WIP: Add Image.RemoveTag

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

internal/localimage/image.go

@@ -67,3 +67,34 @@ func (i *Image) AddTag(tag reference.Named) (bool, error) {
 	}
 	return true, nil
 }
+
+// RemoveTag removes tag from image.
+// If the tag is not present, the method silently succeeds.
+// The image is not removed even if the last tag is removed.
+// Returns true if the tag was found and removed, false if the tags were not changed. // FIXME: can/should this be dropped?
+// FIXME: This allows untagging using name@digest, and name:tag@digest.  Should that be allowed??!!
+func (i *Image) RemoveTag(tag reference.Named) (bool, error) {
+	if reference.IsNameOnly(tag) {
+		return false, fmt.Errorf("Refusing to remove tag %q which has neither a tag nor a digest", tag.String())
+	}
+
+	si, err := i.storageImage()
+	if err != nil {
+		return false, err
+	}
+	tagString := tag.String()
+	if !util.StringInSlice(tagString, si.Names) {
+		return false, nil
+	}
+
+	newNames := []string{}
+	for _, t := range si.Names {
+		if t != tagString {
+			newNames = append(newNames, t)
+		}
+	}
+	if err := i.storage.store.SetNames(si.ID, newNames); err != nil {
+		return false, err
+	}
+	return true, nil
+}

libpod/image/image.go

@@ -573,26 +573,24 @@ func (i *Image) TagImage(tag string) error {
 
 // UntagImage removes a tag from the given image
 func (i *Image) UntagImage(tag string) error {
-	if err := i.reloadImage(); err != nil {
+	// Previously, this code only worked with an _exact_ match of the tag against i.Names(), which contains
+	// reference.Named.String()-formatted data.  So, for any input that worked previously, we can use reference.ParseNormalizedNamed()
+	// here safely without worrying about short names and the like.
+	// FIXME: Should this use normalizeTag anyway?
+	ref, err := reference.ParseNormalizedNamed(tag)
+	if err != nil {
 		return err
 	}
-	var newTags []string
-	tags := i.Names()
-	if !util.StringInSlice(tag, tags) {
+	updated, err := i.localImage.RemoveTag(ref)
+	if err != nil {
 		return nil
 	}
-	for _, t := range tags {
-		if tag != t {
-			newTags = append(newTags, t)
+	if updated {
+		if err := i.reloadImage(); err != nil {
+			return err
 		}
+		i.newImageEvent(events.Untag)
 	}
-	if err := i.imageruntime.store.SetNames(i.ID(), newTags); err != nil {
-		return err
-	}
-	if err := i.reloadImage(); err != nil {
-		return err
-	}
-	i.newImageEvent(events.Untag)
 	return nil
 }