Contract Events

The Sophia language also provides you the possibility to emit Events in your functions. On this page you will learn how to access and decode the event log of a specific transaction.

EventEmitter contract

This example contract that emits events will be used in the following examples:

contract EventEmitter =

    datatype event =
        FirstEvent(int)
        | AnotherEvent(indexed address, string)

    entrypoint emitEvents(value: int, msg: string) =
        Chain.event(FirstEvent(value))
        Chain.event(AnotherEvent(Call.caller, msg))

Decode events using ACI

When initializing a contract instance using the source code and providing the ACI or obtaining it via http compiler (default) you will be able to access the emitEvents entrypoint of the Sophia contract above as follows:

// events emitted by contract calls are automatically decoded
const tx = await contract.emitEvents(1337, 'this message is not indexed');
console.log(tx.decodedEvents);

/*
[
  {
    name: 'AnotherEvent',
    args: [
      'fUq2NesPXcYZ1CcqBcGC3StpdnQw3iVxMA3YSeCNAwfN4myQk',
      'this message is not indexed'
    ],
    contract: {
      name: 'EventEmitter',
      address: 'ct_6y3N9KqQb74QsvR9NrESyhWeLNiA9aJgJ7ua8CvsTuGot6uzh'
    }
  },
  {
    name: 'FirstEvent',
    args: [1337n],
    contract: {
      name: 'EventEmitter',
      address: 'ct_6y3N9KqQb74QsvR9NrESyhWeLNiA9aJgJ7ua8CvsTuGot6uzh'
    }
  }
]
*/

Note:

• As you can see the event log will be automatically decoded in case you perform a ContractCallTx directly

Of course it is also possible to decode the event log if you request the transaction details from the node for a transaction that has been mined already. You can request the transaction details by providing the tx-hash and then decode the event log using the contract as follows:

const txHash = 'th_2YV3AmAz2kXdTnQxXtR2uxQi3KuLS9wfvXyqKkQQ2Y6dE6RnET';
// aeSdk is an instance of the AeSdk class
const txInfo = await aeSdk.api.getTransactionInfoByHash(txHash);

// decode events using contract instance
const decodedUsingContract = contract.$decodeEvents(txInfo.callInfo.log);
console.log(decodedUsingContract);

/*
[
  {
    name: 'AnotherEvent',
    args: [
      'fUq2NesPXcYZ1CcqBcGC3StpdnQw3iVxMA3YSeCNAwfN4myQk',
      'this message is not indexed'
    ],
    contract: {
      name: 'EventEmitter',
      address: 'ct_fKhQBiNQkDfoZcVF1ZzPzY7Lig6FnHDCLyFYBY33ZjfzGYPps'
    }
  },
  {
    name: 'FirstEvent',
    args: [1337n],
    contract: {
      name: 'EventEmitter',
      address: 'ct_fKhQBiNQkDfoZcVF1ZzPzY7Lig6FnHDCLyFYBY33ZjfzGYPps'
    }
  }
]
*/