avahi + apt-cacher-ng + sbuild ?!

Laptop enters the WiFi network and decides that it wants to build some packages using sbuild.
At the same time, on this network there is apt-cacher-ng operating with most of packages cached.
On the other hand, there is a project squid-deb-proxy which provides yet another apt proxy, but with the added bonus of avahi discovery.

Can we throw all of this stuff together and make it work? Well let's try =)

On ubuntu:

$ sudo apt-get install apt-cacher-ng squid-deb-proxy-client

On debian:

Squid-deb-proxy-client is not packaged just fetch and install it. It's really just one python script & one conffile. Or I have published the python script and the config as part of this posts gist.

Next all of the avahi magic, really is just publishing a service file & letting the python-script from the squid-deb-proxy-client package find it, and adding apt-conf.d snippet which calls the above mentioned script and generate correct proxy line.

But we are running apt-cacher-ng! So on the server where apt-cacher-ng is running drop this:

/etc/avahi/services/apt-cacher-ng.service

<?xml version="1.0" standalone='no'?>
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
 <name replace-wildcards="yes">apt-cacher-ng proxy on %h</name>
 <service protocol="ipv4">
  <type>_apt_proxy._tcp</type>
  <port>3142</port>
 </service>
</service-group>

Now on any host that you want automatic apt-proxy discovery, simply install squid-deb-proxy-client & your apt-cacher-ng will be auto-discovered.

What about sbuild? Well, you don't really want to install avahi-daemon and start it inside the chroot, so we can cheat with creating an executable hook:

/etc/schroot/setup.d/51aptproxy
#!/bin/sh
set -e

. "$SETUP_DATA_DIR/common-data"
. "$SETUP_DATA_DIR/common-functions"
. "$SETUP_DATA_DIR/common-config"

APT_AVAHI_DISCOVER=/usr/share/squid-deb-proxy-client/apt-avahi-discover

if [ $STAGE = "setup-start" ] || [ $STAGE = "setup-recover" ]; then
    if type apt-avahi-discover 1>/dev/null; then
        APT_AVAHI_DISCOVER=apt-avahi-discover
    fi
    APT_PROXY=`$APT_AVAHI_DISCOVER`
    if [ -n "$APT_PROXY" ]; then
        info "Setting apt-proxy to avahi proxy at ${APT_PROXY}"
        printf 'Acquire::http { Proxy "%s";};\n' ${APT_PROXY} > "${CHROOT_PATH}/etc/apt/apt.conf.d/30schrootautoproxy"
    fi
fi

Tadah. Now I'm using my apt-cacher-ng whenever I'm on my home WiFi =)

Please advertise your apt-cache proxies!

Now to integrate this properly:

• apt-cacher-ng should auto-create avahi service file in it's init script
• apt-get or some other package should ship apt-avahi-discover script (there is also a C implementation available)
• apt-get or some other package should ship the apt.conf.d snippet
• sbuild / pbuilder / cowbuilder / mk-sbuild / [p|cow]builder-dist should have hooks to retrieve hosts' apt proxy settings and use them in the chroots

For full sources see lp:squid-deb-proxy and my gist with all other config snippets.