How to write a python script for Python runtime

Statement

• The operating system as mentioned in this document is Ubuntu16.04.
• The version of runtime is Python3.6, and for Python2.7, configuration is the same except for the language difference when coding the scripts
• The MQTT client toolkit as mentioned in this document is MQTTBox.
• In this article, the service created based on the Hub module is called localhub service. And for the test case mentioned here, the localhub service, function calculation service, and other services are configured as follows:

# The configuration of Local Hub service
# Configuration file location is: `var/db/baetyl/localhub-conf/service.yml`.
listen:
  - tcp://0.0.0.0:1883
principals:
  - username: 'test'
    password: 'hahaha'
    permissions:
      - action: 'pub'
        permit: ['#']
      - action: 'sub'
        permit: ['#']

# The configuration of Local Function Manager service
# Configuration file location is: var/db/baetyl/function-manager-conf/service.yml
hub:
  address: tcp://localhub:1883
  username: test
  password: hahaha
rules:
  - clientid: localfunc-1
    subscribe:
      topic: py
    function:
      name: sayhi3
    publish:
      topic: py/hi
functions:
  - name: sayhi3
    service: function-sayhi3
    instance:
      min: 0
      max: 10
      idletime: 1m

# The configuration of python function runtime
# Configuration file location is: var/db/baetyl/function-sayhi-conf/service.yml
functions:
  - name: 'sayhi3'
    handler: 'sayhi.handler'
    codedir: 'var/db/baetyl/function-sayhi'

# The configuration of application.yml
# Configuration file location is: var/db/baetyl/application.yml
version: v0
services:
  - name: localhub
    image: hub.baidubce.com/baetyl/baetyl-hub
    replica: 1
    ports:
      - 1883:1883
    mounts:
      - name: localhub-conf
        path: etc/baetyl
        readonly: true
      - name: localhub-data
        path: var/db/baetyl/data
      - name: localhub-log
        path: var/log/baetyl
  - name: function-manager
    image: hub.baidubce.com/baetyl/baetyl-function-manager
    replica: 1
    mounts:
      - name: function-manager-conf
        path: etc/baetyl
        readonly: true
      - name: function-manager-log
        path: var/log/baetyl
  - name: function-sayhi3
    image: hub.baidubce.com/baetyl/baetyl-function-python36
    replica: 0
    mounts:
      - name: function-sayhi-conf
        path: etc/baetyl
        readonly: true
      - name: function-sayhi-code
        path: var/db/baetyl/function-sayhi
        readonly: true
volumes:
  # hub
  - name: localhub-conf
    path: var/db/baetyl/localhub-conf
  - name: localhub-data
    path: var/db/baetyl/localhub-data
  - name: localhub-log
    path: var/db/baetyl/localhub-log
  # function manager
  - name: function-manager-conf
    path: var/db/baetyl/function-manager-conf
  - name: function-manager-log
    path: var/db/baetyl/function-manager-log
  # function python runtime sayhi
  - name: function-sayhi-conf
    path: var/db/baetyl/function-sayhi-conf
  - name: function-sayhi-code
    path: var/db/baetyl/function-sayhi-code

Baetyl officially provides the Python runtime to load python scripts written by users. The following description is about the name of the python script, the execution function name, input, output parameters, and so on.

Function Name Convention

The name of a python script can refer to Python’s universal naming convention, which Baetyl does not specifically limit. If you want to apply a python script to handle an MQTT message, the configuration of Python3.6 runtime service is as follows:

functions:
  - name: 'sayhi3'
    handler: 'sayhi.handler'
    codedir: 'var/db/baetyl/function-sayhi'

Here, we focus on the handler attribute, where sayhi represents the script name and the handler represents the entry function called in the file.

function-sayhi-code/
├── __init__.py
└── sayhi.py

More detailed configuration of Python runtime, please refer to Python runtime configuration.

Parameter Convention

def handler(event, context):
    # do something
    return event

The Python runtime provided by Baetyl supports two parameters: event and context, which are described separately below.

• event: Depend on the Payload in the MQTT message
  • If the original Payload is a json format data, then pass in the data handled by json.loads(Payload)
  • If the original Payload is Byte, string(not Json), then pass in the original Payload。
• context: MQTT message context
  • context.messageQOS // MQTT QoS
  • context.messageTopic // MQTT Topic
  • context.functionName // MQTT functionName
  • context.functionInvokeID //MQTT function invokeID
  • context.invokeid // as above, be used to compatible with CFC

NOTE: When testing in the cloud CFC, please don’t use the context defined by Baetyl directly. The recommended method is to first determine whether the field is exists or not in the context. If exists, read it.

Hello World

Now we will implement a simple python script with the goal of appending a hello world message to each MQTT message. For a dictionary format message, return it directly, and for an none dictionary format message, convert it to string and return.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

def handler(event, context):
    result = {}
    if isinstance(event, dict):
        result['msg'] = event
        result['type'] = 'dict'
        result['say'] = 'hello world'
    else:
        result['msg'] = event.decode("utf-8")
        result['type'] = 'non-dict'
        result['say'] = 'hello world'

    return result

Publish a dict format message:

Publish a dict format message

Publish an non-dict format message:

Publish an non-dict format message

As above, for some general needs, we can implement it through the Python Standard Library. However, for some more complex demands, it is often necessary to import third-party libraries to complete. How to solve the problem? We’ve provided a general solution in How to import third-party libraries for Python runtime.