#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2014-2015 Canonical Limited.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Authors:
# Kapil Thangavelu <kapil.foss@gmail.com>
#
"""
Intro
-----
A simple way to store state in units. This provides a key value
storage with support for versioned, transactional operation,
and can calculate deltas from previous values to simplify unit logic
when processing changes.
Hook Integration
----------------
There are several extant frameworks for hook execution, including
- charmhelpers.core.hookenv.Hooks
- charmhelpers.core.services.ServiceManager
The storage classes are framework agnostic, one simple integration is
via the HookData contextmanager. It will record the current hook
execution environment (including relation data, config data, etc.),
setup a transaction and allow easy access to the changes from
previously seen values. One consequence of the integration is the
reservation of particular keys ('rels', 'unit', 'env', 'config',
'charm_revisions') for their respective values.
Here's a fully worked integration example using hookenv.Hooks::
from charmhelper.core import hookenv, unitdata
hook_data = unitdata.HookData()
db = unitdata.kv()
hooks = hookenv.Hooks()
@hooks.hook
def config_changed():
# Print all changes to configuration from previously seen
# values.
for changed, (prev, cur) in hook_data.conf.items():
print('config changed', changed,
'previous value', prev,
'current value', cur)
# Get some unit specific bookeeping
if not db.get('pkg_key'):
key = urllib.urlopen('https://example.com/pkg_key').read()
db.set('pkg_key', key)
# Directly access all charm config as a mapping.
conf = db.getrange('config', True)
# Directly access all relation data as a mapping
rels = db.getrange('rels', True)
if __name__ == '__main__':
with hook_data():
hook.execute()
A more basic integration is via the hook_scope context manager which simply
manages transaction scope (and records hook name, and timestamp)::
>>> from unitdata import kv
>>> db = kv()
>>> with db.hook_scope('install'):
... # do work, in transactional scope.
... db.set('x', 1)
>>> db.get('x')
1
Usage
-----
Values are automatically json de/serialized to preserve basic typing
and complex data struct capabilities (dicts, lists, ints, booleans, etc).
Individual values can be manipulated via get/set::
>>> kv.set('y', True)
>>> kv.get('y')
True
# We can set complex values (dicts, lists) as a single key.
>>> kv.set('config', {'a': 1, 'b': True'})
# Also supports returning dictionaries as a record which
# provides attribute access.
>>> config = kv.get('config', record=True)
>>> config.b
True
Groups of keys can be manipulated with update/getrange::
>>> kv.update({'z': 1, 'y': 2}, prefix="gui.")
>>> kv.getrange('gui.', strip=True)
{'z': 1, 'y': 2}
When updating values, its very helpful to understand which values
have actually changed and how have they changed. The storage
provides a delta method to provide for this::
>>> data = {'debug': True, 'option': 2}
>>> delta = kv.delta(data, 'config.')
>>> delta.debug.previous
None
>>> delta.debug.current
True
>>> delta
{'debug': (None, True), 'option': (None, 2)}
Note the delta method does not persist the actual change, it needs to
be explicitly saved via 'update' method::
>>> kv.update(data, 'config.')
Values modified in the context of a hook scope retain historical values
associated to the hookname.
>>> with db.hook_scope('config-changed'):
... db.set('x', 42)
>>> db.gethistory('x')
[(1, u'x', 1, u'install', u'2015-01-21T16:49:30.038372'),
(2, u'x', 42, u'config-changed', u'2015-01-21T16:49:30.038786')]
"""
import collections
import contextlib
import datetime
import itertools
import json
import os
import pprint
import sqlite3
import sys
__author__ = 'Kapil Thangavelu <kapil.foss@gmail.com>'
class Storage(object):
"""Simple key value database for local unit state within charms.
Modifications are not persisted unless :meth:`flush` is called.
To support dicts, lists, integer, floats, and booleans values
are automatically json encoded/decoded.
Note: to facilitate unit testing, ':memory:' can be passed as the
path parameter which causes sqlite3 to only build the db in memory.
This should only be used for testing purposes.
