cc_snap: Add new module to install and configure snapd and snap packages.

Support installing and configuring snaps on ubuntu systems. Now,
cloud-config files can provide a list or dictionary of snap:assertions
which will be allow configuration of snapd on a system via 'snap ack'
calls. The snap:commands configuration option supports arbitrary system
commands intended to interact with snappy's cli. This allows users to run
arbitrary snappy commands to create users, download, install and
configure snap packages and snapd.

This branch also deprecates old snappy and snap_config modules leaving
warnings in documentation and runtime for consumers of these modules.
Deprecated snap* modules will be dropped in cloud-init v.18.2 release.

6 files changed, 837 insertions, 5 deletions

diff --git a/cloudinit/config/cc_puppet.py b/cloudinit/config/cc_puppet.py
index 57a170fb..297e0721 100644
--- a/cloudinit/config/cc_puppet.py
+++ b/cloudinit/config/cc_puppet.py
@@ -140,8 +140,9 @@ def handle(name, cfg, cloud, log, _args):
         # (TODO(harlowja) is this really needed??)
         cleaned_lines = [i.lstrip() for i in contents.splitlines()]
         cleaned_contents = '\n'.join(cleaned_lines)
-        puppet_config.readfp(StringIO(cleaned_contents),
-                             filename=p_constants.conf_path)
+        puppet_config.readfp(   # pylint: disable=W1505
+            StringIO(cleaned_contents),
+            filename=p_constants.conf_path)
         for (cfg_name, cfg) in puppet_cfg['conf'].items():
             # Cert configuration is a special case
             # Dump the puppet master ca certificate in the correct place
@@ -149,8 +150,7 @@ def handle(name, cfg, cloud, log, _args):
                 # Puppet ssl sub-directory isn't created yet
                 # Create it with the proper permissions and ownership
                 util.ensure_dir(p_constants.ssl_dir, 0o771)
-                util.chownbyname(p_constants.ssl_dir, 'puppet', 'root')
-                util.ensure_dir(p_constants.ssl_cert_dir)
+
                 util.chownbyname(p_constants.ssl_cert_dir, 'puppet', 'root')
                 util.write_file(p_constants.ssl_cert_path, cfg)
                 util.chownbyname(p_constants.ssl_cert_path, 'puppet', 'root')
diff --git a/cloudinit/config/cc_snap.py b/cloudinit/config/cc_snap.py
new file mode 100644
index 00000000..db965291
--- /dev/null
+++ b/cloudinit/config/cc_snap.py
@@ -0,0 +1,273 @@
+# Copyright (C) 2018 Canonical Ltd.
+#
+# This file is part of cloud-init. See LICENSE file for license information.
+
+"""Snap: Install, configure and manage snapd and snap packages."""
+
+import sys
+from textwrap import dedent
+
+from cloudinit import log as logging
+from cloudinit.config.schema import (
+    get_schema_doc, validate_cloudconfig_schema)
+from cloudinit.settings import PER_INSTANCE
+from cloudinit import util
+
+
+distros = ['ubuntu']
+frequency = PER_INSTANCE
+
+LOG = logging.getLogger(__name__)
+
+schema = {
+    'id': 'cc_snap',
+    'name': 'Snap',
+    'title': 'Install, configure and manage snapd and snap packages',
+    'description': dedent("""\
+        This module provides a simple configuration namespace in cloud-init to
+        both setup snapd and install snaps.
+
+        .. note::
+            Both ``assertions`` and ``commands`` values can be either a
+            dictionary or a list. If these configs are provided as a
+            dictionary, the keys are only used to order the execution of the
+            assertions or commands and the dictionary is merged with any
+            vendor-data snap configuration provided. If a list is provided by
+            the user instead of a dict, any vendor-data snap configuration is
+            ignored.
+
+        The ``assertions`` configuration option is a dictionary or list of
+        properly-signed snap assertions which will run before any snap
+        ``commands``. They will be added to snapd's assertion database by
+        invoking ``snap ack <aggregate_assertion_file>``.
+
+        Snap ``commands`` is a dictionary or list of individual snap
+        commands to run on the target system. These commands can be used to
+        create snap users, install snaps and provide snap configuration.
+
+        .. note::
+            If 'side-loading' private/unpublished snaps on an instance, it is
+            best to create a snap seed directory and seed.yaml manifest in
+            **/var/lib/snapd/seed/** which snapd automatically installs on
+            startup.
+
+        **Development only**: The ``squashfuse_in_container`` boolean can be
+        set true to install squashfuse package when in a container to enable
+        snap installs. Default is false.
+        """),
+    'distros': distros,
+    'examples': [dedent("""\
+        snap:
+            assertions:
+              00: |
+              signed_assertion_blob_here
+              02: |
+              signed_assertion_blob_here
+            commands:
+              00: snap create-user --sudoer --known <snap-user>@mydomain.com
+              01: snap install canonical-livepatch
+              02: canonical-livepatch enable <AUTH_TOKEN>
+    """), dedent("""\
+        # LXC-based containers require squashfuse before snaps can be installed
+        snap:
+            commands:
+                00: apt-get install squashfuse -y
+                11: snap install emoj
+
+    """), dedent("""\
+        # Convenience: the snap command can be omitted when specifying commands
+        # as a list and 'snap' will automatically be prepended.
+        # The following commands are equivalent:
+        snap:
+            commands:
+                00: ['install', 'vlc']
+                01: ['snap', 'install', 'vlc']
+                02: snap install vlc
+                03: 'snap install vlc'
+    """)],
+    'frequency': PER_INSTANCE,
+    'type': 'object',
+    'properties': {
+        'snap': {
+            'type': 'object',
+            'properties': {
+                'assertions': {
+                    'type': ['object', 'array'],  # Array of strings or dict
+                    'items': {'type': 'string'},
+                    'additionalItems': False,  # Reject items non-string
+                    'minItems': 1,
+                    'minProperties': 1,
+                    'uniqueItems': True
+                },
+                'commands': {
+                    'type': ['object', 'array'],  # Array of strings or dict
