cmd/create: Don't block user interaction while fetching the image size

It takes 'skopeo inspect' a few seconds to fetch the image size from the
remote registry, and while that happens the user can't interact with the
image download prompt:
  $ toolbox create
  Image required to create toolbox container.
  <wait for a few seconds>
  Download registry.fedoraproject.org/fedora-toolbox:39 (359.8MB)? [y/N]:

This feels awkward because it's not clear to the user what's going on
during those few seconds.  Moreover, while knowing the image size can be
convenient at times, for example when disk space and network bandwidth
are limited, it's not always important.

It will be better if 'skopeo inspect' ran in the background, while
waiting for the user to respond to the image download prompt, and once
the image size has been fetched, the prompt can be updated to include
it.

So, initially:
  $ toolbox create
  Image required to create toolbox container.
  Download registry.fedoraproject.org/fedora-toolbox:39 (...)? [y/N]:

... and then once the size is available:
  $ toolbox create
  Image required to create toolbox container.
  Download registry.fedoraproject.org/fedora-toolbox:39 (359.8MB)? [y/N]:

If skopeo(1) is missing or too old, then the prompt can continue without
the size, as it did before:
  $ toolbox create
  Image required to create toolbox container.
  Download registry.fedoraproject.org/fedora-toolbox:39 [y/N]:

#752
#1263

.github/workflows/ubuntu-tests.yaml

@@ -44,7 +44,7 @@ jobs:
             fish \
             gcc \
             go-md2man \
-            golang \
+            golang-1.20 \
             meson \
             ninja-build \
             openssl \
@@ -54,6 +54,9 @@ jobs:
             systemd \
             udisks2
 
+      - name: Set up PATH for Go 1.20
+        run: echo "export PATH=/usr/lib/go-1.20/bin:\$PATH" >> $GITHUB_ENV
+
       - name: Checkout Bats
         uses: actions/checkout@v3
         with:

src/cmd/create.go

@@ -576,8 +576,7 @@ func getFullyQualifiedImageFromRepoTags(image string) (string, error) {
 	return imageFull, nil
 }
 
-func getImageSizeFromRegistry(imageFull string) (string, error) {
-	ctx := context.Background()
+func getImageSizeFromRegistry(ctx context.Context, imageFull string) (string, error) {
 	image, err := skopeo.Inspect(ctx, imageFull)
 	if err != nil {
 		return "", err
@@ -601,6 +600,23 @@ func getImageSizeFromRegistry(imageFull string) (string, error) {
 	return imageSizeHuman, nil
 }
 
+func getImageSizeFromRegistryAsync(ctx context.Context, imageFull string) (<-chan string, <-chan error) {
+	retValCh := make(chan string)
+	errCh := make(chan error)
+
+	go func() {
+		imageSize, err := getImageSizeFromRegistry(ctx, imageFull)
+		if err != nil {
+			errCh <- err
+			return
+		}
+
+		retValCh <- imageSize
+	}()
+
+	return retValCh, errCh
+}
+
 func getServiceSocket(serviceName string, unitName string) (string, error) {
 	logrus.Debugf("Resolving path to the %s socket", serviceName)
 
@@ -713,18 +729,7 @@ func pullImage(image, release, authFile string) (bool, error) {
 	}
 
 	if promptForDownload {
-		fmt.Println("Image required to create toolbox container.")
-
-		var prompt string
-
-		if imageSize, err := getImageSizeFromRegistry(imageFull); err != nil {
-			logrus.Debugf("Getting image size failed: %s", err)
-			prompt = fmt.Sprintf("Download %s? [y/N]:", imageFull)
-		} else {
-			prompt = fmt.Sprintf("Download %s (%s)? [y/N]:", imageFull, imageSize)
-		}
-
-		shouldPullImage = askForConfirmation(prompt)
+		shouldPullImage = showPromptForDownload(imageFull)
 	}
 
 	if !shouldPullImage {
@@ -756,6 +761,138 @@ func pullImage(image, release, authFile string) (bool, error) {
 	return true, nil
 }
 
