Strip empty DNS entries to avoid parse errors when creating sandbox D…

…NS in Moby

pkg/compose/create.go

@@ -94,6 +94,8 @@ func (s *composeService) create(ctx context.Context, project *types.Project, opt
 		return err
 	}
 
+	prepareServiceDNS(project)
+
 	if err := s.ensureProjectVolumes(ctx, project); err != nil {
 		return err
 	}
@@ -140,6 +142,17 @@ func (s *composeService) ensureNetworks(ctx context.Context, networks types.Netw
 	return nil
 }
 
+func prepareServiceDNS(project *types.Project) {
+	for k, service := range project.Services {
+		trimmedDNS := utils.Remove(service.DNS, "")
+		if len(trimmedDNS) != len(service.DNS) {
+			logrus.Warnf("The %q service has one or more empty DNS entries. Skipping them.", k)
+		}
+		service.DNS = trimmedDNS
+		project.Services[k] = service
+	}
+}
+
 func (s *composeService) ensureProjectVolumes(ctx context.Context, project *types.Project) error {
 	for k, volume := range project.Volumes {
 		volume.Labels = volume.Labels.Add(api.VolumeLabel, k)

pkg/compose/create_test.go

@@ -275,3 +275,31 @@ func TestDefaultNetworkSettings(t *testing.T) {
 		assert.Check(t, cmp.Nil(networkConfig))
 	})
 }
+
+func TestPrepareServiceDNS(t *testing.T) {
+	t.Run("returns DNS list without empty strings", func(t *testing.T) {
+		const (
+			serviceName = "myService"
+			dns1        = "dns-1"
+			dns2        = "dns-2"
+		)
+		project := composetypes.Project{
+			Services: composetypes.Services{
+				serviceName: composetypes.ServiceConfig{
+					DNS: []string{
+						dns1,
+						"",
+						dns2,
+						"",
+					},
+				},
+			},
+		}
+
+		prepareServiceDNS(&project)
+		dnsConfig := project.Services[serviceName].DNS
+		assert.Equal(t, len(dnsConfig), 2)
+		assert.Equal(t, dnsConfig[0], dns1)
+		assert.Equal(t, dnsConfig[1], dns2)
+	})
+}