+                    'items': {
+                        'oneOf': [
+                            {'type': 'array', 'items': {'type': 'string'}},
+                            {'type': 'string'}]
+                    },
+                    'additionalItems': False,  # Reject non-string & non-list
+                    'minItems': 1,
+                    'minProperties': 1,
+                    'uniqueItems': True
+                },
+                'squashfuse_in_container': {
+                    'type': 'boolean'
+                }
+            },
+            'additionalProperties': False,  # Reject keys not in schema
+            'required': [],
+            'minProperties': 1
+        }
+    }
+}
+
+# TODO schema for 'assertions' and 'commands' are too permissive at the moment.
+# Once python-jsonschema supports schema draft 6 add support for arbitrary
+# object keys with 'patternProperties' constraint to validate string values.
+
+__doc__ = get_schema_doc(schema)  # Supplement python help()
+
+SNAP_CMD = "snap"
+ASSERTIONS_FILE = "/var/lib/cloud/instance/snapd.assertions"
+
+
+def add_assertions(assertions):
+    """Import list of assertions.
+
+    Import assertions by concatenating each assertion into a
+    string separated by a '\n'.  Write this string to a instance file and
+    then invoke `snap ack /path/to/file` and check for errors.
+    If snap exits 0, then all assertions are imported.
+    """
+    if not assertions:
+        return
+    LOG.debug('Importing user-provided snap assertions')
+    if isinstance(assertions, dict):
+        assertions = assertions.values()
+    elif not isinstance(assertions, list):
+        raise TypeError(
+            'assertion parameter was not a list or dict: {assertions}'.format(
+                assertions=assertions))
+
+    snap_cmd = [SNAP_CMD, 'ack']
+    combined = "\n".join(assertions)
+
+    for asrt in assertions:
+        LOG.debug('Snap acking: %s', asrt.split('\n')[0:2])
+
+    util.write_file(ASSERTIONS_FILE, combined.encode('utf-8'))
+    util.subp(snap_cmd + [ASSERTIONS_FILE], capture=True)
+
+
+def prepend_snap_commands(commands):
+    """Ensure user-provided commands start with SNAP_CMD, warn otherwise.
+
+    Each command is either a list or string. Perform the following:
+       - When the command is a list, pop the first element if it is None
+       - When the command is a list, insert SNAP_CMD as the first element if
+         not present.
+       - When the command is a string containing a non-snap command, warn.
+
+    Support cut-n-paste snap command sets from public snappy documentation.
+    Allow flexibility to provide non-snap environment/config setup if needed.
+
+    @commands: List of commands. Each command element is a list or string.
+
+    @return: List of 'fixed up' snap commands.
+    @raise: TypeError on invalid config item type.
+    """
+    warnings = []
+    errors = []
+    fixed_commands = []
+    for command in commands:
+        if isinstance(command, list):
+            if command[0] is None:  # Avoid warnings by specifying None
+                command = command[1:]
+            elif command[0] != SNAP_CMD:  # Automatically prepend SNAP_CMD
+                command.insert(0, SNAP_CMD)
+        elif isinstance(command, str):
+            if not command.startswith('%s ' % SNAP_CMD):
+                warnings.append(command)
+        else:
+            errors.append(str(command))
+            continue
+        fixed_commands.append(command)
+
+    if warnings:
+        LOG.warning(
+            'Non-snap commands in snap config:\n%s', '\n'.join(warnings))
+    if errors:
+        raise TypeError(
+            'Invalid snap config.'
+            ' These commands are not a string or list:\n' + '\n'.join(errors))
+    return fixed_commands
+
+
+def run_commands(commands):
+    """Run the provided commands provided in snap:commands configuration.
+
+     Commands are run individually. Any errors are collected and reported
+     after attempting all commands.
+
+     @param commands: A list or dict containing commands to run. Keys of a
+         dict will be used to order the commands provided as dict values.
+     """
+    if not commands:
+        return
+    LOG.debug('Running user-provided snap commands')
+    if isinstance(commands, dict):
+        # Sort commands based on dictionary key
+        commands = [v for _, v in sorted(commands.items())]
+    elif not isinstance(commands, list):
+        raise TypeError(
+            'commands parameter was not a list or dict: {commands}'.format(
+                commands=commands))
+
+    fixed_snap_commands = prepend_snap_commands(commands)
+
+    cmd_failures = []
+    for command in fixed_snap_commands:
+        shell = isinstance(command, str)
+        try:
+            util.subp(command, shell=shell, status_cb=sys.stderr.write)
+        except util.ProcessExecutionError as e:
+            cmd_failures.append(str(e))
+    if cmd_failures:
+        msg = 'Failures running snap commands:\n{cmd_failures}'.format(
+            cmd_failures=cmd_failures)
+        util.logexc(LOG, msg)
+        raise RuntimeError(msg)
+
+
+# RELEASE_BLOCKER: Once LP: #1628289 is released on xenial, drop this function.
+def maybe_install_squashfuse(cloud):
+    """Install squashfuse if we are in a container."""
+    if not util.is_container():
+        return
+    try:
+        cloud.distro.update_package_sources()
+    except Exception as e:
+        util.logexc(LOG, "Package update failed")
+        raise
+    try:
+        cloud.distro.install_packages(['squashfuse'])
+    except Exception as e:
+        util.logexc(LOG, "Failed to install squashfuse")
+        raise
+
+
+def handle(name, cfg, cloud, log, args):
+    cfgin = cfg.get('snap', {})
+    if not cfgin:
+        LOG.debug(("Skipping module named %s,"
+                   " no 'snap' key in configuration"), name)
+        return
+
+    validate_cloudconfig_schema(cfg, schema)
+    if util.is_true(cfgin.get('squashfuse_in_container', False)):
+        maybe_install_squashfuse(cloud)
+    add_assertions(cfgin.get('assertions', []))
+    run_commands(cfgin.get('commands', []))
+
+# vi: ts=4 expandtab
diff --git a/cloudinit/config/cc_snap_config.py b/cloudinit/config/cc_snap_config.py
index e82c0811..afe297ee 100644
--- a/cloudinit/config/cc_snap_config.py
+++ b/cloudinit/config/cc_snap_config.py
@@ -4,11 +4,15 @@
 #
 # This file is part of cloud-init. See LICENSE file for license information.
 
