fix: accept upload-id-marker together with key-marker in ListMultipartUploads

The posix and azure backends dropped every upload with a key equal to
the key-marker before handing the list to the lister, which then looked
for the upload-id-marker under the next key. An upload-id-marker that
belongs to the key-marker could never be found, so the request failed
with "Invalid uploadId marker", including when a client paged with the
NextKeyMarker and NextUploadIdMarker the gateway returned.

Keep the uploads of the key-marker itself when an upload-id-marker is
set, so the listing continues right after the given upload, as S3 does.
Enable the REST test that covers it.

Fixes #2149

backend/azure/azure.go

@@ -1760,7 +1760,7 @@ func (az *Azure) ListMultipartUploads(ctx context.Context, input *s3.ListMultipa
 			if !ok {
 				continue
 			}
-			if keyMarker != "" && *key <= keyMarker {
+			if keyMarker != "" && (*key < keyMarker || (*key == keyMarker && uploadIDMarker == "")) {
 				continue
 			}
 			if prefix != "" && !strings.HasPrefix(*key, prefix) {

backend/mp-lister.go

@@ -42,7 +42,8 @@ func ListMultipartUploads(uploads []s3response.Upload, prefix, delimiter, keyMar
 // Assumptions about input Uploads:
 //   - Sorted by (Key asc, Initiated asc)
 //   - Filtered by Prefix
-//   - Filtered to start strictly after key-marker when key-marker was provided.
+//   - Filtered to start strictly after key-marker when key-marker was provided,
+//     or at key-marker when upload-id-marker was provided as well.
 type MultipartUploadLister struct {
 	Uploads        []s3response.Upload
 	Prefix         string
@@ -148,13 +149,13 @@ func (l *MultipartUploadLister) Run() (*ListMultipartUploadsPage, error) {
 }
 
 // findUploadIdMarkerIndex finds the index of given uploadId marker in uploads
-// uploadIDMarker must match an upload-id among uploads with the first key after KeyMarker.
-// Since caller filtered to Key > KeyMarker and the list is sorted by key/time,
-// the first key after KeyMarker is Uploads[0].Key (if any).
+// uploadIDMarker must match an upload-id among uploads with the first key at or after KeyMarker.
+// Since caller filtered to Key >= KeyMarker and the list is sorted by key/time,
+// the first key at or after KeyMarker is Uploads[0].Key (if any).
 // -1 is returned if no uploadId is found
 func (l *MultipartUploadLister) findUploadIdMarkerIndex(uploadIDMarker string) int {
 	if len(l.Uploads) == 0 {
-		// key-marker provided but nothing after it => upload-id-marker can never be valid.
+		// key-marker provided but nothing at or after it => upload-id-marker can never be valid.
 		return -1
 	}
 	firstKey := l.Uploads[0].Key

backend/posix/posix.go

@@ -3472,8 +3472,9 @@ func (p *Posix) ListMultipartUploads(ctx context.Context, mpu *s3.ListMultipartU
 		if prefix != "" && !strings.HasPrefix(objectName, prefix) {
 			continue
 		}
-		// filter by keyMarker
-		if keyMarker != "" && objectName <= keyMarker {
+		// filter by keyMarker, keeping the uploads of the key-marker
+		// itself when an upload-id-marker is set
+		if keyMarker != "" && (objectName < keyMarker || (objectName == keyMarker && uploadIDMarker == "")) {
 			continue
 		}