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");
}