Allow retrieval of metadata from `NWConnection` (#163)

* Allow retrieval of metadata for a specific protocol from the underlying `NWConnection`

* Address review comments

* Address review comment

* Add availability annotation to tests

* Rename `NIOTSChannelIsNotATransportServicesChannel ` to `NIOTSChannelIsNotANIOTSConnectionChannel `

Sources/NIOTransportServices/NIOTSConnectionChannel.swift

@@ -893,4 +893,61 @@ extension NIOTSConnectionChannel {
         return SynchronousOptions(channel: self)
     }
 }
+
+
+public struct NIOTSConnectionNotInitialized: Error, Hashable {
+    public init() {}
+}
+
+public struct NIOTSChannelIsNotANIOTSConnectionChannel: Error, Hashable {
+    public init() {}
+}
+
+@available(OSX 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *)
+extension NIOTSConnectionChannel {
+    fileprivate func metadata(definition: NWProtocolDefinition) throws -> NWProtocolMetadata? {
+        guard let nwConnection = self.nwConnection else {
+            throw NIOTSConnectionNotInitialized()
+        }
+        return nwConnection.metadata(definition: definition)
+    }
+}
+
+@available(OSX 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *)
+extension Channel {
+    /// Retrieves the metadata for a specific protocol from the underlying ``NWConnection``
+    /// - Throws: If `self` isn't a `NIOTS` channel with a `NWConnection` this method will throw
+    /// ``NIOTSChannelIsNotATransportServicesChannel`` or ``NIOTSConnectionNotInitialized``.
+    public func getMetadata(definition: NWProtocolDefinition) -> EventLoopFuture<NWProtocolMetadata?> {
+        guard let channel = self as? NIOTSConnectionChannel else {
+            return self.eventLoop.makeFailedFuture(NIOTSChannelIsNotANIOTSConnectionChannel())
+        }
+        if self.eventLoop.inEventLoop {
+            return self.eventLoop.makeCompletedFuture {
+                try channel.metadata(definition: definition)
+            }
+        } else {
+            return self.eventLoop.submit {
+                try channel.metadata(definition: definition)
+            }
+        }
+    }
+    
+    /// Retrieves the metadata for a specific protocol from the underlying ``NWConnection``
+    /// - Precondition: Must be called on the `EventLoop` the `Channel` is running on.
+    /// - Throws: If `self` isn't a `NIOTS` channel with a `NWConnection` this method will throw
+    /// ``NIOTSChannelIsNotATransportServicesChannel`` or ``NIOTSConnectionNotInitialized``.
+    public func getMetadataSync(
+        definition: NWProtocolDefinition,
+        file: StaticString = #fileID,
+        line: UInt = #line
+    ) throws -> NWProtocolMetadata? {
+        self.eventLoop.preconditionInEventLoop(file: file, line: line)
+        guard let channel = self as? NIOTSConnectionChannel else {
+            throw NIOTSChannelIsNotANIOTSConnectionChannel()
+        }
+        return try channel.metadata(definition: definition)
+    }
+}
+
 #endif

Tests/NIOTransportServicesTests/NIOTSBootstrapTests.swift

@@ -173,6 +173,7 @@ final class NIOTSBootstrapTests: XCTestCase {
             XCTFail("can't connect to server1")
             return
         }
+        XCTAssertNotNil(try client1.getMetadata(definition: NWProtocolTCP.definition).wait() as? NWProtocolTCP.Metadata)
         XCTAssertNoThrow(try client1.writeAndFlush(buffer).wait())
 
         // The TLS connection won't actually succeed but it takes Network.framework a while to tell us, we don't

Tests/NIOTransportServicesTests/NIOTSChannelMetadataTests.swift

@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#if canImport(Network)
+import Network
+import NIOCore
+import XCTest
+@testable import NIOTransportServices
+
+@available(OSX 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *)
+final class NIOTSChannelMetadataTests: XCTestCase {
+    func testThrowsIfCalledOnWrongChannel() throws {
+        let eventLoopGroup = NIOTSEventLoopGroup()
+        defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
+        let listenerBootsrap = NIOTSListenerBootstrap(group: eventLoopGroup)
+        let listenerChannel = try listenerBootsrap.bind(host: "localhost", port: 0).wait()
+        defer { XCTAssertNoThrow(try listenerChannel.close().wait()) }
+        
+        XCTAssertThrowsError(try listenerChannel.getMetadata(definition: NWProtocolTLS.definition).wait()) { error in
+            XCTAssertTrue(error is NIOTSChannelIsNotANIOTSConnectionChannel, "unexpected error \(error)")
+        }
+        try! listenerChannel.eventLoop.submit {
+            XCTAssertThrowsError(try listenerChannel.getMetadataSync(definition: NWProtocolTLS.definition)) { error in
+                XCTAssertTrue(error is NIOTSChannelIsNotANIOTSConnectionChannel, "unexpected error \(error)")
+            }
+        }.wait()
+        
+    }
+    func testThowsIfCalledOnANonInitializedChannel() {
+        let eventLoopGroup = NIOTSEventLoopGroup()
+        defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
+        let channel = NIOTSConnectionChannel(eventLoop: eventLoopGroup.next() as! NIOTSEventLoop, tcpOptions: .init(), tlsOptions: .init())
+        XCTAssertThrowsError(try channel.getMetadata(definition: NWProtocolTLS.definition).wait()) { error in
+            XCTAssertTrue(error is NIOTSConnectionNotInitialized, "unexpected error \(error)")
+        }
+        try! channel.eventLoop.submit {
+            XCTAssertThrowsError(try channel.getMetadataSync(definition: NWProtocolTLS.definition)) { error in
+                XCTAssertTrue(error is NIOTSConnectionNotInitialized, "unexpected error \(error)")
+            }
+        }.wait()
+    }
+}
+#endif