Add flag to skip pulling images already present

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)
+}