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Topics and Handlers

WebSocket server works under Web Application Messaging Protocol (WAMP) intended to provide developers with the facilities they need to handle messaging between components, i.e., backend and frontend. WebSocket server in Oro application utilizes Publish & Subscribe (PubSub) pattern, where one component subscribes to a topic, and another component publishes to this topic. WebSocket server router distributes events to all subscribers by calling topic handlers.

Hence, if one wants to define a topic, he should declare a route for it and create a topic handler.

Routing

To declare a route for the topic, create a websocket_routing.yml file in the Resources/config/oro/ directory of your bundle. Fill it with the following contents:

oro_sync.ping:                      # unique machine name of your topic in format "%extension_alias%.topic_name"
    channel: 'oro/ping'             # url of your topic channel
    handler:
        callback: 'oro_sync.ping'   # machine name of topic handler

You can declare parameterized routes as well, for example:

oro_email.event:
    channel: 'oro/email_event/{user_id}/{organization_id}'
    handler:
        callback: 'oro_email.event'
    requirements:
        user_id:
            pattern: '\d+' # regular expression
        organization_id:
            pattern: '\d+'

You will be able to get parameters using getAttributes() from the WampRequest $request argument in your topic handler. You can find more information about routing in the documentation of GosWebSocketBundle.

Topic Handlers

Topic handler is called by WebSocket server router whenever occurs one of these events:

  • client subscribed
  • client unsubscribed
  • client published a message

Each topic handler, according to its logic, decides what to do with the occurred event. For example, in onSubscribe() we can decide whether to allow subscription, and in onPublish(), we can either broadcast a given message to all subscribers or a restricted list.

The topic handler must implement Gos\Bundle\WebSocketBundle\Topic\TopicInterface and be declared as a service with a tag gos_web_socket.topic, for example:

oro_sync.topic.websocket_ping:
    class: Oro\Bundle\SyncBundle\Topic\WebsocketPingTopic
    arguments:
        - 'oro_sync.ping'
        - '@logger'
        - '%oro_sync.websocket_ping.interval%'
    tags:
        - { name: gos_web_socket.topic }

Method getName() of the topic handler must return its machine name, which is used in the websocket_routing.yml file for the handler.callback configuration option.

OroSyncBundle provides an abstract class Oro\Bundle\SyncBundle\Topic\AbstractTopic and two out-of-box implementations of topic handlers for common purposes:

  • Oro\Bundle\SyncBundle\Topic\BroadcastTopic is a topic handler that broadcasts each published message to all subscribers. It is required for such simple topics as oro_sync.maintenance, which informs about maintenance mode activation.
  • Oro\Bundle\SyncBundle\Topic\SecuredTopic is a topic handler that checks if a client can subscribe to the topic.
    Broadcasts to all subscribers each published message. It is required for such topics as`oro_email.event`, which informs users about new emails.

If your topic handler is not intended to contain complex logic, you can use existing handlers, for example:

oro_sync.topic.maintenance:
    class: Oro\Bundle\SyncBundle\Topic\BroadcastTopic
    arguments:
        - 'oro_sync.maintenance'
    tags:
        - { name: gos_web_socket.topic }