How to query the last modification date of a file via HTTP on the iPhone using NSHTTPURLResponse?

Question

In my iPhone application I need to query the last modification date of an internet .m4a file via HTTP, but I DON\'T want to downloadin

Answer 1

This answer assumes your server supports it, but what you do is send a "HEAD" request to the file URL and you get back just the file headers. You can then inspect the header called "Last-Modified" which normally has the date format @"EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'".

Here's some code:

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"HEAD"];
NSHTTPURLResponse *response;
[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
if ([response respondsToSelector:@selector(allHeaderFields)]) 
{
  NSDictionary *dictionary = [response allHeaderFields];
  NSString *lastUpdated = [dictionary valueForKey:@"Last-Modified"];
  NSDate *lastUpdatedServer = [fileDateFormatter dateFromString:lastUpdated];

  if (([localCreateDate earlierDate:lastUpdatedServer] == localCreateDate) && lastUpdatedServer) 
  {
    NSLog(@"local file is outdated: %@ ", localPath);
    isLatest = NO;
  } else {
    NSLog(@"local file is current: %@ ", localPath);
  }

} else {
  NSLog(@"Failed to get server response headers");
}

Of course, you probably want this to be done asynchronously in the background, but this code should point you in the right direction.

Best Regards.