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allow eventhandlers and eventspecs for exception handlers #5295

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allow eventhandlers and eventspecs for exception handlers #5295

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c1f5e55
allow eventhandlers and eventspecs for exception handlers
adhami3310 May 12, 2025
c02e00c
make frontend event handler type checking a tad better
adhami3310 May 15, 2025
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27 changes: 24 additions & 3 deletions reflex/state.py
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@
from reflex.event import (
BACKGROUND_TASK_MARKER,
Event,
EventActionsMixin,
EventHandler,
EventSpec,
fix_events,
Expand Down Expand Up @@ -2359,7 +2360,7 @@ class FrontendEventExceptionState(State):
"""Substate for handling frontend exceptions."""

@event
def handle_frontend_exception(self, stack: str, component_stack: str) -> None:
def handle_frontend_exception(self, stack: str, component_stack: str):
"""Handle frontend exceptions.

If a frontend exception handler is provided, it will be called.
Expand All @@ -2369,11 +2370,31 @@ def handle_frontend_exception(self, stack: str, component_stack: str) -> None:
stack: The stack trace of the exception.
component_stack: The stack trace of the component where the exception occurred.

Returns:
Chained event specs to be executed.

Raises:
TypeError: If the frontend exception handler is not callable.
"""
prerequisites.get_and_validate_app().app.frontend_exception_handler(
Exception(stack)
frontend_exception_handler = (
prerequisites.get_and_validate_app().app.frontend_exception_handler
)

if isinstance(frontend_exception_handler, EventActionsMixin) and callable(
frontend_exception_handler
):
return frontend_exception_handler(stack)
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i think we want to avoid the extra round trip to the client for processing this.

is it possible to do something like

await app.event_namespace.on_event(
    sid=self.router.session.session_id,
    data=fix_events(
        events=[frontend_exception_handler(stack)],
        token=self.router.session.client_token,
        router_data=self.router_data,
    )[0],
)

i guess maybe that would have a dead locking issue because the state is already being processed.

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maybe? i couldn't understand exactly how the flow is going and how to make it do that, which is why i couldn't figure out the backend exception and why this one is a draft

if not callable(frontend_exception_handler):
raise TypeError(
f"Frontend exception handler must be callable. Got {type(frontend_exception_handler)}."
)
value = frontend_exception_handler(Exception(stack))
if value is not None:
console.warn(
f"Frontend exception handler returned a value: {value}. This is not supported with plain functions."
" Consider using an Event in a state class instead."
)


class UpdateVarsInternalState(State):
"""Substate for handling internal state var updates."""
Expand Down
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