api_lambda.py

# This code is a bit ...messy and includes some workarounds
# It functions fine, but needs some cleanup
# Checked the DecimalEncoder and Checks workarounds 20200402 and no progression towards fix

import boto3, json, os, decimal

SM_ARN = 'YOUR_STATEMACHINE_ARN'

sm = boto3.client('stepfunctions')

def lambda_handler(event, context):
    # Print event data to logs .. 
    print("Received event: " + json.dumps(event))

    # Load data coming from APIGateway
    data = json.loads(event['body'])
    data['waitSeconds'] = int(data['waitSeconds'])
    
    # Sanity check that all of the parameters we need have come through from API gateway
    # Mixture of optional and mandatory ones
    checks = []
    checks.append('waitSeconds' in data)
    checks.append(type(data['waitSeconds']) == int)
    checks.append('message' in data)

    # if any checks fail, return error to API Gateway to return to client
    if False in checks:
        response = {
            "statusCode": 400,
            "headers": {"Access-Control-Allow-Origin":"*"},
            "body": json.dumps( { "Status": "Success", "Reason": "Input failed validation" }, cls=DecimalEncoder )
        }
    # If none, start the state machine execution and inform client of 2XX success :)
    else: 
        sm.start_execution( stateMachineArn=SM_ARN, input=json.dumps(data, cls=DecimalEncoder) )
        response = {
            "statusCode": 200,
            "headers": {"Access-Control-Allow-Origin":"*"},
            "body": json.dumps( {"Status": "Success"}, cls=DecimalEncoder )
        }
    return response

# This is a workaround for: http://bugs.python.org/issue16535
# Solution discussed on this thread https://stackoverflow.com/questions/11942364/typeerror-integer-is-not-json-serializable-when-serializing-json-in-python
# https://stackoverflow.com/questions/1960516/python-json-serialize-a-decimal-object
# Credit goes to the group :)
class DecimalEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, decimal.Decimal):
            return int(obj)
        return super(DecimalEncoder, self).default(obj)