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This documentation was last modified: Wednesday, August 28th, 2019 at 9:08 pm

Introduction to the Message Bus

What is a Message Bus?

A Message Bus is mechanism for independent systems to communicate with each other using a set of messages for common commands or notifiers. In the Mycroft ecosystem, the Messagebus is a websocket and the messages contain a message type with an optional JSON data packet. Some messages trigger actions and have side effects; some are simple notifiers of actions that either have occurred or are about to occur. The Messagebus connects the mycroft-core processes and the Skills, and can also be joined by outside systems such as the CLI.

The common messages are listed below. Messages can be sent from the producers listed below and acted upon by Skills or other consumers within mycroft-core. The producers and consumers list below is not exhaustive and some messages might be generated or handled by other processes or advanced Skills.

The base MycroftSkill API handles most of the Messagebus usage automatically. For example, the mycroft.stop message is caught by the skill framework, invoking an overridden MycroftSkills.stop() method within a Skill. Similarly, the MycroftSkill.speak() and MycroftSkill.speak_dialog() methods generate speak messages to be conveyed to the text-to-speech (TTS) and audio systems.

You will really only need to know about the Mycroft Messagebus if you are developing advanced Skills. The MycroftSkill.add_event() method allows you to attach a handler which will be triggered when the message is seen on the Messagebus.

NOTE: We can only currently assist you in writing Skills in Python, so if you choose to write Skills in another programming language, we may not be able to provide assistance – but we don’t want to stop you doing awesome things!

Mycroft Messagebus messages

message type data Emitted By (Producer) Handled By (Consumer) Meaning
speak {"utterance": "words to be spoken", "lang": "en-us"} Request to speak utterance
mycroft.internet.connected Internet connection is now available (only generated on initial connection)
mycroft.stop Stop command (e.g. button pressed)
mycroft.paired Pairing has completed
open System UI is ready
complete_intent_failure Intent processing failed
recognizer_loop:sleep Go into ‘sleep’ mode. Everything except “Hey Mycroft, wake up” will be ignored.
recognizer_loop:wake_up Come out of ‘sleep’ mode.
mycroft.awoken Has come out of sleep mode
recognizer_loop:wakeword {"utterance": "wakeword heard", "session": session_id} client/speech/ Wake Word was heard
recognizer_loop:record_begin client/speech/ Recording has started
recognizer_loop:record_end client/speech/ Recording has ended
recognizer_loop:utterance {"utterances": [text], "lang": self.stt.lang, "session": session_id} client/speech/
recognizer_loop:audio_output_start audio/ Text output (TTS) has begun
recognizer_loop:audio_output_end audio/ Text output (TTS) has ended
enclosure.notify.no_internet audio/ Detetected a connection error during STT
mycroft.mic.mute client/speech/ Turn off the mic (no wakeword or STT processing)
mycroft.mic.unmute client/speech/ Turn on the mic (enable wakeword and STT processing)
mycroft.mic.listen Begin recording for STT processing skills/ audio/ Start playback of tracklist skills/ audio/ Stop playback skills/ audio/ Pause playback (if supported) skills/ audio/ Resume playback (if supported by backend) skills/ audio/ Request track info from audio service audio/ skills/ Reply to track info request skills/ audio/ Skip to next track skills/ audio/ Skip to previous track
mycroft.volume.increase {"play_sound": true} client/enclosure/ Volume Skill Enclosure Volume up
mycroft.volume.decrease {"play_sound": true} client/enclosure/ Volume Skill Enclosure Volume down
mycroft.volume.mute {"speak_message": true} Volume Skill Enclosure Volume muted
mycroft.volume.unmute {"speak_message": true} Volume Skill Enclosure Volume unmuted
mycroft.skill.handler.start {"handler": class/function name}
mycroft.skill.disable_intent {"intent_name": "name"} mycroft/skills/ Disable intent
mycroft.skill.enable_intent {"intent_name": "name"} mycroft/skills/ Enable disabled intent
mycroft.skills.loaded {"id": SKILL ID, "name": SKILL NAME, "folder": FOLDER, "modified": MODIFIED} skills/ mycroft/skills/ A skill has been loaded
mycroft.skills.loading_failure {"id": SKILL ID, "folder": SKILL FOLDER} skills/
mycroft.skills.shutdown {"id": SKILL ID, "folder": SKILL FOLDER} skills/
mycroft.skills.list {"skills": [...] } skills/ List of loaded skills (response to ‘skillmanager.list’)
mycroft.skills.initialized mycroft/skills/ Upon startup, all skills have been loaded
mycroft.skills.settings.update Configuration Skill mycroft/skills/ Pull new skill settings from the server
msm.updating skills/ MSM install has begun
msm.installing skills/ MSM update has begun
msm.install.succeeded { "skill" : name } skills/ MSM install succeeded for given skill
msm.install.failed { "skill" : name, "error" : code } skills/ MSM install failed for given skill
msm.installed skills/ MSM install is complete
msm.updated skills/ MSM update is complete
msm.removing skills/ MSM remove has begun
msm.remove.succeeded { "skill" : name } skills/ MSM remove succeeded for given skill
msm.remove.failed { "skill" : name, "error" : code } skills/ MSM remove failed for given skill
msm.removed skills/ MSM remove is complete
skillmanager.update skills/ Request immediate update of all skills
skillmanager.list CLI (client/text/ skills/ Request a response with ‘mycroft.skills.list’
System administrative actions
system.wifi.setup / mycroft.wifi.start mycroft-wifi-setup: Kick off a a wifi-setup session
system.wifi.reset / mycroft.wifi.reset mycroft-wifi-setup: Clear the saved wifi settings
system.ntp.sync mycroft-wifi-setup: Force the system clock to synchronize with NTP servers
system.ssh.enable / mycroft.enable.ssh mycroft-wifi-setup: Configure system to allow SSH connections
system.ssh.disable / mycroft.disable.ssh mycroft-wifi-setup: Configure system to block SSH connections
system.reboot mycroft-wifi-setup: Force a Linux reboot
system.shutdown mycroft-wifi-setup: Force a Linux shutdown
system.update mycroft-wifi-setup: Force an apt-get update on mycroft-mark-1 or mycroft-picroft package (as appropriate)

