Fail gracefully if Docker is not configured with ipv6.

PiperOrigin-RevId: 343927315

pkg/test/dockerutil/container.go

@@ -17,6 +17,7 @@ package dockerutil
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net"
@@ -351,6 +352,9 @@ func (c *Container) SandboxPid(ctx context.Context) (int, error) {
 	return resp.ContainerJSONBase.State.Pid, nil
 }
 
+// ErrNoIP indicates that no IP address is available.
+var ErrNoIP = errors.New("no IP available")
+
 // FindIP returns the IP address of the container.
 func (c *Container) FindIP(ctx context.Context, ipv6 bool) (net.IP, error) {
 	resp, err := c.client.ContainerInspect(ctx, c.id)
@@ -365,7 +369,7 @@ func (c *Container) FindIP(ctx context.Context, ipv6 bool) (net.IP, error) {
 		ip = net.ParseIP(resp.NetworkSettings.DefaultNetworkSettings.IPAddress)
 	}
 	if ip == nil {
-		return net.IP{}, fmt.Errorf("invalid IP: %q", ip)
+		return net.IP{}, ErrNoIP
 	}
 	return ip, nil
 }

test/iptables/iptables_test.go

@@ -89,6 +89,10 @@ func iptablesTest(t *testing.T, test TestCase, ipv6 bool) {
 	// Get the container IP.
 	ip, err := d.FindIP(ctx, ipv6)
 	if err != nil {
+		// If ipv6 is not configured, don't fail.
+		if ipv6 && err == dockerutil.ErrNoIP {
+			t.Skipf("No ipv6 address is available.")
+		}
 		t.Fatalf("failed to get container IP: %v", err)
 	}