feat(server): lossy avatar thumbnails, gzip upload and separate avatar endpoints

server/src/WebDrop.Core/AvatarData.cs

@@ -10,14 +10,20 @@ public static class AvatarData
     /// <summary>空间头像会跟着空间信息发给所有成员和空间列表,动图上限比账号头像小,约 1.5 MB</summary>
     public const int MaxSpaceGifChars = 2_000_000;
 
+    /// <summary>缩略图(列表、聊天里默认分发的有损小图)的上限:静态约 75 KB,动图约 370 KB</summary>
+    public const int MaxThumbStaticChars = 100_000;
+    public const int MaxThumbGifChars = 500_000;
+
     private static readonly string[] Prefixes = ["data:image/png;base64,", "data:image/jpeg;base64,", "data:image/webp;base64,", "data:image/gif;base64,"];
 
+    public static void ValidateThumb(string thumb) => Validate(thumb, MaxThumbGifChars, MaxThumbStaticChars);
+
     /// <summary>不合法时抛 BadRequest</summary>
-    public static void Validate(string avatar, int maxGifChars)
+    public static void Validate(string avatar, int maxGifChars, int maxStaticChars = MaxStaticChars)
     {
         var prefix = Prefixes.FirstOrDefault(p => avatar.StartsWith(p, StringComparison.Ordinal));
         var gif = prefix?.Contains("gif", StringComparison.Ordinal) == true;
-        if (prefix is null || avatar.Length > (gif ? maxGifChars : MaxStaticChars) || avatar.Length <= prefix.Length) throw new WebDropException(ErrorCode.BadRequest);
+        if (prefix is null || avatar.Length > (gif ? maxGifChars : maxStaticChars) || avatar.Length <= prefix.Length) throw new WebDropException(ErrorCode.BadRequest);
         byte[] bytes;
         try { bytes = Convert.FromBase64String(avatar[prefix.Length..]); }
         catch (FormatException) { throw new WebDropException(ErrorCode.BadRequest); }