Bootstrap: test that returning futures from foreign ELs are okay (#55)

Motivation:

NIO on BSD Sockets had an issue where it wouldn't tolerate futures from
foreign EventLoops being returned from the channel initializers. NIOTS
should also have a test that tests this situation despite the fact that
it didn't have the same bug.

Modification:

- add a test case
- add more assertions

Result:

Better tests.

Sources/NIOTransportServices/NIOTSConnectionBootstrap.swift

@@ -173,7 +173,8 @@ public final class NIOTSConnectionBootstrap {
             return channelOptions.applyAllChannelOptions(to: conn).flatMap {
                 initializer(conn)
             }.flatMap {
-                conn.register()
+                conn.eventLoop.assertInEventLoop()
+                return conn.register()
             }.flatMap {
                 let connectPromise: EventLoopPromise<Void> = conn.eventLoop.makePromise()
                 connectAction(conn, connectPromise)

Sources/NIOTransportServices/NIOTSListenerBootstrap.swift

@@ -263,7 +263,8 @@ public final class NIOTSListenerBootstrap {
             return serverChannelOptions.applyAllChannelOptions(to: serverChannel).flatMap {
                 serverChannelInit(serverChannel)
             }.flatMap {
-                serverChannel.pipeline.addHandler(AcceptHandler(childChannelInitializer: childChannelInit,
+                eventLoop.assertInEventLoop()
+                return serverChannel.pipeline.addHandler(AcceptHandler(childChannelInitializer: childChannelInit,
                                                                        childChannelOptions: childChannelOptions))
             }.flatMap {
                 serverChannel.register()

Tests/NIOTransportServicesTests/NIOTSBootstrapTests.swift

@@ -0,0 +1,109 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2019 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
+// swift-tools-version:4.0
+//
+// swift-tools-version:4.0
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#if canImport(Network)
+import XCTest
+import Network
+import NIO
+import NIOTransportServices
+import NIOConcurrencyHelpers
+import Foundation
+
+@available(OSX 10.14, iOS 12.0, tvOS 12.0, *)
+final class NIOTSBootstrapTests: XCTestCase {
+    var groupBag: [NIOTSEventLoopGroup]? = nil // protected by `self.lock`
+    let lock = Lock()
+
+    override func setUp() {
+        self.lock.withLock {
+            XCTAssertNil(self.groupBag)
+            self.groupBag = []
+        }
+    }
+
+    override func tearDown() {
+        XCTAssertNoThrow(try self.lock.withLock {
+            guard let groupBag = self.groupBag else {
+                XCTFail()
+                return
+            }
+            XCTAssertNoThrow(try groupBag.forEach {
+                XCTAssertNoThrow(try $0.syncShutdownGracefully())
+            })
+            self.groupBag = nil
+        })
+    }
+
+    func freshEventLoop() -> EventLoop {
+        let group: NIOTSEventLoopGroup = .init(loopCount: 1, defaultQoS: .default)
+        self.lock.withLock {
+            self.groupBag!.append(group)
+        }
+        return group.next()
+    }
+
+    func testBootstrapsTolerateFuturesFromDifferentEventLoopsReturnedInInitializers() throws {
+        let childChannelDone = self.freshEventLoop().makePromise(of: Void.self)
+        let serverChannelDone = self.freshEventLoop().makePromise(of: Void.self)
+        let serverChannel = try assertNoThrowWithValue(NIOTSListenerBootstrap(group: self.freshEventLoop())
+            .childChannelInitializer { channel in
+                channel.eventLoop.preconditionInEventLoop()
+                defer {
+                    childChannelDone.succeed(())
+                }
+                return self.freshEventLoop().makeSucceededFuture(())
+            }
+            .serverChannelInitializer { channel in
+                channel.eventLoop.preconditionInEventLoop()
+                defer {
+                    serverChannelDone.succeed(())
+                }
+                return self.freshEventLoop().makeSucceededFuture(())
+            }
+            .bind(host: "127.0.0.1", port: 0)
+            .wait())
+        defer {
+            XCTAssertNoThrow(try serverChannel.close().wait())
+        }
+
+        let client = try assertNoThrowWithValue(NIOTSConnectionBootstrap(group: self.freshEventLoop())
+            .channelInitializer { channel in
+                channel.eventLoop.preconditionInEventLoop()
+                return self.freshEventLoop().makeSucceededFuture(())
+            }
+            .connect(to: serverChannel.localAddress!)
+            .wait())
+        defer {
+            XCTAssertNoThrow(try client.syncCloseAcceptingAlreadyClosed())
+        }
+        XCTAssertNoThrow(try childChannelDone.futureResult.wait())
+        XCTAssertNoThrow(try serverChannelDone.futureResult.wait())
+    }
+}
+
+extension Channel {
+    func syncCloseAcceptingAlreadyClosed() throws {
+        do {
+            try self.close().wait()
+        } catch ChannelError.alreadyClosed {
+            /* we're happy with this one */
+        } catch let e {
+            throw e
+        }
+    }
+}
+
+#endif