ApiGatewayResolver root routes and strip_prefixes

[BVMiko]

I ran into an issue when using a route with the rule "/" along with strip_prefixes feature. This rule is unable to trigger due to the path variable being reduced down to an empty string instead of a forward slash.

from aws_lambda_powertools.event_handler.api_gateway import ApiGatewayResolver
app = ApiGatewayResolver(strip_prefixes=["/some-path"])
@app.get('/')
def my_func():
    return {'execution_status':'success'}

Expected Behavior

Accessing domain.com/some-path would execute my_func().

Current Behavior

Accessing domain.com/some-path returns a 404. Of note though, accessing domain.com/some-path/ (note the trailing slash) will execute my_func().

Possible Solution

Add an conditional here which will map an empty string to "/".

Steps to Reproduce (for bugs)

1. Set up the code example above
2. Set up ApiGateway to use a custom domain, and bind the Lambda to a custom path of some-path
3. Visit https://CUSTOMDOMAIN/some-path and https://CUSTOMDOMAIN/some-path/ and note the different results

[michaelbrewer]

Nice one @BVMiko , i put in a review comment for adding a test case.

Otherwise, i was thinking whether it should be "" instead of "/"? Then this would work when the request is /some-path

from aws_lambda_powertools.event_handler.api_gateway import ApiGatewayResolver
app = ApiGatewayResolver(strip_prefixes=["/some-path"])
@app.get("")
def my_func():
    return {'execution_status':'success'}

As the original request path of /some-path does different from /some-path/. Although @app.get("") does like strange.

[BVMiko]

I believe that the common standard among other routing frameworks is that all paths should have a leading slash, so @api.get("/") is usually the root path. Unfortunately the Flask and FastAPI docs don't explicitly state this, though all examples are written this way. I did find this Flask issue describing a related oversight of forgetting to enforce a leading slash though.

As for implementation, Flask and FastAPI both seem to do things differently by building and caching the full paths within each route. However ExpressJS, looks like it handles routing similar to the current ApiGatewayRouter though it does ensure a leading slash.

[michaelbrewer]

@BVMiko - agreed. But strip_prefix is supposed to remove the matching prefix from the request.

And that this is on the context of "strip_prefixes" is "/custom-mapping", and the actual request is without a trailing "/" and would look like "/custom-mapping". So naturally I would except the resulting path to be "".

Internally this was not happening due to the addition of a "/" for the starts with check. Because we wanted to allow for "/pay" and "/payment" strip prefixes to be set in any order. As "/pay" would be a partial match. It would remove before "/payment".

So the ultimate solution could just be to reverse the order of the prefixes and remove the "/" we add in the starts with check.

[michaelbrewer]

@BVMiko - thinking it through. If the request path resolves to a empty string (""), after the strip prefixes. Then it makes sense that the base is now actually "/".

We just need to document that there is no difference between a request path of "/pay" and "/pay/" when the strip prefix is "/pay".

[BVMiko]

@michaelbrewer - I updated the testcase and the docs to reflect the new explicit change; let me know if you'd like the wording modified.

[to-mc]

Fixed in v1.20.2.