Add a request waiter box for the connection pool (#397)

Author: fabianfett

Diff for: Sources/AsyncHTTPClient/ConnectionPool/HTTPConnectionPool+Waiter.swift

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 RequestID: Hashable {
+        private let objectIdentifier: ObjectIdentifier
+
+        init(_ request: HTTPScheduledRequest) {
+            self.objectIdentifier = ObjectIdentifier(request)
+        }
+    }
+
+    struct Waiter {
+        var requestID: RequestID {
+            RequestID(self.request)
+        }
+
+        var request: HTTPScheduledRequest
+
+        private var eventLoopRequirement: EventLoop? {
+            switch self.request.eventLoopPreference.preference {
+            case .delegateAndChannel(on: let eventLoop),
+                 .testOnly_exact(channelOn: let eventLoop, delegateOn: _):
+                return eventLoop
+            case .delegate(on: _),
+                 .indifferent:
+                return nil
+            }
+        }
+
+        init(request: HTTPScheduledRequest) {
+            self.request = request
+        }
+
+        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
+        }
+    }
+}

Diff for: Tests/AsyncHTTPClientTests/HTTPConnectionPool+WaiterTests+XCTest.swift

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2018-2019 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
+//
+//===----------------------------------------------------------------------===//
+//
+// HTTPConnectionPool+WaiterTests+XCTest.swift
+//
+import XCTest
+
+///
+/// NOTE: This file was generated by generate_linux_tests.rb
+///
+/// Do NOT edit this file directly as it will be regenerated automatically when needed.
+///
+
+extension HTTPConnectionPool_WaiterTests {
+    static var allTests: [(String, (HTTPConnectionPool_WaiterTests) -> () throws -> Void)] {
+        return [
+            ("testCanBeRunIfEventLoopIsSpecified", testCanBeRunIfEventLoopIsSpecified),
+            ("testCanBeRunIfNoEventLoopIsSpecified", testCanBeRunIfNoEventLoopIsSpecified),
+        ]
+    }
+}

Diff for: Tests/AsyncHTTPClientTests/HTTPConnectionPool+WaiterTests.swift

@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 mockRequest = MockScheduledRequest(eventLoopPreference: .init(.testOnly_exact(channelOn: theRightEL, delegateOn: theFalseEL)))
+
+        let waiter = HTTPConnectionPool.Waiter(request: mockRequest)
+
+        XCTAssertTrue(waiter.canBeRun(on: theRightEL))
+        XCTAssertFalse(waiter.canBeRun(on: theFalseEL))
+    }
+
+    func testCanBeRunIfNoEventLoopIsSpecified() {
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 2)
+
+        let mockRequest = MockScheduledRequest(eventLoopPreference: .indifferent)
+        let waiter = HTTPConnectionPool.Waiter(request: mockRequest)
+
+        for el in eventLoopGroup.makeIterator() {
+            XCTAssertTrue(waiter.canBeRun(on: el))
+        }
+    }
+}
+
+private class MockScheduledRequest: HTTPScheduledRequest {
+    init(eventLoopPreference: HTTPClient.EventLoopPreference) {
+        self.eventLoopPreference = eventLoopPreference
+    }
+
+    var logger: Logger { preconditionFailure("Unimplemented") }
+    var connectionDeadline: NIODeadline { preconditionFailure("Unimplemented") }
+    let eventLoopPreference: HTTPClient.EventLoopPreference
+
+    func requestWasQueued(_: HTTPRequestScheduler) {
+        preconditionFailure("Unimplemented")
+    }
+
+    func fail(_: Error) {
+        preconditionFailure("Unimplemented")
+    }
+}

Diff for: Tests/LinuxMain.swift

@@ -36,6 +36,7 @@ import XCTest
         testCase(HTTPClientSOCKSTests.allTests),
         testCase(HTTPClientTests.allTests),
         testCase(HTTPConnectionPool_FactoryTests.allTests),
+        testCase(HTTPConnectionPool_WaiterTests.allTests),
         testCase(HTTPRequestStateMachineTests.allTests),
         testCase(LRUCacheTests.allTests),
         testCase(RequestBagTests.allTests),