+# RELEASE_BLOCKER: Remove this deprecated module in 18.3
 """
 Snap Config
 -----------
 **Summary:** snap_config modules allows configuration of snapd.
 
+**Deprecated**: Use :ref:`snap` module instead. This module will not exist
+in cloud-init 18.3.
+
 This module uses the same ``snappy`` namespace for configuration but
 acts only only a subset of the configuration.
 
@@ -154,6 +158,9 @@ def handle(name, cfg, cloud, log, args):
         LOG.debug('No snappy config provided, skipping')
         return
 
+    log.warning(
+        'DEPRECATION: snap_config module will be dropped in 18.3 release.'
+        ' Use snap module instead')
     if not(util.system_is_snappy()):
         LOG.debug("%s: system not snappy", name)
         return
diff --git a/cloudinit/config/cc_snappy.py b/cloudinit/config/cc_snappy.py
index eecb8178..bab80bbe 100644
--- a/cloudinit/config/cc_snappy.py
+++ b/cloudinit/config/cc_snappy.py
@@ -1,10 +1,14 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 
+# RELEASE_BLOCKER: Remove this deprecated module in 18.3
 """
 Snappy
 ------
 **Summary:** snappy modules allows configuration of snappy.
 
+**Deprecated**: Use :ref:`snap` module instead. This module will not exist
+in cloud-init 18.3.
+
 The below example config config would install ``etcd``, and then install
 ``pkg2.smoser`` with a ``<config-file>`` argument where ``config-file`` has
 ``config-blob`` inside it. If ``pkgname`` is installed already, then
@@ -271,6 +275,10 @@ def handle(name, cfg, cloud, log, args):
         LOG.debug("%s: 'auto' mode, and system not snappy", name)
         return
 
