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"""Virtual AMQ Exchange.
Implementations of the standard exchanges defined
by the AMQ protocol (excluding the `headers` exchange).
"""
from __future__ import annotations
import re
from kombu.utils.text import escape_regex
class ExchangeType:
"""Base class for exchanges.
Implements the specifics for an exchange type.
Arguments:
channel (ChannelT): AMQ Channel.
"""
type = None
def __init__(self, channel):
self.channel = channel
def lookup(self, table, exchange, routing_key, default):
"""Lookup all queues matching `routing_key` in `exchange`.
Returns:
str: queue name, or 'default' if no queues matched.
"""
raise NotImplementedError('subclass responsibility')
def prepare_bind(self, queue, exchange, routing_key, arguments):
"""Prepare queue-binding.
Returns:
Tuple[str, Pattern, str]: of `(routing_key, regex, queue)`
to be stored for bindings to this exchange.
"""
return routing_key, None, queue
def equivalent(self, prev, exchange, type,
durable, auto_delete, arguments):
"""Return true if `prev` and `exchange` is equivalent."""
return (type == prev['type'] and
durable == prev['durable'] and
auto_delete == prev['auto_delete'] and
(arguments or {}) == (prev['arguments'] or {}))
class DirectExchange(ExchangeType):
"""Direct exchange.
The `direct` exchange routes based on exact routing keys.
"""
type = 'direct'
def lookup(self, table, exchange, routing_key, default):
return {
queue for rkey, _, queue in table
if rkey == routing_key
}
def deliver(self, message, exchange, routing_key, **kwargs):
_lookup = self.channel._lookup
_put = self.channel._put
for queue in _lookup(exchange, routing_key):
_put(queue, message, **kwargs)
class TopicExchange(ExchangeType):
"""Topic exchange.
The `topic` exchange routes messages based on words separated by
dots, using wildcard characters ``*`` (any single word), and ``#``
(one or more words).
"""
type = 'topic'
#: map of wildcard to regex conversions
wildcards = {'*': r'.*?[^\.]',
'#': r'.*?'}
#: compiled regex cache
_compiled = {}
def lookup(self, table, exchange, routing_key, default):
return {
queue for rkey, pattern, queue in table
if self._match(pattern, routing_key)
}
def deliver(self, message, exchange, routing_key, **kwargs):
_lookup = self.channel._lookup
_put = self.channel._put
deadletter = self.channel.deadletter_queue
for queue in [q for q in _lookup(exchange, routing_key)
if q and q != deadletter]:
_put(queue, message, **kwargs)
def prepare_bind(self, queue, exchange, routing_key, arguments):
return routing_key, self.key_to_pattern(routing_key), queue
def key_to_pattern(self, rkey):
"""Get the corresponding regex for any routing key."""
return '^%s$' % (r'\.'.join(
self.wildcards.get(word, word)
for word in escape_regex(rkey, '.#*').split('.')
))
def _match(self, pattern, string):
"""Match regular expression (cached).
Same as :func:`re.match`, except the regex is compiled and cached,
then reused on subsequent matches with the same pattern.
"""
try:
compiled = self._compiled[pattern]
except KeyError:
compiled = self._compiled[pattern] = re.compile(pattern, re.U)
return compiled.match(string)
class FanoutExchange(ExchangeType):
"""Fanout exchange.
The `fanout` exchange implements broadcast messaging by delivering
copies of all messages to all queues bound to the exchange.
To support fanout the virtual channel needs to store the table
as shared state. This requires that the `Channel.supports_fanout`
attribute is set to true, and the `Channel._queue_bind` and
`Channel.get_table` methods are implemented.
See Also:
the redis backend for an example implementation of these methods.
"""
type = 'fanout'
def lookup(self, table, exchange, routing_key, default):
return {queue for _, _, queue in table}
def deliver(self, message, exchange, routing_key, **kwargs):
if self.channel.supports_fanout:
self.channel._put_fanout(
exchange, message, routing_key, **kwargs)
#: Map of standard exchange types and corresponding classes.
STANDARD_EXCHANGE_TYPES = {
'direct': DirectExchange,
'topic': TopicExchange,
'fanout': FanoutExchange,
}
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