contrib/plan9/9mail

unbundle20: retrieve unbundler instances through a factory function

To support multiple bundle2 formats, we will need a function returning
the proper unbundler according to the header. We introduce such aa
function and change the usage in the code base. The function will get
smarter in later changesets.

This is somewhat similar to the dispatching we do for 'HG10' and 'HG11'.

The main target is to allow HG2Y support in an extension to ease transition of
companies using the experimental protocol in production (yeah...) But I've no
doubt this will be useful when playing with a future HG21.

#!/bin/rc
# 9mail - Mercurial email wrapper for upas/marshal

fn usage {
	echo >[1=2] usage: mercurial/9mail -f from to [cc]
	exit usage
}

from=()
cc=()
to=()

switch($1){
case -f
	from=$2
case *
	usage
}

to=($3)
if(~ $#* 4)
	cc=(-C $4)

upasname=$from
upas/marshal $cc $to