2⃣
callWithSyncFeeERC2771
Transactions with on-chain payments and ERC2771 authentication support
If you are using
@gelatonetwork/relay-sdk v3 or contracts from the package @gelatonetwork/relay-context v2 please follow this migration guide to migrate to the new versions.After reading this page:
- You'll see some code which will help you send a relay request within minutes.
Please proceed to our Security Considerations page and read it thoroughly before advancing with your implementation. It is crucial to understand all potential security risks and measures to mitigate them.
const callWithSyncFeeERC2771 = async (
request: CallWithSyncFeeERC2771Request,
options?: RelayRequestOptions
): Promise<RelayResponse>
- options?:
relayRequestOptionsis an optional object.
type RelayResponse = {
taskId: string;
};
const request = {
chainId: BigNumberish;
target: string;
data: BytesLike;
user: string;
userNonce?: BigNumberish;
userDeadline?: BigNumberish;
feeToken: string;
isRelayContext?: boolean;
};
chainId: the chain ID of the chain where thetargetsmart contract is deployed.target: the address of the target smart contract.data: encoded payload data (usually a function selector plus the required arguments) used to call the requiredtargetaddress.user: the address of the user's EOA.userNonce: optional, this is a nonce similar to Ethereum nonces, stored in a local mapping on the relay contracts. It is used to enforce nonce ordering of relay calls, if the user requires it. Otherwise, this is an optional parameter and if not passed, the relay-SDK will automatically query on-chain for the current value.userDeadline: optional, the amount of time in seconds that a user is willing for the relay call to be active in the relay backend before it is dismissed.- This way the user knows that if the transaction is not sent within a certain timeframe, it will expire. Without this, an adversary could pick up the transaction in the mempool and send it later. This could transfer money, or change state at a point in time which would be highly undesirable to the user.
feeToken: the address of the token that is to be used for payment.isRelayContext: an optional boolean (default:true) denoting what data you would prefer appended to the end of the calldata.- If set to
true, Gelato Relay will append thefeeCollectoraddress, thefeeTokenaddress, and the uint256feeto the calldata. - If set to
false, Gelato Relay will only append thefeeCollectoraddress to the calldata. - As this is an optional parameter with a default value of
true, explicit passing is only required if you are usingGelatoRelayFeeCollectorfrom our relay-context-contracts.
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// SPDX-License-Identifier: MIT
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pragma solidity 0.8.17;
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import {
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GelatoRelayContextERC2771
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} from "@gelatonetwork/relay-context/contracts/GelatoRelayContextERC2771.sol";
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import {Address} from "@openzeppelin/contracts/utils/Address.sol";
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// Inheriting GelatoRelayContext gives access to:
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// 1. _getFeeCollector(): returns the address of Gelato's feeCollector
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// 2. _getFeeToken(): returns the address of the fee token
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// 3. _getFee(): returns the fee to pay
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// 4. _transferRelayFee(): transfers the required fee to Gelato's feeCollector.abi
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// 5. _transferRelayFeeCapped(uint256 maxFee): transfers the fee to Gelato
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// only if fee < maxFee
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// 6. function _getMsgSender(): decodes and returns the user's address from the
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// calldata, which can be used to refer to user safely instead of msg.sender
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// (which is Gelato Relay in this case).
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// 7. _getMsgData(): returns the original msg.data without appended information
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// 8. onlyGelatoRelay modifier: allows only Gelato Relay's smart contract
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// to call the function
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contract CounterRelayContextERC2771 is GelatoRelayContextERC2771 {
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using Address for address payable;
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mapping(address => uint256) public contextCounter;
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// emitting an event for testing purposes
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event IncrementCounter(address msgSender);
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// `increment` is the target function to call.
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// This function increments a counter variable which is
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// mapped to every _getMsgSender(), the address of the user.
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// This way each user off-chain has their own counter
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// variable on-chain.
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function increment() external onlyGelatoRelayERC2771 {
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// Payment to Gelato
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// NOTE: be very careful here!
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// if you do not use the onlyGelatoRelay modifier,
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// anyone could encode themselves as the fee collector
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// in the low-level data and drain tokens from this contract.
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_transferRelayFee();
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// Incrementing the counter mapped to the _getMsgSender()
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contextCounter[_getMsgSender()]++;
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emit IncrementCounter(_getMsgSender());
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}
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}
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import { GelatoRelay, CallWithSyncFeeERC2771Request } from "@gelatonetwork/relay-sdk";
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const relay = new GelatoRelay();
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// target contract address
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const counter = "<your counter contract address>";
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// using a human-readable ABI for generating the payload
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const abi = ["function increment()"];
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// address of the token used to pay fees
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const feeToken = "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE";
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// connect to the blockchain via a front-end provider
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const provider = new ethers.providers.Web3Provider(window.ethereum);
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const signer = provider.getSigner();
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const user = signer.getAddress();
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// generate the target payload
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const contract = new ethers.Contract(counter, abi, signer);
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const { data } = await contract.populateTransaction.increment();
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// populate the relay SDK request body
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const request: CallWithSyncFeeERC2771Request = {
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chainId: provider.network.chainId,
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target: counter,
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data: data,
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user: user,
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feeToken: feeToken,
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isRelayContext: true,
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};
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// send relayRequest to Gelato Relay API
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const relayResponse = await relay.callWithSyncFeeERC2771(request, provider);
Last modified 28d ago