HEADER request allHeaderFields not working - ios

Question

The purpose of my code is to compare the modification dates of a server file and a local file, in case that the server file is newer, it will download it.
My first attempt was to use a synchronous request using the code from http://iphoneincubator.com/blog/server-communication/how-to-download-a-file-only-if-it-has-been-updated
But it didn't worked.
After that I've been struggling to find the solution, tried asynchronous request, tried different codes I found around stackoverflow, google, etc. but nothing works.
If in terminal I do curl -I <url-to-file> I get the header values so I know is not a server problem.
This is the code I'm struggling with right now (It's written in Appdelegate.m)
- (void)downloadFileIfUpdated {
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL: url
cachePolicy: NSURLRequestReloadIgnoringLocalCacheData
timeoutInterval: 10];
[request setHTTPMethod:#"HEAD"];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
if(!connection) {
NSLog(#"connection failed");
} else {
NSLog(#"connection succeeded");
}
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[self downloadFileIfUpdated]
}
#pragma mark NSURLConnection delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSString *lastModifiedString = nil;
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if ([response respondsToSelector:#selector(allHeaderFields)]) {
lastModifiedString = [[response allHeaderFields] objectForKey:#"Last-Modified"];
}
[Here is where the formatting-date-code and downloading would take place]
}
Right now, as it is, it gives me the error No visible #interface for 'NSURLResponse' declares de selector 'allHeaderFields'.
When I use the synchronous approach the error is that NSLog(#"%#",lastModifiedString)returns (null).
PS: If there is a better way I can explain myself or the code, please let me know.
UPDATE
The URL I'm using is of type ftp://and that may be the problem of why I don't get any HEADERS. But I can't figure out how to do it then.

Answer 1

Change your code to this... in the 'if' conditional, you were checking response instead of httpResponse:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSString *lastModifiedString = nil;
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if ([httpResponse respondsToSelector:#selector(allHeaderFields)]) {
lastModifiedString = [[httpResponse allHeaderFields] objectForKey:#"Last-Modified"];
}
// [Here is where the formatting-date-code and downloading would take place]
}
... and once you feel comfortable that the response is going to always be an NSHTTPURLResponse, you could probably just get rid of the conditional statement:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
NSString *lastModifiedString = [[httpResponse allHeaderFields] objectForKey:#"Last-Modified"];
// [Here is where the formatting-date-code and downloading would take place]
}