:orphan:


Basic Subscriptions
===================

As a default, subscriptions use exact matching, i.e. a subscriber for
topic ``com.myapp.topic1`` will receive events for publications to topic
``com.myapp.topic1`` only. (There are also :doc:`pattern-based
subscriptions <Pattern-Based-Subscriptions>` which can be selected
via an option when subscribing.)

    Note: There are some :doc:`specific rules <URI-Format>` regarding the
    formatting of URIs used to identify topics.

WAMP mandates a single subscription per session for each URI. If a
client issues a second subscription request for an URI, the WAMP router
returns the same subscription ID (as it would for any other client
issuing a subscription request for this URI). Only a single event is
dispatched to the subscriber, irrespective of how many subscription
requests it has issued.

WAMP client libraries may allow multiple independent registrations from
within the code which can be managed separately, but this is above the
WAMP protocol level. For an example of this, see the `Autobahn\|JS
documentation <https://github.com/crossbario/autobahn-js/blob/master/doc/reference.md>`__.

Here's an example for a simple subscription in JavaScript using
Autobahn\|JS:

.. code:: javascript

    session.subscribe("com.myapp.topic1", myTopicHandler);

This is equivalent to

.. code:: javascript

    session.subscribe("com.myapp.topic1", myTopicHandler, { match: "exact" });

With exact matching, there is no need to explicitly set the matching
policy as an option.