app.py

import boto3
import requests

# This function capitalizes all text in the original object
def lambda_handler(event, context):
    object_context = event["getObjectContext"]
    # Get the presigned URL to fetch the requested original object 
    # from S3
    s3_url = object_context["inputS3Url"]
    # Extract the route and request token from the input context
    request_route = object_context["outputRoute"]
    request_token = object_context["outputToken"]
    
    # Get the original S3 object using the presigned URL
    response = requests.get(s3_url)
    original_object = response.content.decode("utf-8")

    # Transform all text in the original object to uppercase
    # You can replace it with your custom code based on your use case
    transformed_object = original_object.upper()

    # Write object back to S3 Object Lambda
    s3 = boto3.client('s3')
    # The WriteGetObjectResponse API sends the transformed data
    # back to S3 Object Lambda and then to the user
    s3.write_get_object_response(
        Body=transformed_object,
        RequestRoute=request_route,
        RequestToken=request_token)

    # Exit the Lambda function: return the status code  
    return {'status_code': 200}