How do I upgrade nw_connection to a websocket connection?

it is failing to upgrade the connection status and throwing an error.

It’s hard to offer insight into that without knowing what the error is. Regardless, here’s a simple WebSocket client in C:

@import Foundation;
@import Network;

int main(int argc, char **argv) {
    #pragma unused(argc)
    #pragma unused(argv)

    NSLog(@"will start");

    nw_endpoint_t endpoint = nw_endpoint_create_url("ws://127.0.0.1:12345/test");
    nw_parameters_t params = nw_parameters_create_secure_tcp(NW_PARAMETERS_DISABLE_PROTOCOL, NW_PARAMETERS_DEFAULT_CONFIGURATION);
    nw_protocol_stack_t stack = nw_parameters_copy_default_protocol_stack(params);
    nw_protocol_options_t ws = nw_ws_create_options(nw_ws_version_13);
    nw_protocol_stack_prepend_application_protocol(stack, ws);
    nw_connection_t connection = nw_connection_create(endpoint, params);
    nw_connection_set_state_changed_handler(connection, ^(nw_connection_state_t state, nw_error_t error) {
        NSLog(@"state did change, new: %d, error: %@", (int) state, error);
    });
    nw_connection_set_queue(connection, dispatch_get_main_queue());
    nw_connection_start(connection);
    
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, 1000 * NSEC_PER_MSEC), 1000 * NSEC_PER_MSEC, 500 * NSEC_PER_MSEC);
    dispatch_source_set_event_handler(timer, ^{
        NSLog(@"will send");
        NSString * message = [NSString stringWithFormat:@"Hello Cruel World %@", [NSDate date]];
        const char * messageC = message.UTF8String;
        dispatch_data_t content = dispatch_data_create(messageC, strlen(messageC), dispatch_get_main_queue(), DISPATCH_DATA_DESTRUCTOR_DEFAULT);
        
        nw_protocol_metadata_t metadata = nw_ws_create_metadata(nw_ws_opcode_text);
        nw_content_context_t context = nw_content_context_create("send");
        nw_content_context_set_metadata_for_protocol(context, metadata);
        
        nw_connection_send(connection, content, context, true, ^(nw_error_t error) {
            NSLog(@"did send, error: %@", error);
        });
    });
    dispatch_activate(timer);
    
    dispatch_main();

    return EXIT_SUCCESS;
}

Annoyingly, my go-to WebSocket test site, websocket.org, is no longer available so I ended up creating a simple server to match. That code is pasted in below.

If anyone has an alternative WebSocket test site, please post the details here. My code here only tests the Mac-to-Mac case, and I’ve been bitten by stuff like that before (for example, back in the day, certain Secure Transport features would work Mac-to-Mac but fail with third-party TLS stacks; or was it the other way around? :-).

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

@import Foundation;
@import Network;

static void startReceive(nw_connection_t connection) {
    nw_connection_receive(connection, 1, 65536, ^(dispatch_data_t content, nw_content_context_t context, bool isComplete, nw_error_t error) {
        #pragma unused(context)
        #pragma unused(isComplete)
        if (error != NULL) {
            NSLog(@"connection receive did fail, error: %@", error);
            return;
        }
        if (content != NULL) {
            size_t size = dispatch_data_get_size(content);
            NSLog(@"connection did receive content, size: %zu", size);
        }
        startReceive(connection);
    });
}

int main(int argc, char **argv) {
    #pragma unused(argc)
    #pragma unused(argv)

    NSLog(@"will start");
    
    NSMutableArray * connections = [[NSMutableArray alloc] init];

    nw_parameters_t params = nw_parameters_create_secure_tcp(NW_PARAMETERS_DISABLE_PROTOCOL, NW_PARAMETERS_DEFAULT_CONFIGURATION);
    nw_protocol_stack_t stack = nw_parameters_copy_default_protocol_stack(params);
    nw_protocol_options_t ws = nw_ws_create_options(nw_ws_version_13);
    nw_protocol_stack_prepend_application_protocol(stack, ws);
    nw_endpoint_t localEndpoint = nw_endpoint_create_host("::", "12345");
    nw_parameters_set_local_endpoint(params, localEndpoint);
    nw_listener_t listener = nw_listener_create(params);
    nw_listener_set_state_changed_handler(listener, ^(nw_listener_state_t state, nw_error_t error) {
        NSLog(@"listener state did change, new: %d, error: %@", (int) state, error);
    });
    nw_listener_set_new_connection_handler(listener, ^(nw_connection_t  connection) {
        NSLog(@"listener did accept connection");
        [connections addObject:connection];
        nw_connection_set_state_changed_handler(connection, ^(nw_connection_state_t state, nw_error_t error) {
            NSLog(@"connection state did change, new: %d, error: %@", (int) state, error);
        });
        nw_connection_set_queue(connection, dispatch_get_main_queue());
        nw_connection_start(connection);
        startReceive(connection);
    });
    nw_listener_set_queue(listener, dispatch_get_main_queue());
    nw_listener_start(listener);

