feat: support batch response error message

transfer/batch.go

@@ -3,6 +3,13 @@ package transfer
 // BatchItem is a Git LFS batch item.
 type BatchItem struct {
 	Pointer
-	Args    Args
+
+	// Present is used to determine the action to take for the batch item.
 	Present bool
+
+	// Args is an optional oid-line key-value pairs.
+	Args Args
+
+	// Error is an optional error message.
+	Error string
 }

transfer/processor.go

@@ -107,13 +107,18 @@ func (p *Processor) BatchData(op string, presentAction string, missingAction str
 	}
 	oids := make([]string, 0)
 	for _, item := range batch {
-		action := missingAction
-		if item.Present {
-			action = presentAction
-		}
-		line := fmt.Sprintf("%s %s", item.Pointer, action)
-		if len(item.Args) > 0 {
-			line = fmt.Sprintf("%s %s", line, item.Args)
+		var line string
+		if item.Error != "" {
+			line = fmt.Sprintf("message %s", item.Error)
+		} else {
+			action := missingAction
+			if item.Present {
+				action = presentAction
+			}
+			line = fmt.Sprintf("%s %s", item.Pointer, action)
+			if len(item.Args) > 0 {
+				line = fmt.Sprintf("%s %s", line, item.Args)
+			}
 		}
 		oids = append(oids, line)
 	}