[lxc-devel] [lxc/master] Make lxc-start-ephemeral Python 3.2-compatible

[cjwatson on Github]

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From e0e34b7e93ab75a8a4d006ba8429f7fd63de1b93 Mon Sep 17 00:00:00 2001
From: Colin Watson <cjwatson at ubuntu.com>
Date: Thu, 26 Jan 2017 14:32:08 +0000
Subject: [PATCH] Make lxc-start-ephemeral Python 3.2-compatible

On Ubuntu 12.04 LTS with Python 3.2, `lxc-start-ephemeral` breaks as
follows:

    Traceback (most recent call last):
      File "/usr/bin/lxc-start-ephemeral", line 371, in attach_as_user
      File "/usr/lib/python3.2/subprocess.py", line 515, in check_output
      File "/usr/lib/python3.2/subprocess.py", line 732, in __init__
    LookupError: unknown encoding: ANSI_X3.4-1968

This is because `universal_newlines=True` causes `subprocess` to use
`io.TextIOWrapper`, and in versions of Python earlier than 3.3 that
fetched the preferred encoding using `locale.getpreferredencoding()`
rather than `locale.getpreferredencoding(False)`, thereby changing the
locale and causing codecs to be reloaded.  However, `attach_as_user`
runs inside the container and thus can't rely on having access to the
same Python standard library on disk.

The workaround is to decode by hand instead, avoiding the temporary
change of locale.

Signed-off-by: Colin Watson <cjwatson at ubuntu.com>
---
 src/lxc/tools/lxc-start-ephemeral.in | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/lxc/tools/lxc-start-ephemeral.in b/src/lxc/tools/lxc-start-ephemeral.in
index 7e0c8ea..90d5f6f 100644
--- a/src/lxc/tools/lxc-start-ephemeral.in
+++ b/src/lxc/tools/lxc-start-ephemeral.in
@@ -28,6 +28,7 @@
 import argparse
 import gettext
 import lxc
+import locale
 import os
 import sys
 import subprocess
@@ -363,9 +364,14 @@ if os.path.exists("/proc/self/ns/pid"):
             if args.user:
                 username = args.user
 
-            line = subprocess.check_output(
-                ["getent", "passwd", username],
-                universal_newlines=True).rstrip("\n")
+            # This should really just use universal_newlines=True, but we do
+            # the decoding by hand instead for compatibility with Python
+            # 3.2; that used locale.getpreferredencoding() internally rather
+            # than locale.getpreferredencoding(False), and the former breaks
+            # here because we can't reload codecs at this point unless the
+            # container has the same version of Python installed.
+            line = subprocess.check_output(["getent", "passwd", username])
+            line = line.decode(locale.getpreferredencoding(False)).rstrip("\n")
             _, _, pw_uid, pw_gid, _, pw_dir, _ = line.split(":", 6)
             pw_uid = int(pw_uid)
             pw_gid = int(pw_gid)