Support for --cleanup flag

The --cleanup flag will cause watchtower to automatically remove the old
image after a container is restart with a new image.

container/client.go

@@ -21,6 +21,7 @@ type Client interface {
 	StartContainer(Container) error
 	RenameContainer(Container, string) error
 	IsContainerStale(Container) (bool, error)
+	RemoveImage(Container) error
 }
 
 func NewClient(dockerHost string, tlsConfig *tls.Config, pullImages bool) Client {
@@ -147,6 +148,13 @@ func (client DockerClient) IsContainerStale(c Container) (bool, error) {
 	return false, nil
 }
 
+func (client DockerClient) RemoveImage(c Container) error {
+	imageID := c.ImageID()
+	log.Infof("Removing image %s", imageID)
+	_, err := client.api.RemoveImage(imageID)
+	return err
+}
+
 func (client DockerClient) waitForStop(c Container, waitTime time.Duration) error {
 	timeout := time.After(waitTime)
 

container/client_test.go

@@ -399,3 +399,38 @@ func TestIsContainerStale_InspectImageError(t *testing.T) {
 	assert.EqualError(t, err, "uh-oh")
 	api.AssertExpectations(t)
 }
+
+func TestRemoveImage_Success(t *testing.T) {
+	c := Container{
+		imageInfo: &dockerclient.ImageInfo{
+			Id: "abc123",
+		},
+	}
+
+	api := mockclient.NewMockClient()
+	api.On("RemoveImage", "abc123").Return([]*dockerclient.ImageDelete{}, nil)
+
+	client := DockerClient{api: api}
+	err := client.RemoveImage(c)
+
+	assert.NoError(t, err)
+	api.AssertExpectations(t)
+}
+
+func TestRemoveImage_Error(t *testing.T) {
+	c := Container{
+		imageInfo: &dockerclient.ImageInfo{
+			Id: "abc123",
+		},
+	}
+
+	api := mockclient.NewMockClient()
+	api.On("RemoveImage", "abc123").Return([]*dockerclient.ImageDelete{}, errors.New("oops"))
+
+	client := DockerClient{api: api}
+	err := client.RemoveImage(c)
+
+	assert.Error(t, err)
+	assert.EqualError(t, err, "oops")
+	api.AssertExpectations(t)
+}

container/container.go

@@ -34,6 +34,10 @@ func (c Container) Name() string {
 	return c.containerInfo.Name
 }
 
+func (c Container) ImageID() string {
+	return c.imageInfo.Id
+}
+
 func (c Container) ImageName() string {
 	imageName := c.containerInfo.Config.Image
 

container/container_test.go

@@ -23,6 +23,16 @@ func TestName(t *testing.T) {
 	assert.Equal(t, "foo", c.Name())
 }
 
+func TestImageID(t *testing.T) {
+	c := Container{
+		imageInfo: &dockerclient.ImageInfo{
+			Id: "foo",
+		},
+	}
+
+	assert.Equal(t, "foo", c.ImageID())
+}
+
 func TestImageName_Tagged(t *testing.T) {
 	c := Container{
 		containerInfo: &dockerclient.ContainerInfo{

container/mockclient/mock.go

@@ -35,3 +35,8 @@ func (m *MockClient) IsContainerStale(c container.Container) (bool, error) {
 	args := m.Called(c)
 	return args.Bool(0), args.Error(1)
 }
+
+func (m *MockClient) RemoveImage(c container.Container) error {
+	args := m.Called(c)
+	return args.Error(0)
+}