README.md

Python CORS example

When calling a function from a frontend application in a browser, you may receive an error about missing CORS headers. Here's how you can allow cross-origin requests to a Python serverless function.

Requirements

This example assumes you are familiar with how serverless functions work. If needed, you can check Scaleway official documentation

This example uses the Scaleway Serverless Framework Plugin. Please set up your environment with the requirements stated in the Scaleway Serverless Framework Plugin before trying out the example.

Example explanation

Context: This example shows how to handle preflight CORS requests that will be sent by a browser when invoking a function. It uses totally permissive, open CORS. You may want to modify this to make it more secure.

Explanation The function of the example is to allow most CORS requests. For more documentation on how to control access for CORS requests, see HTTP response headers

Testing with serverless offline for Python

In order to test your function locally before deployment in a serverless function, you can install our python offline testing library with:

pip install -r requirements-dev.txt

Launch your function locally:

python handler.py

Test your local function using curl:

curl localhost:8080

Setup

Once your environment is set up, you can run:

npm install
serverless deploy

Running

Then, from the given URL, you can run:

# Options request
curl -i -X OPTIONS <function URL>

# Get request
curl -i -X GET <function URL>

The output should be similar to:

HTTP/2 200
access-control-allow-headers: *
access-control-allow-methods: *
access-control-allow-origin: *
content-length: 21
content-type: text/plain
date: Tue, 17 Jan 2023 14:02:46 GMT
server: envoy
x-envoy-upstream-service-time: 222

This is checking CORS%

You can also check the output of your function in a browser. It should be: "This is checking CORS".