Download only the HTTP headers in Cocoa - objective-c

Question

I'm trying to port one of my Android applications to work natively on Mac OS X.
For the initialisation of the application, it needs to connect to a server and read only the headers of the server's response. The server (3rd party server) will respond with 82274 bytes of data, but the only useful data to me are the headers; specifically I only need to read the session cookie and retrieve its value. This means that all of the other data is redundant.
Through Googling, the only working looking response is as follows:
// Create the request.
NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:#"http://www.grooveshark.com/"]];
[theRequest setHTTPMethod:#"HEAD"];
[theRequest setValue:#"MySpecialUserAgent/1.0" forHTTPHeaderField:#"User-Agent"];
[theRequest setTimeoutInterval:15.0];
[theRequest setCachePolicy:NSURLRequestReloadIgnoringCacheData];
However this still downloads the entire page.
Can anyone point me in the right direction?

Answer 1

Let's see what happens if we hit that URL.
› curl -v -X HEAD http://www.grooveshark.com
* About to connect() to www.grooveshark.com port 80 (#0)
* Trying 8.20.213.76...
* connected
* Connected to www.grooveshark.com (8.20.213.76) port 80 (#0)
> HEAD / HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5
> Host: www.grooveshark.com
> Accept: */*
>
< HTTP/1.1 301 Moved Permanently
< Server: richhickey
< Date: Sat, 15 Dec 2012 20:27:38 GMT
< Content-Type: text/html; charset=UTF-8
< Connection: close
< Location: http://grooveshark.com
< Vary: Accept-Encoding
< X-Hostname: rhl081
< X-Hostname: rhl081
<
* Closing connection #0
So www.grooveshark.com redirects to grooveshark.com. Let's see if that page honors HEAD requests correctly.
› curl -v -X HEAD http://grooveshark.com
* About to connect() to grooveshark.com port 80 (#0)
* Trying 8.20.213.76...
* connected
* Connected to grooveshark.com (8.20.213.76) port 80 (#0)
> HEAD / HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5
> Host: grooveshark.com
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: richhickey
< Date: Sat, 15 Dec 2012 20:28:06 GMT
< Content-Type: text/html; charset=UTF-8
< Connection: close
< Vary: Accept-Encoding
< Set-Cookie: PHPSESSID=844a5e6bdd6d84a97afd8f42faf4eb95; expires=Sat, 22-Dec-2012 20:28:06 GMT; path=/; domain=.grooveshark.com
< Expires: Thu, 19 Nov 1981 08:52:00 GMT
< Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
< Pragma: no-cache
< Vary: Accept-Encoding
< X-Hostname: rhl061
< Set-Cookie: ismobile=no;domain=.grooveshark.com;path=/
< X-country: US
<
* Closing connection #0
That looks good. I suspect that your request is falling back to a GET when following that redirect. It looks like Chris Suter ran into the same thing and gave an example solution: http://sutes.co.uk/2009/12/nsurlconnection-using-head-met.html
In the future you might want to try running your requests through a local proxy so that you can see them in flight. That would probably reveal that you make a HEAD request to www.grooveshark.com followed by a GET to grooveshark.com.