[peroo]

They couldn't change all URLs to be relative, so instead they wrote a filter which would rewrite absolute URLs to match the selected hostname. A simple fix for a relatively complex problem.

[VBprogrammer]

Or a hack which will never be removed from the code-base, depending on your point of view.

I'm intrigued as to why changing to relative domains wasn't possible. If nothing else pushing 'http://www.theguardian.com' out for every link adds to a lot of bytes up for a busy site.

[cbr]

    pushing 'http://www.theguardian.com' out for every link
    adds to a lot of bytes up for a busy site

Fewer than you'd think after gzip compression:

    $ curl -s http://www.theguardian.com/us | wc -c
    223195
    $ curl -s http://www.theguardian.com/us | \
       sed s'~http://www.theguardian.com~~' | wc -c
    215473
    $ curl -s http://www.theguardian.com/us | \
       gzip | wc -c
    33783
    $ curl -s http://www.theguardian.com/us | \
       sed s'~http://www.theguardian.com~~' | gzip | wc -c
    33554

They have 7.7k of extra html due to repeating "http://www.theguardian.com" for every link, but gzip compressed this is only a difference of 229 bytes.