Add flag to skip pulling images already present

actions/api.go

@@ -43,6 +43,7 @@ type RunnerConfig struct {
 	EventName       string          // name of event to run
 	EventPath       string          // path to JSON file to use for event.json in containers, relative to WorkingDir
 	ReuseContainers bool            // reuse containers to maintain state
+	ForcePull       bool            // force pulling of the image, if already present
 }
 
 type environmentApplier interface {

actions/runner_exec.go

@@ -49,10 +49,25 @@ func (runner *runnerImpl) addImageExecutor(action *model.Action, executors *[]co
 
 	case *model.UsesDockerImage:
 		image = uses.Image
-		*executors = append(*executors, container.NewDockerPullExecutor(container.NewDockerPullExecutorInput{
-			DockerExecutorInput: in,
-			Image:               image,
-		}))
+
+		pull := runner.config.ForcePull
+		if !pull {
+			imageExists, err := container.ImageExistsLocally(runner.config.Ctx, image)
+			if err != nil {
+				return "", fmt.Errorf("unable to determine if image already exists for image %q", image)
+			}
+
+			if imageExists {
+				pull = false
+			}
+		}
+
+		if pull {
+			*executors = append(*executors, container.NewDockerPullExecutor(container.NewDockerPullExecutorInput{
+				DockerExecutorInput: in,
+				Image:               image,
+			}))
+		}
 
 	case *model.UsesPath:
 		contextDir := filepath.Join(runner.config.WorkingDir, uses.String())

cmd/root.go

@@ -31,6 +31,7 @@ func Execute(ctx context.Context, version string) {
 	rootCmd.Flags().StringP("action", "a", "", "run action")
 	rootCmd.Flags().BoolVarP(&runnerConfig.ReuseContainers, "reuse", "r", false, "reuse action containers to maintain state")
 	rootCmd.Flags().StringVarP(&runnerConfig.EventPath, "event", "e", "", "path to event JSON file")
+	rootCmd.Flags().BoolVarP(&runnerConfig.ForcePull, "pull", "p", false, "pull docker image(s) if already present")
 	rootCmd.PersistentFlags().BoolP("verbose", "v", false, "verbose output")
 	rootCmd.PersistentFlags().BoolVarP(&runnerConfig.Dryrun, "dryrun", "n", false, "dryrun mode")
 	rootCmd.PersistentFlags().StringVarP(&runnerConfig.WorkflowPath, "file", "f", "./.github/main.workflow", "path to workflow file")

container/docker_images.go

@@ -0,0 +1,33 @@
+package container
+
+import (
+	"context"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/filters"
+	"github.com/docker/docker/client"
+)
+
+// ImageExistsLocally returns a boolean indicating if an image with the
+// requested name (and tag) exist in the local docker image store
+func ImageExistsLocally(ctx context.Context, imageName string) (bool, error) {
+	cli, err := client.NewClientWithOpts(client.FromEnv)
+	if err != nil {
+		return false, err
+	}
+	cli.NegotiateAPIVersion(ctx)
+
+	filters := filters.NewArgs()
+	filters.Add("reference", imageName)
+
+	imageListOptions := types.ImageListOptions{
+		Filters: filters,
+	}
+
+	images, err := cli.ImageList(ctx, imageListOptions)
+	if err != nil {
+		return false, err
+	}
+
+	return len(images) > 0, nil
+}

container/docker_images_test.go

@@ -0,0 +1,42 @@
+package container
+
+import (
+	"context"
+	"io/ioutil"
+	"testing"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/client"
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func init() {
+	log.SetLevel(log.DebugLevel)
+}
+
+func TestImageExistsLocally(t *testing.T) {
+	// to help make this test reliable and not flaky, we need to have
+	// an image that will exist, and onew that won't exist
+
+	exists, err := ImageExistsLocally(context.TODO(), "library/alpine:this-random-tag-will-never-exist")
+	assert.Nil(t, err)
+	assert.Equal(t, false, exists)
+
+	// pull an image
+	cli, err := client.NewClientWithOpts(client.FromEnv)
+	assert.Nil(t, err)
+	cli.NegotiateAPIVersion(context.TODO())
+
+	// Chose alpine latest because it's so small
+	// maybe we should build an image instead so that tests aren't reliable on dockerhub
+	reader, err := cli.ImagePull(context.TODO(), "alpine:latest", types.ImagePullOptions{})
+	assert.Nil(t, err)
+	defer reader.Close()
+	_, err = ioutil.ReadAll(reader)
+	assert.Nil(t, err)
+
+	exists, err = ImageExistsLocally(context.TODO(), "alpine:latest")
+	assert.Nil(t, err)
+	assert.Equal(t, true, exists)
+}