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Bug: AppSync Events wildcard route matches channels sharing a segment prefix #8545
Description
Expected Behaviour
With handlers on /default/* and /default/users/*, a publish to /default/usersettings should be handled by /default/*, because usersettings is not inside the users segment.
Current Behaviour
/default/usersettings is routed to the /default/users/* handler. Channels like /default/users-archive/1 are routed there too.
find_best_route (event_handler/events_appsync/functions.py) turns a trailing [^/]+ into .* with pattern[:-6] + ".*". "[^/]+" is only 5 characters, so the preceding / is cut as well. /default/users/* becomes ^/default/users.*$ instead of the ^/default/users/.*$ documented in the function's docstring. It then wins over /default/* as the more specific route.
Code snippet
from aws_lambda_powertools.event_handler import AppSyncEventsResolver
from aws_lambda_powertools.event_handler.events_appsync.functions import find_best_route
app = AppSyncEventsResolver()
@app.on_publish("/default/*")
def generic(payload):
return {"handler": "generic"}
@app.on_publish("/default/users/*")
def users(payload):
return {"handler": "users"}
print(find_best_route({"/default/*": 1, "/default/users/*": 1}, "/default/usersettings"))
# prints "/default/users/*", expected "/default/*"Possible Solution
Strip only the wildcard: pattern[: -len("[^/]+")] + ".*". I have a fix with regression tests ready and can open a PR.
Steps to Reproduce
Run the snippet above. Publishing an event to /default/usersettings through app.resolve(...) returns {"handler": "users"}.
Powertools for AWS Lambda (Python) version
latest (develop, 3.35.0)
AWS Lambda function runtime
3.12
Packaging format used
PyPi
Debugging logs
No response
Activity
boring-cyborg commentedon Oct 13, 2026
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powertools-for-aws-oss-automation commentedon Oct 13, 2026
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powertools-for-aws-oss-automation commentedon Oct 15, 2026
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github-actions commentedon Oct 22, 2026
This is now released under 3.37.0 version!