From: Brian Candler <B.Candler@...>
Date: 2007-06-30T04:17:13+09:00
Subject: Re: Tricky socks question: changing source IP on Net::HTTP

> I've got an interface with multiple IP addresses and I'm looking to
> make HTTP requests from the non-primary IP.
> 
> How would I pull that off?

In principle, you 'bind' the socket to the correct local IP address before
you 'connect'

Unfortunately, TCPSocket#open (or #new) does the connect before it gives you
a chance to bind. So you'll need to replace TCPSocket.open with something
messy along the lines of

    s = Socket.new(Socket::PF_INET, Socket::SOCK_STREAM, Socket::IPPROTO_TCP)
    s.bind(Socket.pack_sockaddr_in(0, "1.2.3.4"))  # chosen local IP
    s.connect(Socket.pack_sockaddr_in(80, "pragprog.com"))

Test this and check that it works at the TCP layer, e.g. by adding

    s.write("GET / HTTP/1.0\r\n\r\n")
    puts s.read

If that works, then unfortunately net/http.rb doesn't seem to have a
suitable hook, so copy the source and look for TCPSocket.open to see where
you need to modify it.

Good luck,

Brian.