server: load ai from combined-cloud-config.json

Attempt to load autoinstall from
/run/cloud-init/combined-cloud-config.json first, if present.
Fallback to existing methods, which requires that cloud-init in the snap
is able to unpickle the data created by cloud-init outside the snap.
See also LP: #2022102.

subiquity/server/server.py

@@ -22,9 +22,7 @@
 
 from aiohttp import web
 
-from cloudinit import safeyaml, stages
 from cloudinit.config.cc_set_passwords import rand_user_password
-from cloudinit.distros import ug_util
 
 import jsonschema
 
@@ -49,6 +47,7 @@
     )
 from subiquitycore.utils import arun_command, run_command
 
+from subiquity.cloudinit import get_host_combined_cloud_config
 from subiquity.common.api.server import (
     bind,
     controller_for_request,
@@ -533,6 +532,48 @@ async def start_site(self, runner: web.AppRunner):
     def base_relative(self, path):
         return os.path.join(self.base_model.root, path)
 
+    def load_cloud_config(self):
+        # cloud-init 23.3 introduced combined-cloud-config, which helps to
+        # prevent subiquity from having to go load cloudinit modules.
+        # This matters because a downgrade pickle deserialization issue may
+        # occur when the cloud-init outside the snap (which writes the pickle
+        # data) is newer than the one inside the snap (which reads the pickle
+        # data if we do stages.Init()).  LP: #2022102
+
+        # The stages.Init() code path should be retained until we can assume a
+        # minimum cloud-init version of 23.3 (when Subiquity drops support for
+        # Ubuntu 22.04.2 LTS and earlier, presumably)
+
+        cloud_cfg = get_host_combined_cloud_config()
+        if len(cloud_cfg) > 0:
+            log.debug("loading cloud config from combined-cloud-config")
+            system_info = cloud_cfg.get('system_info', {})
+            default_user = system_info.get('default_user', {})
+            self.installer_user_name = default_user.get('name')
+
+        else:
+            log.debug("loading cloud-config from stages.Init()")
+            from cloudinit import stages
+            from cloudinit.distros import ug_util
+
+            init = stages.Init()
+            init.read_cfg()
+            init.fetch(existing="trust")
+            cloud = init.cloudify()
+            cloud_cfg = cloud.cfg
+
+            users = ug_util.normalize_users_groups(cloud_cfg, cloud.distro)[0]
+            self.installer_user_name = ug_util.extract_default(users)[0]
+
+        if 'autoinstall' in cloud_cfg:
+            log.debug('autoinstall found in cloud-config')
+            cfg = cloud_cfg['autoinstall']
+            target = self.base_relative(cloud_autoinstall_path)
+            from cloudinit import safeyaml
+            write_file(target, safeyaml.dumps(cfg))
+        else:
+            log.debug('no autoinstall found in cloud-config')
+
     async def wait_for_cloudinit(self):
         if self.opts.dry_run:
             self.cloud_init_ok = True
@@ -549,19 +590,9 @@ async def wait_for_cloudinit(self):
             self.cloud_init_ok = True
         log.debug("waited %ss for cloud-init", time.time() - ci_start)
         if "status: done" in status_txt:
-            log.debug("loading cloud config")
-            init = stages.Init()
-            init.read_cfg()
-            init.fetch(existing="trust")
-            self.cloud = init.cloudify()
-            if 'autoinstall' in self.cloud.cfg:
-                cfg = self.cloud.cfg['autoinstall']
-                target = self.base_relative(cloud_autoinstall_path)
-                write_file(target, safeyaml.dumps(cfg))
+            self.load_cloud_config()
         else:
-            log.debug(
-                "cloud-init status: %r, assumed disabled",
-                status_txt)
+            log.debug("cloud-init status: %r, assumed disabled", status_txt)
 
     def select_autoinstall(self):
         # precedence
@@ -626,13 +657,9 @@ def use_passwd(passwd):
             use_passwd(rand_user_password())
             return
 
-        (users, _groups) = ug_util.normalize_users_groups(
-            self.cloud.cfg, self.cloud.distro)
-        (username, _user_config) = ug_util.extract_default(users)
-
-        self.installer_user_name = username
+        username = self.installer_user_name
 
-        if username is None:
+        if self.installer_user_name is None:
             # extract_default can return None, if there is no default user
             self.installer_user_passwd_kind = PasswordKind.NONE
         elif self._user_has_password(username):

subiquity/server/tests/test_server.py

@@ -154,10 +154,6 @@ async def test_interactive_sections_one(self):
 
 
 class TestDefaultUser(SubiTestCase):
-    @patch('subiquity.server.server.ug_util.normalize_users_groups',
-           Mock(return_value=(None, None)))
-    @patch('subiquity.server.server.ug_util.extract_default',
-           Mock(return_value=(None, None)))
     @patch('subiquity.server.server.user_key_fingerprints',
            Mock(side_effect=Exception('should not be called')))
     async def test_no_default_user(self):