Pumpkin-MC/Pumpkin · error

expected ServerListPingEvent

Error message

expected ServerListPingEvent

What it means

This panic comes from the `EventLike` trait's `data_from_event` glue for ServerListPingEvent. The event dispatcher hands an `Event` enum to the handler bridge, which destructures it into its typed payload; if the variant is not `Event::ServerListPingEvent`, the bridge panics with "expected ServerListPingEvent". This means the internal event-routing invariants were violated — the dispatcher delivered an event to a handler registered for a different event type.

Solutions

1. Verify the handler is registered under EventType::ServerListPingEvent so the dispatcher routes matching variants to it.
2. Update the plugin API and dispatcher to the same version so Event enum variants and EventType keys stay in sync.
3. Check any custom event forwarding code for a swap between ServerListPingEvent and another Event variant.
4. Replace the panic with a logged error / no-op if the bridge should tolerate misrouted events.

Example fix

// before
Event::ServerListPingEvent(data) => data,
_ => panic!("expected ServerListPingEvent"),
// after
Event::ServerListPingEvent(data) => data,
other => {
    log::warn!("misrouted event {:?}, expected ServerListPingEvent", other.event_type());
    return Default::default();
}

// assert route correctness before invoking the bridge
assert_eq!(<ServerListPingHandler as EventLike>::EVENT_TYPE, event.event_type(), "misrouted event");

fn as_server_list_ping<'a>(event: &'a Event) -> Option<&'a ServerListPingEventData> {
    if let Event::ServerListPingEvent(data) = event { Some(data) } else { None }
}

// Rust panics are not catchable across FFI; use catch_unwind at the dispatch boundary
let result = std::panic::catch_unwind(AssertUnwindSafe(|| bridge.data_from_event(event)));
if result.is_err() { log::error!("misrouted event for ServerListPingEvent handler"); }

When it happens

Trigger: Calling `data_from_event` (directly or via the plugin-event bridge) with an `Event` variant other than `Event::ServerListPingEvent` — e.g. an event bus that registered a ServerListPing listener under the wrong EventType key, or hand-rolled dispatch code that passes raw events to the wrong trait implementation.

Common situations: Plugin API version changes that renamed/reordered Event variants so old dispatch tables map to the wrong handler; a custom scheduler or event forwarder that mixes up EventType registration keys; writing a custom EventLike impl and copying the wrong Data type into it.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• unexpected event
• unexpected event
• unexpected event
• unexpected event
• unexpected event

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/160c4e9ad19e726c. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-plugin-api/src/events/server/server_list_ping.rs:18

use crate::wit::pumpkin::plugin::event::{Event, EventType, ServerListPingEventData};

use super::super::FromIntoEvent;

/// Fires when the server prepares a Java status/list ping response.
///
/// Register this as a blocking event handler to customize the MOTD, favicon,
/// and reported player counts for WASM plugins.
pub struct ServerListPingEvent;

impl FromIntoEvent for ServerListPingEvent {
    const EVENT_TYPE: EventType = EventType::ServerListPingEvent;
    type Data = ServerListPingEventData;

    fn data_from_event(event: Event) -> Self::Data {
        match event {
            Event::ServerListPingEvent(data) => data,
            _ => panic!("expected ServerListPingEvent"),
        }
    }

    fn data_into_event(data: Self::Data) -> Event {
        Event::ServerListPingEvent(data)
    }
}

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