Finalize a channel (happy)

Finalization of a state channel is a necessary step before defunding it. In the so-called 'happy' case, all participants cooperate to achieve this.

A participant wishing to end the state channel will sign a state with isFinal = true. Then, the other participants may support that state. Once a full set of n such signatures exists (this set is known as a finalization proof) the channel is said to be 'closed' or 'finalized'.

In most cases, the channel would be finalized and defunded off chain, and no contract calls are necessary.

Call conclude

In the case where assets were deposited against the channel on chain (the case of direct funding), anyone in possession of a finalization proof may use it to finalize the outcome on-chain. They would do this by calling conclude on the adjudicator. This enables assets to be released.

The conclude method allows anyone with sufficient off-chain state to immediately finalize an outcome for a channel without having to wait for a challenge to expire (more on that later).

The off-chain state(s) is submitted (in an optimized format), and once relevant checks have passed, an expired challenge is stored against the channelId. (This is an implementation detail -- the important point is that the chain shows that the channel has been finalized.)

In the following example the participants support the state by countersigning it, without increasing the turn number:

// In lesson6.test.ts
/* Import ethereum wallet utilities */
import {BigNumber, ethers} from 'ethers';
const {AddressZero, HashZero} = ethers.constants;
/* Import statechannels wallet utilities */
import {
Channel,
State,
getFixedPart,
hashOutcome,
signStates,
hashAppPart
} from '@statechannels/nitro-protocol';
/* Construct a final state */
const participants = [];
const wallets: ethers.Wallet[] = [];
for (let i = 0; i < 3; i++) {
wallets[i] = ethers.Wallet.createRandom();
participants[i] = wallets[i].address;
}
const chainId = '0x1234';
const channelNonce = BigNumber.from(0).toHexString();
const channel: Channel = {chainId, channelNonce, participants};
const largestTurnNum = 4;
const state: State = {
isFinal: true,
channel,
outcome: [],
appDefinition: AddressZero,
appData: HashZero,
challengeDuration: 1,
turnNum: largestTurnNum
};
/* Generate a finalization proof */
const whoSignedWhat = [0, 0, 0];
const sigs = await signStates([state], wallets, whoSignedWhat);
/*
Call conclude
*/
const numStates = 1;
const fixedPart = getFixedPart(state);
const appPartHash = hashAppPart(state);
const outcomeHash = hashOutcome(state.outcome);
const tx = NitroAdjudicator.conclude(
largestTurnNum,
fixedPart,
appPartHash,
outcomeHash,
numStates,
whoSignedWhat,
sigs
);

Notice we imported hashOutcome and hashAppPart in order to provide the conclude method with the correct calldata.

Last updated on by geoknee