Routing

When the Consumer receives a message from RabbitMQ, it prepares an Envelope object of that message, for the handler. However, the prepared envelope somehow needs to be routed to its handler, where it’s actually consumed. The envelope may be routed based on the message type, payload, or any other criteria; It depends on the routing logic. For this reason, the consumer doesn’t make the routing decisions itself, it delegates the routing to a router. The router sits between the consumer and handlers. Its responsibility is, to route each incoming envelope to its handler, returning the handler to the consumer for execution.

Router

class rabbitleap.routing.Router(**kwargs)

Base class for routers.

Subclasses MUST implement find_handler()

Router.find_handler(envelope)

Find a handler

This method expects an Envelope object as an argument and returns a Handler instance to its caller or None, indicating the given envelope is unroutable.

Subclasses routers MUST implement method.

Rule Router

class rabbitleap.routing.RuleRouter(consumer, default_rule=None)

Bases: rabbitleap.routing.Router

Rule router.

Rule Router is an implementation of the base class Router. It uses routing rules to route envelopes to handlers. The rule router maintains a list routing rules, through which it goes sequentially to find a handler for a given envelope. Rules added to the router are appended to the end of its rules list, and since the router goes through the routing rules sequentially in the order they’re added, more specific rules should be added first, then the general ones later.

A routing rule is an instance of the class Rule. It has 3 fields, a Matcher, target, and target arguments field. The matcher is used to determines whether the target can handle the envelope. The target can be a Handler class or a Router instance (sub-router). The target arguments is a dictionary passed to the newly created handler for initialization.

When the target is a Handler class, the router creates an instance of it, then returns the instance to the caller. However, if the target is a Router instance, it would act as a sub-router (child router). The parent router delegates finding the handler to the child router. The sub-router doesn’t have to be of the same type, it can be any Router implementation. Chained routers let one router delegates the routing to the next one.

The rule router returns None when the given envelope is unroutable (no handler can handle it). However, the rule router may be configured with a default routing rule which catches all unroutable envelopes, check set_default_rule().

Rule router always creates a new handler instance when its find_handler() is called, even for the same envelope, except when the rule’s target is a Router instance, which may have different implementation and may not return a new instance.

Actually, the Consumer itself is a Rule Router. It implements extra stuff to communicate with RabbitMQ.

RuleRouter.add_rule(rule)

Add a routing rule to the routing rules list.

A routing rule is added to the end of routing rules list, just before the default rule which is always the last one.

A routing rule is an instance of the class Rule. It has 3 fields, a Matcher, target, and target arguments field. The matcher is used to determines whether the target can handler the envelope. The target can be a Handler class or a Router instance (sub-router). The target arguments is a dictionary passed to the newly created handler for initialization.

Since the rules of the Rule Router are checked sequentially in the order they added, more specific rules should be added first, then generic ones later.

Parameters:rule (Rule) – routing rule instance.

RuleRouter.set_default_rule(rule)

Set default rule.

Default rule, when set, it catches all unroutable envelopes.

Parameters:rule (Rule) – default routing rule which catches all unmatched messages. None will unset default rule

RuleRouter.find_handler(envelope)

Find and return a handler

The router goes through the routing rules list sequentially to find a handler for the given envelope.

When the target, in matched Rule, is a Handler class, an instance of it is created and returned. However, if the target is a Router instance, it would act as a sub-router. The sub-router’s find_handler() is invoked to get a Handler instance.

None is returned when the given envelope is unroutable (no handler can handle it). However, if a default rule is set, its handler instance will be returned

NOTE: The router always creates a new handler instance for each find handler call, even for the same message.

Parameters:envelope (Envelope) – Message envelope Return Handler:Handler instance

Routing Rule

class rabbitleap.routing.Rule(matcher, target, target_kwargs=None)

A matching rule.

A rule (routing rule) is an object that links a matcher (Matcher) instance, to a target.

The matcher is used to determines whether the target can handler the envelope. The target can be a Handler class or a Router instance (sub-router). The target arguments is a dictionary passed to the newly created handler for initialization.

Matchers

class rabbitleap.routing.Matcher

Base class for matchers

This is the base class for matcher. Matcher is used by Rule to check if its target can handle the given Envelope or not

Subclasses MUST implement match() method.

Matcher.match(envelope)

Return True or False indicating the target can handle the message.

This method accepts an Envelope object as an argument and returns boolean, indicating whether the target can handle the envelope or not.

Subclasses MUST implement this method

Parameters:envelope (Envelope) – Message envelope Returns:can handle or not Return type:bool

class rabbitleap.routing.AnyMatches

Bases: rabbitleap.routing.Matcher

Match all messages macher

This matcher matches nothing. It always returns False. It’s used in RuleRouter when a default rule is set to catch all unroutable envelopes

AnyMatches.match(envelope)

Always return True

class rabbitleap.routing.NoneMatches

Bases: rabbitleap.routing.Matcher

Match noting macher

This matcher matches nothing. It always returns False.

NoneMatches.match(envelope)

Always return False

class rabbitleap.routing.MessageTypeMatches(message_type_pattern)

Bases: rabbitleap.routing.Matcher

Match messages based on message type macher

This matcher does match based on the message type.

The message type is provided as a regular expression string or a compiled re.Pattern

The matcher returns True when find a match in the message type, or False otherwise.

MessageTypeMatches.match(envelope)

Return True or False indicating the target can handle the message.

This method accepts an Envelope object as an argument and returns boolean, indicating whether the target can handle the envelope or not.

Subclasses MUST implement this method

Parameters:envelope (Envelope) – Message envelope Returns:can handle or not Return type:bool