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Lock & Release Token

Lock existing tokens on the source chain and release from a pre-funded pool on the destination. Users get the original token on both sides — no synthetics.

Use this when you don't control the token and can manage liquidity on each destination chain.

Choosing a Bridge Pattern
PatternToken controlLiquidity neededDestination token
Burn & MintYou control itNoSame token (minted)
Lock & MintYou don't control itNoWrapped/synthetic version
Lock & ReleaseYou don't control itYes, pre-fundedOriginal token

Prerequisites​

  • A working Hardhat project with VIA contracts — complete the Hello World guide first
  • Testnet tokens on two chains — see Testnet Tokens
  • Liquidity — you must pre-fund destination contracts before users can bridge

Step 1: Copy the Contract​

Copy VIALockerRelease.sol from the Contract Source page into your contracts/ directory. See the full reference for API details.

Step 2: Deploy​

Create scripts/deploy-bridge.ts:

import { ethers } from "hardhat";

const TOKEN_ADDRESS = ""; // ERC20 token address on THIS chain

async function main() {
  const Bridge = await ethers.getContractFactory("VIALockerRelease");
  const bridge = await Bridge.deploy(TOKEN_ADDRESS);
  await bridge.waitForDeployment();
  console.log("VIALockerRelease deployed to:", await bridge.getAddress());
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Deploy on both chains. The TOKEN_ADDRESS can differ per chain (e.g., USDC has different addresses on Ethereum vs Polygon).

npx hardhat run scripts/deploy-bridge.ts --network sepolia
npx hardhat run scripts/deploy-bridge.ts --network amoy

Step 3: Configure​

Same pattern as Hello World — Step 7. On each chain, call setMessageGateway() and setMessageEndpoints() pointing at the peer bridge contract.

Step 4: Fund Liquidity​

Before anyone can bridge TO a chain, that chain's bridge contract must hold tokens. Create scripts/deposit.ts:

import { ethers } from "hardhat";

const BRIDGE_ADDRESS = ""; // VIALockerRelease on destination chain
const TOKEN_ADDRESS = "";  // ERC20 token on destination chain
const AMOUNT = ethers.parseEther("10000");

async function main() {
  const token = await ethers.getContractAt("IERC20", TOKEN_ADDRESS);
  const bridge = await ethers.getContractAt("VIALockerRelease", BRIDGE_ADDRESS);

  console.log("Approving...");
  const approveTx = await token.approve(BRIDGE_ADDRESS, AMOUNT);
  await approveTx.wait();

  console.log("Depositing liquidity...");
  const depositTx = await bridge.deposit(AMOUNT);
  await depositTx.wait();
  console.log("Done. Bridge has", ethers.formatEther(AMOUNT), "tokens available.");
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});
npx hardhat run scripts/deposit.ts --network amoy

Step 5: Bridge Tokens​

Create scripts/bridge.ts:

import { ethers } from "hardhat";

const BRIDGE_ADDRESS = ""; // VIALockerRelease on source chain
const TOKEN_ADDRESS = "";  // ERC20 token on source chain
const DEST_CHAIN_ID = 80002;
const RECIPIENT = "";
const AMOUNT = ethers.parseEther("100");

async function main() {
  const token = await ethers.getContractAt("IERC20", TOKEN_ADDRESS);
  const bridge = await ethers.getContractAt("VIALockerRelease", BRIDGE_ADDRESS);

  console.log("Approving...");
  const approveTx = await token.approve(BRIDGE_ADDRESS, AMOUNT);
  await approveTx.wait();

  const recipientBytes32 = ethers.zeroPadValue(RECIPIENT, 32);

  console.log("Bridging...");
  const tx = await bridge.bridge(
    recipientBytes32,
    DEST_CHAIN_ID,
    AMOUNT,
    { value: ethers.parseEther("0.001") }
  );
  await tx.wait();
  console.log("TX:", tx.hash);
  console.log("Tokens locked. Wait 1-5 minutes for release on destination.");
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});
npx hardhat run scripts/bridge.ts --network sepolia

Liquidity Management​

danger

The destination contract must hold enough tokens before users bridge. If the pool is empty, messageProcess() reverts with InsufficientLiquidity, tokens stay locked on source, and recovery is manual. See Error Reference.

  • Monitor token.balanceOf(bridgeAddress) on every destination chain
  • Watch the Error event on the gateway contract — fires when a release fails
  • Owner can withdraw via withdraw() — use a multisig in production

Next Steps​