Why i get timeout erros when page is not available - objective-c

Question

I use NSString method initWithContentsOfURL:usedEncoding:error: to get content of some page. I notice, when page that i try to access is not exist this method is executed long time and then fail with timeout error. I tried to use NSURLRequest and NSURLConnection classes for the same purposes, but get the same result - execution long time and then timeout error.
When i try to open the same page in browser, i get response more quickly and it returns page is not available error.
It looks like cocoa methods don't do a dns resolution for page name, or they have longer timeout for that operation.
So my question, does cocoa method that i use do dns resolve? How to do that if they didn't?
Samples of code i use:
NSURL* url = [NSURL URLWithString:#"http://unexisting.domain.local"];
NSError* err = nil;
NSString* content = [NSString stringWithContentsOfURL:url usedEncoding:nil error:&err];
if (err) {
NSLog(#"error: %#", err);
} else {
NSLog(#"content: %#", content);
}
NSURL* url = [NSURL URLWithString:#"http://unexisting.domain.local"];
NSURLRequest* request = [NSURLRequest requestWithURL:url];
NSURLResponse* response = nil;
NSError* err = nil;
NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
if (err) {
NSLog(#"error: %#", err);
} else {
NSString* content = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"content: %#", content);
}
Thanks!

Answer 1

Gene M. answered how to do that with using of SCNetworkReachability. Here is sample code:
bool success = false;
const char *host_name = [#"stackoverflow.com"
cStringUsingEncoding:NSASCIIStringEncoding];
SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL,
host_name);
SCNetworkReachabilityFlags flags;
success = SCNetworkReachabilityGetFlags(reachability, &flags);
bool isAvailable = success && (flags & kSCNetworkFlagsReachable) &&
!(flags & kSCNetworkFlagsConnectionRequired);
if (isAvailable) {
NSLog(#"Host is reachable: %d", flags);
}else{
NSLog(#"Host is unreachable");
}

Answer 2

It's definitely good practice to monitor the reachability (device connectivity) and react to it as noted above.
You can also implement the NSURLConnectionDelegate protocol and its methods such as
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog(#"**ERROR** %#", error);
// Respond to error
}
If you're not connected you should get an NSURLConnection error code of 999 and NSURLErrorCancelled = -999 and/or a NSURLErrorNotConnectedToInternet = -1009 if you're not connected, etc. At least you'd have a report back of what's going on.
Docs:
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Constants/Reference/reference.html