Managing Gas on the Destination Chain When Bridging

Detailed Instructions

Before initiating any bridge transaction, you must first quantify the gas expenditure on the destination chain. This involves understanding the target chain's fee model (e.g., EIP-1559 on Ethereum, priority fees on Avalanche) and the specific gas cost for the operation you intend to perform, such as a token swap or NFT mint. Start by using a blockchain explorer or gas estimation API for the destination network.

• Sub-step 1: Identify the target operation's gas limit. For a simple ERC-20 transfer on Ethereum, this might be 65,000 gas, but a complex smart contract interaction could require 200,000+ gas.
• Sub-step 2: Check the current gas price. Use tools like Etherscan's Gas Tracker for Ethereum or equivalent for other chains. Convert this price to the native token (e.g., ETH, MATIC, AVAX).
• Sub-step 3: Calculate total cost. Multiply the gas limit by the current gas price. For example, if the limit is 200,000 units and the gas price is 50 Gwei, the cost is 200,000 * 50 Gwei = 0.01 ETH.

Tip: Always add a 10-20% buffer to your estimate to account for network congestion and price volatility between the time of estimation and transaction execution.

Detailed Instructions

To avoid holding the destination chain's native token, you can utilize a gas relayer or meta-transaction service. These services pay the gas fee on your behalf and are reimbursed in the bridged asset. Key options include native bridge gas services (like Arbitrum's retryable tickets), third-party relayers (like Biconomy), or protocols implementing EIP-2771 for gasless transactions.

• Sub-step 1: Evaluate available relayers. Check if your chosen bridge (e.g., Hop, Across) has a built-in gas abstraction feature. For Arbitrum, retryable tickets are automatically created, requiring you to fund them with ETH on L1.
• Sub-step 2: Fund the relayer contract. If using a third-party service, you may need to deposit funds into their contract. For example, to use Biconomy's Gasless Relayer on Polygon, you would approve and deposit USDC into their GasTank contract.
• Sub-step 3: Configure transaction parameters. When constructing your bridge call, include the relayer's address and any required signature. For a meta-transaction, your call might be wrapped in a executeMetaTransaction function.

solidityCopy
// Example: Initiating a gasless swap via a relayer (pseudo-code)
bytes memory data = abi.encodeWithSelector(swapRouter.swapExactTokensForTokens.selector, amountIn, amountOutMin, path, to, deadline);
relayerContract.execute(user, contractAddress, data, signature);

Tip: Always verify the relayer's security and fee structure. Some take a percentage of your transaction, while others charge a fixed fee in the gas token.

Detailed Instructions

This step involves initiating the cross-chain transfer while embedding gas provisioning instructions. The exact method depends on your chosen strategy from Step 2. For bridges with native support, this is often automatic. For custom setups, you must explicitly include gas payment details in the transaction payload.

• Sub-step 1: Construct the bridge transaction payload. Include the destination chain ID, recipient address, amount, and crucially, the gas limit and gas funding instructions. For example, when bridging via LayerZero, you might set _adapterParams to specify extra gas for the destination.
• Sub-step 2: Specify the gas payment token. If the bridge allows paying fees in a stablecoin, indicate this. On Celer cBridge, you can select "Pay gas in USDC" at the UI level, which corresponds to setting the feeToken parameter in the smart contract call.
• Sub-step 3: Execute and monitor. Send the transaction on the source chain. Use the bridge's dashboard or a cross-chain explorer (like LayerZero Scan) to track the message's status. Confirm that the gas provisioning step on the destination is queued or completed.

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// Example: Bridging with Stargate with custom gas (simplified)
const stargateRouter = new ethers.Contract(routerAddress, abi, signer);
await stargateRouter.swap(
    chainId_dest,           // e.g., 101 for Arbitrum
    poolId_src,
    poolId_dest,
    msg.sender,
    amountLD,
    amountLDMin,
    { dstGasForCall: 500000 }, // Gas allocated for a destination contract call
    "0x",                    // No payload for a simple transfer
    "0x0000000000000000000000000000000000000000" // Native ETH for gas
);

Tip: The parameter dstGasForCall is critical. If you are only receiving assets, 0 may suffice. For a contract interaction, estimate carefully to avoid a failed transaction on arrival.

Detailed Instructions

After bridging, you must verify execution and handle failures on the destination chain. The assets may arrive, but the subsequent action (e.g., swap, stake) requires the gas you provisioned. If gas funding fails, the transaction may be stuck in a pending state.

