WebSockets Serving

This example illustrates how to set up a WebSocket server and handle a connection.

To use the example with Swift Package Manager, type swift build and then run .build/debug/WebSocketsServer.

To use the example with Xcode, run the WebSockets Server target. This will launch the Perfect HTTP Server.

Navigate in your web browser to http://localhost:8181/

Initiating a WebSocket Session

Add one or more URL routes using the Routing.Routes subscript functions. These routes will be the endpoints for the WebSocket session. Set the route handler to WebSocketHandler and provide your custom closure which will return your own session handler.

The following code is taken from the example project and shows how to enable the system and add a WebSocket handler.

func addWebSocketsHandler() {
    
    // Add a default route which lets us serve the static index.html file
    Routing.Routes["*"] = { request, response in StaticFileHandler().handleRequest(request: request, response: response) }
    
    // Add the endpoint for the WebSocket example system
    Routing.Routes[.Get, "/echo"] = {
        request, response in
        
        // To add a WebSocket service, set the handler to WebSocketHandler.
        // Provide your closure which will return your service handler.
        WebSocketHandler(handlerProducer: {
            (request: WebRequest, protocols: [String]) -> WebSocketSessionHandler? in
            
            // Check to make sure the client is requesting our "echo" service.
            guard protocols.contains("echo") else {
                return nil
            }
            
            // Return our service handler.
            return EchoHandler()
        }).handleRequest(request: request, response: response)
    }
}

Handling WebSocket Sessions

A WebSocket service handler must impliment the WebSocketSessionHandler protocol. This protocol requires the function handleSession(request: WebRequest, socket: WebSocket). This function will be called once the WebSocket connection has been established, at which point it is safe to begin reading and writing messages.

The initial WebRequest object which instigated the session is provided for reference. Messages are transmitted through the provided WebSocket object. Call WebSocket.sendStringMessage or WebSocket.sendBinaryMessage to send data to the client. Call WebSocket.readStringMessage or WebSocket.readBinaryMessage to read data from the client. By default, reading will block indefinitely until a message arrives or a network error occurs. A read timeout can be set with WebSocket.readTimeoutSeconds. When the session is over call WebSocket.close().

The example EchoHandler consists of the following.

class EchoHandler: WebSocketSessionHandler {
	
	// The name of the super-protocol we implement.
	// This is optional, but it should match whatever the client-side WebSocket is initialized with.
	let socketProtocol: String? = "echo"
	
	// This function is called by the WebSocketHandler once the connection has been established.
	func handleSession(request: WebRequest, socket: WebSocket) {
		
		// Read a message from the client as a String.
		// Alternatively we could call `WebSocket.readBytesMessage` to get the data as a String.
		socket.readStringMessage {
			// This callback is provided:
			//	the received data
			//	the message's op-code
			//	a boolean indicating if the message is complete (as opposed to fragmented)
			string, op, fin in
			
			// The data parameter might be nil here if either a timeout or a network error, such as the client disconnecting, occurred.
			// By default there is no timeout.
			guard let string = string else {
				// This block will be executed if, for example, the browser window is closed.
				socket.close()
				return
			}
			
			// Print some information to the console for informational purposes.
			print("Read msg: \(string) op: \(op) fin: \(fin)")
			
			// Echo the data we received back to the client.
			// Pass true for final. This will usually be the case, but WebSockets has the concept of fragmented messages.
			// For example, if one were streaming a large file such as a video, one would pass false for final.
			// This indicates to the receiver that there is more data to come in subsequent messages but that all the data is part of the same logical message.
			// In such a scenario one would pass true for final only on the last bit of the video.
			socket.sendStringMessage(string, final: true) {
				
				// This callback is called once the message has been sent.
				// Recurse to read and echo new message.
				self.handleSession(request, socket: socket)
			}
		}
	}
}

FastCGI Caveat

WebSockets serving is only supported with the stand-alone Perfect HTTP server. At this time, the WebSocket server does not operate with the Perfect FastCGI server.