+    log.warning(
+        'DEPRECATION: snappy module will be dropped in 18.3 release.'
+        ' Use snap module instead')
+
     set_snappy_command()
 
     pkg_ops = get_package_ops(packages=mycfg['packages'],
diff --git a/cloudinit/config/tests/test_snap.py b/cloudinit/config/tests/test_snap.py
new file mode 100644
index 00000000..c2dd6afe
--- /dev/null
+++ b/cloudinit/config/tests/test_snap.py
@@ -0,0 +1,533 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+import re
+from six import StringIO
+
+from cloudinit.config.cc_snap import (
+    ASSERTIONS_FILE, add_assertions, handle, prepend_snap_commands,
+    maybe_install_squashfuse, run_commands, schema)
+from cloudinit.config.schema import validate_cloudconfig_schema
+from cloudinit import util
+from cloudinit.tests.helpers import CiTestCase, mock, wrap_and_call
+
+
+SYSTEM_USER_ASSERTION = """\
+type: system-user
+authority-id: LqvZQdfyfGlYvtep4W6Oj6pFXP9t1Ksp
+brand-id: LqvZQdfyfGlYvtep4W6Oj6pFXP9t1Ksp
+email: foo@bar.com
+password: $6$E5YiAuMIPAwX58jG$miomhVNui/vf7f/3ctB/f0RWSKFxG0YXzrJ9rtJ1ikvzt
+series:
+- 16
+since: 2016-09-10T16:34:00+03:00
+until: 2017-11-10T16:34:00+03:00
+username: baz
+sign-key-sha3-384: RuVvnp4n52GilycjfbbTCI3_L8Y6QlIE75wxMc0KzGV3AUQqVd9GuXoj
+
+AcLBXAQAAQoABgUCV/UU1wAKCRBKnlMoJQLkZVeLD/9/+hIeVywtzsDA3oxl+P+u9D13y9s6svP
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+v1z+1+URx6Xlq3Jq18y5pZ6fY3IDJ6km2nQPMzcm4Q=="""
+
+ACCOUNT_ASSERTION = """\
+type: account-key
+authority-id: canonical
+revision: 2
+public-key-sha3-384: BWDEoaqyr25nF5SNCvEv2v7QnM9QsfCc0PBMYD_i2NGSQ32EF2d4D0
+account-id: canonical
+name: store
+since: 2016-04-01T00:00:00.0Z
+body-length: 717
+sign-key-sha3-384: -CvQKAwRQ5h3Ffn10FILJoEZUXOv6km9FwA80-Rcj-f-6jadQ89VRswH
+
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+
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+oG3Ie3WOHrVjCLXIdYslpL1O4nadqR6Xv58pHj6k"""
+
+
+class FakeCloud(object):
+    def __init__(self, distro):
+        self.distro = distro
+
+
+class TestAddAssertions(CiTestCase):
+
+    with_logs = True
+
+    def setUp(self):
+        super(TestAddAssertions, self).setUp()
+        self.tmp = self.tmp_dir()
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_add_assertions_on_empty_list(self, m_subp):
+        """When provided with an empty list, add_assertions does nothing."""
+        add_assertions([])
+        self.assertEqual('', self.logs.getvalue())
+        m_subp.assert_not_called()
+
+    def test_add_assertions_on_non_list_or_dict(self):
+        """When provided an invalid type, add_assertions raises an error."""
+        with self.assertRaises(TypeError) as context_manager:
+            add_assertions(assertions="I'm Not Valid")
+        self.assertEqual(
+            "assertion parameter was not a list or dict: I'm Not Valid",
+            str(context_manager.exception))
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_add_assertions_adds_assertions_as_list(self, m_subp):
+        """When provided with a list, add_assertions adds all assertions."""
+        self.assertEqual(
+            ASSERTIONS_FILE, '/var/lib/cloud/instance/snapd.assertions')
+        assert_file = self.tmp_path('snapd.assertions', dir=self.tmp)
+        assertions = [SYSTEM_USER_ASSERTION, ACCOUNT_ASSERTION]
+        wrap_and_call(
+            'cloudinit.config.cc_snap',
+            {'ASSERTIONS_FILE': {'new': assert_file}},
+            add_assertions, assertions)
+        self.assertIn(
+            'Importing user-provided snap assertions', self.logs.getvalue())
+        self.assertIn(
+            'sertions', self.logs.getvalue())
+        self.assertEqual(
+            [mock.call(['snap', 'ack', assert_file], capture=True)],
+            m_subp.call_args_list)
+        compare_file = self.tmp_path('comparison', dir=self.tmp)
+        util.write_file(compare_file, '\n'.join(assertions).encode('utf-8'))
+        self.assertEqual(
+            util.load_file(compare_file), util.load_file(assert_file))
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_add_assertions_adds_assertions_as_dict(self, m_subp):
+        """When provided with a dict, add_assertions adds all assertions."""
+        self.assertEqual(
+            ASSERTIONS_FILE, '/var/lib/cloud/instance/snapd.assertions')
+        assert_file = self.tmp_path('snapd.assertions', dir=self.tmp)
+        assertions = {'00': SYSTEM_USER_ASSERTION, '01': ACCOUNT_ASSERTION}
+        wrap_and_call(
+            'cloudinit.config.cc_snap',
+            {'ASSERTIONS_FILE': {'new': assert_file}},
+            add_assertions, assertions)
+        self.assertIn(
+            'Importing user-provided snap assertions', self.logs.getvalue())
+        self.assertIn(
+            "DEBUG: Snap acking: ['type: system-user', 'authority-id: Lqv",
+            self.logs.getvalue())
+        self.assertIn(
+            "DEBUG: Snap acking: ['type: account-key', 'authority-id: canonic",
+            self.logs.getvalue())
+        self.assertEqual(
+            [mock.call(['snap', 'ack', assert_file], capture=True)],
+            m_subp.call_args_list)
+        compare_file = self.tmp_path('comparison', dir=self.tmp)
+        combined = '\n'.join(assertions.values())
+        util.write_file(compare_file, combined.encode('utf-8'))
+        self.assertEqual(
+            util.load_file(compare_file), util.load_file(assert_file))
+
+
+class TestPrepentSnapCommands(CiTestCase):
+
+    with_logs = True
+
+    def test_prepend_snap_commands_errors_on_neither_string_nor_list(self):
+        """Raise an error for each command which is not a string or list."""
