Update BackpressureMiddlerware to use RedisClient

Author: finestructure

Sources/App/Core/BackpressureMiddleware.swift

@@ -0,0 +1,60 @@
+// Copyright Dave Verwer, Sven A. Schmidt, and other contributors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Dependencies
+import Redis
+import Vapor
+
+
+final class BackpressureMiddleware: AsyncMiddleware {
+
+    let slidingWindow: Duration
+    let countLimit: Int
+
+    public func respond(to request: Request, chainingTo next: AsyncResponder) async throws -> Response {
+        guard let cfray = request.headers.first(name: "cf-ray") else {
+            return try await next.respond(to: request)
+        }
+        let epochSeconds = Int(Date().timeIntervalSince1970)
+        let combinedKey = "\(cfray):\(epochSeconds)"
+
+        let slidingWindow = Int(slidingWindow.components.seconds)
+
+        @Dependency(\.redis) var redis
+
+        guard var countOverWindow = try? await redis.increment(key: combinedKey) else {
+            request.logger.log(level: .warning, "BackpressureMiddleware failed to increment key '\(combinedKey)'.")
+            return try await next.respond(to: request)
+        }
+
+        for i in epochSeconds - slidingWindow ..< epochSeconds {
+            let key = "\(cfray):\(i)"
+            if let value = (try? await redis.get(key)).flatMap(Int.init) {
+                countOverWindow += value
+            }
+        }
+
+        if countOverWindow >= countLimit {
+            request.logger.log(level: .warning, "BackpressureMiddleware acting on request with cf-ray '\(cfray)' due to \(countOverWindow) requests in the last \(slidingWindow) seconds.")
+            throw Abort(.tooManyRequests)
+        } else {
+            return try await next.respond(to: request)
+        }
+    }
+
+    init(slidingWindow: Duration, countLimit: Int) {
+        self.slidingWindow = slidingWindow
+        self.countLimit = countLimit
+    }
+}