fix: changes empty mp parts error on CompleteMultipartUpload

Fixes #1328

If `CompleteMultipartUpload` is attempted with empty `Parts` list, the gateway used to return `InvalidRequest`. Now it's changed to `MalformedXML`.

s3api/controllers/object-post.go

@@ -278,7 +278,7 @@ func (c S3ApiController) CompleteMultipartUpload(ctx *fiber.Ctx) (*Response, err
 			MetaOpts: &MetaOptions{
 				BucketOwner: parsedAcl.Owner,
 			},
-		}, s3err.GetAPIError(s3err.ErrEmptyParts)
+		}, s3err.GetAPIError(s3err.ErrMalformedXML)
 	}
 
 	var mpuObjectSize *int64

s3api/controllers/object-post_test.go

@@ -404,7 +404,7 @@ func TestS3ApiController_CompleteMultipartUpload(t *testing.T) {
 						BucketOwner: "root",
 					},
 				},
-				err: s3err.GetAPIError(s3err.ErrEmptyParts),
+				err: s3err.GetAPIError(s3err.ErrMalformedXML),
 			},
 		},
 		{

s3err/s3err.go

@@ -82,7 +82,6 @@ const (
 	ErrInvalidPartNumberMarker
 	ErrInvalidObjectAttributes
 	ErrInvalidPart
-	ErrEmptyParts
 	ErrInvalidPartNumber
 	ErrInvalidPartOrder
 	ErrInvalidCompleteMpPartNumber
@@ -311,11 +310,6 @@ var errorCodeResponse = map[ErrorCode]APIError{
 		Description:    "One or more of the specified parts could not be found.  The part may not have been uploaded, or the specified entity tag may not match the part's entity tag.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
-	ErrEmptyParts: {
-		Code:           "InvalidRequest",
-		Description:    "You must specify at least one part",
-		HTTPStatusCode: http.StatusBadRequest,
-	},
 	ErrInvalidPartNumber: {
 		Code:           "InvalidArgument",
 		Description:    "Part number must be an integer between 1 and 10000, inclusive.",

tests/integration/tests.go

@@ -13012,7 +13012,7 @@ func CompleteMultipartUpload_empty_parts(s *S3Conf) error {
 			},
 		})
 		cancel()
-		if err := checkApiErr(err, s3err.GetAPIError(s3err.ErrEmptyParts)); err != nil {
+		if err := checkApiErr(err, s3err.GetAPIError(s3err.ErrMalformedXML)); err != nil {
 			return err
 		}