+        orig_commands = ['ls', 1, {'not': 'gonna work'}, ['snap', 'list']]
+        with self.assertRaises(TypeError) as context_manager:
+            prepend_snap_commands(orig_commands)
+        self.assertEqual(
+            "Invalid snap config. These commands are not a string or list:\n"
+            "1\n{'not': 'gonna work'}",
+            str(context_manager.exception))
+
+    def test_prepend_snap_commands_warns_on_non_snap_string_commands(self):
+        """Warn on each non-snap for commands of type string."""
+        orig_commands = ['ls', 'snap list', 'touch /blah', 'snap install x']
+        fixed_commands = prepend_snap_commands(orig_commands)
+        self.assertEqual(
+            'WARNING: Non-snap commands in snap config:\n'
+            'ls\ntouch /blah\n',
+            self.logs.getvalue())
+        self.assertEqual(orig_commands, fixed_commands)
+
+    def test_prepend_snap_commands_prepends_on_non_snap_list_commands(self):
+        """Prepend 'snap' for each non-snap command of type list."""
+        orig_commands = [['ls'], ['snap', 'list'], ['snapa', '/blah'],
+                         ['snap', 'install', 'x']]
+        expected = [['snap', 'ls'], ['snap', 'list'],
+                    ['snap', 'snapa', '/blah'],
+                    ['snap', 'install', 'x']]
+        fixed_commands = prepend_snap_commands(orig_commands)
+        self.assertEqual('', self.logs.getvalue())
+        self.assertEqual(expected, fixed_commands)
+
+    def test_prepend_snap_commands_removes_first_item_when_none(self):
+        """Remove the first element of a non-snap command when it is None."""
+        orig_commands = [[None, 'ls'], ['snap', 'list'],
+                         [None, 'touch', '/blah'],
+                         ['snap', 'install', 'x']]
+        expected = [['ls'], ['snap', 'list'],
+                    ['touch', '/blah'],
+                    ['snap', 'install', 'x']]
+        fixed_commands = prepend_snap_commands(orig_commands)
+        self.assertEqual('', self.logs.getvalue())
+        self.assertEqual(expected, fixed_commands)
+
+
+class TestRunCommands(CiTestCase):
+
+    with_logs = True
+
+    def setUp(self):
+        super(TestRunCommands, self).setUp()
+        self.tmp = self.tmp_dir()
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_run_commands_on_empty_list(self, m_subp):
+        """When provided with an empty list, run_commands does nothing."""
+        run_commands([])
+        self.assertEqual('', self.logs.getvalue())
+        m_subp.assert_not_called()
+
+    def test_run_commands_on_non_list_or_dict(self):
+        """When provided an invalid type, run_commands raises an error."""
+        with self.assertRaises(TypeError) as context_manager:
+            run_commands(commands="I'm Not Valid")
+        self.assertEqual(
+            "commands parameter was not a list or dict: I'm Not Valid",
+            str(context_manager.exception))
+
+    def test_run_command_logs_commands_and_exit_codes_to_stderr(self):
+        """All exit codes are logged to stderr."""
+        outfile = self.tmp_path('output.log', dir=self.tmp)
+
+        cmd1 = 'echo "HI" >> %s' % outfile
+        cmd2 = 'bogus command'
+        cmd3 = 'echo "MOM" >> %s' % outfile
+        commands = [cmd1, cmd2, cmd3]
+
+        mock_path = 'cloudinit.config.cc_snap.sys.stderr'
+        with mock.patch(mock_path, new_callable=StringIO) as m_stderr:
+            with self.assertRaises(RuntimeError) as context_manager:
+                run_commands(commands=commands)
+
+        self.assertIsNotNone(
+            re.search(r'bogus: (command )?not found',
+                      str(context_manager.exception)),
+            msg='Expected bogus command not found')
+        expected_stderr_log = '\n'.join([
+            'Begin run command: {cmd}'.format(cmd=cmd1),
+            'End run command: exit(0)',
+            'Begin run command: {cmd}'.format(cmd=cmd2),
+            'ERROR: End run command: exit(127)',
+            'Begin run command: {cmd}'.format(cmd=cmd3),
+            'End run command: exit(0)\n'])
+        self.assertEqual(expected_stderr_log, m_stderr.getvalue())
+
+    def test_run_command_as_lists(self):
+        """When commands are specified as a list, run them in order."""
+        outfile = self.tmp_path('output.log', dir=self.tmp)
+
+        cmd1 = 'echo "HI" >> %s' % outfile
+        cmd2 = 'echo "MOM" >> %s' % outfile
+        commands = [cmd1, cmd2]
+        mock_path = 'cloudinit.config.cc_snap.sys.stderr'
+        with mock.patch(mock_path, new_callable=StringIO):
+            run_commands(commands=commands)
+
+        self.assertIn(
+            'DEBUG: Running user-provided snap commands',
+            self.logs.getvalue())
+        self.assertEqual('HI\nMOM\n', util.load_file(outfile))
+        self.assertIn(
+            'WARNING: Non-snap commands in snap config:', self.logs.getvalue())
+
+    def test_run_command_dict_sorted_as_command_script(self):
+        """When commands are a dict, sort them and run."""
+        outfile = self.tmp_path('output.log', dir=self.tmp)
+        cmd1 = 'echo "HI" >> %s' % outfile
+        cmd2 = 'echo "MOM" >> %s' % outfile
+        commands = {'02': cmd1, '01': cmd2}
+        mock_path = 'cloudinit.config.cc_snap.sys.stderr'
+        with mock.patch(mock_path, new_callable=StringIO):
+            run_commands(commands=commands)
+
+        expected_messages = [
+            'DEBUG: Running user-provided snap commands']
+        for message in expected_messages:
+            self.assertIn(message, self.logs.getvalue())
