iOS gzip handling in NSURLConnection

I've read that NSURLConnection automatically decompresses request that are gzipped. Without having to specify accept-encoding or anything in the request. In doing an asynchronous NSURLConnection, I print the lengths of the returned data in each didReceiveData call, but it appears to be the uncompressed length.

Does NSURLConnection decompress the data before sending to didReceiveData? How can I tell if the data being received was originally compressed?

Thanks!