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Server

MessageBusEventHandler

Module: ovos_messagebus.event_handler.MessageBusEventHandler

MessageBusEventHandler is a Tornado WebSocketHandler subclass that implements the OVOS message bus. All connected clients share a single module-level connection list (client_connections in event_handler.py:27). The handler broadcasts every received message to every client.

Module attributes

Attribute Type Description
client_connections list Module-level list of all open MessageBusEventHandler instances

Key methods

open()

Tornado calls open() when a new WebSocket connection opens. The method writes a connected message (with context.session.session_id = "default") to the new client only, then appends self to the module-level client_connections list.

on_message(message)

Tornado calls on_message() for each incoming WebSocket frame. The handler broadcasts the raw message string to all connections in client_connections (including the sender) by calling write_message() on each.

When self.filter is True (read from mycroft.conf["websocket"]["filter"]), the handler deserializes the message first and logs its type, source, destination, and session, unless the type is in filter_logs. If deserialization fails, the handler logs the failure at DEBUG level and still broadcasts the raw frame unchanged. This filter mode supports debug monitoring only. It does not affect delivery.

on_close()

Removes the handler from client_connections when the connection drops.

check_origin(origin) → bool

Always returns True. OVOS does not enforce CORS or origin checks. Any WebSocket client can connect.

max_message_size (property)

Returns the configured maximum WebSocket message size in bytes:

config.get("websocket", {}).get("max_msg_size", 10) * 1024 * 1024

Default: 10 MB.

Broadcast behavior

The bus is a pure fan-out. It does no routing, no filtering, and no topic subscriptions at the server level. The bus forwards every message from every client to every client. Subscription filtering happens entirely in the client library (ovos-bus-client).

load_message_bus_config()

Module: ovos_messagebus.load_config

from ovos_messagebus.load_config import load_message_bus_config

config = load_message_bus_config()
# config.host, config.port, config.route, config.ssl

load_message_bus_config() reads mycroft.conf["websocket"] and returns a MessageBusConfig namedtuple:

Field Source key Default
host host 0.0.0.0
port port 8181
route route /core
ssl ssl False

Keyword arguments passed to load_message_bus_config() override values from the config file:

config = load_message_bus_config(port=8182)

main()

Module: ovos_messagebus.__main__

Entry point for the bus server process.

from ovos_messagebus.__main__ import main

main()

Execution flow:

  1. Call load_message_bus_config() to get the host, port, route, and ssl settings.
  2. Build a Tornado web.Application that maps config.route to MessageBusEventHandler.
  3. If config.ssl is truthy, resolve ssl_options from websocket.ssl_cert and websocket.ssl_key (generating and caching a self-signed certificate under the XDG data directory when unset), then bind the application to config.port and config.host with those ssl_options, serving wss://. Otherwise bind it plainly, serving ws://.
  4. Start the Tornado IOLoop in a daemon thread.
  5. Block the main thread on wait_for_exit_signal() (from ovos-utils).
  6. On signal (SIGTERM or SIGINT), the daemon thread exits with the process.

Because the IOLoop runs in a daemon thread, it terminates automatically when the main thread receives a shutdown signal. No explicit cleanup step is needed.

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