feat(api): count upload frames separately and send Retry-After when rate limited

server/src/WebDrop.Api/WebDropApp.cs

@@ -68,7 +68,7 @@ public static class WebDropApp
                     "X-WD-Role", "X-WD-Endpoint", "X-WD-Cap", "X-WD-Max-Downloads", "X-WD-Account",
                     "X-WD-Event-Id", "X-WD-Event-Kind", "X-WD-Event-Channel", "X-WD-Event-Domain",
                     "X-WD-Event-Epoch", "X-WD-Event-Frames", "X-WD-Event-Manifest", "X-WD-Event-Signature", "X-WD-Event-Target")
-                .WithExposedHeaders("X-WD-Last-Seq")
+                .WithExposedHeaders("X-WD-Last-Seq", "Retry-After")
                 .SetPreflightMaxAge(TimeSpan.FromHours(1))));
         }
 
@@ -76,13 +76,17 @@ public static class WebDropApp
         {
             r.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
             // 限流状态只在内存里,按 IP 分区,不落盘
-            r.GlobalLimiter = PartitionedRateLimiter.Create<HttpContext, string>(ctx =>
+            r.GlobalLimiter = PartitionedRateLimiter.Create<HttpContext, string>(ctx => IsFrameUpload(ctx.Request)
-                RateLimitPartition.GetFixedWindowLimiter(ClientKey(ctx), _ => PerMinute(options.RequestsPerMinute)));
+                ? RateLimitPartition.GetFixedWindowLimiter("frames:" + ClientKey(ctx), _ => PerMinute(options.FrameRequestsPerMinute))
+                : RateLimitPartition.GetFixedWindowLimiter(ClientKey(ctx), _ => PerMinute(options.RequestsPerMinute)));
             r.AddPolicy(Endpoints.CreatePolicy, ctx =>
                 RateLimitPartition.GetFixedWindowLimiter(ClientKey(ctx), _ => PerMinute(options.ChannelCreatesPerMinute)));
             r.OnRejected = async (context, ct) =>
             {
                 context.HttpContext.Response.StatusCode = StatusCodes.Status429TooManyRequests;
+                // 告诉客户端多久后窗口重置,弱网和上传重试据此等待,不再盲目重试
+                if (context.Lease.TryGetMetadata(MetadataName.RetryAfter, out var retryAfter))
+                    context.HttpContext.Response.Headers.RetryAfter = Math.Max(1, (int)Math.Ceiling(retryAfter.TotalSeconds)).ToString(System.Globalization.CultureInfo.InvariantCulture);
                 await context.HttpContext.Response.WriteAsJsonAsync(
                     new ErrorBody { Error = ErrorCode.RateLimited.ToWire() }, ApiJson.Default.ErrorBody, cancellationToken: ct);
             };
@@ -134,6 +138,9 @@ public static class WebDropApp
         }
     }
 
+    private static bool IsFrameUpload(HttpRequest request) =>
+        HttpMethods.IsPost(request.Method) && request.Path.Value is { } path && path.EndsWith("/frames", StringComparison.Ordinal);
+
     private static string ClientKey(HttpContext ctx) => ctx.Connection.RemoteIpAddress?.ToString() ?? "unknown";
 
     private static FixedWindowRateLimiterOptions PerMinute(int permits) => new()

server/src/WebDrop.Api/WebDropOptions.cs

@@ -21,6 +21,11 @@ public sealed class WebDropOptions
     public string? PasskeyRpId { get; set; }
 
     public int RequestsPerMinute { get; set; } = 600;
+    /// <summary>
+    /// 上传帧(POST .../frames)单独计数。每帧最多约 1 MiB,和普通 API 请求放在一个 600/分钟的桶里,
+    /// 持续上传速度就被锁在约 10 MiB/s;帧的总量另有空间配额和单条上限保护。
+    /// </summary>
+    public int FrameRequestsPerMinute { get; set; } = 6000;
     public int ChannelCreatesPerMinute { get; set; } = 30;
     public int ShareDraftTtlSeconds { get; set; } = 86_400;
     public int SweepIntervalSeconds { get; set; } = 30;