Synnefo » Pithos

# Copyright 2011-2012 GRNET S.A. All rights reserved.

# 

# Redistribution and use in source and binary forms, with or

# without modification, are permitted provided that the following

# conditions are met:

# 

#   1. Redistributions of source code must retain the above

#      copyright notice, this list of conditions and the following

#      disclaimer.

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#   2. Redistributions in binary form must reproduce the above

#      copyright notice, this list of conditions and the following

#      disclaimer in the documentation and/or other materials

#      provided with the distribution.

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# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

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# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

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import sys

import os

import time

import uuid as uuidlib

import logging

import binascii

from base import DEFAULT_QUOTA, DEFAULT_VERSIONING, NotAllowedError, QuotaError, BaseBackend

from pithos.lib.hashmap import HashMap

# Default modules and settings.

DEFAULT_DB_MODULE = 'pithos.backends.lib.sqlalchemy'

DEFAULT_DB_CONNECTION = 'sqlite:///backend.db'

DEFAULT_BLOCK_MODULE = 'pithos.backends.lib.hashfiler'

DEFAULT_BLOCK_PATH = 'data/'

DEFAULT_QUEUE_MODULE = 'pithos.backends.lib.rabbitmq'

DEFAULT_QUEUE_CONNECTION = 'rabbitmq://guest:guest@localhost:5672/pithos'

( CLUSTER_NORMAL, CLUSTER_HISTORY, CLUSTER_DELETED ) = range(3)

inf = float('inf')

ULTIMATE_ANSWER = 42

logger = logging.getLogger(__name__)

def backend_method(func=None, autocommit=1):

    if func is None:

        def fn(func):

            return backend_method(func, autocommit)

        return fn

    if not autocommit:

        return func

    def fn(self, *args, **kw):

        self.wrapper.execute()

        try:

            ret = func(self, *args, **kw)

            self.wrapper.commit()

            return ret

        except:

            self.wrapper.rollback()

            raise

    return fn

class ModularBackend(BaseBackend):

    """A modular backend.

    Uses modules for SQL functions and storage.

    """

    def __init__(self, db_module=None, db_connection=None,

                 block_module=None, block_path=None,

                 queue_module=None, queue_connection=None):

        db_module = db_module or DEFAULT_DB_MODULE

        db_connection = db_connection or DEFAULT_DB_CONNECTION

        block_module = block_module or DEFAULT_BLOCK_MODULE

        block_path = block_path or DEFAULT_BLOCK_PATH

        #queue_module = queue_module or DEFAULT_QUEUE_MODULE

        #queue_connection = queue_connection or DEFAULT_QUEUE_CONNECTION

        self.hash_algorithm = 'sha256'

        self.block_size = 4 * 1024 * 1024 # 4MB

        self.default_policy = {'quota': DEFAULT_QUOTA, 'versioning': DEFAULT_VERSIONING}

        def load_module(m):

            __import__(m)

            return sys.modules[m]

        self.db_module = load_module(db_module)

        self.wrapper = self.db_module.DBWrapper(db_connection)

        params = {'wrapper': self.wrapper}

        self.permissions = self.db_module.Permissions(**params)

        for x in ['READ', 'WRITE']:

            setattr(self, x, getattr(self.db_module, x))

        self.node = self.db_module.Node(**params)

        for x in ['ROOTNODE', 'SERIAL', 'HASH', 'SIZE', 'MTIME', 'MUSER', 'UUID', 'CLUSTER']:

            setattr(self, x, getattr(self.db_module, x))

        self.block_module = load_module(block_module)

        params = {'path': block_path,

                  'block_size': self.block_size,

                  'hash_algorithm': self.hash_algorithm}

        self.store = self.block_module.Store(**params)

        if queue_module and queue_connection:

            self.queue_module = load_module(queue_module)

            params = {'exchange': queue_connection}

            self.queue = self.queue_module.Queue(**params)

        else:

            class NoQueue:

                def send(self, key, value):

                    pass

            self.queue = NoQueue()

    def close(self):

        self.wrapper.close()

    @backend_method

    def list_accounts(self, user, marker=None, limit=10000):

        """Return a list of accounts the user can access."""