"""
def __init__(self, path=None):
self.db_path = path
if path is None:
if 'UNIT_STATE_DB' in os.environ:
self.db_path = os.environ['UNIT_STATE_DB']
else:
self.db_path = os.path.join(
os.environ.get('CHARM_DIR', ''), '.unit-state.db')
if self.db_path != ':memory:':
with open(self.db_path, 'a') as f:
os.fchmod(f.fileno(), 0o600)
self.conn = sqlite3.connect('%s' % self.db_path)
self.cursor = self.conn.cursor()
self.revision = None
self._closed = False
self._init()
def close(self):
if self._closed:
return
self.flush(False)
self.cursor.close()
self.conn.close()
self._closed = True
def get(self, key, default=None, record=False):
self.cursor.execute('select data from kv where key=?', [key])
result = self.cursor.fetchone()
if not result:
return default
if record:
return Record(json.loads(result[0]))
return json.loads(result[0])
def getrange(self, key_prefix, strip=False):
"""
Get a range of keys starting with a common prefix as a mapping of
keys to values.
:param str key_prefix: Common prefix among all keys
:param bool strip: Optionally strip the common prefix from the key
names in the returned dict
:return dict: A (possibly empty) dict of key-value mappings
"""
self.cursor.execute("select key, data from kv where key like ?",
['%s%%' % key_prefix])
result = self.cursor.fetchall()
if not result:
return {}
if not strip:
key_prefix = ''
return dict([
(k[len(key_prefix):], json.loads(v)) for k, v in result])
def update(self, mapping, prefix=""):
"""
Set the values of multiple keys at once.
:param dict mapping: Mapping of keys to values
:param str prefix: Optional prefix to apply to all keys in `mapping`
before setting
"""
for k, v in mapping.items():
self.set("%s%s" % (prefix, k), v)
def unset(self, key):
"""
Remove a key from the database entirely.
"""
self.cursor.execute('delete from kv where key=?', [key])
if self.revision and self.cursor.rowcount:
self.cursor.execute(
'insert into kv_revisions values (?, ?, ?)',
[key, self.revision, json.dumps('DELETED')])
def unsetrange(self, keys=None, prefix=""):
"""
Remove a range of keys starting with a common prefix, from the database
entirely.
:param list keys: List of keys to remove.
:param str prefix: Optional prefix to apply to all keys in ``keys``
before removing.
"""
if keys is not None:
keys = ['%s%s' % (prefix, key) for key in keys]
self.cursor.execute('delete from kv where key in (%s)' % ','.join(['?'] * len(keys)), keys)
if self.revision and self.cursor.rowcount:
self.cursor.execute(
'insert into kv_revisions values %s' % ','.join(['(?, ?, ?)'] * len(keys)),
list(itertools.chain.from_iterable((key, self.revision, json.dumps('DELETED')) for key in keys)))
else:
self.cursor.execute('delete from kv where key like ?',
['%s%%' % prefix])
if self.revision and self.cursor.rowcount:
self.cursor.execute(
'insert into kv_revisions values (?, ?, ?)',
['%s%%' % prefix, self.revision, json.dumps('DELETED')])
def set(self, key, value):
"""
Set a value in the database.
:param str key: Key to set the value for
:param value: Any JSON-serializable value to be set
"""
serialized = json.dumps(value)
self.cursor.execute('select data from kv where key=?', [key])
exists = self.cursor.fetchone()
# Skip mutations to the same value
if exists:
if exists[0] == serialized:
return value
if not exists:
self.cursor.execute(
'insert into kv (key, data) values (?, ?)',
(key, serialized))
else:
self.cursor.execute('''
update kv
set data = ?
where key = ?''', [serialized, key])
# Save
if not self.revision:
return value
self.cursor.execute(
'select 1 from kv_revisions where key=? and revision=?',
[key, self.revision])
exists = self.cursor.fetchone()
if not exists:
self.cursor.execute(
'''insert into kv_revisions (
revision, key, data) values (?, ?, ?)''',
(self.revision, key, serialized))
else:
self.cursor.execute(
'''
update kv_revisions
set data = ?
where key = ?
and revision = ?''',
[serialized, key, self.revision])
return value
def delta(self, mapping, prefix):
"""
return a delta containing values that have changed.
