TaggedRequestResponseHandler

Sources/NIOExtras/NIORequestIdentifiable.swift

@@ -0,0 +1,19 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2022 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+public protocol NIORequestIdentifiable {
+    associatedtype RequestID: Hashable
+
+    var requestID: RequestID { get }
+}

Sources/NIOExtras/TaggedRequestResponseHandler.swift

@@ -0,0 +1,130 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2017-2022 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import NIOCore
+
+/// `NIOTaggedRequestResponseHandler` receives a `Request` alongside an `EventLoopPromise<Response>` from the
+/// `Channel`'s outbound side. It will fulfill the promise with the `Response` once it's received from the `Channel`'s
+/// inbound side. Requests and responses can arrive out-of-order and are matched by the virtue of being
+/// `NIORequestIdentifiable`.
+///
+/// `NIOTaggedRequestResponseHandler` does support pipelining `Request`s and it will send them pipelined further down the
+/// `Channel`. Should `RequestResponseHandler` receive an error from the `Channel`, it will fail all promises meant for
+/// the outstanding `Reponse`s and close the `Channel`. All requests enqueued after an error occured will be immediately
+/// failed with the first error the channel received.
+///
+/// `NIOTaggedRequestResponseHandler` does _not_ require that the `Response`s arrive on `Channel` in the same order as
+/// the `Request`s were submitted. They are matched by their `requestID` property (from `NIORequestIdentifiable`).
+public final class NIOTaggedRequestResponseHandler<Request: NIORequestIdentifiable,
+                                                   Response: NIORequestIdentifiable>: ChannelDuplexHandler
+                                                  where Request.RequestID == Response.RequestID {
+    public typealias InboundIn = Response
+    public typealias InboundOut = Never
+    public typealias OutboundIn = (Request, EventLoopPromise<Response>)
+    public typealias OutboundOut = Request
+
+    private enum State {
+        case operational
+        case error(Error)
+
+        var isOperational: Bool {
+            switch self {
+            case .operational:
+                return true
+            case .error:
+                return false
+            }
+        }
+    }
+
+    private var state: State = .operational
+    private var promiseBuffer: [Request.RequestID: EventLoopPromise<Response>]
+
+
+    /// Create a new `RequestResponseHandler`.
+    ///
+    /// - parameters:
+    ///    - initialBufferCapacity: `RequestResponseHandler` saves the promises for all outstanding responses in a
+    ///          buffer. `initialBufferCapacity` is the initial capacity for this buffer. You usually do not need to set
+    ///          this parameter unless you intend to pipeline very deeply and don't want the buffer to resize.
+    public init(initialBufferCapacity: Int = 4) {
+        self.promiseBuffer = [:]
+        self.promiseBuffer.reserveCapacity(initialBufferCapacity)
+    }
+
+    public func channelInactive(context: ChannelHandlerContext) {
+        switch self.state {
+        case .error:
+            // We failed any outstanding promises when we entered the error state and will fail any
+            // new promises in write.
+            assert(self.promiseBuffer.count == 0)
+        case .operational:
+            let promiseBuffer = self.promiseBuffer
+            self.promiseBuffer.removeAll()
+            promiseBuffer.forEach { promise in
+                promise.value.fail(NIOExtrasErrors.ClosedBeforeReceivingResponse())
+            }
+        }
+        context.fireChannelInactive()
+    }
+
+    public func channelRead(context: ChannelHandlerContext, data: NIOAny) {
+        guard self.state.isOperational else {
+            // we're in an error state, ignore further responses
+            assert(self.promiseBuffer.count == 0)
+            return
+        }
+
+        let response = self.unwrapInboundIn(data)
+        if let promise = self.promiseBuffer.removeValue(forKey: response.requestID) {
+            promise.succeed(response)
+        } else {
+            context.fireErrorCaught(NIOExtrasErrors.ResponseForInvalidRequest<Response>(id: response.requestID))
+        }
+    }
+
+    public func errorCaught(context: ChannelHandlerContext, error: Error) {
+        guard self.state.isOperational else {
+            assert(self.promiseBuffer.count == 0)
+            return
+        }
+        self.state = .error(error)
+        let promiseBuffer = self.promiseBuffer
+        self.promiseBuffer.removeAll()
+        context.close(promise: nil)
+        promiseBuffer.forEach {
+            $0.value.fail(error)
+        }
+    }
+
+    public func write(context: ChannelHandlerContext, data: NIOAny, promise: EventLoopPromise<Void>?) {
+        let (request, responsePromise) = self.unwrapOutboundIn(data)
+        switch self.state {
+        case .error(let error):
+            assert(self.promiseBuffer.count == 0)
+            responsePromise.fail(error)
+            promise?.fail(error)
+        case .operational:
+            self.promiseBuffer[request.requestID] = responsePromise
+            context.write(self.wrapOutboundOut(request), promise: promise)
+        }
+    }
+}
+
+extension NIOExtrasErrors {
+    public struct ResponseForInvalidRequest<Response: NIORequestIdentifiable>: NIOExtrasError, Equatable {
+        var id: Response.RequestID
+    }
+}
+