setup: Add option to handle configuration prompts during install

This is optional and does not affect normal installations. However, when
performing configuration migration in FreedomBox (due to unattended-upgrades
refusing it), it is useful as a part of strategy to read configuration, force
install new configuration files and apply configuration again. This option can
be used on such cases.

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

actions/packages

@@ -41,6 +41,9 @@ def parse_arguments():
     subparser.add_argument(
         '--skip-recommends', action='store_true',
         help='whether to skip installing recommended packages')
+    subparser.add_argument(
+        '--force-configuration', choices=['new', 'old'],
+        help='force old/new configuration files during install')
     subparser.add_argument(
         'module', help='name of module for which package is being installed')
     subparser.add_argument('packages', nargs='+',
@@ -85,11 +88,19 @@ def subcommand_install(arguments):
         print('Access check failed:', exception, file=sys.stderr)
         sys.exit(99)
 
+    extra_arguments = []
     if arguments.skip_recommends:
-        _run_apt_command(
-            ['install', '--no-install-recommends'] + arguments.packages)
-    else:
-        _run_apt_command(['install'] + arguments.packages)
+        extra_arguments.append('--no-install-recommends')
+
+    if arguments.force_configuration == 'old':
+        extra_arguments += [
+            '-o', 'Dpkg::Options::=--force-confdef', '-o',
+            'Dpkg::Options::=--force-confold'
+        ]
+    elif arguments.force_configuration == 'new':
+        extra_arguments += ['-o', 'Dpkg::Options::=--force-confnew']
+
+    _run_apt_command(['install'] + extra_arguments + arguments.packages)
 
 
 def _assert_managed_packages(module, packages):

plinth/package.py

@@ -68,23 +68,42 @@ class Transaction(object):
         self.percentage = 0
         self.stderr = None
 
-    def install(self, skip_recommends=False):
+    def install(self, skip_recommends=False, force_configuration=None):
         """Run an apt-get transaction to install given packages.
 
         FreedomBox Service (Plinth) needs to be running as root when calling
         this. Currently, this is meant to be only during first time setup when
         --setup is argument is passed.
 
+        If force_configuration is set to 'new', dpkg options will be enabled to
+        make it force overwrite (without prompts) new configuration in place of
+        old configuration (with a backup). This is useful when writing
+        migration scripts in FreedomBox to handle the upgrades when
+        unattended-upgrades refuse to upgrade a package due to configuration
+        prompts.
+
+        If force_configuration is set to 'old', dpkg options will be enabled to
+        make it keep the old configuration (without prompts). This is useful
+        when the Debian packages introduce new configuration with just
+        cosmetics (such as updates to comments) and keeping the old
+        configuration has same semantics.
+
+        If force_configuration is None, no special options are passed to
+        apt/dpkg for configuration file behavior.
+
         """
         try:
             self._run_apt_command(['update'])
+            extra_arguments = []
             if skip_recommends:
-                self._run_apt_command(
-                    ['install', '--skip-recommends', self.module_name] +
-                    self.package_names)
-            else:
-                self._run_apt_command(['install', self.module_name] +
-                                      self.package_names)
+                extra_arguments.append('--skip-recommends')
+
+            if force_configuration is not None:
+                extra_arguments.append(
+                    '--force-configuration={}'.format(force_configuration))
+
+            self._run_apt_command(['install'] + extra_arguments +
+                                  [self.module_name] + self.package_names)
         except subprocess.CalledProcessError as exception:
             logger.exception('Error installing package: %s', exception)
             raise

plinth/setup.py

@@ -101,7 +101,8 @@ class Helper(object):
             self.is_finished = True
             self.current_operation = None
 
-    def install(self, package_names, skip_recommends=False):
+    def install(self, package_names, skip_recommends=False,
+                force_configuration=None):
         """Install a set of packages marking progress."""
         if self.allow_install is False:
             # Raise error if packages are not already installed.
@@ -120,7 +121,7 @@ class Helper(object):
             'step': 'install',
             'transaction': transaction,
         }
-        transaction.install(skip_recommends)
+        transaction.install(skip_recommends, force_configuration)
 
     def call(self, step, method, *args, **kwargs):
         """Call an arbitrary method during setup and note down its stage."""