d.NewClientT(t)

integration/networking/resolvconf_test.go

@@ -25,9 +25,7 @@ func TestResolvConfLocalhostIPv6(t *testing.T) {
 
 	ctx := setupTest(t)
 
-	tmpFileName := network.WriteTempResolvConf(t, "127.0.0.53")
-
-	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
+	d := daemon.New(t, daemon.WithResolvConf(network.GenResolvConf("127.0.0.53")))
 	d.StartWithBusybox(ctx, t)
 	defer d.Stop(t)
 
@@ -51,7 +49,7 @@ func TestResolvConfLocalhostIPv6(t *testing.T) {
 		Force: true,
 	})
 
-	output := strings.ReplaceAll(result.Stdout.String(), tmpFileName, "RESOLV.CONF")
+	output := strings.ReplaceAll(result.Stdout.String(), d.ResolvConfPathOverride, "RESOLV.CONF")
 	assert.Check(t, is.Equal(output, `# Generated by Docker Engine.
 # This file can be edited; Docker Engine will not make further changes once it
 # has been modified.
@@ -79,8 +77,7 @@ func TestInternalNetworkDNS(t *testing.T) {
 	network.StartDaftDNS(t, "127.0.0.1")
 
 	// Set up a temp resolv.conf pointing at that DNS server, and a daemon using it.
-	tmpFileName := network.WriteTempResolvConf(t, "127.0.0.1")
-	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName))
+	d := daemon.New(t, daemon.WithResolvConf(network.GenResolvConf("127.0.0.1")))
 	d.StartWithBusybox(ctx, t)
 	defer d.Stop(t)
 

testutil/daemon/daemon.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"net/http"
 	"os"
@@ -88,6 +89,8 @@ type Daemon struct {
 	usernsRemap                string
 	rootlessUser               *user.User
 	rootlessXDGRuntimeDir      string
+	resolvConfContent          string
+	ResolvConfPathOverride     string // Path to a replacement for "/etc/resolv.conf", or empty.
 
 	// swarm related field
 	swarmListenAddr string
@@ -146,6 +149,15 @@ func NewDaemon(workingDir string, ops ...Option) (*Daemon, error) {
 		op(d)
 	}
 
+	if len(d.resolvConfContent) > 0 {
+		path := filepath.Join(d.Folder, "resolv.conf")
+		if err := os.WriteFile(path, []byte(d.resolvConfContent), 0644); err != nil {
+			return nil, fmt.Errorf("failed to write docker resolv.conf to %q: %v", path, err)
+		}
+		d.extraEnv = append(d.extraEnv, "DOCKER_TEST_RESOLV_CONF_PATH="+path)
+		d.ResolvConfPathOverride = path
+	}
+
 	if d.rootlessUser != nil {
 		if err := os.Chmod(SockRoot, 0o777); err != nil {
 			return nil, err

testutil/daemon/ops.go

@@ -135,3 +135,11 @@ func WithEnvVars(vars ...string) Option {
 		d.extraEnv = append(d.extraEnv, vars...)
 	}
 }
+
+// WithResolvConf allows a test to provide content for a resolv.conf file to be used
+// as the basis for resolv.conf in the container, instead of the host's /etc/resolv.conf.
+func WithResolvConf(content string) Option {
+	return func(d *Daemon) {
+		d.resolvConfContent = content
+	}
+}