Feature request: Add a flag to ALBResolver to URL-decode query parameters #7621
Description
Use case
(follow up from Discord thread: https://discord.com/channels/1006478942305263677/1432874977454985288)
Background: According to https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html, for ALB requests
If the query parameters are URL-encoded, the load balancer does not decode them. You must decode them in your Lambda function
This decoding should happen before input validation; I think datetime types are especially problematic for this if you're trying to pass them as ISO-format strings. For example: .../?start=2025-12-20T16%3A56%3A02.032000%2000%3A00&end=2025-12-30T16%3A56%3A02.032000%2000%3A00
Solution/User Experience
It would be nice for ALBResolver to optionally do this decoding for you (I understand it could be a behavior change, so you probably wouldn't want it to be enabled by default).
An example of this behavior in some other frameworks that process ALB events:
brefphp/bref#456
fastify/aws-lambda-fastify#91
Alternative solutions
I was able to work around this by adding a middleware for my ALB handler:
from aws_lambda_powertools.middleware_factory import lambda_handler_decorator
@lambda_handler_decorator
def alb_query_parameter_decoder(
handler: Callable[[dict, LambdaContext], dict],
event: dict,
context: LambdaContext,
) -> dict:
query_params = event.get("queryStringParameters")
if query_params:
for k, v in query_params.items():
try:
query_params[k] = unquote(v)
except Exception:
pass
return handler(event, context)Acknowledgment
- This feature request meets Powertools for AWS Lambda (Python) Tenets
- Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET