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@ubuntu.com>

diff --git a/src/lxc/lxc-start-ephemeral.in b/src/lxc/lxc-start-ephemeral.in
index d8240ab0ddeca39cc3fcc69c5fb244457e1c3a02..9a42ba1e288018fcc5c9bfba990c3e7b456f5d18 100644 (file)
--- a/src/lxc/lxc-start-ephemeral.in
+++ b/src/lxc/lxc-start-ephemeral.in
@@ -28,6 +28,7 @@
 import argparse
 import gettext
 import lxc
+import locale
 import os
 import sys
 import subprocess
@@ -337,9 +338,14 @@ 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)