Building a Server/Client application in Cocoa

Question

I built a fairly simple program that watches a folder, manipulates files as they are added, and gives a simple progress view of whats going on. The folder is watched via a subclass of NSOperation that passes information in an NSDictionary to my progress view, via the NSNotificationCenter.

Now I need to break things up and run the watched folder/processing part on my server, and build a client to monitor the progress from multiple workstations. My problem is I don't know how to accomplish this and my searches aren't really helping me.

It seems I'm getting a lot of out dated solutions (WebObjects, Portable Distributed Objects) or incomplete information. It seems like I'd want to use NSStream to pass data back and forth, but everything I find on NSStream looks like it's set up for client side because it's looking for an IP address. What would be the best way to go about setting up both a server, and a client to connect to it?

score 7 · Accepted Answer · answered Aug 13 '11 at 03:37

I would suggest using TCP for something like this. Since (I assume) you are writing this software for BSD (Mac OS X and iPhone are both BSD) you can use BSD C sockets, or an Objective-C wrapper for this. One good library for a client is CocoaAsyncSocket. I personally have written a lightweight Objective-C socket class for TCP networking called SocketKit. Usage of this library is something as follows:

// open a connection
SKTCPSocket * socket = [[SKTCPSocket alloc] initWithRemoteHost:@"SERVER_IP" port:SERVER_PORT];
// write data
[socket writeData:someData];
// read data
NSData * someData = [socket readData:4];
// close the socket
[socket close];
[socket release];

From a server standpoint, you can listen on a port using the SKTCPSocketServer class:

SKTCPSocket * aSocket = nil;
SKTCPSocketServer * server = [[SKTCPSocketServer alloc] initListeningOnPort:1337];
@try {
    [server listen];
    while ((aSocket = (SKTCPSocket *)[server acceptConnection]) != nil) {
        // do something with aSocket
        [aSocket close];
    }
} @catch (NSException * e) {
    NSLog(@"Exception : %@", e);
}
[server stopServer];
[server release];

Of course using TCP sockets means writing your own network protocol. A simple example would be sending a four byte length field, followed by the data of an NSDictionary or something of that nature. This could allow you to accomplish something similar to a very basic Distributed Objects system.

Didn't mean to leave this question dead for the last couple of days. Have just been busy and haven't gotten back into this project. Thanks for the info I'll take a look at both CocoaAsyncSocket and SocketKit it sounds like this is what I'm looking for. — Kris, Aug 15 '11 at 21:38
CocoaAsyncSocket turned out to be what I needed. I'm having a little problems getting data to write to the connected socket as events happen... But right now I'm getting an initial read upon connection so I'm sure there is something I missed in the documentation. Thanks again! — Kris, Aug 17 '11 at 04:21

score 4 · Answer 2 · answered Aug 13 '11 at 01:35

Why not take a look at Bonjour for zero-configuration networking (i.e. so you don't have to find the IP address of your server)?

Since Bonjour is also supported on Windows and iOS (iPhone/iPad) you can even make your app multi-platform (e.g. server on Windows and Mac client or vice versa) or even have an iPhone act as a client of your server (don't know if this makes sense in your case but I'm just suggesting).

score 0 · Answer 3 · answered Aug 13 '11 at 01:44

This, unfortunately, is a place where Cocoa is pretty weak. Forget about WebObjects (Apple has). You probably should forget about Distributed Objects. There isn't really a built-in client/server solution on Mac. iOS has some decent peer-to-peer stuff, but it's still pretty useless for client/server.

My recommendation is to use a simple REST API. Build your server with cocoahttpserver. Build your client with NSURLConnection or ASIHTTPRequest. Keep it simple. I like JSON for the protocol. YAJL has worked well for me, but for something really simple, there are lots of options.

Building a Server/Client application in Cocoa

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