+        self.assertEqual('MOM\nHI\n', util.load_file(outfile))
+
+
+class TestSchema(CiTestCase):
+
+    with_logs = True
+
+    def test_schema_warns_on_snap_not_as_dict(self):
+        """If the snap configuration is not a dict, emit a warning."""
+        validate_cloudconfig_schema({'snap': 'wrong type'}, schema)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap: 'wrong type' is not of type"
+            " 'object'\n",
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    def test_schema_disallows_unknown_keys(self, _):
+        """Unknown keys in the snap configuration emit warnings."""
+        validate_cloudconfig_schema(
+            {'snap': {'commands': ['ls'], 'invalid-key': ''}}, schema)
+        self.assertIn(
+            'WARNING: Invalid config:\nsnap: Additional properties are not'
+            " allowed ('invalid-key' was unexpected)",
+            self.logs.getvalue())
+
+    def test_warn_schema_requires_either_commands_or_assertions(self):
+        """Warn when snap configuration lacks both commands and assertions."""
+        validate_cloudconfig_schema(
+            {'snap': {}}, schema)
+        self.assertIn(
+            'WARNING: Invalid config:\nsnap: {} does not have enough'
+            ' properties',
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    def test_warn_schema_commands_is_not_list_or_dict(self, _):
+        """Warn when snap:commands config is not a list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'commands': 'broken'}}, schema)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap.commands: 'broken' is not of type"
+            " 'object', 'array'\n",
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    def test_warn_schema_when_commands_is_empty(self, _):
+        """Emit warnings when snap:commands is an empty list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'commands': []}}, schema)
+        validate_cloudconfig_schema(
+            {'snap': {'commands': {}}}, schema)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap.commands: [] is too short\n"
+            "WARNING: Invalid config:\nsnap.commands: {} does not have enough"
+            " properties\n",
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    def test_schema_when_commands_are_list_or_dict(self, _):
+        """No warnings when snap:commands are either a list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'commands': ['valid']}}, schema)
+        validate_cloudconfig_schema(
+            {'snap': {'commands': {'01': 'also valid'}}}, schema)
+        self.assertEqual('', self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.add_assertions')
+    def test_warn_schema_assertions_is_not_list_or_dict(self, _):
+        """Warn when snap:assertions config is not a list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'assertions': 'broken'}}, schema)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap.assertions: 'broken' is not of"
+            " type 'object', 'array'\n",
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.add_assertions')
+    def test_warn_schema_when_assertions_is_empty(self, _):
+        """Emit warnings when snap:assertions is an empty list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'assertions': []}}, schema)
+        validate_cloudconfig_schema(
+            {'snap': {'assertions': {}}}, schema)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap.assertions: [] is too short\n"
+            "WARNING: Invalid config:\nsnap.assertions: {} does not have"
+            " enough properties\n",
+            self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.add_assertions')
+    def test_schema_when_assertions_are_list_or_dict(self, _):
+        """No warnings when snap:assertions are a list or dict."""
+        validate_cloudconfig_schema(
+            {'snap': {'assertions': ['valid']}}, schema)
+        validate_cloudconfig_schema(
+            {'snap': {'assertions': {'01': 'also valid'}}}, schema)
+        self.assertEqual('', self.logs.getvalue())
+
+
+class TestHandle(CiTestCase):
+
+    with_logs = True
+
+    def setUp(self):
+        super(TestHandle, self).setUp()
+        self.tmp = self.tmp_dir()
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    @mock.patch('cloudinit.config.cc_snap.add_assertions')
+    @mock.patch('cloudinit.config.cc_snap.validate_cloudconfig_schema')
+    def test_handle_no_config(self, m_schema, m_add, m_run):
+        """When no snap-related configuration is provided, nothing happens."""
+        cfg = {}
+        handle('snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+        self.assertIn(
+            "DEBUG: Skipping module named snap, no 'snap' key in config",
+            self.logs.getvalue())
+        m_schema.assert_not_called()
+        m_add.assert_not_called()
+        m_run.assert_not_called()
+
+    @mock.patch('cloudinit.config.cc_snap.run_commands')
+    @mock.patch('cloudinit.config.cc_snap.add_assertions')
+    @mock.patch('cloudinit.config.cc_snap.maybe_install_squashfuse')
+    def test_handle_skips_squashfuse_when_unconfigured(self, m_squash, m_add,
+                                                       m_run):
+        """When squashfuse_in_container is unset, don't attempt to install."""
+        handle(
+            'snap', cfg={'snap': {}}, cloud=None, log=self.logger, args=None)
+        handle(
+            'snap', cfg={'snap': {'squashfuse_in_container': None}},
+            cloud=None, log=self.logger, args=None)
+        handle(
+            'snap', cfg={'snap': {'squashfuse_in_container': False}},
