iphone - NSURLConnection is run many times

Question

I connect asynchronously with server each 5 seconds. The URL is the same, but POST-body is changed each time. Now I create NSURL, NSURLRequest and NSURLConnection from the scratch each time.

I think it'd be more effective to set connection once and just use that one further. I am a newbie and not sure if that possible. There is no mutable NSURLConnection, but may it's need to create NSURLConnection like:

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: url];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

and change NSMutableURLRequest POST-data to send another request to server. Which way is right?

Answer 1

I assume what you're concerned about is the overhead of creating the HTTP connection. NSURLConnection is smart enough to handle this for you using HTTP/1.1 and reusing existing connections. It does not use pipelining last time I checked, but for your purpose, connection reuse should be sufficient. I do encourage you to put a network sniffer on this and make sure that it's working as you want them to.

The cost of creating the objects themselves is trivial on the order of once per 5s and you shouldn't try to optimize that (though of course you should reuse the NSURL). It's the opening a connection to the server that's expensive, especially on iPhone.

If you find you really do need pipelining, you unfortunately will have to roll your own. I've heard that CFHTTPStream can do it, but I don't see a lot of evidence of that. CocoaAsyncSocket is your best bet for low-level access to the sockets without having to write low-level code.

Since latency on the cell network can be very bad, it's possible that your connection will take longer than 5s to complete. Do make sure that one connection is done before starting the next, or you'll start making more and more open connections.