Guidelines for Mycroft Messagebus usage

Private messages can be placed on the Messagebus following these naming conventions:
subsystem.message or skill.skillname.message

  • Messages MUST use verbs for requests – such as;

    • mic.mute
    • mic.unmute
    • skill.mycrofttimer.cancel.all
  • Messages MUST use the future tense for pre-action notifications – such as;

    • mic.muting
    • mic.unmuting
  • Messages MUST use the past tense for post-action notifications – such as;

    • mic.muted
    • mic.unmuted
    • skill.mycrofttimer.expired

Command line invocation syntax

python3 -m mycroft.messagebus.send xxx.yyy.zzz  


python3 -m mycroft.messagebus.send xxx.yyy.zzz '{"name": "value"}'  

Connecting message handlers within a MycroftSkill

def initialize(self):  

def handle_listener_started(self, message):  
    # code to excecute when active listening begins...

def handle_listener_ended(self, message):  
    # code to excecute when active listening begins...  

Generating messages within a MycroftSkill

def some_method(self):  
                              {'utterances': ["inject a user utterance"],  
                               'lang': 'en-us'}))  

Connecting to the Mycroft Messagebus in Python

Here is an example Python script to connect to the messagebus:

#! /usr/bin/env python3

import sys
from websocket import create_connection
uri = 'ws://' + sys.argv[1] + ':8181/core'
ws = create_connection(uri)
print("Sending " + sys.argv[2] + " to " + uri + "...")
if len(sys.argv) >= 4:
    data = sys.argv[3]
    data = "{}"

message = '{"type": "' + sys.argv[2] + '", "data": ' + data +'}'  
result = ws.send(message)  
print("Receiving..." )
result = ws.recv()  
print("Received '%s'" % result)

Unfortunately, we cannot provide support or examples for other languages.

If you have further questions, then the best place to ask them is our Community Forum or in the ~dev Channel on Mycroft Chat.

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