"""
previous = self.getrange(prefix, strip=True)
if not previous:
pk = set()
else:
pk = set(previous.keys())
ck = set(mapping.keys())
delta = DeltaSet()
# added
for k in ck.difference(pk):
delta[k] = Delta(None, mapping[k])
# removed
for k in pk.difference(ck):
delta[k] = Delta(previous[k], None)
# changed
for k in pk.intersection(ck):
c = mapping[k]
p = previous[k]
if c != p:
delta[k] = Delta(p, c)
return delta
@contextlib.contextmanager
def hook_scope(self, name=""):
"""Scope all future interactions to the current hook execution
revision."""
assert not self.revision
self.cursor.execute(
'insert into hooks (hook, date) values (?, ?)',
(name or sys.argv[0],
datetime.datetime.utcnow().isoformat()))
self.revision = self.cursor.lastrowid
try:
yield self.revision
self.revision = None
except Exception:
self.flush(False)
self.revision = None
raise
else:
self.flush()
def flush(self, save=True):
if save:
self.conn.commit()
elif self._closed:
return
else:
self.conn.rollback()
def _init(self):
self.cursor.execute('''
create table if not exists kv (
key text,
data text,
primary key (key)
)''')
self.cursor.execute('''
create table if not exists kv_revisions (
key text,
revision integer,
data text,
primary key (key, revision)
)''')
self.cursor.execute('''
create table if not exists hooks (
version integer primary key autoincrement,
hook text,
date text
)''')
self.conn.commit()
def gethistory(self, key, deserialize=False):
self.cursor.execute(
'''
select kv.revision, kv.key, kv.data, h.hook, h.date
from kv_revisions kv,
hooks h
where kv.key=?
and kv.revision = h.version
''', [key])
if deserialize is False:
return self.cursor.fetchall()
return map(_parse_history, self.cursor.fetchall())
def debug(self, fh=sys.stderr):
self.cursor.execute('select * from kv')
pprint.pprint(self.cursor.fetchall(), stream=fh)
self.cursor.execute('select * from kv_revisions')
pprint.pprint(self.cursor.fetchall(), stream=fh)
def _parse_history(d):
return (d[0], d[1], json.loads(d[2]), d[3],
datetime.datetime.strptime(d[-1], "%Y-%m-%dT%H:%M:%S.%f"))
class HookData(object):
"""Simple integration for existing hook exec frameworks.
Records all unit information, and stores deltas for processing
by the hook.
Sample::
from charmhelper.core import hookenv, unitdata
changes = unitdata.HookData()
db = unitdata.kv()
hooks = hookenv.Hooks()
@hooks.hook
def config_changed():
# View all changes to configuration
for changed, (prev, cur) in changes.conf.items():
print('config changed', changed,
'previous value', prev,
'current value', cur)
# Get some unit specific bookeeping
if not db.get('pkg_key'):
key = urllib.urlopen('https://example.com/pkg_key').read()
db.set('pkg_key', key)
if __name__ == '__main__':
with changes():
hook.execute()
"""
def __init__(self):
self.kv = kv()
self.conf = None
self.rels = None
@contextlib.contextmanager
def __call__(self):
from charmhelpers.core import hookenv
hook_name = hookenv.hook_name()
with self.kv.hook_scope(hook_name):
self._record_charm_version(hookenv.charm_dir())
delta_config, delta_relation = self._record_hook(hookenv)
yield self.kv, delta_config, delta_relation
def _record_charm_version(self, charm_dir):
# Record revisions.. charm revisions are meaningless
# to charm authors as they don't control the revision.
# so logic dependnent on revision is not particularly
# useful, however it is useful for debugging analysis.
charm_rev = open(
os.path.join(charm_dir, 'revision')).read().strip()
charm_rev = charm_rev or '0'
revs = self.kv.get('charm_revisions', [])
if charm_rev not in revs:
revs.append(charm_rev.strip() or '0')
self.kv.set('charm_revisions', revs)
def _record_hook(self, hookenv):
data = hookenv.execution_environment()
self.conf = conf_delta = self.kv.delta(data['conf'], 'config')
self.rels = rels_delta = self.kv.delta(data['rels'], 'rels')
self.kv.set('env', dict(data['env']))
self.kv.set('unit', data['unit'])
self.kv.set('relid', data.get('relid'))
return conf_delta, rels_delta
class Record(dict):
__slots__ = ()
def __getattr__(self, k):
if k in self:
return self[k]
raise AttributeError(k)
class DeltaSet(Record):
__slots__ = ()
Delta = collections.namedtuple('Delta', ['previous', 'current'])
_KV = None
def kv():
global _KV
if _KV is None:
_KV = Storage()
return _KV