storagedriver/s3: Fixed a Delete noop edgecase

Delete was not working when the subpath immediately followed the given path started with an ascii lower than "/" such as dash "-" and underscore "_" and requests no files to be deleted.

(cherry picked from commit 5d8fa0ce94b68cce70237805db92cdd8d40de282)
Signed-off-by: Collin Shoop <cshoop@digitalocean.com>

registry/storage/driver/s3-aws/s3.go

@@ -806,7 +806,21 @@ func min(a, b int) int {
 // We must be careful since S3 does not guarantee read after delete consistency
 func (d *driver) Delete(ctx context.Context, path string) error {
 	s3Objects := make([]*s3.ObjectIdentifier, 0, listMax)
-	s3Path := d.s3Path(path)
+
+	// manually add the given path if it's a file
+	stat, err := d.Stat(ctx, path)
+	if err != nil {
+		return err
+	}
+	if stat != nil && !stat.IsDir() {
+		path := d.s3Path(path)
+		s3Objects = append(s3Objects, &s3.ObjectIdentifier{
+			Key: &path,
+		})
+	}
+
+	// list objects under the given path as a subpath (suffix with slash "/")
+	s3Path := d.s3Path(path) + "/"
 	listObjectsInput := &s3.ListObjectsInput{
 		Bucket: aws.String(d.Bucket),
 		Prefix: aws.String(s3Path),
@@ -820,14 +834,10 @@ ListLoop:
 		// if there were no more results to return after the first call, resp.IsTruncated would have been false
 		// and the loop would be exited without recalling ListObjects
 		if err != nil || len(resp.Contents) == 0 {
-			return storagedriver.PathNotFoundError{Path: path}
+			break ListLoop
 		}
 
 		for _, key := range resp.Contents {
-			// Stop if we encounter a key that is not a subpath (so that deleting "/a" does not delete "/ab").
-			if len(*key.Key) > len(s3Path) && (*key.Key)[len(s3Path)] != '/' {
-				break ListLoop
-			}
 			s3Objects = append(s3Objects, &s3.ObjectIdentifier{
 				Key: key.Key,
 			})
@@ -843,8 +853,12 @@ ListLoop:
 		}
 	}
 
-	// need to chunk objects into groups of 1000 per s3 restrictions
 	total := len(s3Objects)
+	if total == 0 {
+		return storagedriver.PathNotFoundError{Path: path}
+	}
+
+	// need to chunk objects into groups of 1000 per s3 restrictions
 	for i := 0; i < total; i += 1000 {
 		_, err := d.S3.DeleteObjects(&s3.DeleteObjectsInput{
 			Bucket: aws.String(d.Bucket),