Events

CosmWasm can emit Cosmos Events (opens in a new tab). These events are stored in the block execution result as metadata, allowing the contract to attach metadata to what exactly happened during execution.

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Some important details about the keys:

Whitespaces will be trimmed (i.e. removed from the begin and end)
Empty keys (that includes keys only consisting of whitespaces) are not allowed
Keys cannot start with an underscore (_). These types of keys are reserved for wasmd

By default CosmWasm emits the wasm event to which you can add attributes like so:

wasm_event.rs

let response: Response<Empty> = Response::new()
    .add_attribute("custom_attribute", "value");

Custom events

As mentioned above, CosmWasm only emits the event wasm by default. If you want to emit other events, such as domain-specific events like user_added, you can construct a fully custom event and attach it to the response.

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Note that those custom events will be prefixed with wasm- by the runtime.

custom_event.rs

let event = Event::new("custom_event")
    .add_attribute("custom_attribute", "value");
 
let response: Response<Empty> = Response::new()
    .add_event(event);

Actor Model Gas