M. Uli Kusterer emailed me to say I’d forgotten that some people still have non-broadband connections. I had supposed that NSURLConnection would simply return an immediate error if the internet link is down – it turns out that it may autoconnect if the user has a dialup connection, for instance.

The way around that is to use the network reachability APIs. Here’s one way to insert that into the example below:

#include <SystemConfiguration/SCNetworkReachability.h>
- (id)initWithURL:(NSURL*)theURL delegate:(id)theDelegate {
   if ((self = [super init])) {
      SCNetworkConnectionFlags flags = 0;
      if (SCNetworkCheckReachabilityByName([[theURL host] UTF8String], &flags)) {
         const SCNetworkConnectionFlags mask =
         if ((flags&mask)==kSCNetworkFlagsReachable) {
            delegate = theDelegate;
            data = nil;
            conn = [[NSURLConnection alloc]
               initWithRequest:[NSURLRequest requestWithURL:theURL]
            return self;
      [self autorelease];
      self = nil;
   return self;

This changes the alloc/init pair to return nil whenever the URL host is unreachable… you’ll have to test for that of course.

Update: the downside to the above approach is that the SCNetworkCheckReachabilityByName() function will block until it gets the information – which may take several seconds, perhaps more on some systems. The solution I’m actually using is more complex, installing a reachability transition callback, which sets a global flag that is tested before activating the NSURLConnection.