+func showPromptForDownload(imageFull string) bool {
+	fmt.Println("Image required to create toolbox container.")
+
+	prompt := fmt.Sprintf("Download %s ( ... MB)? [y/N]:", imageFull)
+
+	parentCtx := context.Background()
+	askCtx, askCancel := context.WithCancelCause(parentCtx)
+	defer askCancel(errors.New("clean-up"))
+
+	askCh, askErrCh := askForConfirmationAsync(askCtx, prompt, false)
+
+	imageSizeCtx, imageSizeCancel := context.WithCancelCause(parentCtx)
+	defer imageSizeCancel(errors.New("clean-up"))
+
+	imageSizeCh, imageSizeErrCh := getImageSizeFromRegistryAsync(imageSizeCtx, imageFull)
+
+	var imageSize string
+	var shouldPullImage bool
+
+	select {
+	case val := <-askCh:
+		shouldPullImage = val
+		cause := fmt.Errorf("%w: received confirmation without image size", context.Canceled)
+		imageSizeCancel(cause)
+	case err := <-askErrCh:
+		shouldPullImage = false
+		cause := fmt.Errorf("failed to ask for confirmation without image size: %w", err)
+		imageSizeCancel(cause)
+	case val := <-imageSizeCh:
+		imageSize = val
+		cause := fmt.Errorf("%w: received image size", context.Canceled)
+		askCancel(cause)
+	case err := <-imageSizeErrCh:
+		cause := fmt.Errorf("failed to get image size: %w", err)
+		askCancel(cause)
+	}
+
+	if imageSizeCtx.Err() != nil && askCtx.Err() == nil {
+		cause := context.Cause(imageSizeCtx)
+		logrus.Debugf("Show prompt for download: image size canceled: %s", cause)
+		return shouldPullImage
+	}
+
+	var done bool
+
+	if imageSizeCtx.Err() == nil && askCtx.Err() != nil {
+		select {
+		case val := <-askCh:
+			logrus.Debugf("Show prompt for download: received pending confirmation without image size")
+			shouldPullImage = val
+			done = true
+		case err := <-askErrCh:
+			logrus.Debugf("Show prompt for download: failed to ask for confirmation without image size: %s",
+				err)
+		}
+	} else {
+		panic("code should not be reached")
+	}
+
+	cause := context.Cause(askCtx)
+	logrus.Debugf("Show prompt for download: ask canceled: %s", cause)
+
+	if done {
+		return shouldPullImage
+	}
+
+	var restoreCursor bool
+
+	if errors.Is(cause, context.Canceled) {
+		imageSizeLen := len(imageSize)
+		var padding1 int
+		var padding2 int
+		var padding3 int
+		var padding4 int
+
+		if imageSizeLen < 7 {
+			padding4 = 7 - imageSizeLen
+		}
+
+		if padding4 > 1 {
+			padding3 = padding4 - 1
+			padding4 = 1
+		}
+
+		if padding3 > 1 {
+			padding2 = padding3 - 1
+			padding3 = 1
+		}
+
+		if padding2 > 1 {
+			padding1 = padding2 - 1
+			padding2 = 1
+		}
+
+		prompt = fmt.Sprintf("Download %s (%*s%s%*s)? %*s[y/N]:%*s",
+			imageFull,
+			padding1, "",
+			imageSize,
+			padding2, "",
+			padding3, "",
+			padding4, "")
+
+		// Save the cursor position.
+		fmt.Printf("\033[s")
+
+		restoreCursor = true
+	} else {
+		prompt = fmt.Sprintf("Download %s? [y/N]:", imageFull)
+
+		// Delete entire line regardless of cursor position.
+		fmt.Printf("\033[2K")
+	}
+
+	fmt.Printf("\r")
+
+	askAgainCtx, askAgainCancel := context.WithCancelCause(parentCtx)
+	defer askAgainCancel(errors.New("clean-up"))
+
+	askAgainCh, askAgainErrCh := askForConfirmationAsync(askAgainCtx, prompt, restoreCursor)
+
+	select {
+	case val := <-askAgainCh:
+		logrus.Debug("Show prompt for download: received confirmation with image size")
+		shouldPullImage = val
+	case err := <-askAgainErrCh:
+		logrus.Debugf("Show prompt for download: failed to ask for confirmation with image size: %s", err)
+		shouldPullImage = false
+	}
+
+	return shouldPullImage
+}
+
 // systemdNeedsEscape checks whether a byte in a potential dbus ObjectPath needs to be escaped
 func systemdNeedsEscape(i int, b byte) bool {
 	// Escape everything that is not a-z-A-Z-0-9

src/go.mod

@@ -1,6 +1,6 @@
 module github.com/containers/toolbox
 
-go 1.14
+go 1.20
 
 require (
 	github.com/HarryMichal/go-version v1.0.1