        logger.debug("list_accounts: %s %s %s", user, marker, limit)

        allowed = self._allowed_accounts(user)

        start, limit = self._list_limits(allowed, marker, limit)

        return allowed[start:start + limit]

    @backend_method

    def get_account_meta(self, user, account, domain, until=None):

        """Return a dictionary with the account metadata for the domain."""

        logger.debug("get_account_meta: %s %s %s", account, domain, until)

        path, node = self._lookup_account(account, user == account)

        if user != account:

            if until or node is None or account not in self._allowed_accounts(user):

                raise NotAllowedError

        try:

            props = self._get_properties(node, until)

            mtime = props[self.MTIME]

        except NameError:

            props = None

            mtime = until

        count, bytes, tstamp = self._get_statistics(node, until)

        tstamp = max(tstamp, mtime)

        if until is None:

            modified = tstamp

        else:

            modified = self._get_statistics(node)[2] # Overall last modification.

            modified = max(modified, mtime)

        if user != account:

            meta = {'name': account}

        else:

            meta = {}

            if props is not None:

                meta.update(dict(self.node.attribute_get(props[self.SERIAL], domain)))

            if until is not None:

                meta.update({'until_timestamp': tstamp})

            meta.update({'name': account, 'count': count, 'bytes': bytes})

        meta.update({'modified': modified})

        return meta

    @backend_method

    def update_account_meta(self, user, account, domain, meta, replace=False):

        """Update the metadata associated with the account for the domain."""

        logger.debug("update_account_meta: %s %s %s %s", account, domain, meta, replace)

        if user != account:

            raise NotAllowedError

        path, node = self._lookup_account(account, True)

        self._put_metadata(user, node, domain, meta, replace)

    @backend_method

    def get_account_groups(self, user, account):

        """Return a dictionary with the user groups defined for this account."""

        logger.debug("get_account_groups: %s", account)

        if user != account:

            if account not in self._allowed_accounts(user):

                raise NotAllowedError

            return {}

        self._lookup_account(account, True)

        return self.permissions.group_dict(account)

    @backend_method

    def update_account_groups(self, user, account, groups, replace=False):

        """Update the groups associated with the account."""

        logger.debug("update_account_groups: %s %s %s", account, groups, replace)

        if user != account:

            raise NotAllowedError

        self._lookup_account(account, True)

        self._check_groups(groups)

        if replace:

            self.permissions.group_destroy(account)

        for k, v in groups.iteritems():

            if not replace: # If not already deleted.

                self.permissions.group_delete(account, k)

            if v:

                self.permissions.group_addmany(account, k, v)

    @backend_method

    def get_account_policy(self, user, account):

        """Return a dictionary with the account policy."""

        logger.debug("get_account_policy: %s", account)

        if user != account:

            if account not in self._allowed_accounts(user):

                raise NotAllowedError

            return {}

        path, node = self._lookup_account(account, True)

        return self._get_policy(node)

    @backend_method

    def update_account_policy(self, user, account, policy, replace=False):

        """Update the policy associated with the account."""

        logger.debug("update_account_policy: %s %s %s", account, policy, replace)

        if user != account:

            raise NotAllowedError

        path, node = self._lookup_account(account, True)

        self._check_policy(policy)

        self._put_policy(node, policy, replace)

    @backend_method

    def put_account(self, user, account, policy={}):

        """Create a new account with the given name."""

        logger.debug("put_account: %s %s", account, policy)

        if user != account:

            raise NotAllowedError

        node = self.node.node_lookup(account)

        if node is not None:

            raise NameError('Account already exists')

        if policy:

            self._check_policy(policy)

        node = self._put_path(user, self.ROOTNODE, account)

        self._put_policy(node, policy, True)

    @backend_method

    def delete_account(self, user, account):

        """Delete the account with the given name."""

        logger.debug("delete_account: %s", account)

        if user != account:

            raise NotAllowedError

        node = self.node.node_lookup(account)

        if node is None:

            return

        if not self.node.node_remove(node):

            raise IndexError('Account is not empty')

        self.permissions.group_destroy(account)

    @backend_method

    def list_containers(self, user, account, marker=None, limit=10000, shared=False, until=None):

        """Return a list of containers existing under an account."""