• Sub-step 1: Track the transaction hash. Use the bridge's provided transaction ID to monitor progress on both the source and destination block explorers. For example, an Arbitrum retryable ticket will have a unique Ticket ID on L1 and a corresponding transaction hash on L2.
• Sub-step 2: Check for completion or errors. On the destination chain, verify if the final transaction was included in a block. If it failed due to insufficient gas, you may need to manually submit it with additional gas. For retryable tickets, you have about one week to manually "redeem" them.
• Sub-step 3: Manually intervene if necessary. If automatic execution fails, you may need to interact directly with the destination chain contract. For an expired retryable ticket on Arbitrum, you would call the Inbox.forceRedemption function with the ticket ID.

bashCopy
# Example: Checking status of an Arbitrum retryable ticket via CLI
cast call --rpc-url https://arb1.arbitrum.io/rpc 0x1bF5C82a9Defa5B7D8a5F4d8C7B7F2D6b5B7a8C9 \
  "getRetryableTicket(bytes32 ticketId)(uint128,uint128,address,uint64,uint64,address,bytes)" \
  0x1234...abcd

Tip: Set up alerting (e.g., via Tenderly or OpenZeppelin Defender) for failed destination transactions to ensure you can respond within any time-sensitive windows for manual redemption.

Detailed Instructions

Before initiating a cross-chain transfer, you must accurately estimate the gas cost on the destination chain. This is crucial because the relayer or gas abstraction service will need to cover this cost. Use the destination chain's RPC provider to simulate the transaction.

• Sub-step 1: Construct the calldata for the intended action on the destination chain (e.g., a token swap or contract interaction).
• Sub-step 2: Call an estimation function like eth_estimateGas on the destination chain's RPC endpoint (e.g., https://polygon-rpc.com).
• Sub-step 3: Factor in a buffer (e.g., 20%) to account for gas price volatility and ensure the transaction does not fail.

Tip: For complex interactions, consider using a gas estimation library like ethers.js's estimateGas method on a populated transaction object.

Detailed Instructions

Integrate a gas abstraction provider like Biconomy, Gas Station Network (GSN), or a custom relayer. This entity will pay the gas on the destination chain, allowing your user to transact with only the source chain's native token.

• Sub-step 1: Register your dApp and obtain API keys or a Paymaster contract address from your chosen provider (e.g., Biconomy's dashboard).
• Sub-step 2: Configure your smart contract on the destination chain to be compatible with the provider's standards, such as implementing the IForwarder interface for GSN.
• Sub-step 3: Set up the client-side SDK (e.g., @biconomy/ethers-lite) and initialize it with your provider credentials and chain IDs.

Tip: Ensure the provider supports the specific destination chain (e.g., Polygon, Arbitrum) and has sufficient funds in its Paymaster to cover user transactions.

Detailed Instructions

When creating the bridge transaction on the source chain, you must encode the gas abstraction parameters into the bridging payload. This tells the bridge and relayer how to handle gas on the other side.

• Sub-step 1: Encode the destination chain transaction calldata (from Step 1) and the estimated gas limit (e.g., 250,000 units).
• Sub-step 2: Specify the gas token address (e.g., 0x0000000000000000000000000000000000000000 for native gas) and the refund address for any unused gas.
• Sub-step 3: Use the bridge's SDK (e.g., SocketDL's Bridge class) to build the transaction, passing the gas data object.

javascriptCopy
const bridgeParams = {
  fromChainId: 1, // Ethereum
  toChainId: 137, // Polygon
  asset: tokenAddress,
  amount: '1000000000000000000', // 1 token
  userAddress: '0xUser...',
  gasLimit: '300000',
  gasToken: '0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE', // Native gas placeholder
};

Detailed Instructions

Initiate the bridge transaction and monitor its progress through both chains, confirming the gas sponsorship was successful on the destination.

• Sub-step 1: Sign and send the bridge transaction from the user's wallet on the source chain. The user only pays gas for this initial transaction.
• Sub-step 2: Track the transaction using the bridge's transaction hash and a block explorer. Wait for the bridge's attestation or relayer to pick up the message.
• Sub-step 3: On the destination chain, verify the transaction was executed and that the gas fees were deducted from the Paymaster or relayer's balance, not the user's. Check the destination transaction receipt for the from field to confirm it was the relayer address.

Tip: Implement webhook listeners or polling for bridge status updates (e.g., using SocketDL's status API endpoint) to provide real-time feedback in your UI.