+            cloud=None, log=self.logger, args=None)
+        self.assertEqual([], m_squash.call_args_list)  # No calls
+        # snap configuration missing assertions and commands will default to []
+        self.assertIn(mock.call([]), m_add.call_args_list)
+        self.assertIn(mock.call([]), m_run.call_args_list)
+
+    @mock.patch('cloudinit.config.cc_snap.maybe_install_squashfuse')
+    def test_handle_tries_to_install_squashfuse(self, m_squash):
+        """If squashfuse_in_container is True, try installing squashfuse."""
+        cfg = {'snap': {'squashfuse_in_container': True}}
+        mycloud = FakeCloud(None)
+        handle('snap', cfg=cfg, cloud=mycloud, log=self.logger, args=None)
+        self.assertEqual(
+            [mock.call(mycloud)], m_squash.call_args_list)
+
+    def test_handle_runs_commands_provided(self):
+        """If commands are specified as a list, run them."""
+        outfile = self.tmp_path('output.log', dir=self.tmp)
+
+        cfg = {
+            'snap': {'commands': ['echo "HI" >> %s' % outfile,
+                                  'echo "MOM" >> %s' % outfile]}}
+        handle('snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+        self.assertEqual('HI\nMOM\n', util.load_file(outfile))
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_handle_adds_assertions(self, m_subp):
+        """Any configured snap assertions are provided to add_assertions."""
+        assert_file = self.tmp_path('snapd.assertions', dir=self.tmp)
+        compare_file = self.tmp_path('comparison', dir=self.tmp)
+        cfg = {
+            'snap': {'assertions': [SYSTEM_USER_ASSERTION, ACCOUNT_ASSERTION]}}
+        wrap_and_call(
+            'cloudinit.config.cc_snap',
+            {'ASSERTIONS_FILE': {'new': assert_file}},
+            handle, 'snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+        content = '\n'.join(cfg['snap']['assertions'])
+        util.write_file(compare_file, content.encode('utf-8'))
+        self.assertEqual(
+            util.load_file(compare_file), util.load_file(assert_file))
+
+    @mock.patch('cloudinit.config.cc_snap.util.subp')
+    def test_handle_validates_schema(self, m_subp):
+        """Any provided configuration is runs validate_cloudconfig_schema."""
+        assert_file = self.tmp_path('snapd.assertions', dir=self.tmp)
+        cfg = {'snap': {'invalid': ''}}  # Generates schema warning
+        wrap_and_call(
+            'cloudinit.config.cc_snap',
+            {'ASSERTIONS_FILE': {'new': assert_file}},
+            handle, 'snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+        self.assertEqual(
+            "WARNING: Invalid config:\nsnap: Additional properties are not"
+            " allowed ('invalid' was unexpected)\n",
+            self.logs.getvalue())
+
+
+class TestMaybeInstallSquashFuse(CiTestCase):
+
+    with_logs = True
+
+    def setUp(self):
+        super(TestMaybeInstallSquashFuse, self).setUp()
+        self.tmp = self.tmp_dir()
+
+    @mock.patch('cloudinit.config.cc_snap.util.is_container')
+    def test_maybe_install_squashfuse_skips_non_containers(self, m_container):
+        """maybe_install_squashfuse does nothing when not on a container."""
+        m_container.return_value = False
+        maybe_install_squashfuse(cloud=FakeCloud(None))
+        self.assertEqual([mock.call()], m_container.call_args_list)
+        self.assertEqual('', self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.util.is_container')
+    def test_maybe_install_squashfuse_raises_install_errors(self, m_container):
+        """maybe_install_squashfuse logs and raises package install errors."""
+        m_container.return_value = True
+        distro = mock.MagicMock()
+        distro.update_package_sources.side_effect = RuntimeError(
+            'Some apt error')
+        with self.assertRaises(RuntimeError) as context_manager:
+            maybe_install_squashfuse(cloud=FakeCloud(distro))
+        self.assertEqual('Some apt error', str(context_manager.exception))
+        self.assertIn('Package update failed\nTraceback', self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.util.is_container')
+    def test_maybe_install_squashfuse_raises_update_errors(self, m_container):
+        """maybe_install_squashfuse logs and raises package update errors."""
+        m_container.return_value = True
+        distro = mock.MagicMock()
+        distro.update_package_sources.side_effect = RuntimeError(
+            'Some apt error')
+        with self.assertRaises(RuntimeError) as context_manager:
+            maybe_install_squashfuse(cloud=FakeCloud(distro))
+        self.assertEqual('Some apt error', str(context_manager.exception))
+        self.assertIn('Package update failed\nTraceback', self.logs.getvalue())
+
+    @mock.patch('cloudinit.config.cc_snap.util.is_container')
+    def test_maybe_install_squashfuse_happy_path(self, m_container):
+        """maybe_install_squashfuse logs and raises package install errors."""
+        m_container.return_value = True
+        distro = mock.MagicMock()  # No errors raised
+        maybe_install_squashfuse(cloud=FakeCloud(distro))
+        self.assertEqual(
+            [mock.call()], distro.update_package_sources.call_args_list)
+        self.assertEqual(
+            [mock.call(['squashfuse'])],
+            distro.install_packages.call_args_list)
+
+# vi: ts=4 expandtab
diff --git a/cloudinit/util.py b/cloudinit/util.py
index 823d80bf..cae8b196 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1827,7 +1827,8 @@ def subp_blob_in_tempfile(blob, *args, **kwargs):
 
