Custom Events in Extensions

While the default Kiosk implementation for list-purchase flow always emits events, custom features covered in the purchase-cap section do not. And this is intentional - to keep the space available for custom events integration.

If we were to map default functionality of the Kiosk to analogous “custom” features, the map would look like:

When building custom events, it is important to keep in mind, that sender and timestamp are default meta-properties of all emitted events. So adding a sender field in an event is not necessary and even more - it increases the event emission price (which is typically paid by user).

Each of the PurchaseCap-enabled actions follows the general principle of the list-purchase flow, however there are no events emitted. An extension utilizing these functions should create and emit custom events.

The example below uses Extensions API, make sure to look through this section beforehand.

/// This module follows the default Kiosk functionality without anything added.
/// Practically the example does not have any value and serves the illustration 
/// purpose as well as a potential base for custom extensions
module examples::marketplace_ext {
	use sui::kiosk::{Self, Kiosk, KioskOwnerCap, PurchaseCap};
	use sui::tx_context::TxContext;
	use sui::object::{Self, ID};
	use sui::kiosk_extension;
	use sui::event;

	/// Trying to delist an item in someone else’s Kiosk
	const ENotOwner: u64 = 0;

	/// A custom extension flag
	struct Extension has drop {}

	// === Events ===

	/// A custom event for a new listing. We only emit Kiosk ID and the price,
	/// because other fields such as “sender” are already a part of the event.
	/// And the type `T` here allows filtering events by type.
	struct MarketItemListed<phantom T> has copy, drop {
		kiosk: ID,
		item_id: ID,
		price: u64
	}

	/// A custom event for delisting. We only emit Kiosk ID and Item ID, 
	/// because the rest can be identified on the indexing side 
	struct MarketItemDelisted<phantom T> has copy, drop {
		kiosk: ID,
		item_id: ID
	}

    // Similarly, a purchase event can be implemented
    // struct MarketItemPurchased<phantom T> has copy, drop { ... }

	/// Installs the extension into user’s Kiosk.
	public fun add(
		self: &mut Kiosk, cap: &KioskOwnerCap, ctx: &mut TxContext
	) {
		kiosk_extension::add(Extension {}, self, cap, 0, ctx)
	}

	/// Custom list function which emits an event specific to the Extension
	public fun list<T: key + store>(
		self: &mut Kiosk, 
		cap: &KioskOwnerCap, 
		item_id: ID, 
		price: u64, 
		ctx: &mut TxContext
	) {
		// omitting the purchase cap and storage parts
		// see Extensions API for details

		event::emit(MarketItemListed<T> {
    		kiosk: object::id(&self),
    		item_id,
    		price,
		})
	}
	
	/// Custom delist function which emits 
	public fun delist<T: key + store>(
		self: &mut Kiosk, cap: &KioskOwnerCap, item_id: ID,
	) {
		assert!(kiosk::has_access(self, cap), ENotOwner);

		event::emit(MarketItemDelisted<T> {
			kiosk: object::id(&self),
			item_id
		})
	}

	// 
}