When pulling from a non hg repository URL (e.g. http://www.kernel.org/hg) you geta pretty obscure error (zlib: uknown compression type). The attached patch modifies hgweb.py and hg.py to supply and check a 'Content-type: application/hg-0.1' HTTP header for the branches, between and changegroup commands, so that we know it's a proper hg repo before snarfing the input. Comments appreciated!

#!/bin/sh

hg init
mkfifo p

hg serve --stdio < p &
P=$!
(echo lock; echo addchangegroup; sleep 5) > p &
Q=$!
sleep 1
kill -HUP $P
sleep 1
ls .hg