Transaction manager

The transactionManager service is used to track a transaction's status as it propagates through the blockchain.

Methods in Dai.js that start transactions are asynchronous, so they return promises. These promises can be passed as arguments to the transaction manager to set up callbacks when transactions change their status to pending, mined, confirmed or error.

const txMgr = maker.service('transactionManager');
// instance of transactionManager
const open = maker.service('cdp').openCdp();
// open is a promise--note the absence of `await`

Pass the promise to transactionManager.listen with callbacks, as shown below.

txMgr.listen(open, {
pending: tx => {
// do something when tx is pending
},
mined: tx => {
// do something when tx is mined
},
confirmed: tx => {
// do something when tx is confirmed
},
error: tx => {
// do someting when tx fails
}
});
await txMgr.confirm(open);
// 'confirmed' callback will fire after 5 blocks

Note that the confirmed event will not fire unless transactionManager.confirm is called. This async function waits a number of blocks (default 5) after the transaction has been mined to resolve. To change this globally, set the confirmedBlockCount attribute in Maker options. To change it for just one call, pass the number of blocks to wait as the second argument:

await txMgr.confirm(open, 3);

Transaction Metadata

There are functions such as lockEth() which are composed of several internal transactions. These can be more accurately tracked by accessing tx.metadatain the callback which contains both the contract and the method the internal transactions were created from.

Transaction Object Methods

A TransactionObject also has a few methods to provide further details on the transaction:

  • hash : transaction hash

  • fees() : amount of ether spent on gas

  • timeStamp() : timestamp of when transaction was mined

  • timeStampSubmitted() : timestamp of when transaction was submitted to the network

const lock = cdp.lockEth(1);
txMgr.listen(lock, {
pending: tx => {
const {contract, method} = tx.metadata;
if(contract === 'WETH' && method === 'deposit') {
console.log(tx.hash); // print hash for WETH.deposit
}
}
})