pvc/node-daemon/pvcnoded/zkhandler.py

#!/usr/bin/env python3

# zkhandler.py - Secure versioned ZooKeeper updates
# Part of the Parallel Virtual Cluster (PVC) system
#
#    Copyright (C) 2018-2020 Joshua M. Boniface <joshua@boniface.me>
#
#    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 3 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, see <https://www.gnu.org/licenses/>.
#
###############################################################################

import uuid

# Child list function
def listchildren(zk_conn, key):
    try:
        children = zk_conn.get_children(key)
        return children
    except Exception:
        return None

# Key deletion function
def deletekey(zk_conn, key, recursive=True):
    try:
        zk_conn.delete(key, recursive=recursive)
        return True
    except Exception:
        return False

# Data read function
def readdata(zk_conn, key):
    try:
        data_raw = zk_conn.get(key)
        data = data_raw[0].decode('utf8')
        return data
    except Exception:
        return None

# Data write function
def writedata(zk_conn, kv):
    # Commit the transaction
    try:
        # Start up a transaction
        zk_transaction = zk_conn.transaction()

        # Proceed one KV pair at a time
        for key in sorted(kv):
            data = kv[key]
            if not data:
                data = ''

            # Check if this key already exists or not
            if not zk_conn.exists(key):
                # We're creating a new key
                zk_transaction.create(key, str(data).encode('utf8'))
            else:
                # We're updating a key with version validation
                orig_data = zk_conn.get(key)
                version = orig_data[1].version

                # Set what we expect the new version to be
                new_version = version + 1

                # Update the data
                zk_transaction.set_data(key, str(data).encode('utf8'))

                # Set up the check
                try:
                    zk_transaction.check(key, new_version)
                except TypeError:
                    print('Zookeeper key "{}" does not match expected version'.format(key))
                    return False

        zk_transaction.commit()
        return True
    except Exception:
        return False

# Key rename function
def renamekey(zk_conn, kv):
    # This one is not transactional because, inexplicably, transactions don't
    # support either the recursive delete or recursive create operations that
    # we need. Why? No explanation in the docs that I can find.

    try:
        # Proceed one KV pair at a time
        for key in sorted(kv):
            old_name = key
            new_name = kv[key]

            old_data = zk_conn.get(old_name)[0]

            child_keys = list()

            # Find the children of old_name recursively
            def get_children(key):
                children = zk_conn.get_children(key)
                if not children:
                    child_keys.append(key)
                else:
                    for ckey in children:
                        get_children('{}/{}'.format(key, ckey))
            get_children(old_name)

            # Get the data out of each of the child keys
            child_data = dict()
            for ckey in child_keys:
                child_data[ckey] = zk_conn.get(ckey)[0]

            # Create the new parent key
            zk_conn.create(new_name, old_data, makepath=True)

            # For each child key, create the key and add the data
            for ckey in child_keys:
                new_ckey_name = ckey.replace(old_name, new_name)
                zk_conn.create(new_ckey_name, child_data[ckey], makepath=True)

            # Remove recursively the old key
            zk_conn.delete(old_name, recursive=True)

        return True
    except Exception:
        return False

# Write lock function
def writelock(zk_conn, key):
    count = 1
    while True:
        try:
            lock_id = str(uuid.uuid1())
            lock = zk_conn.WriteLock('{}'.format(key), lock_id)
            break
        except Exception:
            count += 1
            if count > 5:
                break
            else:
                continue
    return lock

# Read lock function
def readlock(zk_conn, key):
    count = 1
    while True:
        try:
            lock_id = str(uuid.uuid1())
            lock = zk_conn.ReadLock('{}'.format(key), lock_id)
            break
        except Exception:
            count += 1
            if count > 5:
                break
            else:
                continue
    return lock

# Exclusive lock function
def exclusivelock(zk_conn, key):
    count = 1
    while True:
        try:
            lock_id = str(uuid.uuid1())
            lock = zk_conn.Lock('{}'.format(key), lock_id)
            break
        except Exception:
            count += 1
            if count > 5:
                break
            else:
                continue
    return lock