How-to-write-a-python-script-for-python-runtime.md

How to write a python script for python runtime

Statement

• The operating system as mentioned in this document is Darwin.
• The MQTT client toolkit as mentioned in this document is MQTTBOX.
• In the test case mentioned in this document, the configuration of the Local Hub Module and Local Function Module is as follows:

# Local Hub Module Configuration
name: localhub
listen:
  - tcp://:1883
principals:
  - username: 'test'
    password: 'be178c0543eb17f5f3043021c9e5fcf30285e557a4fc309cce97ff9ca6182912'
    permissions:
      - action: 'pub'
        permit: ['#']
      - action: 'sub'
        permit: ['#']

# Local Function Module Configuration
name: localfunc
hub:
  address: tcp://localhub:1883
  username: test
  password: hahaha
rules:
  - id: rule-e1iluuac1
    subscribe:
      topic: py
      qos: 0
    compute:
      function: get
    publish:
      topic: py/hi
      qos: 0
functions:
  - id: func-nyeosbbch
    name: 'get'
    runtime: 'python27'
    handler: 'get.handler'
    codedir: 'var/db/openedge/module/func-nyeosbbch'
    entry: "hub.baidubce.com/openedge/openedge-function-runtime-python27:0.1.1"

OpenEdge officially provides the Python27 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 OpenEdge does not specifically limit. If you want to apply a Python script to handle an MQTT message, the configuration of the Local Function Module is as follows:

functions:
  - id: func-nyeosbbch
    name: 'sayhi'
    runtime: 'python27'
    handler: 'sayhi.handler'
    codedir: 'var/db/openedge/module/func-nyeosbbch'
    entry: "hub.baidubce.com/openedge/openedge-function-runtime-python27:0.1.1"

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

func-nyeosbbch
    sayhi.py 

More detailed configuration of Local Function Module, please refer to Local-Function-Module-Configuration-Interpretation.

Parameter Convention

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

The Python 27 runtime provided by OpenEdge 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 orininal 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 OpenEdge 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 function 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 python
# -*- 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
        result['type'] = 'non-dict'
        result['say'] = 'hello world'

    return result

• Publish a dict format message：

• Publish an non-dict format message：

As above, for some general needs, we can do it through the standard library of the system python environment. However, for some more complex demands, it is often necessary to import some third-party libraries to complete. How to solve this problem? We will provide a general solution below.

Import Third-Party Libraries

Generally, using the standard library of the system python environment can not meet our needs. In actual practice, it is often necessary to import some third-party libraries. An example is given below.

Suppose we want to crawl a website and get the response. Here, we can import a third-party library requests. How to import it, as shown below:

• Step 1: pip download requests // download requests package and its dependency package(idna、urllib3、chardet、certifi)
• Step 2: cp requests-package /directory/to/Python/script // copy requests package and its dependency package to the directory of the Python script
• Step 3: touch __init__.py // make the directory of the Python script as a package
• Step 4: import requests // import the third-party library requests, and write the Python script
• Step 5: python your_script.py // execute your Python script

If the above operation is normal, the resulting script directory structure is as shown in the following figure.

Now we write the Python script get.py to get the headers information of https://openedge.tech, assuming that the trigger condition is that Python27 runtime receives the "A" command from the Local Hub Module. More detailed contents are as follows:

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

import requests

def handler(event, context):
    """
    data: {"action": "A"}
    """
	if 'action' in event:
		if event['action'] == 'A':
			r = requests.get('https://openedge.tech')
			if str(r.status_code) == '200':
				event['info'] = r.headers
			else:
				event['info'] = 'exception found'
		else:
			event['info'] = 'action error'

	else:
		event['error'] = 'action not found'

	return event

As above, after receiving the message publish to the topic py, the Local Hub will call the get.py script to handle, and then publish the result to the topic py/hi. Here, we subscribe the topic py/hi via MQTTBOX and publish the message {"action": "A"} to the Local Hub by the topic py, and observe the received message of the topic py/hi, as normal, the headers information of https://openedge.tech can be obtained normally.