OS X: how to watch socket read events with NSRunLoop?

Question

I'm writing a Cocoa app. There is a socket in the application, and whenever the socket becomes readable I want to read data from the socket, process the data, and update the user interface accordingly. I want to integrate the read event check in the main loop, i.e. I want to attach the socket to the main loop and have the main loop call a callback whenever that socket becomes readable.

I've written a test application, but for some reason it doesn't work:

#include <stdio.h>
#include <Foundation/NSAutoReleasePool.h>
#include <Foundation/NSRunLoop.h>
#include <Foundation/NSPort.h>

@interface MyDelegate : NSObject <NSPortDelegate> {
}
- (void)handlePortMessage:(NSPortMessage *)portMessage;
@end

@implementation MyDelegate
- (void)handlePortMessage:(NSPortMessage *)portMessage {
    printf("Haiz\n");
}
@end

int
main() {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSSocketPort *server = [NSSocketPort alloc];
    MyDelegate *foo = [MyDelegate alloc];
    [server initWithTCPPort: 1234];
    [server setDelegate: foo];
    [[NSRunLoop mainRunLoop] addPort: server forMode: NSDefaultRunLoopMode];
    [[NSRunLoop mainRunLoop] run];
    [pool release];
    return 0;
}

The app is supposed to listen on localhost port 1234, and whenever someone connects to the server or sends data to the server, the app is supposed to print "Haiz" on the console. However the app does nothing at all. The socket is created and I can telnet to port 1234, but the app doesn't print anything to the console.

What am I doing wrong?

Answer 1

From the documentation:

An NSSocketPort object can be used as an endpoint for distributed object connections.

That's not what you're doing here.

You want either NSFileHandle around a socket file descriptor from the BSD sockets API, or a CFSocket. This will let you put the socket on the run loop.

Answer 2

You want to use NSSocketPort in the way you're doing, but then create a NSFileHandle to accept connections on the socket. You can get callbacks on the main thread just like you're expecting, first for new connections, and then for data on those connections. Use this O'Reilly article and just ignore the HTTP stuff.