Serverless function snippet to return an S3 file

serverless_get_s3_file.py

def get(event, context):

    response = _get_error_responce('Incorrect URL format: Use /foobar/<a>/<b>/?type=<url/file>')

    if 'queryStringParameters' in event and 'pathParameters' in event:
        if event['pathParameters'] and 'a' in event['pathParameters'] and 'b' in event['pathParameters']:
            a = event['pathParameters']['a']
            b = event['pathParameters']['b']

            s3_key = 's3key/to/file/{a}/{b}'.format(a=a, b=b)

            if event['queryStringParameters'] and 'type' in event['queryStringParameters']:
                type = event['queryStringParameters']['type']
                if type == 'file':
                    try:
                        obj_ref = s3_resource.Object(bucket_name=BUCKET, key=s3_key)
                    except Exception as e:
                        obj_ref = None
                        response = _get_error_responce(e)

                    if obj_ref:
                        try:
                            obj = obj_ref.get()
                            response = {
                                'statusCode': 200,
                                'headers': {
                                    'Content-Type': obj['ContentType']
                                },
                                'body': base64.encodebytes(obj['Body'].read()).decode(),
                                'isBase64Encoded': True
                            }
                        except Exception as e:
                            response = _get_error_responce(e)
                elif type == 'url':
                    try:
                        url = s3_client.generate_presigned_url('get_object', Params={
                            'Bucket': BUCKET,
                            'Key': s3_key
                        }, ExpiresIn=100)
                    except Exception as e:
                        url = None
                        response = _get_error_responce(e)

                    if url:
                        response = {
                            "statusCode": 200,
                            "body": json.dumps({
                                "url": url
                            })
                        }
                else:
                    response = _get_error_responce('Illegal type: {}'.format(type))

    return response