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>

3 files changed, 23 insertions, 7 deletions

diff --git a/man/make.conf.5 b/man/make.conf.5
index 876a8a330..02cc8098d 100644
--- a/man/make.conf.5
+++ b/man/make.conf.5
@@ -268,6 +268,13 @@ space.  Make sure you have built both binutils and gdb with USE=zlib
 support for this to work.  See \fBsplitdebug\fR for general split debug
 information (upon which this feature depends).
 .TP
+.B compress\-index
+If set then a compressed copy of 'Packages' index file will be written.
+This feature is intended for Gentoo binhosts using certain webservers
+(such as, but not limited to, Nginx with gzip_static module) to avoid
+redundant on\-the\-fly compression.  The resulting file will be called
+'Packages.gz' and its modification time will match that of 'Packages'.
+.TP
 .B config\-protect\-if\-modified
 This causes the \fBCONFIG_PROTECT\fR behavior to be skipped for files
 that have not been modified since they were installed. This feature is
diff --git a/pym/portage/const.py b/pym/portage/const.py
index ceef5c56b..c2049f871 100644
--- a/pym/portage/const.py
+++ b/pym/portage/const.py
@@ -89,7 +89,7 @@ SUPPORTED_FEATURES       = frozenset([
                            "assume-digests", "binpkg-logs", "buildpkg", "buildsyspkg", "candy",
                            "ccache", "chflags", "clean-logs",
                            "collision-protect", "compress-build-logs", "compressdebug",
-                           "config-protect-if-modified",
+                           "compress-index", "config-protect-if-modified",
                            "digest", "distcc", "distcc-pump", "distlocks",
                            "downgrade-backup", "ebuild-locks", "fakeroot",
                            "fail-clean", "force-mirror", "force-prefix", "getbinpkg",
diff --git a/pym/portage/dbapi/bintree.py b/pym/portage/dbapi/bintree.py
index 03675031e..77fc0c4ef 100644
--- a/pym/portage/dbapi/bintree.py
+++ b/pym/portage/dbapi/bintree.py
@@ -41,6 +41,7 @@ import sys
 import tempfile
 import textwrap
 import warnings
+from gzip import GzipFile
 from itertools import chain
 try:
 	from urllib.parse import urlparse
@@ -1186,13 +1187,21 @@ class binarytree(object):
 			pkgindex.packages.append(d)
 
 			self._update_pkgindex_header(pkgindex.header)
-			pkgindex_filename = os.path.join(self.pkgdir, "Packages")
-			f = atomic_ofstream(pkgindex_filename)
-			pkgindex.write(f)
-			f.close()
-			# some seconds might have elapsed since TIMESTAMP
+			contents = codecs.getwriter(_encodings['repo.content'])(io.BytesIO())
+			pkgindex.write(contents)
+			contents = contents.getvalue()
 			atime = mtime = long(pkgindex.header["TIMESTAMP"])
-			os.utime(pkgindex_filename, (atime, mtime))
+
+			pkgindex_filename = os.path.join(self.pkgdir, "Packages")
+			output_files = [(atomic_ofstream(pkgindex_filename, mode="wb"), pkgindex_filename)]
+			if "compress-index" in self.settings.features:
+				gz_fname = pkgindex_filename + ".gz"
+				output_files.append((GzipFile(gz_fname, mode="wb"), gz_fname))
+			for f, fname in output_files:
+				f.write(contents)
+				f.close()
+				# some seconds might have elapsed since TIMESTAMP
+				os.utime(fname, (atime, mtime))
 		finally:
 			if pkgindex_lock:
 				unlockfile(pkgindex_lock)