Add public API to send an unsolicited pong message (#28)

Sources/HummingbirdWSCore/WebSocket.swift

@@ -133,6 +133,17 @@ public final class HBWebSocket {
         }
     }
 
+    /// Send an unsolicited Pong message
+    ///
+    /// This can be used as a unidirectional heartbeat.
+    /// See [RFC6455](https://www.rfc-editor.org/rfc/rfc6455.html#section-5.5.3)
+    /// - Parameter promise: promise that is completed when pong message has been sent
+    public func sendPong(_ buffer: ByteBuffer, promise: EventLoopPromise<Void>?) {
+        self.channel.eventLoop.execute {
+            self.send(buffer: buffer, opcode: .pong)
+        }
+    }
+
     /// Send ping and setup task to check for pong and send new ping
     public func initiateAutoPing(interval: TimeAmount) {
         guard self.channel.isActive else {

Tests/HummingbirdWebSocketTests/WebSocketTests.swift

@@ -346,6 +346,24 @@ final class HummingbirdWebSocketTests: XCTestCase {
         try promise.wait()
     }
 
+    func testUnsolicitedPong() throws {
+        let promise = TimeoutPromise(eventLoop: Self.eventLoopGroup.next(), timeout: .seconds(10))
+
+        let app = try self.setupClientAndServer(
+            onServer: { ws in
+                ws.onPong { _ in
+                    promise.succeed()
+                }
+            },
+            onClient: { ws in
+                ws.sendPong(.init(), promise: nil)
+            }
+        )
+        defer { app.stop() }
+
+        try promise.wait()
+    }
+
     func testQuery() throws {
         let app = HBApplication(configuration: .init(address: .hostname(port: 8080)))
         // add HTTP to WebSocket upgrade