Listener middleware

Listener middleware is only run for the listener in which it's passed. You can pass any number of middleware functions to the listener using the middleware parameter, which must be a list that contains one to many middleware functions.

If your listener middleware is a quite simple one, you can use a listener matcher, which returns bool value (True for proceeding) instead of requiring next() method call.

Refer to the module document to learn the available listener arguments.

# Listener middleware which filters out messages with "bot_message" subtype
def no_bot_messages(message, next):
    subtype = message.get("subtype")
    if subtype != "bot_message":
       next()

# This listener only receives messages from humans
@app.event(event="message", middleware=[no_bot_messages])
def log_message(logger, event):
    logger.info(f"(MSG) User: {event['user']}\nMessage: {event['text']}")

# Listener matchers: simplified version of listener middleware
def no_bot_messages(message) -> bool:
    return message.get("subtype") != "bot_message"

@app.event(
    event="message", 
    matchers=[no_bot_messages]
    # or matchers=[lambda message: message.get("subtype") != "bot_message"]
)
def log_message(logger, event):
    logger.info(f"(MSG) User: {event['user']}\nMessage: {event['text']}")