Pumpkin-MC/Pumpkin · warning · InventoryError

Multiple players dragging in a container at once

Error message

Multiple players dragging in a container at once

What it means

InventoryError::MultiplePlayersDragging is returned when multiple players attempt to perform a drag-style item distribution in the same container at the same time. Drag interactions are stateful (a drag must span start/middle/end packets), so the library forbids interleaved drags from different players to keep distributions consistent.

Solutions

  1. Reject the second drag with this error and require the client to restart its drag
  2. Add a timeout that clears stale drag state so a missing End packet cannot block future drags
  3. Serialize drag handling per container and cancel the first drag when a second player initiates one
  4. Log which player IDs conflicted to spot abusive clients

Example fix

// before
container.handle_drag(player_id, drag)?;
// after
match container.handle_drag(player_id, drag) {
    Err(InventoryError::MultiplePlayersDragging) => {
        player.send_message("Another player is dragging items; try again.");
    }
    r => r?,
}
Defensive patterns

Strategy: try-catch

Validate before calling

fn drag_allowed(container: &Container, player_id: i32) -> bool {
    match container.active_drag() {
        None => true,
        Some(d) => d.player_id == player_id,
    }
}

Try / catch

match container.handle_drag(player_id, drag) {
    Err(InventoryError::MultiplePlayersDragging) => {
        player.send_message("Another player is dragging; try again shortly.");
    }
    r => r?,
}

Prevention

When it happens

Trigger: Two players sending Drag-packet sequences (left/medium/right drag) targeting the same open container concurrently; a second drag starting before the first player's drag completes with its End packet.

Common situations: Busy public chests where several players drag-split stacks simultaneously; clients that abort drags without sending the End packet, leaving drag state stuck.

Related errors

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/88db2ac53e81ee56. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-inventory/src/error.rs:21

/// Errors that can occur during inventory operations.
///
/// These errors represent various failure conditions when handling inventory
/// interactions, such as invalid slot indices, permission issues, or protocol errors.
#[derive(Error, Debug)]
pub enum InventoryError {
    /// Failed to acquire a lock on an inventory or slot.
    #[error("Unable to lock")]
    LockError,
    /// The specified slot index is invalid or out of bounds.
    #[error("Invalid slot")]
    InvalidSlot,
    /// A player attempted to interact with a container that is closed.
    ///
    /// The parameter is the player's entity ID.
    #[error("Player '{0}' tried to interact with a closed container")]
    ClosedContainerInteract(i32),
    /// Multiple players attempted to drag items in the same container simultaneously.
    #[error("Multiple players dragging in a container at once")]
    MultiplePlayersDragging,
    /// Drag operation was performed out of order (e.g., end before start).
    #[error("Out of order dragging")]
    OutOfOrderDragging,
    /// The received inventory packet is malformed or invalid.
    #[error("Invalid inventory packet")]
    InvalidPacket,
    /// The player lacks permission to perform this inventory operation.
    #[error("Player does not have enough permissions")]
    PermissionError,
}

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