        logger.debug("list_containers: %s %s %s %s %s", account, marker, limit, shared, until)

        if user != account:

            if until or account not in self._allowed_accounts(user):

                raise NotAllowedError

            allowed = self._allowed_containers(user, account)

            start, limit = self._list_limits(allowed, marker, limit)

            return allowed[start:start + limit]

        if shared:

            allowed = [x.split('/', 2)[1] for x in self.permissions.access_list_shared(account)]

            allowed = list(set(allowed))

            start, limit = self._list_limits(allowed, marker, limit)

            return allowed[start:start + limit]

        node = self.node.node_lookup(account)

        return [x[0] for x in self._list_objects(node, account, '', '/', marker, limit, False, None, [], until)]

    @backend_method

    def get_container_meta(self, user, account, container, domain, until=None):

        """Return a dictionary with the container metadata for the domain."""

        logger.debug("get_container_meta: %s %s %s %s", account, container, domain, until)

        if user != account:

            if until or container not in self._allowed_containers(user, account):

                raise NotAllowedError

        path, node = self._lookup_container(account, container)

        props = self._get_properties(node, until)

        mtime = props[self.MTIME]

        count, bytes, tstamp = self._get_statistics(node, until)

        tstamp = max(tstamp, mtime)

        if until is None:

            modified = tstamp

        else:

            modified = self._get_statistics(node)[2] # Overall last modification.

            modified = max(modified, mtime)

        if user != account:

            meta = {'name': container}

        else:

            meta = dict(self.node.attribute_get(props[self.SERIAL], domain))

            if until is not None:

                meta.update({'until_timestamp': tstamp})

            meta.update({'name': container, 'count': count, 'bytes': bytes})

        meta.update({'modified': modified})

        return meta

    @backend_method

    def update_container_meta(self, user, account, container, domain, meta, replace=False):

        """Update the metadata associated with the container for the domain."""

        logger.debug("update_container_meta: %s %s %s %s %s", account, container, domain, meta, replace)

        if user != account:

            raise NotAllowedError

        path, node = self._lookup_container(account, container)

        self._put_metadata(user, node, domain, meta, replace)

    @backend_method

    def get_container_policy(self, user, account, container):

        """Return a dictionary with the container policy."""

        logger.debug("get_container_policy: %s %s", account, container)

        if user != account:

            if container not in self._allowed_containers(user, account):

                raise NotAllowedError

            return {}

        path, node = self._lookup_container(account, container)

        return self._get_policy(node)

    @backend_method

    def update_container_policy(self, user, account, container, policy, replace=False):

        """Update the policy associated with the container."""

        logger.debug("update_container_policy: %s %s %s %s", account, container, policy, replace)

        if user != account:

            raise NotAllowedError

        path, node = self._lookup_container(account, container)

        self._check_policy(policy)

        self._put_policy(node, policy, replace)

    @backend_method

    def put_container(self, user, account, container, policy={}):

        """Create a new container with the given name."""

        logger.debug("put_container: %s %s %s", account, container, policy)

        if user != account:

            raise NotAllowedError

        try:

            path, node = self._lookup_container(account, container)

        except NameError:

            pass

        else:

            raise NameError('Container already exists')

        if policy:

            self._check_policy(policy)

        path = '/'.join((account, container))

        node = self._put_path(user, self._lookup_account(account, True)[1], path)

        self._put_policy(node, policy, True)

    @backend_method

    def delete_container(self, user, account, container, until=None):

        """Delete/purge the container with the given name."""

        logger.debug("delete_container: %s %s %s", account, container, until)

        if user != account:

            raise NotAllowedError

        path, node = self._lookup_container(account, container)

        if until is not None:

            hashes = self.node.node_purge_children(node, until, CLUSTER_HISTORY)

            for h in hashes:

                self.store.map_delete(h)

            self.node.node_purge_children(node, until, CLUSTER_DELETED)

            self.queue.send('#', {'op': 'del objects'})

            return

        if self._get_statistics(node)[0] > 0:

            raise IndexError('Container is not empty')

        hashes = self.node.node_purge_children(node, inf, CLUSTER_HISTORY)

        for h in hashes:

            self.store.map_delete(h)

        self.node.node_purge_children(node, inf, CLUSTER_DELETED)

        self.node.node_remove(node)

        self.queue.send('#', {'op': 'del objects'})

