Sounds confusing? No worries, it's really not. Here are some standard HTTP headers from a random website.
[root@vps ~]# curl --head https://ma.ttias.be HTTP/1.1 200 OK Date: Thu, 28 Aug 2008 17:58:15 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 X-Pingback: https://ma.ttias.be/xmlrpc.php Set-Cookie: PHPSESSID=sudpae35dbuesipfiouipcbue0; path=/ Connection: close Content-Type: text/html; charset=UTF-8
Nothing special about it, perhaps the X-Pingback is a bit odd -- it's added by wordpress to allowed automatic pingbacks to certain articles. You have your typical date, server, connection & content-type shown to you.
Some sites however ... like to add some special things. Slashdot for instance adds a new Futurama quote with every page you load. It's hidden to 99,9% of the users out there -- only the geeks who actually look at the headers will see this.
[root@vps ~]# curl --head http://slashdot.org HTTP/1.1 200 OK Date: Thu, 28 Aug 2008 18:02:27 GMT Server: Apache/1.3.41 (Unix) mod_perl/1.31-rc4 SLASH_LOG_DATA: shtml X-Powered-By: Slash 2.005001217 X-Bender: They're tormenting me with uptempo singing and dancing! Cache-Control: private Pragma: private Connection: close Content-Type: text/html; charset=iso-8859-1
Note the X-Bender: They're tormenting me with uptempo singing and dancing! quote in there! You'll also find quotes by Leela & Fry.
- X-Bender: I only know enough binary to ask where the bathroom is.
- X-Bender: Gimme your biggest, strongest, cheapest drink.
- X-Leela: This is by a wide margin the least likely thing that has ever happened.
- X-Leela: This toads the wet sprocket.
- X-Fry: You mean Bender is the evil Bender? I'm shocked! Shocked! Well not that shocked.
- X-Fry: I must be a robot. Why else would human women refuse to date me?
It's probably been known for a while, but it was knew to me. Kinda cool -- now I'm looking at ways to add fancy headers for this server as well ... :-) You can read more about it on this Fun With HTTP Headers article!
Edit: turns out it is incredibly easy to add a custom http header to apache. Just enable the use of .htaccess and you can add all the headers you like. Add the following line, to create a "X-Who-Rocks"-header!
Header set X-Who-Rocks "Mattias Geniar"
This is what the headers for this site now look like! Muchos better! :-)
[root@vps httpdocs]# curl --head https://ma.ttias.be HTTP/1.1 200 OK Date: Thu, 28 Aug 2008 18:23:48 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 X-Pingback: https://ma.ttias.be/xmlrpc.php Set-Cookie: PHPSESSID=ibmsf43qjjnkc6h6fudfok0sp5; path=/ X-Who-Rocks: Mattias Geniar Connection: close Content-Type: text/html; charset=UTF-8