Add a bind timeout. (#54)

Motivation:

In Network.framework it is possible for a bind operation to take a while
to complete if it ends up waiting for appropriate network conditions. As
a result, unlike in the POSIX case, we need to give users the ability
to configure the maximum amount of time they'd be willing to wait for a
bind call to succeed.

Modifications:

- Add a bind timeout.

Result:

Users won't have to wait forever.

Sources/NIOTransportServices/NIOTSErrors.swift

@@ -57,5 +57,15 @@ public enum NIOTSErrors {
     /// `UnableToResolveEndpoint` is thrown when an attempt is made to resolve a local endpoint, but
     /// insufficient information is available to create it.
     public struct UnableToResolveEndpoint: NIOTSError { }
+
+    /// `BindTimeout` is thrown when a timeout set for a `NWListenerBootstrap.bind` call has been exceeded
+    /// without successfully binding the address.
+    public struct BindTimeout: NIOTSError {
+        public var timeout: TimeAmount
+
+        public init(timeout: TimeAmount) {
+            self.timeout = timeout
+        }
+    }
 }
 #endif

Sources/NIOTransportServices/NIOTSListenerBootstrap.swift

@@ -31,6 +31,7 @@ public final class NIOTSListenerBootstrap {
     private var childQoS: DispatchQoS?
     private var tcpOptions: NWProtocolTCP.Options = .init()
     private var tlsOptions: NWProtocolTLS.Options?
+    private var bindTimeout: TimeAmount?
 
     /// Create a `NIOTSListenerBootstrap` for the `EventLoopGroup` `group`.
     ///
@@ -140,6 +141,14 @@ public final class NIOTSListenerBootstrap {
         return self
     }
 
+    /// Specifies a timeout to apply to a bind attempt.
+    //
+    /// - parameters:
+    ///     - timeout: The timeout that will apply to the bind attempt.
+    public func bindTimeout(_ timeout: TimeAmount) -> Self {
+        self.bindTimeout = timeout
+        return self
+    }
 
     /// Specifies a QoS to use for the server channel, instead of the default QoS for the
     /// event loop.
@@ -186,18 +195,16 @@ public final class NIOTSListenerBootstrap {
     ///     - host: The host to bind on.
     ///     - port: The port to bind on.
     public func bind(host: String, port: Int) -> EventLoopFuture<Channel> {
-        return self.bind0 { channel in
-            let p: EventLoopPromise<Void> = channel.eventLoop.makePromise()
+        return self.bind0 { (channel, promise) in
             do {
                 // NWListener does not actually resolve hostname-based NWEndpoints
                 // for use with requiredLocalEndpoint, so we fall back to
                 // SocketAddress for this.
                 let address = try SocketAddress.makeAddressResolvingHost(host, port: port)
-                channel.bind(to: address, promise: p)
+                channel.bind(to: address, promise: promise)
             } catch {
-                p.fail(error)
+                promise.fail(error)
             }
-            return p.futureResult
         }
     }
 
@@ -206,8 +213,8 @@ public final class NIOTSListenerBootstrap {
     /// - parameters:
     ///     - address: The `SocketAddress` to bind on.
     public func bind(to address: SocketAddress) -> EventLoopFuture<Channel> {
-        return self.bind0 { channel in
-            channel.bind(to: address)
+        return self.bind0 { (channel, promise) in
+            channel.bind(to: address, promise: promise)
         }
     }
 
@@ -216,15 +223,13 @@ public final class NIOTSListenerBootstrap {
     /// - parameters:
     ///     - unixDomainSocketPath: The _Unix domain socket_ path to bind to. `unixDomainSocketPath` must not exist, it will be created by the system.
     public func bind(unixDomainSocketPath: String) -> EventLoopFuture<Channel> {
-        return self.bind0 { channel in
-            let p: EventLoopPromise<Void> = channel.eventLoop.makePromise()
+        return self.bind0 { (channel, promise) in
             do {
                 let address = try SocketAddress(unixDomainSocketPath: unixDomainSocketPath)
-                channel.bind(to: address, promise: p)
+                channel.bind(to: address, promise: promise)
             } catch {
-                p.fail(error)
+                promise.fail(error)
             }
-            return p.futureResult
         }
     }
 
@@ -233,12 +238,12 @@ public final class NIOTSListenerBootstrap {
     /// - parameters:
     ///     - endpoint: The `NWEndpoint` to bind this channel to.
     public func bind(endpoint: NWEndpoint) -> EventLoopFuture<Channel> {
-        return self.bind0 { channel in
-            channel.triggerUserOutboundEvent(NIOTSNetworkEvents.BindToNWEndpoint(endpoint: endpoint))
+        return self.bind0 { (channel, promise) in
+            channel.triggerUserOutboundEvent(NIOTSNetworkEvents.BindToNWEndpoint(endpoint: endpoint), promise: promise)
         }
     }
 
-    private func bind0(_ binder: @escaping (Channel) -> EventLoopFuture<Void>) -> EventLoopFuture<Channel> {
+    private func bind0(_ binder: @escaping (Channel, EventLoopPromise<Void>) -> Void) -> EventLoopFuture<Channel> {
         let eventLoop = self.group.next() as! NIOTSEventLoop
         let serverChannelInit = self.serverChannelInit ?? { _ in eventLoop.makeSucceededFuture(()) }
         let childChannelInit = self.childChannelInit
@@ -263,7 +268,20 @@ public final class NIOTSListenerBootstrap {
             }.flatMap {
                 serverChannel.register()
             }.flatMap {
-                binder(serverChannel)
+                let bindPromise = eventLoop.makePromise(of: Void.self)
+                binder(serverChannel, bindPromise)
+
+                if let bindTimeout = self.bindTimeout {
+                    let cancelTask = eventLoop.scheduleTask(in: bindTimeout) {
+                        bindPromise.fail(NIOTSErrors.BindTimeout(timeout: bindTimeout))
+                        serverChannel.close(promise: nil)
+                    }
+
+                    bindPromise.futureResult.whenComplete { (_: Result<Void, Error>) in
+                        cancelTask.cancel()
+                    }
+                }
+                return bindPromise.futureResult
             }.map {
                 serverChannel as Channel
             }.flatMapError { error in

Tests/NIOTransportServicesTests/NIOTSListenerChannelTests.swift

@@ -259,5 +259,21 @@ class NIOTSListenerChannelTests: XCTestCase {
         XCTAssertEqual(promisedChannel.remoteAddress, connection.localAddress)
         XCTAssertEqual(promisedChannel.localAddress, connection.remoteAddress)
     }
+
+    func testBindTimeout() throws {
+        // Testing the bind timeout is damn fiddly, because I don't know a reliable way to force it
+        // to happen. The best approach I can think of is to set the timeout to "now".
+        // If you see this test fail, verify that it isn't a simple timing issue first.
+        let listener = NIOTSListenerBootstrap(group: self.group)
+            .bindTimeout(.nanoseconds(0))
+
+        do {
+            let channel = try listener.bind(host: "localhost", port: 0).wait()
+            XCTAssertNoThrow(try channel.close().wait())
+            XCTFail("Did not throw")
+        } catch {
+            XCTAssertEqual(error as? NIOTSErrors.BindTimeout, NIOTSErrors.BindTimeout(timeout: .nanoseconds(0)), "unexpected error: \(error)")
+        }
+    }
 }
 #endif