Thoughts on switching our archive compression method

[Ryan Schmidt]

It would be nice if we could easily switch our precompiled archives from bzip2-compressed tarballs (tbz2) to better compression methods as they become available. For example, xz-compressed tarballs (txz) would be better today. OS X 10.9 Mavericks and later has built-in support for xz compression (https://trac.macports.org/ticket/56237) so we could use that to avoid needing to use the xz port or needing to bundle a copy of xz (https://trac.macports.org/ticket/52000).

Currently, users have to specify what archive type they want for each server listed in archive_sites.conf. The default archive_sites.conf fortunately has everything commented out, so users get the MacPorts built-in defaults, so we could change the behavior in the future and users would automatically get it.

We could remove the compression type setting in archive_sites.conf. (Or there could be a new value of the compression type setting that means to do the following.) And instead of having an rmd160 file for each archive, have an information file which could be encoded in any convenient format such as json or plist or whatever we're using for the PortIndex. MacPorts would fetch the information file first, and it would contain a field stating the compression format (filename extension) for this archive and a field for its rmd160 signature. From this MacPorts can deduce what archive filename to download. It would also give us a place to store any additional information about archives that we might want to store in the future.

If that were in place, along with support in base for decompressing xz without needing the xz port, then we could begin compressing new archives for 10.9 and later with xz without needing to recompress the entire collection of existing archives. Over time we can do that as well, of course.