add:

更新

backend/IM_API/Dtos/Message/MessagTypeDto.cs

@@ -0,0 +1,26 @@
+namespace IM_API.Dtos.Message
+{
+    public class RequestMessageType
+    {
+        public Guid FileId { get; set; }
+        public long Size { get; set; }
+    }
+    public class BaseMessageType: RequestMessageType
+    {
+        public string Url { get; set; }
+        public string Provider { get; set; }
+        public string Format { get; set; }
+        public string Text { get; set; }
+    }
+    public class ImageDto() : BaseMessageType
+    {
+        public string Thumb { get; set; }
+        public int W { get; set; }
+        public int H { get; set; }
+    }
+
+    public class VideoDto() : ImageDto
+    {
+        public int Duration { get; set; }
+    }
+}