path: root/kombu/mixins.py

# -*- coding: utf-8 -*-
"""
kombu.mixins
============

Useful mixin classes.

"""
from __future__ import absolute_import, unicode_literals

import socket

from contextlib import contextmanager
from functools import partial
from itertools import count
from time import sleep

from .common import ignore_errors
from .five import range
from .messaging import Consumer, Producer
from .log import get_logger
from .utils.compat import nested
from .utils.encoding import safe_repr
from .utils.limits import TokenBucket
from .utils.objects import cached_property

__all__ = ['ConsumerMixin']

logger = get_logger(__name__)
debug, info, warn, error = logger.debug, logger.info, logger.warn, logger.error

W_CONN_LOST = """\
Connection to broker lost, trying to re-establish connection...\
"""

W_CONN_ERROR = """\
Broker connection error, trying again in %s seconds: %r.\
"""


class ConsumerMixin(object):
    """Convenience mixin for implementing consumer programs.

    It can be used outside of threads, with threads, or greenthreads
    (eventlet/gevent) too.

    The basic class would need a :attr:`connection` attribute
    which must be a :class:`~kombu.Connection` instance,
    and define a :meth:`get_consumers` method that returns a list
    of :class:`kombu.Consumer` instances to use.
    Supporting multiple consumers is important so that multiple
    channels can be used for different QoS requirements.

    Example:
        .. code-block:: python

            class Worker(ConsumerMixin):
                task_queue = Queue('tasks', Exchange('tasks'), 'tasks'))

                def __init__(self, connection):
                    self.connection = None

                def get_consumers(self, Consumer, channel):
                    return [Consumer(queues=[self.task_queue],
                                     callbacks=[self.on_task])]

                def on_task(self, body, message):
                    print('Got task: {0!r}'.format(body))
                    message.ack()

    Methods:

        * :meth:`extra_context`

            Optional extra context manager that will be entered
            after the connection and consumers have been set up.

            Takes arguments ``(connection, channel)``.

        * :meth:`on_connection_error`

            Handler called if the connection is lost/ or
            is unavailable.

            Takes arguments ``(exc, interval)``, where interval
            is the time in seconds when the connection will be retried.

            The default handler will log the exception.

        * :meth:`on_connection_revived`

            Handler called as soon as the connection is re-established
            after connection failure.

            Takes no arguments.

        * :meth:`on_consume_ready`

            Handler called when the consumer is ready to accept
            messages.

            Takes arguments ``(connection, channel, consumers)``.
            Also keyword arguments to ``consume`` are forwarded
            to this handler.

        * :meth:`on_consume_end`

            Handler called after the consumers are canceled.
            Takes arguments ``(connection, channel)``.

        * :meth:`on_iteration`

            Handler called for every iteration while draining
            events.

            Takes no arguments.

        * :meth:`on_decode_error`

            Handler called if a consumer was unable to decode
            the body of a message.

            Takes arguments ``(message, exc)`` where message is the
            original message object.

            The default handler will log the error and
            acknowledge the message, so if you override make
            sure to call super, or perform these steps yourself.

    """

    #: maximum number of retries trying to re-establish the connection,
    #: if the connection is lost/unavailable.
    connect_max_retries = None

    #: When this is set to true the consumer should stop consuming
    #: and return, so that it can be joined if it is the implementation
    #: of a thread.
    should_stop = False

    def get_consumers(self, Consumer, channel):
        raise NotImplementedError('Subclass responsibility')

    def on_connection_revived(self):
        pass

    def on_consume_ready(self, connection, channel, consumers, **kwargs):
        pass

    def on_consume_end(self, connection, channel):
        pass

    def on_iteration(self):
        pass

    def on_decode_error(self, message, exc):
        error("Can't decode message body: %r (type:%r encoding:%r raw:%r')",
              exc, message.content_type, message.content_encoding,
              safe_repr(message.body))
        message.ack()

    def on_connection_error(self, exc, interval):
        warn(W_CONN_ERROR, interval, exc, exc_info=1)

