I am trying to sniff the http headers by using tcpdump.
This filter works well but I can't understand it -
(((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
I've googled it but I can't find any useful info
Here is the whole tcpdump command
sudo tcpdump -A 'dst [dest host] or src [src host] and tcp and
(((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' -i eth0