    @backend_method

    def list_objects(self, user, account, container, prefix='', delimiter=None, marker=None, limit=10000, virtual=True, domain=None, keys=[], shared=False, until=None, size_range=None):

        """Return a list of objects existing under a container."""

        logger.debug("list_objects: %s %s %s %s %s %s %s %s %s %s %s", account, container, prefix, delimiter, marker, limit, virtual, domain, keys, shared, until)

        allowed = []

        if user != account:

            if until:

                raise NotAllowedError

            allowed = self.permissions.access_list_paths(user, '/'.join((account, container)))

            if not allowed:

                raise NotAllowedError

        else:

            if shared:

                allowed = self.permissions.access_list_shared('/'.join((account, container)))

                if not allowed:

                    return []

        path, node = self._lookup_container(account, container)

        return self._list_objects(node, path, prefix, delimiter, marker, limit, virtual, domain, keys, until, size_range, allowed)

    @backend_method

    def list_object_meta(self, user, account, container, domain, until=None):

        """Return a list with all the container's object meta keys for the domain."""

        logger.debug("list_object_meta: %s %s %s %s", account, container, domain, until)

        allowed = []

        if user != account:

            if until:

                raise NotAllowedError

            allowed = self.permissions.access_list_paths(user, '/'.join((account, container)))

            if not allowed:

                raise NotAllowedError

        path, node = self._lookup_container(account, container)

        before = until if until is not None else inf

        return self.node.latest_attribute_keys(node, domain, before, CLUSTER_DELETED, allowed)

    @backend_method

    def get_object_meta(self, user, account, container, name, domain, version=None):

        """Return a dictionary with the object metadata for the domain."""

        logger.debug("get_object_meta: %s %s %s %s %s", account, container, name, domain, version)

        self._can_read(user, account, container, name)

        path, node = self._lookup_object(account, container, name)

        props = self._get_version(node, version)

        if version is None:

            modified = props[self.MTIME]

        else:

            try:

                modified = self._get_version(node)[self.MTIME] # Overall last modification.

            except NameError: # Object may be deleted.

                del_props = self.node.version_lookup(node, inf, CLUSTER_DELETED)

                if del_props is None:

                    raise NameError('Object does not exist')

                modified = del_props[self.MTIME]

        meta = dict(self.node.attribute_get(props[self.SERIAL], domain))

        meta.update({'name': name, 'bytes': props[self.SIZE], 'hash':props[self.HASH]})

        meta.update({'version': props[self.SERIAL], 'version_timestamp': props[self.MTIME]})

        meta.update({'modified': modified, 'modified_by': props[self.MUSER], 'uuid': props[self.UUID]})

        return meta

    @backend_method

    def update_object_meta(self, user, account, container, name, domain, meta, replace=False):

        """Update the metadata associated with the object for the domain and return the new version."""

        logger.debug("update_object_meta: %s %s %s %s %s %s", account, container, name, domain, meta, replace)

        self._can_write(user, account, container, name)

        path, node = self._lookup_object(account, container, name)

        src_version_id, dest_version_id = self._put_metadata(user, node, domain, meta, replace)

        self._apply_versioning(account, container, src_version_id)

        return dest_version_id

    @backend_method

    def get_object_permissions(self, user, account, container, name):

        """Return the action allowed on the object, the path

        from which the object gets its permissions from,

        along with a dictionary containing the permissions."""

        logger.debug("get_object_permissions: %s %s %s", account, container, name)

        allowed = 'write'

        if user != account:

            path = '/'.join((account, container, name))

            if self.permissions.access_check(path, self.WRITE, user):

                allowed = 'write'

            elif self.permissions.access_check(path, self.READ, user):

                allowed = 'read'

            else:

                raise NotAllowedError

        path = self._lookup_object(account, container, name)[0]

        return (allowed,) + self.permissions.access_inherit(path)

    @backend_method

    def update_object_permissions(self, user, account, container, name, permissions):

        """Update the permissions associated with the object."""

        logger.debug("update_object_permissions: %s %s %s %s", account, container, name, permissions)

        if user != account:

            raise NotAllowedError

        path = self._lookup_object(account, container, name)[0]

        self._check_permissions(path, permissions)

        self.permissions.access_set(path, permissions)

    @backend_method

    def get_object_public(self, user, account, container, name):

