how to indentify a perticular application layer protocols like skype/fbook/torrent

Hi, I am just writing the my own customize tshark which give all info about layer l2, l3,l4 .But when i have started for Application layer then i got the problem about the header file info of http(other application protocols header) .

I saw the pcaket-http.h and .c file but i can't use all these file for my small function, it will like a tshark itself . For l2 we have ether_header that way we can take mac and type ,but how i can get the host address of the http packet .