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# Copyright (C) 2008 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Persistent maps from string->string using CHK stores."""
import osutils
class CHKMap(object):
"""A persistent map from string to string backed by a CHK store."""
def __init__(self, store, root_key):
"""Create a CHKMap object.
:param store: The store the CHKMap is stored in.
:param root_key: The root key of the map. None to create an empty
CHKMap.
"""
self._store = store
if root_key is None:
self._root_node = RootNode()
else:
self._root_node = root_key
def apply_delta(self, delta):
"""Apply a delta to the map.
:param delta: An iterable of old_key, new_key, new_value tuples.
If new_key is not None, then new_key->new_value is inserted
into the map; if old_key is not None, then the old mapping
of old_key is removed.
"""
for old, new, value in delta:
if old is not None and old != new:
# unmap
self._unmap(old)
for old, new, value in delta:
if new is not None:
# map
self._map(new, value)
return self._save()
def _ensure_root(self):
"""Ensure that the root node is an object not a key."""
if type(self._root_node) == tuple:
# Demand-load the root
bytes = self._read_bytes(self._root_node)
root_key = self._root_node
self._root_node = RootNode()
self._root_node.deserialise(bytes, root_key)
def _read_bytes(self, key):
stream = self._store.get_record_stream([key], 'unordered', True)
return stream.next().get_bytes_as('fulltext')
@classmethod
def from_dict(klass, store, initial_value):
"""Create a CHKMap in store with initial_value as the content.
:param store: The store to record initial_value in, a VersionedFiles
object with 1-tuple keys supporting CHK key generation.
:param initial_value: A dict to store in store. Its keys and values
must be bytestrings.
:return: The root chk of te resulting CHKMap.
"""
result = CHKMap(store, None)
for key, value in initial_value.items():
result._map(key, value)
return result._save()
def iteritems(self):
"""Iterate over the entire CHKMap's contents."""
self._ensure_root()
for name, key, in self._root_node._nodes.iteritems():
bytes = self._read_bytes(key)
yield name, ValueNode.deserialise(bytes).value
def _map(self, key, value):
"""Map key to value."""
self._ensure_root()
# Store the value
bytes = ValueNode(value).serialise()
sha1, _, _ = self._store.add_lines((None,), (), osutils.split_lines(bytes))
# And link into the root
self._root_node.add_child(key, ("sha1:" + sha1,))
def _unmap(self, key):
"""remove key from the map."""
self._ensure_root()
self._root_node.remove_child(key)
def _save(self):
"""Save the map completely.
:return: The key of the root node.
"""
if type(self._root_node) == tuple:
# Already saved.
return self._root_node
# TODO: flush root_nodes children?
bytes = self._root_node.serialise()
sha1, _, _ = self._store.add_lines((None,), (),
osutils.split_lines(bytes))
result = ("sha1:" + sha1,)
self._root_node._key = result
return result
class RootNode(object):
"""A root node in a CHKMap."""
def __init__(self):
self._nodes = {}
def add_child(self, name, child):
"""Add a child to the node.
If the node changes, it's key is reset.
:param name: The name of the child. A bytestring.
:param child: The child, a key tuple for the childs value.
"""
self._nodes[name] = child
self._key = None
def deserialise(self, bytes, key):
"""Set the nodes value to that contained in bytes.
:param bytes: The bytes of the node.
:param key: The key that the serialised node has.
"""
lines = bytes.splitlines()
nodes = {}
if lines[0] != 'chkroot:':
raise ValueError("not a serialised root node: %r" % bytes)
for line in lines[1:]:
name, value = line.split('\x00')
nodes[name] = (value,)
self._nodes = nodes
self._key = key
def remove_child(self, name):
"""Remove name from the node.
If the node changes, it's key is reset.
:param name: The name to remove from the node.
"""
del self._nodes[name]
self._key = None
def serialise(self):
"""Flatten the node to a bytestring.
:return: A bytestring.
"""
lines = ["chkroot:\n"]
for name, child in sorted(self._nodes.items()):
lines.append("%s\x00%s\n" % (name, child[0]))
return "".join(lines)
class ValueNode(object):
"""A value in a CHKMap."""
def __init__(self, value):
"""Create a ValueNode.
:param value: The value of this node, must be a bytestring.
"""
self.value = value
@classmethod
def deserialise(klass, bytes):
"""Get a ValueNode from a serialised bytestring.
:param bytes: The bytes returned by an earlier serialisation.
"""
if not bytes.startswith("chkvalue:\n"):
raise ValueError("not a chkvalue %r" % bytes)
return ValueNode(bytes[10:])
def serialise(self):
"""Flatten the value to a bytestring.
:return: A bytestring.
"""
return "chkvalue:\n" + self.value
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