        """Return the public id of the object if applicable."""

        logger.debug("get_object_public: %s %s %s", account, container, name)

        self._can_read(user, account, container, name)

        path = self._lookup_object(account, container, name)[0]

        p = self.permissions.public_get(path)

        if p is not None:

            p += ULTIMATE_ANSWER

        return p

    @backend_method

    def update_object_public(self, user, account, container, name, public):

        """Update the public status of the object."""

        logger.debug("update_object_public: %s %s %s %s", account, container, name, public)

        self._can_write(user, account, container, name)

        path = self._lookup_object(account, container, name)[0]

        if not public:

            self.permissions.public_unset(path)

        else:

            self.permissions.public_set(path)

    @backend_method

    def get_object_hashmap(self, user, account, container, name, version=None):

        """Return the object's size and a list with partial hashes."""

        logger.debug("get_object_hashmap: %s %s %s %s", account, container, name, version)

        self._can_read(user, account, container, name)

        path, node = self._lookup_object(account, container, name)

        props = self._get_version(node, version)

        hashmap = self.store.map_get(binascii.unhexlify(props[self.HASH]))

        return props[self.SIZE], [binascii.hexlify(x) for x in hashmap]

    def _update_object_hash(self, user, account, container, name, size, hash, permissions, src_node=None, is_copy=False):

        if permissions is not None and user != account:

            raise NotAllowedError

        self._can_write(user, account, container, name)

        if permissions is not None:

            path = '/'.join((account, container, name))

            self._check_permissions(path, permissions)

        account_path, account_node = self._lookup_account(account, True)

        container_path, container_node = self._lookup_container(account, container)

        path, node = self._put_object_node(container_path, container_node, name)

        pre_version_id, dest_version_id = self._put_version_duplicate(user, node, src_node=src_node, size=size, hash=hash, is_copy=is_copy)

        # Check quota.

        versioning = self._get_policy(container_node)['versioning']

        if versioning != 'auto':

            size_delta = size - 0 # TODO: Get previous size.

        else:

            size_delta = size

        if size_delta > 0:

            account_quota = long(self._get_policy(account_node)['quota'])

            container_quota = long(self._get_policy(container_node)['quota'])

            if (account_quota > 0 and self._get_statistics(account_node)[1] + size_delta > account_quota) or \

               (container_quota > 0 and self._get_statistics(container_node)[1] + size_delta > container_quota):

                # This must be executed in a transaction, so the version is never created if it fails.

                raise QuotaError

        if permissions is not None:

            self.permissions.access_set(path, permissions)

        self._apply_versioning(account, container, pre_version_id)

        return pre_version_id, dest_version_id

    @backend_method

    def update_object_hashmap(self, user, account, container, name, size, hashmap, domain, meta={}, replace_meta=False, permissions=None):

        """Create/update an object with the specified size and partial hashes."""

        logger.debug("update_object_hashmap: %s %s %s %s %s", account, container, name, size, hashmap)

        if size == 0: # No such thing as an empty hashmap.

            hashmap = [self.put_block('')]

        map = HashMap(self.block_size, self.hash_algorithm)

        map.extend([binascii.unhexlify(x) for x in hashmap])

        missing = self.store.block_search(map)

        if missing:

            ie = IndexError()

            ie.data = [binascii.hexlify(x) for x in missing]

            raise ie

        hash = map.hash()

        pre_version_id, dest_version_id = self._update_object_hash(user, account, container, name, size, binascii.hexlify(hash), permissions)

        self._put_metadata_duplicate(pre_version_id, dest_version_id, domain, meta, replace_meta)

        self.store.map_put(hash, map)

        self.queue.send('#', {'op': 'add object', 'id': dest_version_id})

        return dest_version_id

    def _copy_object(self, user, src_account, src_container, src_name, dest_account, dest_container, dest_name, dest_domain=None, dest_meta={}, replace_meta=False, permissions=None, src_version=None, is_move=False):

        self._can_read(user, src_account, src_container, src_name)

        path, node = self._lookup_object(src_account, src_container, src_name)

        # TODO: Will do another fetch of the properties in duplicate version...

        props = self._get_version(node, src_version) # Check to see if source exists.

