How to write a simple Ping method in Cocoa/Objective-C

Question

I need to write a simple ping method in Cocoa/Objective-C. It also needs to work on the iPhone.

I found an example that uses icmp, will this work on the iPhone?

I'm leaning towards a solution using NSNetServices, is this a good idea?

The method only needs to ping a few times and return the average and -1 if the host is down or unreachable.

Solution 1

The code below seems to be working synchronously:

const char *hostName = [@"stackoverflow.com"
                        cStringUsingEncoding:NSASCIIStringEncoding];
SCNetworkConnectionFlags flags = 0;
if (SCNetworkCheckReachabilityByName(hostName, &flags) && flags > 0) {
  NSLog(@"Host is reachable: %d", flags);
}
else {
  NSLog(@"Host is unreachable");
}

Note: SystemConfiguration.framework is required

Solution 2

NOTE- I would recommend Chris' solution below which actually answers the question asked, directly. This post from 12 years ago was in response to the original authors upvoted answer, to which I had a better solution. As the author upvoted the answer above that used Reachability, I assumed that he was in fact more interested in reachability than actually in sending a ping, hence my answer. Please consider this before downvoting this answer.

StreamSCNetworkCheckReachabilityByName is deprecated and NOT available for the iPhone. Note: SystemConfiguration.framework is required

bool success = false;
const char *host_name = [@"stackoverflow.com" 
                         cStringUsingEncoding:NSASCIIStringEncoding];

SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL,
                                                                        host_name);
SCNetworkReachabilityFlags flags;
success = SCNetworkReachabilityGetFlags(reachability, &flags);

//prevents memory leak per Carlos Guzman's comment
CFRelease(reachability);

bool isAvailable = success && (flags & kSCNetworkFlagsReachable) && 
                             !(flags & kSCNetworkFlagsConnectionRequired);
if (isAvailable) {
    NSLog(@"Host is reachable: %d", flags);
}else{
    NSLog(@"Host is unreachable");
}

Solution 3

I had this same problem, and ended up writing a simple wrapper around SimplePing to achieve this, wrote a blog about it and there's some code on github, hopefully will help someone here:

http://splinter.com.au/how-to-ping-a-server-in-objective-c-iphone

Solution 4

You are not missing anything -- "Reachability" doesn't actually test that the target domain is in fact reachable, it only assesses if there is a pathway out of the machine by which the target domain is potentially reachable. So long as you have some outbound connection (e.g., an active wirless or wired connection), and a routing configuration that leads to the target, then the site is "reachable" as far as SCNetworkReachability is concerned.

Solution 5

Pinging on the iPhone works a bit different than on other platforms, due to the fact that you don't have root access. See this sample code from Apple.

View more solutions

Comments

[William Remacle]

Unfortunately, SCNetworkCheckReachabilityByName is now deprecated.

[bestsss]

8 votes and +bounty for code that totally doesn't do what question was about, i.e. ping/traceroute but it's a DNS lookup, basically.

[ahmet alp balkan]

This file is removed from all around apple developer library.

[Bill Patterson]

Upvote for a solution that actually answers the question (vs all this useless Reachability stuff which people seem to like but which is totally not addressing the question asked!). Thank you!

[user623396]

Yes, this is the actual answer.

[Adro]

The code is not only deprecated but also looking up the DNS

[Vadim]

“You cannot delete this accepted answer”. Sorry guys! 😃

[Carlos Guzman]

Hi. Excelent code and helpful, but only one thing. You require add the code CFRelease(reachability) after call SCNetworkReachabilityGetFlags to release reachability variable (to prevent memory leaks) as is mentioned in documentation

[adib]

SCNetworkReachability is a poor indicator of whether a host is online. On a LAN situation, reachability seems to always returns that the host is reachable whenever there is a WiFi connection although it's really an invalid host name.

[adib]

SCNetworkReachabilityGetFlags is a poor substitute of ping – if the device is connected to a network, kSCNetworkFlagsReachable will be set and kSCNetworkFlagsConnectionRequired will be unset even though the target host is offline.

[Gene Myers]

I was improving on the accepted answer. I don't debate that SCNetworkReachabilityGetFlags is a poor substitute for 'ping', but if you are just trying to determine reachability, as was rjstelling objective, then this is a fine solution. If you need to monitor latency or provide a heartbeat, then a 'ping' solution is arguably better.