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Gno Events

Overview​

Events in Gno are a fundamental aspect of interacting with and monitoring on-chain applications. They serve as a bridge between the on-chain environment and off-chain services, making it simpler for developers, analytics tools, and monitoring services to track and respond to activities happening in Gno.land.

Gno events are pieces of data that log specific activities or changes occurring within the state of an on-chain app. These activities are user-defined; they might be token transfers, changes in ownership, updates in user profiles, and more. Each event is recorded in the ABCI results of each block, ensuring that action that happened is verifiable and accessible to off-chain services.

Emitting Events​

To emit an event, you can use the Emit() function from the std package provided in the Gno standard library. The Emit() function takes in a string representing the type of event, and an even number of arguments after representing key:value pairs.

Read more about events & Emit() in Effective Gno, and the Emit() reference here.

Data contained in a Gno Event​

An event contained in an ABCI response of a block will include the following data:

{
    "@type": "/tm.gnoEvent", // TM2 type
    "type": "OwnershipChange", // Type/name of event defined in Gno
    "pkg_path": "gno.land/r/demo/example", // Path of the emitter
    "func": "ChangeOwner", // Gno function that emitted the event
    "attrs": [ // Slice of key:value pairs emitted
        {
            "key": "oldOwner",
            "value": "g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5"
        },
        {
            "key": "newOwner",
            "value": "g1zzqd6phlfx0a809vhmykg5c6m44ap9756s7cjj"
        }
    ]
}

You can fetch the ABCI response of a specific block by using the /block_results RPC endpoint.