    @contextmanager
    def extra_context(self, connection, channel):
        yield

    def run(self, _tokens=1, **kwargs):
        restart_limit = self.restart_limit
        errors = (self.connection.connection_errors +
                  self.connection.channel_errors)
        while not self.should_stop:
            try:
                if restart_limit.can_consume(_tokens):  # pragma: no cover
                    for _ in self.consume(limit=None, **kwargs):
                        pass
                else:
                    sleep(restart_limit.expected_time(_tokens))
            except errors:
                warn(W_CONN_LOST, exc_info=1)

    @contextmanager
    def consumer_context(self, **kwargs):
        with self.Consumer() as (connection, channel, consumers):
            with self.extra_context(connection, channel):
                self.on_consume_ready(connection, channel, consumers, **kwargs)
                yield connection, channel, consumers

    def consume(self, limit=None, timeout=None, safety_interval=1, **kwargs):
        elapsed = 0
        with self.consumer_context(**kwargs) as (conn, channel, consumers):
            for i in limit and range(limit) or count():
                if self.should_stop:
                    break
                self.on_iteration()
                try:
                    conn.drain_events(timeout=safety_interval)
                except socket.timeout:
                    conn.heartbeat_check()
                    elapsed += safety_interval
                    if timeout and elapsed >= timeout:
                        raise
                except socket.error:
                    if not self.should_stop:
                        raise
                else:
                    yield
                    elapsed = 0
        debug('consume exiting')

    def maybe_conn_error(self, fun):
        """Use :func:`kombu.common.ignore_errors` instead."""
        return ignore_errors(self, fun)

    def create_connection(self):
        return self.connection.clone()

    @contextmanager
    def establish_connection(self):
        with self.create_connection() as conn:
            conn.ensure_connection(self.on_connection_error,
                                   self.connect_max_retries)
            yield conn

    @contextmanager
    def Consumer(self):
        with self.establish_connection() as conn:
            self.on_connection_revived()
            info('Connected to %s', conn.as_uri())
            channel = conn.default_channel
            cls = partial(Consumer, channel,
                          on_decode_error=self.on_decode_error)
            with self._consume_from(*self.get_consumers(cls, channel)) as c:
                yield conn, channel, c
            debug('Consumers canceled')
            self.on_consume_end(conn, channel)
        debug('Connection closed')

    def _consume_from(self, *consumers):
        return nested(*consumers)

    @cached_property
    def restart_limit(self):
        return TokenBucket(1)

    @cached_property
    def connection_errors(self):
        return self.connection.connection_errors

    @cached_property
    def channel_errors(self):
        return self.connection.channel_errors


class ConsumerProducerMixin(ConsumerMixin):
    """Version of ConsumerMixin having separate connection for also
    publishing messages.

    Example:
        .. code-block:: python

            class Worker(ConsumerProducerMixin):

                def __init__(self, connection):
                    self.connection = connection

                def get_consumers(self, Consumer, channel):
                    return [Consumer(queues=Queue('foo'),
                                     on_message=self.handle_message,
                                     accept='application/json',
                                     prefetch_count=10)]

                def handle_message(self, message):
                    self.producer.publish(
                        {'message': 'hello to you'},
                        exchange='',
                        routing_key=message.properties['reply_to'],
                        correlation_id=message.properties['correlation_id'],
                        retry=True,
                    )
    """
    _producer_connection = None

    def on_consume_end(self, connection, channel):
        if self._producer_connection is not None:
            self._producer_connection.close()
            self._producer_connection = None

    @property
    def producer(self):
        return Producer(self.producer_connection)

    @property
    def producer_connection(self):
        if self._producer_connection is None:
            conn = self.connection.clone()
            conn.ensure_connection(self.on_connection_error,
                                   self.connect_max_retries)
            self._producer_connection = conn
        return self._producer_connection