Mailinglist Archive: zypp-devel (75 mails)

[Josef Reidinger <jreidinger@xxxxxxx>]

Peter Poeml wrote:
> Hi zypp devels,
> especially Duncan, Marius, Jiri,
>
> I think that you are probably very busy with release of openSUSE 11.0.
> Maybe you have a few minutes nevertheless to share some insight. These
> questions block Gerards work. With the complexity of libzypps media
> handling, it seems difficult to proceed in the best direction, without
> your help. Your advice would be very much appreciated.
>
> On Tue, May 20, 2008 at 05:44:39PM +0200, Gerard Farràs i Ballabriga wrote:
> > Hello, good afternoon :-)
> >
> > There are some new ideas and changes about implementation details of
> > the concept of failover [1].
> >
> > Before, our idea was to modify MediaCurl class [2] to parse a list of
> > mirrors like this [3].
> >
> > But now, new idea is to use only metalink files ([4] [5]) and don't
> > use anymore this type of mirror lists.
> >
> > Libzypp could download files using an external program (ej. aria2c
> > [6]) to avoid having to implement all the logic from zero.
>
> I implemented a proof-of-concept in Yum in 20 minutes (and less than 10
> changed lines). Instead of calling python-urlgrabber, I called aria2c
> for fetching files (putting them into the cache), and it works fine to
> implement part 1 and part 3 of http://en.opensuse.org/Libzypp/Failover. 
>
> In libzypp, it seems to be much more complicated.
>
> Our question is: 
>
> How can we easily add a new handler (fetching files with an external
> program) with as few intrusion into libzypp's media handling as
> possible? 

create new handler

> Is there a central place where one could hook into?

I think that MediaAccess line 129 is good place to look for external 
program and create new handler. something like
if (existExternalProgram())
  _handler = new MediaExternalDownloader;
else
  _handler = new MediaCurl
> It would be great if it is possible to use e.g. aria2c as external
> downloader, which already implements nearly everything that we need.
> It meanwhile seems to me that implementing more stuff in libzypp will
> not only reinvent the wheel in many regards but also increase the media
> handling's complexity even further.
>
> An underlying assumption that I have is that there always is some
> kind of package caching directory where files are downloaded (and used
> later), so it wouldn't matter if the files are put there by libcurl or
> by the external process. Is this assumption correct?
Yes, if checksum match then libzypp use package from cache 
(/var/cache/zypp/packages/'repoalias'/).
> > Why this change?
> >
> >  - Because we think than we are reinventing the wheel in things like:
> >
> >                 * Parse HTTP codes and act according to these.
> >                 * To choose the fastest mirror.
> >
> > How to implement?
> >
> >  I think we can do the implementation with some changes:
> >
> >         - Modify media/MediaAccess.cc [7] and check if there are available
> > tools like aria2c in the target system.
> >         - If we get a negative response we must use MediaCurl (like now).
> >         - If we get a positive response we can use a "new" class called
> > MediaArise (or something like this) which uses aria2c to download
> > files using Medialink from network.
> >
> > What do you think about this idea? Any comments for this
> > implementation? Dr. Poeml, please, feel free to correct me if there
> > are any error.
> >
> > Obviously, any suggestion or comment will be more than welcome :-).
> >
> > Thanks :-)
> >
> > Gerard
> >
> > [1] http://en.opensuse.org/Libzypp/Failover
> > [2] http://svn.opensuse.org/svn/zypp/trunk/libzypp/zypp/media/MediaCurl.h
> > [3] 
> > http://download.opensuse.org/distribution/10.3/repo/oss/suse/repodata/primary.xml.gz?mirrorlist
> > [4] http://www.metalinker.org/
> > [5] 
> > http://download.opensuse.org/distribution/10.3/repo/oss/suse/repodata/primary.xml.gz.metalink
> > [6] http://aria2.sourceforge.net/
> > [7] http://svn.opensuse.org/svn/zypp/trunk/libzypp/zypp/media/MediaAccess.cc
>
> Thank you for your comments!
>
> Peter

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