NSNetService doesn't contain any addresses

Question

I'm hosting a service in a Mac application and connecting with an iOS app. While the iOS app will find the service, the service doesn't contain any addresses, so I can't connect a socket.

This is my hosting code on the Mac:

- (void)start {

    queue = dispatch_queue_create("KeyboardServer", DISPATCH_QUEUE_CONCURRENT);

    socket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:queue];

    NSError *error = nil;

    if ([socket acceptOnPort:0 error:&error]) {

        service = [[NSNetService alloc] initWithDomain:@"local." type:@"_probonjore._tcp." name:@"TestServer" port:[socket localPort]];

        service.delegate = self;

        [service publish];

    } else {
        NSLog(@"Unable to create server");
    }
}

This is the connecting code on iOS:

- (BOOL)connectToServer:(NSNetService *)service {

    NSArray *addresses = service.addresses;

    socket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:queue];

    for (NSData *address in addresses) {

        NSError *error;

        if ([socket connectToAddress:address error:&error]) {
            NSLog(@"Socket connected!");

            return true;
        }
    }

    return false;
}

The problem is, service.addresses is always empty and the loop instantly exits.

Is there any way to have it automatically choose a port, or do I just have to pick one at random and hope it won't be taken already? — Lepidora, Mar 23 '19 at 20:01
I just checked and the socket library (GCDAsyncSocket) automatically picks a port if you pass it 0. The service is publishing on port 51417 last time I ran it. — Lepidora, Mar 23 '19 at 20:05

score 2 · Answer 1 · answered Mar 24 '19 at 21:24

For anyone curious, I searched around and found a solution.

In the

- (void)netServiceBrowser:(NSNetServiceBrowser *)browser didFindService:(NSNetService *)service moreComing:(BOOL)moreComing

function, you need to:

Add the service to an array to stop the object being deallocated as soon as it goes out of scope
Set the delegate on the object so that you can respond to its address resolution
Call the function to make it resolve

Which looks like this:

- (void)netServiceBrowser:(NSNetServiceBrowser *)browser didFindService:(NSNetService *)service moreComing:(BOOL)moreComing {

    NSLog(@"Found Service %@", [service name]);

    [services addObject:service];

    [service setDelegate:self];

    [service resolveWithTimeout:5.0f];
}

You then want to implement

- (void)netService:(NSNetService *)sender didNotResolve:(NSDictionary *)errorDict

and

- (void)netServiceDidResolveAddress:(NSNetService *)service

To catch when the address either resolves or doesn't resolve.

NSNetService doesn't contain any addresses

1 Answers1