upgrades: Refactor use of lsb_release

Tests:
- On unstable and testing:
  - Ran functional tests for upgrades.
  - Ran actions "upgrades setup" and "upgrades setup-repositories".
- On testing:
  - In develop mode, activated backports.

Signed-off-by: James Valleroy <jvalleroy@mailbox.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

actions/upgrades

@@ -13,7 +13,8 @@ import sys
 
 from plinth.action_utils import run_apt_command
 from plinth.modules.apache.components import check_url
-from plinth.modules.upgrades import is_backports_current, SOURCES_LIST
+from plinth.modules.upgrades import (get_current_release, is_backports_current,
+                                     SOURCES_LIST)
 
 AUTO_CONF_FILE = '/etc/apt/apt.conf.d/20auto-upgrades'
 LOG_FILE = '/var/log/unattended-upgrades/unattended-upgrades.log'
@@ -218,8 +219,7 @@ def _check_and_backports_sources(develop=False):
               'backports.')
         return
 
-    release = subprocess.check_output(['lsb_release', '--release',
+    release, dist = get_current_release()
-                                       '--short']).decode().strip()
     if release == 'unstable' or (release == 'testing' and not develop):
         print(f'System release is {release}. Skip enabling backports.')
         return
@@ -228,8 +228,6 @@ def _check_and_backports_sources(develop=False):
     if protocol == 'tor+http':
         print('Package download over Tor is enabled.')
 
-    dist = subprocess.check_output(['lsb_release', '--codename',
-                                    '--short']).decode().strip()
     if not _is_release_file_available(protocol, dist):
         print(f'Release file for {dist}-backports is not available yet.')
         return
@@ -251,8 +249,7 @@ def _add_apt_preferences():
     # Don't try to remove 50freedombox3.pref as this file is shipped with the
     # Debian package and is removed using maintainer scripts.
 
-    dist = subprocess.check_output(['lsb_release', '--codename',
+    _, dist = get_current_release()
-                                    '--short']).decode().strip()
     if dist == 'sid':
         print(f'System distribution is {dist}. Skip setting apt preferences '
               'for backports.')

plinth/modules/upgrades/__init__.py

@@ -148,13 +148,22 @@ def is_backports_enabled():
     return os.path.exists(SOURCES_LIST)
 
 
+def get_current_release():
+    """Return current release and codename as a tuple."""
+    output = subprocess.check_output(
+        ['lsb_release', '--release', '--codename',
+         '--short']).decode().strip()
+    lines = output.split('\n')
+    return lines[0], lines[1]
+
+
 def is_backports_current():
     """Return whether backports are enabled for the current release."""
     if not is_backports_enabled:
         return False
 
-    dist = subprocess.check_output(['lsb_release', '--codename', '--short'
+    _, dist = get_current_release()
-                                    ]).decode().strip() + '-backports'
+    dist += '-backports'
     sources = sourceslist.SourcesList()
     for source in sources:
         if source.dist == dist:
@@ -168,8 +177,7 @@ def can_activate_backports():
     if is_backports_current():
         return False
 
-    release = subprocess.check_output(['lsb_release', '--release',
+    release, _ = get_current_release()
-                                       '--short']).decode().strip()
     if release == 'unstable' or (release == 'testing' and not cfg.develop):
         return False
 

plinth/modules/upgrades/views.py

@@ -3,8 +3,6 @@
 FreedomBox app for upgrades.
 """
 
-import subprocess
-
 from django.contrib import messages
 from django.shortcuts import redirect
 from django.urls import reverse_lazy
@@ -31,8 +29,8 @@ class UpgradesConfigurationView(AppView):
     def get_context_data(self, *args, **kwargs):
         context = super().get_context_data(*args, **kwargs)
         context['can_activate_backports'] = upgrades.can_activate_backports()
-        context['dist'] = subprocess.check_output(
+        _, dist = upgrades.get_current_release()
-            ['lsb_release', '--codename', '--short']).decode().strip()
+        context['dist'] = dist
         context['is_busy'] = package.is_package_manager_busy()
         context['log'] = get_log()
         context['refresh_page_sec'] = 3 if context['is_busy'] else None