 
 def subp(args, data=None, rcs=None, env=None, capture=True, shell=False,
-         logstring=False, decode="replace", target=None, update_env=None):
+         logstring=False, decode="replace", target=None, update_env=None,
+         status_cb=None):
 
     # not supported in cloud-init (yet), for now kept in the call signature
     # to ease maintaining code shared between cloud-init and curtin
@@ -1848,6 +1849,9 @@ def subp(args, data=None, rcs=None, env=None, capture=True, shell=False,
     if target_path(target) != "/":
         args = ['chroot', target] + list(args)
 
+    if status_cb:
+        command = ' '.join(args) if isinstance(args, list) else args
+        status_cb('Begin run command: {command}\n'.format(command=command))
     if not logstring:
         LOG.debug(("Running command %s with allowed return codes %s"
                    " (shell=%s, capture=%s)"), args, rcs, shell, capture)
@@ -1888,6 +1892,8 @@ def subp(args, data=None, rcs=None, env=None, capture=True, shell=False,
                               env=env, shell=shell)
         (out, err) = sp.communicate(data)
     except OSError as e:
+        if status_cb:
+            status_cb('ERROR: End run command: invalid command provided\n')
         raise ProcessExecutionError(
             cmd=args, reason=e, errno=e.errno,
             stdout="-" if decode else b"-",
@@ -1912,9 +1918,14 @@ def subp(args, data=None, rcs=None, env=None, capture=True, shell=False,
 
     rc = sp.returncode
     if rc not in rcs:
+        if status_cb:
+            status_cb(
+                'ERROR: End run command: exit({code})\n'.format(code=rc))
         raise ProcessExecutionError(stdout=out, stderr=err,
                                     exit_code=rc,
                                     cmd=args)
+    if status_cb:
+        status_cb('End run command: exit({code})\n'.format(code=rc))
     return (out, err)