        src_version_id = props[self.SERIAL]

        hash = props[self.HASH]

        size = props[self.SIZE]

        is_copy = not is_move and (src_account, src_container, src_name) != (dest_account, dest_container, dest_name) # New uuid.

        pre_version_id, dest_version_id = self._update_object_hash(user, dest_account, dest_container, dest_name, size, hash, permissions, src_node=node, is_copy=is_copy)

        self._put_metadata_duplicate(src_version_id, dest_version_id, dest_domain, dest_meta, replace_meta)

        return dest_version_id

    @backend_method

    def copy_object(self, user, src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta={}, replace_meta=False, permissions=None, src_version=None):

        """Copy an object's data and metadata."""

        logger.debug("copy_object: %s %s %s %s %s %s %s %s %s %s %s", src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta, replace_meta, permissions, src_version)

        dest_version_id = self._copy_object(user, src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta, replace_meta, permissions, src_version, False)

        self.queue.send('#', {'op': 'add object', 'id': dest_version_id})

        return dest_version_id

    @backend_method

    def move_object(self, user, src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta={}, replace_meta=False, permissions=None):

        """Move an object's data and metadata."""

        logger.debug("move_object: %s %s %s %s %s %s %s %s %s %s", src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta, replace_meta, permissions)

        if user != src_account:

            raise NotAllowedError

        dest_version_id = self._copy_object(user, src_account, src_container, src_name, dest_account, dest_container, dest_name, domain, meta, replace_meta, permissions, None, True)

        if (src_account, src_container, src_name) != (dest_account, dest_container, dest_name):

            self._delete_object(user, src_account, src_container, src_name)

        self.queue.send('#', {'op': 'add object', 'id': dest_version_id})

        return dest_version_id

    def _delete_object(self, user, account, container, name, until=None):

        if user != account:

            raise NotAllowedError

        if until is not None:

            path = '/'.join((account, container, name))

            node = self.node.node_lookup(path)

            if node is None:

                return

            hashes = self.node.node_purge(node, until, CLUSTER_NORMAL)

            hashes += self.node.node_purge(node, until, CLUSTER_HISTORY)

            for h in hashes:

                self.store.map_delete(h)

            self.node.node_purge(node, until, CLUSTER_DELETED)

            try:

                props = self._get_version(node)

            except NameError:

                self.permissions.access_clear(path)

            self.queue.send('#', {'op': 'del objects'})

            return

        path, node = self._lookup_object(account, container, name)

        src_version_id, dest_version_id = self._put_version_duplicate(user, node, size=0, hash=None, cluster=CLUSTER_DELETED)

        self._apply_versioning(account, container, src_version_id)

        self.permissions.access_clear(path)

    @backend_method

    def delete_object(self, user, account, container, name, until=None):

        """Delete/purge an object."""

        logger.debug("delete_object: %s %s %s %s", account, container, name, until)

        self._delete_object(user, account, container, name, until)

    @backend_method

    def list_versions(self, user, account, container, name):

        """Return a list of all (version, version_timestamp) tuples for an object."""

        logger.debug("list_versions: %s %s %s", account, container, name)

        self._can_read(user, account, container, name)

        path, node = self._lookup_object(account, container, name)

        versions = self.node.node_get_versions(node)

        return [[x[self.SERIAL], x[self.MTIME]] for x in versions if x[self.CLUSTER] != CLUSTER_DELETED]

    @backend_method

    def get_uuid(self, user, uuid):

        """Return the (account, container, name) for the UUID given."""

        logger.debug("get_uuid: %s", uuid)

        info = self.node.latest_uuid(uuid)

        if info is None:

            raise NameError

        path, serial = info

        account, container, name = path.split('/', 2)

        self._can_read(user, account, container, name)

        return (account, container, name)

    @backend_method

    def get_public(self, user, public):

        """Return the (account, container, name) for the public id given."""

        logger.debug("get_public: %s", public)

        if public is None or public < ULTIMATE_ANSWER:

            raise NameError

        path = self.permissions.public_path(public - ULTIMATE_ANSWER)

        if path is None:

            raise NameError

        account, container, name = path.split('/', 2)

        self._can_read(user, account, container, name)

        return (account, container, name)

    @backend_method(autocommit=0)

    def get_block(self, hash):

        """Return a block's data."""

