beginObservingReachabilityStatusForHost:

beginObservingReachabilityStatusForHost.m

	- (void) beginObservingReachabilityStatusForHost:(NSString *)host {
	    SCNetworkReachabilityRef        reachabilityRef     = NULL;
    
	    void (^callbackBlock)(SCNetworkReachabilityFlags) = ^(SCNetworkReachabilityFlags flags) {
	        BOOL reachable = (flags & kSCNetworkReachabilityFlagsReachable) != 0;
	        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
	            [self host:host didBecomeReachable:reachable];
	        }];
	    };
    
	    SCNetworkReachabilityContext context = {
	        .version = 0,
	        .info = (void *)CFBridgingRetain(callbackBlock),
	        .release = CFRelease
	    };
    
    
	    if ([host length] > 0){
	        reachabilityRef = SCNetworkReachabilityCreateWithName(kCFAllocatorDefault, [host UTF8String]);
	        if (SCNetworkReachabilitySetCallback(reachabilityRef, ReachabilityCallback, &context)){
	            if (!SCNetworkReachabilitySetDispatchQueue(reachabilityRef, [self scNetworkQueue]) ){
	                // Remove our callback if we can't use the queue
	                SCNetworkReachabilitySetCallback(reachabilityRef, NULL, NULL);
	            }
	            [self setCurrentReachability:reachabilityRef];
	        }
	    }
	}
	
	
static void ReachabilityCallback(SCNetworkReachabilityRef __unused target, SCNetworkConnectionFlags flags, void* info) {
    void (^callbackBlock)(SCNetworkReachabilityFlags) = (__bridge id)info;
    callbackBlock(flags);
}