Portage writes a compressed copy of 'Packages' index file.

Portage writes a compressed copy of 'Packages' index file.

This behaviour is enabled by FEATURES="compress-index". The
resulting file is 'Packages.gz' and its modification time will
match that of 'Packages'.

Web-servers use that copy to avoid repeated on-the-fly compression.

In order to re-use 'atomic_ofstream' usage of 'codecs.zlib_codec'
has been considered and discarded, because 'GzipFile' yields
smaller files. (According to Mark's tests 62% smaller.)

Example usage, Nginx:

  location =/Packages {
    gzip_static on;
    default_type text/plain;
  }

Apache httpd (use with caution):

  RewriteRule ^(.*)/Packages$ $1/Packages.gz [T=text/plain,E=GZIP:gzip,L]
  <FilesMatch "Packages\.gz$">
    Header set Content-Encoding gzip
  </FilesMatch>