internal/images: gate docker pull for thumbnails

Fixes #1091

Change-Id: I31fda636cec4b4ae06c74cc2c04b6986f10222c3

internal/images/docker.go

@@ -23,16 +23,28 @@ import (
 	"log"
 	"os/exec"
 	"strings"
+
+	"go4.org/syncutil"
 )
 
 // TODO(mpl): refactor somewhere with pkg/test/dockertest
 
 const thumbnailImage = "gcr.io/perkeep-containers/thumbnail"
 
+var (
+	thumbnailPullGate  = syncutil.NewGate(1)
+	haveThumbnailImage bool
+)
+
 func setUpThumbnailContainer() error {
 	if !haveDocker() {
 		return errors.New("'docker' command not found")
 	}
+	thumbnailPullGate.Start()
+	defer thumbnailPullGate.Done()
+	if haveThumbnailImage {
+		return nil
+	}
 	if ok, err := haveImage(thumbnailImage); !ok || err != nil {
 		if err != nil {
 			return fmt.Errorf("error running docker to check for %s: %v", thumbnailImage, err)
@@ -42,6 +54,7 @@ func setUpThumbnailContainer() error {
 			return fmt.Errorf("error pulling %s: %v", thumbnailImage, err)
 		}
 	}
+	haveThumbnailImage = true
 	return nil
 }
 

internal/images/images.go

@@ -640,7 +640,6 @@ func HEIFToJPEG(fr io.Reader, size *Dimensions) ([]byte, error) {
 	bin, err := exec.LookPath("heiftojpeg")
 	if err != nil {
 		pathErr := err
-		// TODO(mpl): "pre-pull" the image on Perkeep startup or something like that?
 		if err := setUpThumbnailContainer(); err != nil {
 			return nil, fmt.Errorf("heiftojpeg not found in PATH (%v), and could not fallback on docker image because %v. You need to install github.com/pushd/heif, or set up docker.", pathErr, err)
 		}