Add a waiter box for the connection pool

Sources/AsyncHTTPClient/ConnectionPool/HTTPConnectionPool+Waiter.swift

@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2021 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import NIO
+
+extension HTTPConnectionPool {
+    struct Waiter {
+        struct ID: Hashable {
+            private let objectIdentifier: ObjectIdentifier
+
+            init(_ request: HTTPScheduledRequest) {
+                self.objectIdentifier = ObjectIdentifier(request)
+            }
+        }
+
+        let id: ID
+        let request: HTTPScheduledRequest
+        let eventLoopRequirement: EventLoop?
+
+        init(request: HTTPScheduledRequest, eventLoopRequirement: EventLoop?) {
+            self.id = ID(request)
+            self.request = request
+            self.eventLoopRequirement = eventLoopRequirement
+        }
+
+        func canBeRun(on option: EventLoop) -> Bool {
+            guard let requirement = self.eventLoopRequirement else {
+                // if no requirement exists we can run on any EventLoop
+                return true
+            }
+
+            return requirement === option
+        }
+    }
+}

Tests/AsyncHTTPClientTests/HTTPConnectionPool+WaiterTests.swift

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2021 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+@testable import AsyncHTTPClient
+import Logging
+import NIO
+import XCTest
+
+class HTTPConnectionPool_WaiterTests: XCTestCase {
+    func testCanBeRunIfEventLoopIsSpecified() {
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 2)
+
+        let theRightEL = eventLoopGroup.next()
+        let theFalseEL = eventLoopGroup.next()
+
+        let waiter = HTTPConnectionPool.Waiter(request: MockScheduledRequest(), eventLoopRequirement: theRightEL)
+
+        XCTAssertTrue(waiter.canBeRun(on: theRightEL))
+        XCTAssertFalse(waiter.canBeRun(on: theFalseEL))
+    }
+
+    func testCanBeRunIfNoEventLoopIsSpecified() {
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 2)
+
+        let waiter = HTTPConnectionPool.Waiter(request: MockScheduledRequest(), eventLoopRequirement: nil)
+
+        for el in eventLoopGroup.makeIterator() {
+            XCTAssertTrue(waiter.canBeRun(on: el))
+        }
+    }
+}
+
+private class MockScheduledRequest: HTTPScheduledRequest {
+    init() {}
+
+    var logger: Logger { preconditionFailure("Unimplemented") }
+    var connectionDeadline: NIODeadline { preconditionFailure("Unimplemented") }
+    var eventLoopPreference: HTTPClient.EventLoopPreference { preconditionFailure("Unimplemented") }
+
+    func requestWasQueued(_: HTTPRequestScheduler) {
+        preconditionFailure("Unimplemented")
+    }
+
+    func fail(_: Error) {
+        preconditionFailure("Unimplemented")
+    }
+}