When is a NSURLResponse not a NSHTTPURLResponse?

I've seen a lot of code, including Apple's SimpleURLConnections sample, that simply cast any NSURLResponse to a NSHTTPURLResponse. If it is always a NSHTTPURLResponse why do the NSURLConnections not return NSHTTPURLResponse?

I'm worried that if I simply downcast the response, I'm introducing buggy code.

For instance, is it OK to do this without checking isKindOfClass?

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)requ开发者_如何学JAVAest redirectResponse:(NSURLResponse *)redirectResponse
{
 NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)redirectResponse;
 // do stuff
}

The safer way to do it is with introspection.

if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
   NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)redirectResponse;
   // do stuff
}

It is ok if you are sure that your connection runs via HTTP protocol:

An NSHTTPURLResponse object represents a response to an HTTP URL load request. It’s a subclass of NSURLResponse that provides methods for accessing information specific to HTTP protocol responses.

If you are connecting via FTP, for example, then casting NSURLResponse to NSHTTPURLResponse will be incorrect.