[ee122] HTTP Questions

[vern at cs.berkeley.edu]

> I've used my old client to get pages from servers and not all have the
> "Content-Length" header. www.google.com for example. What is the protocol
> regarding this possibility?

If you're issuing an HTTP 1.0 request and don't include the keep-alive
option, then the server marks the end of its reply by closing the connection.

> If I wanted to implement all of the functionality of dig, how would I do
> this? Is there a simple protocall spec somewhere?

The nitty gritty of the DNS protocol is specified in RFC 1035.  dig has
to be able to construct such requests directly (rather than using a library
to do so) in order to fully control things like recursive/iterative, and
to have raw access to replies in order to dump them out.

> Also, what is the wireshark command to do the tcpdump, I tried it with the
> same arguments as tcpdump but it didn't work.

tshark is the component that comes with the Wireshark package for doing
tcpdump-style packet capture.  If instead you mean how do you get wireshark
to itself capture packets, there's a pull-down menu for this at the top
of the window; however, on the instructional machines this doesn't work
because wireshark can't be given the necessary permissions to access
the packet filter.

		Vern