        logger.debug("get_block: %s", hash)

        block = self.store.block_get(binascii.unhexlify(hash))

        if not block:

            raise NameError('Block does not exist')

        return block

    @backend_method(autocommit=0)

    def put_block(self, data):

        """Store a block and return the hash."""

        logger.debug("put_block: %s", len(data))

        return binascii.hexlify(self.store.block_put(data))

    @backend_method(autocommit=0)

    def update_block(self, hash, data, offset=0):

        """Update a known block and return the hash."""

        logger.debug("update_block: %s %s %s", hash, len(data), offset)

        if offset == 0 and len(data) == self.block_size:

            return self.put_block(data)

        h = self.store.block_update(binascii.unhexlify(hash), offset, data)

        return binascii.hexlify(h)

    # Path functions.

    def _generate_uuid(self):

        return str(uuidlib.uuid4())

    def _put_object_node(self, path, parent, name):

        path = '/'.join((path, name))

        node = self.node.node_lookup(path)

        if node is None:

            node = self.node.node_create(parent, path)

        return path, node

    def _put_path(self, user, parent, path):

        node = self.node.node_create(parent, path)

        self.node.version_create(node, None, 0, None, user, self._generate_uuid(), CLUSTER_NORMAL)

        return node

    def _lookup_account(self, account, create=True):

        node = self.node.node_lookup(account)

        if node is None and create:

            node = self._put_path(account, self.ROOTNODE, account) # User is account.

        return account, node

    def _lookup_container(self, account, container):

        path = '/'.join((account, container))

        node = self.node.node_lookup(path)

        if node is None:

            raise NameError('Container does not exist')

        return path, node

    def _lookup_object(self, account, container, name):

        path = '/'.join((account, container, name))

        node = self.node.node_lookup(path)

        if node is None:

            raise NameError('Object does not exist')

        return path, node

    def _get_properties(self, node, until=None):

        """Return properties until the timestamp given."""

        before = until if until is not None else inf

        props = self.node.version_lookup(node, before, CLUSTER_NORMAL)

        if props is None and until is not None:

            props = self.node.version_lookup(node, before, CLUSTER_HISTORY)

        if props is None:

            raise NameError('Path does not exist')

        return props

    def _get_statistics(self, node, until=None):

        """Return count, sum of size and latest timestamp of everything under node."""

        if until is None:

            stats = self.node.statistics_get(node, CLUSTER_NORMAL)

        else:

            stats = self.node.statistics_latest(node, until, CLUSTER_DELETED)

        if stats is None:

            stats = (0, 0, 0)

        return stats

    def _get_version(self, node, version=None):

        if version is None:

            props = self.node.version_lookup(node, inf, CLUSTER_NORMAL)

            if props is None:

                raise NameError('Object does not exist')

        else:

            try:

                version = int(version)

            except ValueError:

                raise IndexError('Version does not exist')

            props = self.node.version_get_properties(version)

            if props is None or props[self.CLUSTER] == CLUSTER_DELETED:

                raise IndexError('Version does not exist')

        return props

    def _put_version_duplicate(self, user, node, src_node=None, size=None, hash=None, cluster=CLUSTER_NORMAL, is_copy=False):

        """Create a new version of the node."""

        props = self.node.version_lookup(node if src_node is None else src_node, inf, CLUSTER_NORMAL)

        if props is not None:

            src_version_id = props[self.SERIAL]

            src_hash = props[self.HASH]

            src_size = props[self.SIZE]

        else:

            src_version_id = None

            src_hash = None

            src_size = 0

        if size is None:

            hash = src_hash # This way hash can be set to None.

            size = src_size

        uuid = self._generate_uuid() if (is_copy or src_version_id is None) else props[self.UUID]

        if src_node is None:

            pre_version_id = src_version_id

        else:

            pre_version_id = None

            props = self.node.version_lookup(node, inf, CLUSTER_NORMAL)

            if props is not None:

                pre_version_id = props[self.SERIAL]

        if pre_version_id is not None:

            self.node.version_recluster(pre_version_id, CLUSTER_HISTORY)

        dest_version_id, mtime = self.node.version_create(node, hash, size, src_version_id, user, uuid, cluster)

