refactor progress

packages/api/src/middleware/ConcurrencyLimitMiddleware.tsx

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {Logger} from '@fluxer/api/src/Logger';
+import {recordCounter} from '@fluxer/telemetry/src/Metrics';
+import type {MiddlewareHandler} from 'hono';
+
+const MAX_CONCURRENT_REQUESTS = 500;
+const SKIP_PATHS = new Set(['/_health', '/internal/telemetry']);
+
+let inFlightRequests = 0;
+
+export const ConcurrencyLimitMiddleware: MiddlewareHandler = async (ctx, next) => {
+	if (SKIP_PATHS.has(ctx.req.path)) {
+		await next();
+		return;
+	}
+
+	if (inFlightRequests >= MAX_CONCURRENT_REQUESTS) {
+		recordCounter({name: 'api.concurrency_limit.rejected'});
+		Logger.warn(
+			{inFlightRequests, max: MAX_CONCURRENT_REQUESTS},
+			'[concurrency-limit] Rejecting request, server at capacity',
+		);
+		ctx.header('Retry-After', '5');
+		ctx.status(503);
+		ctx.res = ctx.json({message: 'Server is at capacity, please retry shortly'}, 503);
+		return;
+	}
+
+	inFlightRequests += 1;
+	try {
+		await next();
+	} finally {
+		inFlightRequests -= 1;
+	}
+};