    dispatch_main();
}

I’m working with WebSockets today and I wanted a Swift version of the above. I ended up porting it line-for-line, so I thought I’d share it here for the benefit of others (and, most importantly, Future Quinn™ :-).

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

import Foundation
import Network

func main() {
    print("will start")

    let endpoint = NWEndpoint.url(URL(string: "ws://127.0.0.1:12345/test")!)
    let params = NWParameters.tcp
    let stack = params.defaultProtocolStack
    let ws = NWProtocolWebSocket.Options(.version13)
    stack.applicationProtocols.insert(ws, at: 0)
    let connection = NWConnection(to: endpoint, using: params)
    connection.stateUpdateHandler = { newState in
        print("state did change, new: \(newState)")
    }
    connection.start(queue: .main)
    
    let timer = DispatchSource.makeTimerSource(queue: .main)
    timer.schedule(deadline: .now() + 1.0, repeating: 1.0)
    timer.setEventHandler {
        print("will send")
        
        let message = Data("Hello Cruel World \(Date())".utf8)
        let metadata = NWProtocolWebSocket.Metadata(opcode: .text)
        let context = NWConnection.ContentContext(identifier: "send", metadata: [metadata])
        connection.send(content: message, contentContext: context, isComplete: true, completion: NWConnection.SendCompletion.contentProcessed({ error in
            print("did send, error: \(error.flatMap { "\($0)" } ?? "-")")
        }))
    }
    timer.activate()
    
    withExtendedLifetime(connection) {
        dispatchMain()
    }
}

main()
exit(EXIT_SUCCESS)

import Foundation
import Network

private func startReceive(connection: NWConnection) {
    connection.receiveMessage { content, _, _, error in
        if let error = error {
            print("connection receive did fail, error: \(error)")
            return
        }
        if let content = content {
            print("connection did receive content, count: \(content.count)")
        }
        startReceive(connection: connection)
    }
}

func main() throws {
    print("will start")

    var connections: [NWConnection] = []

    let params = NWParameters.tcp
    let stack = params.defaultProtocolStack
    let ws = NWProtocolWebSocket.Options(.version13)
    stack.applicationProtocols.insert(ws, at: 0)
    let listener = try NWListener(using: params, on: 12345)
    listener.stateUpdateHandler = { newState in
        print("listener state did change, new: \(newState)")
    }
    listener.newConnectionHandler = { connection in
        print("listener did accept connection")
        connections.append(connection)
        connection.stateUpdateHandler = { newState in
            print("connection state did change, new: \(newState)")
        }
        connection.start(queue: .main)
        startReceive(connection: connection)
    }
    listener.start(queue: .main)

    withExtendedLifetime(listener) {
        dispatchMain()
    }
}

try! main()

it corresponds to POSIX error ECONNREFUSED

That suggests a low-level connectivity problem. Notably, I’m not seeing that here in my office. Here’s what I did:

1. Using Xcode 13.2.1 on macOS 12.1, I created a new command-line tool project with the C client code from my first post (I assume you’re using C rather than Swift because you commented on my first post, not my second).

2. I changed nw_endpoint_create_url("ws://127.0.0.1:12345/test") to nw_endpoint_create_url("wss://echo.websocket.events/.ws").

3. I changed NW_PARAMETERS_DISABLE_PROTOCOL to NW_PARAMETERS_DEFAULT_CONFIGURATION, to enable TLS (my code used an ws URL, whereas your example is clearly intended to use wss and hence you need TLS).

4. I ran it. It printed:

   2022-01-14 09:39:58.488498+0000 xxot[839:6135282] will start
   2022-01-14 09:39:58.513357+0000 xxot[839:6136041] state did change, new: 2, error: (null)
   2022-01-14 09:39:58.999719+0000 xxot[839:6136043] state did change, new: 3, error: (null)
   2022-01-14 09:39:59.512637+0000 xxot[839:6136041] will send
   

As you can see, the connection went through just fine (state 3 is nw_connection_state_ready).

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"