        return pre_version_id, dest_version_id

    def _put_metadata_duplicate(self, src_version_id, dest_version_id, domain, meta, replace=False):

        if src_version_id is not None:

            self.node.attribute_copy(src_version_id, dest_version_id)

        if not replace:

            self.node.attribute_del(dest_version_id, domain, (k for k, v in meta.iteritems() if v == ''))

            self.node.attribute_set(dest_version_id, domain, ((k, v) for k, v in meta.iteritems() if v != ''))

        else:

            self.node.attribute_del(dest_version_id, domain)

            self.node.attribute_set(dest_version_id, domain, ((k, v) for k, v in meta.iteritems()))

    def _put_metadata(self, user, node, domain, meta, replace=False):

        """Create a new version and store metadata."""

        src_version_id, dest_version_id = self._put_version_duplicate(user, node)

        self._put_metadata_duplicate(src_version_id, dest_version_id, domain, meta, replace)

        return src_version_id, dest_version_id

    def _list_limits(self, listing, marker, limit):

        start = 0

        if marker:

            try:

                start = listing.index(marker) + 1

            except ValueError:

                pass

        if not limit or limit > 10000:

            limit = 10000

        return start, limit

    def _list_objects(self, parent, path, prefix='', delimiter=None, marker=None, limit=10000, virtual=True, domain=None, keys=[], until=None, size_range=None, allowed=[]):

        cont_prefix = path + '/'

        prefix = cont_prefix + prefix

        start = cont_prefix + marker if marker else None

        before = until if until is not None else inf

        filterq = keys if domain else []

        sizeq = size_range

        objects, prefixes = self.node.latest_version_list(parent, prefix, delimiter, start, limit, before, CLUSTER_DELETED, allowed, domain, filterq, sizeq)

        objects.extend([(p, None) for p in prefixes] if virtual else [])

        objects.sort(key=lambda x: x[0])

        objects = [(x[0][len(cont_prefix):], x[1]) for x in objects]

        start, limit = self._list_limits([x[0] for x in objects], marker, limit)

        return objects[start:start + limit]

    # Policy functions.

    def _check_policy(self, policy):

        for k in policy.keys():

            if policy[k] == '':

                policy[k] = self.default_policy.get(k)

        for k, v in policy.iteritems():

            if k == 'quota':

                q = int(v) # May raise ValueError.

                if q < 0:

                    raise ValueError

            elif k == 'versioning':

                if v not in ['auto', 'none']:

                    raise ValueError

            else:

                raise ValueError

    def _put_policy(self, node, policy, replace):

        if replace:

            for k, v in self.default_policy.iteritems():

                if k not in policy:

                    policy[k] = v

        self.node.policy_set(node, policy)

    def _get_policy(self, node):

        policy = self.default_policy.copy()

        policy.update(self.node.policy_get(node))

        return policy

    def _apply_versioning(self, account, container, version_id):

        if version_id is None:

            return

        path, node = self._lookup_container(account, container)

        versioning = self._get_policy(node)['versioning']

        if versioning != 'auto':

            hash = self.node.version_remove(version_id)

            self.store.map_delete(hash)

    # Access control functions.

    def _check_groups(self, groups):

        # raise ValueError('Bad characters in groups')

        pass

    def _check_permissions(self, path, permissions):

        # raise ValueError('Bad characters in permissions')

        # Check for existing permissions.

        paths = self.permissions.access_list(path)

        if paths:

            ae = AttributeError()

            ae.data = paths

            raise ae

    def _can_read(self, user, account, container, name):

        if user == account:

            return True

        path = '/'.join((account, container, name))

        if not self.permissions.access_check(path, self.READ, user) and not self.permissions.access_check(path, self.WRITE, user):

            raise NotAllowedError

    def _can_write(self, user, account, container, name):

        if user == account:

            return True

        path = '/'.join((account, container, name))

        if not self.permissions.access_check(path, self.WRITE, user):

            raise NotAllowedError

    def _allowed_accounts(self, user):

        allow = set()

        for path in self.permissions.access_list_paths(user):

            allow.add(path.split('/', 1)[0])

        return sorted(allow)

    def _allowed_containers(self, user, account):

        allow = set()

        for path in self.permissions.access_list_paths(user, account):

            allow.add(path.split('/', 2)[1])

        return sorted(allow)