Question

I’m trying to add some simple peer-to-peer connection functionality to an iOS library. Coding for outgoing connections was simple enough; a call to CFStreamCreatePairWithSocketToHost connects to a remote host and sets up streams for reading/writing from/to it. Simple enough.

However, I couldn’t find an equivalently easy way to set up a socket to listen for/accept incoming connections. So I went back to basics and used socket(), bind(), listen(), and accept() to implement low-level connection handling, patterned largely after the example here:

http://www.pcs.cnu.edu/~dgame/sockets/server.c

That’s all fine, but now that I’m able to accept incoming connections I’m wondering how to go about creating CFReadStream and CFWriteStream instances to manage them. Is there a straightforward way of doing so?

As an aside, I’m aware that a CocoaAsyncSocket library exists that supports asynchronous server sockets, but I’m really not interested in an async solution.

Answer 1

Okay, turns out that the answer was actually fairly simple. You can use:

void CFStreamCreatePairWithSocket (
    CFAllocatorRef alloc,
    CFSocketNativeHandle sock,
    CFReadStreamRef *readStream,
    CFWriteStreamRef *writeStream
);

…to bind a CFReadStream and CFWriteStream to an already connected socket. That flow seems a little backwards to me (i.e. what if bytes have already been read from the socket, etc., and why isn’t it possible to just bind something to the listening/server socket such that every time a new connection is accepted corresponding CFReadStream and CFWriteStream instances are automatically set up?), but whatever.

The code goes like:

int connectedSocketId = accept(socketId, (struct sockaddr *)&clientSocket, &addrlen);
if (connectedSocketId != -1) {
    //successful connection
    CFReadStreamRef clientInput = NULL;
    CFWriteStreamRef clientOutput = NULL;
    CFStreamCreatePairWithSocket(kCFAllocatorDefault, connectedSocketId, &clientInput, &clientOutput);

    if (clientInput && clientOutput) {
        CFReadStreamSetProperty(clientInput, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanTrue);
        CFWriteStreamSetProperty(clientOutput, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanTrue);
        if (! CFReadStreamOpen(clientInput) || ! CFWriteStreamOpen(clientOutput)) {
            NSLog(@"Could not initialize streams!");
        }
        else {
            //use the streams
        }
    }
}

So the important things to realize were:

1. It’s not necessary to bind anything to the socket you are listening on; instead it’s possible to bind CFReadStream and CFWriteStream instances arbitrarily to any already connected socket, even if you’ve already read/written data from/to it.

2. For all its fancy verboseness, a CFSocketNativeHandle is just an int. Oh how I loathe unnecessary aliasing of primitive types to things that sound like they aren’t primitive types.