Emulate GCP Cloud functions locally

When building a backend on Google Cloud Platform, it takes about a minute to deploy, so it is smooth to build an environment that emulates locally during development. Here's how to emulate Cloud Functions in a Python environment.

Conclusion

Create a function called hello in main.py and put it

main.py

def hello(request):
    request_json = request.get_json()
    if request.args and 'message' in request.args:
        return request.args.get('message')+'get'
    elif request_json and 'message' in request_json:
        return request_json['message']+'post'
    else:
        return f'Hello Worlds!'

In that folder, type the terminal below.

terminal.

functions-framework --target=hello

When specifying the port, it is as follows.

terminal.

functions-framework --target=hello  --port=8081

curl command

A curl command for debugging.

get.communication

curl  -X GET "localhost:8081/?message=Hi,get"

post.communication

curl -X POST -H "Content-Type: application/json" -d '{"message":"hi,post"}' localhost:8081/

About cors settings

main.py

def hello(request):
    request_json = request.get_json()
    headers = {
        'Access-Control-Allow-Origin': '*',
    }
    """
    headers = {
        'Access-Control-Allow-Origin': 'https://example.com',
    }
    """
    if request.args and 'message' in request.args:
        return (request.args.get('message')+'get', 200, headers)
    elif request_json and 'message' in request_json:
        return (request_json['message']+'post', 200, headers)
    else:
        return (f'Hello Worlds!', 200, headers)

Deployment

If all goes well, deploy to GCP.

terminal.

 gcloud functions deploy hello \
--runtime python37 --trigger-http --allow-unauthenticated

https://cloud.google.com/functions/docs/quickstart

official

https://github.com/GoogleCloudPlatform/functions-framework-python

Application example

In reality, the return value is often in JSON format, so that's the case.

main.py

import json

def hello(request):
    request_json = request.get_json()
    headers = {
        'Access-Control-Allow-Origin': 'http://localhost:8080',
    }
    """
    headers = {
        'Access-Control-Allow-Origin': 'https://example.com',
    }
    """
    print('called')

    if request.args and 'message' in request.args:
        input = request.args.get('message')
        rtrn = {'output':'hi %s(get)'%(input)}
        return (json.dumps(rtrn), 200, headers)
    elif request_json and 'message' in request_json:
        input = request_json['message']
        rtrn = {'output':'hi %s(post)'%(input)}
        return (json.dumps(rtrn), 200, headers)
    else:
        rtrn = {'output':'hi (no args)'}
        return (json.dumps(rtrn), 200, headers)

For non-standard modules, you need to create requirement.txt, but in this case it's just json so you don't need it.