[Soc-coordination] Debdelta APT Integration - Report 3

[Ishan Jayawardena]

I have been working on adding the URI replacement functionality to the
downloader. By replacing the original URLs produced by the downloader
with the URL of a debdelta repository, we can construct debdelta URIs.
Following is my approach,

First, I defined the "Aquire::Debdelta::Replace-Rule::Replace-URI"
config item in the pkgInitConfig() method to point to the debdelta
repository at "http://debdeltas.debian.net/debian-deltas/". I did this
as a temporary workaround. Ideally, this URL must be mentioned with
the -o command line option, in apt's configuration file or in the
sources.list file, because we believe maintaining two different
configuration files for apt and debdelta is not productive.

Then, in the debPackagesIndex::debPackagesIndex() method, I did the
following to define a replacement URI for each URI that is constructed
by the downloader.
    _config->Set("Aquire::Debdelta::Replace-Rule::URI-Space::"+URI,
                _config->Find("Aquire::Debdelta::Replace-Rule::Replace-URI"));

Finally, I wrote the method, pkgAcqDebdelta::ReplaceURI() in which I
applied the actual replacement. I used the Configuration::Tree()
method to iterate through the children of the
"Aquire::Debdelta::Replace-Rule::URI-Space::" item and replaced each
of them with the replacement rule in
"Aquire::Debdelta::Replace-Rule::Replace-URI" item.

Currently, I am studying the original debdelta code base to add some
modifications to it to suit some of our requirements. The main
requirement is to add proper progress reporting, both in downloading
and extracting deltas. For this, I need to look into the method/format
etc. that the upstream uses already and reuse them appropriately.
Another requirement is to find a better solution to debpatch's
printing errors/warnings directly to stdout making debpatch difficult
to use within the pipe in the debdelta method.
Also, I need to test and verify the replacement rule's functionality
with an actual replacement URI together with some real packages.

My APT branch in Launchpad: https://code.launchpad.net/~udeshike/apt/apt-ishan
-- 
Regards,
Ishan Jayawardena.