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First, know that NSSocketPort is not for TCP/IP or UDP or anything like that - It is for DistributedObjects.

To do “regular” networking, you want to use the SocketClasses, CFNetwork, or NSStream.

Then why do the docs say it can be used either for DistributedObjects or raw messaging?

I think by “raw messaging,” they mean direct use of NSPortMessage. That’s no good if you want to work with HTTP or other specific protocols.

The above entries are exceedingly misleading: in truth, NSSocketPort is a great way to setup sockets quickly, using any protocol and family supported by the low-level UNIX socket APIs. However, NSSocketPort doesn’t provide the required facilities itself to actually read and write data into the communications channel: for that, your best bet is to wrap the native file handle (obtained from [NSSocketPort socket]) in an NSFileHandle object and use the methods provided by the file handle wrapper class to communicate via the socket.

NSSocketPort* sock = [[NSSocketPort alloc] initWithTCPPort: 80 host: @””]; NSFileHandle* sHandle = [[NSFileHandle alloc] initWithFileDescriptor: [sock socket] closeOnDealloc: YES];

You can also trivially create a server socket using the above technique:

NSSocketPort * serverSock = [[NSSocketPort alloc] initWithTCPPort: 8081]; NSFileHandle * socketHandle = [[NSFileHandle alloc] initWithFileDescriptor: [serverSock socket] closeOnDealloc: YES]; [socketHandle acceptConnectionInBackgroundAndNotify]; [[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(notified:) name: NSFileHandleConnectionAcceptedNotification object: socketHandle];

Why isn’t this in Apple’s documentation?

An undocumented “feature”: if you attempt to use initRemoteWithTCPPort:host: with an invalid or unavailable host name, the result is nil. If you then try to get a file handle, [nil socket] will return 0, and you will end up with a handle for your machine’s STDIN. Since this depends on the network connection status of the machine – not just on the correctness of the arguments – you should always verify that the result is non-nil.

The above client code is wrong. First, the method is named “initRemoteWithTCPPort:host:”, not “initWithTCPPort:host:”. Second, a host string must just be a server name or IP address, not a URL. “” would be appropriate. Third, whenever I try to run it, the file descriptor I get from [serverSock socket] is -1. I think my problem is related to this note in Apple’s documentation: “A connection is not opened to the remote host until data is sent.” In other words, I think you must use the NSSocketPort to send something (probably a non-trivial process not designed for typical users’ consumption) before [serverSock socket] will give you a useful result.

I would fix the example myself (perhaps remove it completely), except that I’m not sure whether there is no simple way to get a file handle from an NSSocketPort, so I don’t want to mess with it. Presumably the poster has gotten code like this to work?

For a good complete example on using NSSocketPort (or, rather, if you read the whole thing, don’t use it is the conclusion) in server code, read

Another argument against using NSSocketPort for your networking (setting aside that it wasn’t designed for it) is that it doesn’t exist on the iPhone.

A question because of converting CF calls to Cocoa. How can I create a NSSocketPort from an existing fileDescriptor and get the ip address of the corresponding host?

This is very similar to acceptor and reactor in Ace Framework.