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Advanced Mini CoursesGasless Onboarding (ERC4337, Bundlers, Paymasters, EIP7702)

The Secret to Web3 Growth: Erasing the #1 Onboarding Killer!

Work in Progress

Please Note: This tutorial is currently under active development. The content, code examples, and explanations may be incomplete, contain errors, or change significantly without notice. Use with caution!

Are You Losing Users Before They Even Start?

Let me ask you something… Have you poured your heart and soul into building an amazing decentralized application (dApp), only to watch potential users vanish the moment they face the dreaded ā€œConnect Wallet & Get Gasā€ wall?

You know the one. That confusing, frustrating roadblock where users have to:

  • Figure out what a ā€œwalletā€ even is and install one (MetaMask? Phantom? Argh!).
  • Navigate the treacherous waters of buying crypto on an exchange (KYC? Fees? Waiting?!).
  • Transfer just the right amount of native tokens (like ETH) to pay for something called ā€œgasā€ā€¦ before they can even do anything cool in your app!

Sound familiar? This isn’t just a little friction. This is the #1 reason Web3 struggles with mainstream adoption. It’s the conversion killer silently sabotaging your growth, turning excited prospects into frustrated drop-offs. It’s like building the world’s greatest theme park but making people solve a calculus problem just to buy a ticket!

But what if you could make all that pain disappear?

What if you could onboard users as smoothly, as instantly, as the best Web2 apps? Imagine users diving straight into your dApp’s core value, experiencing the magic without the wallet-and-gas headache.

That’s the secret we’re unlocking today.

This isn’t just another technical tutorial. This is your playbook for creating seamless, gasless onboarding experiences. We’ll take a simple, real-world scenario – giving users 100 free Platform Credits (CRED) just for signing up, which they can use to buy cool NFTs or access premium features – and dissect why the standard Web3 way makes even this simple ā€œtry before you buyā€ model painful. Then, step-by-step, we’ll reveal the expert patterns (from clever off-chain signatures to the power of Account Abstraction) that transform that clunky process into a smooth, invisible flow.

Who is this for?

  • The Visionary Beginner: You see the potential of Web3 but are baffled by the onboarding nightmare. You need the foundational secrets to build apps people actually use.
  • The Savvy Developer: You know the basics, but you’re ready for the advanced strategies – meta-transactions, ERC-2612 permits, the game-changing ERC-4337 Account Abstraction, and even a peek at the future with EIP-7702. You want the tactical edge.

Our Mission: We start with a user signing up (maybe just with an email) and instantly receiving 100 free PlatformCredits (CRED). They want to use these credits to buy an NFT from our MyNFT contract or unlock a special community channel. Sounds simple, right? Let’s expose the hidden complexities of the ā€œstandardā€ Web3 flow that prevent this, and then embark on a journey to eliminate them, one powerful technique at a time.

Ready to turn those onboarding hurdles into highways? Let’s dive in!

1. The Gauntlet: Why the ā€œStandardā€ Web3 Flow Scares Users Away

Alright, let’s walk through the ā€œnormalā€ way someone might try to use their free 100 Platform Credits (CRED) to buy our NFT today. Brace yourself – this is the bumpy ride we’re about to pave over.

Imagine Sarah signs up for your awesome platform with just her email and instantly sees ā€œ100 Free Credits Added!ā€ in her account. Fantastic! But wait… these credits are on the blockchain (as CRED tokens). To actually use them, she needs a wallet.

  1. The Wallet Ritual (To Use the Credits): First hurdle? ā€œInstall MetaMask to use your credits.ā€ Sarah navigates browser extensions, installs the wallet, nervously writes down a secret phrase she barely understands, hoping she doesn’t lose it or get hacked. The platform magically associates her email signup with this new wallet address, and the 100 CRED tokens appear. Friction Point #1: Technical setup & security anxiety just to access the free credits.
  2. The Excitement… and the Wall: Awesome! Sarah now sees her 100 CRED in her wallet. She browses your NFT marketplace, finds one she likes for 100 credits, and clicks ā€œBuy NFTā€ā€¦ and BAM! ā€œInsufficient funds for gas.ā€ Gas? She needs ETH? But she only has CRED tokens! Friction Point #2: The Gas Trap - Having the required platform credits isn’t enough.
  3. The ā€œEasyā€ On-Ramp Quest?: ā€œAha!ā€ thinks the dApp developer, ā€œWe’ll add an on-ramp!ā€ So, Sarah sees a button: ā€œBuy ETH with Cardā€. Seems easier, right? She clicks it. Now she faces:
    • On-Ramp KYC: Depending on the provider (like Wyre, MoonPay, Onramper) and amount, she might still need KYC. Upload ID? Selfie? Ugh.
    • Minimum Purchase Madness: The real kicker – she only needs maybe $0.50 worth of ETH for gas, but the on-ramp forces her to buy a minimum of $50 or $100! She has to spend significant money just to facilitate a tiny network fee for using the token she already owns.
    • Fees & Spread: Credit card fees, network fees, provider spreads… that $50 purchase might only yield $45 worth of ETH in her wallet.
    • Waiting (Again): Card processing, fraud checks, blockchain confirmation… it’s faster than an exchange withdrawal, but still not instant.
    • Friction Point #3: On-ramps force over-purchase, add steps, and highlight the absurdity of needing ETH just for gas.
  4. The Connection Dance: Assuming she grits her teeth and buys the oversized chunk of ETH, Sarah returns to your NFT site. ā€œConnect Wallet.ā€ Click. Pop-up. ā€œAllow this site to see your address?ā€ Click. Okay, connected again. Minor friction, but still a step.
  5. ā€œApproveā€ What Now?: Sarah clicks ā€œBuy NFTā€. But wait! Another pop-up. ā€œGrant permission for the NFT contract to access your PlatformCredits?ā€ Huh? She has to sign a transaction, using a fraction of the ETH she was forced to overbuy, just to allow the purchase later. Click. Wait for the blockchain… Friction Point #4: Confusing ā€˜approve’ step, requires ETH gas (even if overpaid for).
  6. The Actual Purchase: FINALLY! The approve transaction is confirmed. Sarah clicks ā€œBuy NFTā€ again. Another pop-up. Sign another transaction. Use more of that expensive ETH for gas again! Click. Wait for the blockchain… Success? Maybe? She just spent $50+ to use her free 100 credits for a transaction costing pennies in actual gas. Friction Point #5: Second transaction, more ETH gas, more waiting, feeling ripped off.

Six steps (including the initial wallet setup just to use the free credits!), multiple gas payments in a currency she had to buy separately just to use the platform credits, confusing jargon, and lots of waiting. Is it any wonder users give up?

Feeling the Pain Already?

Okay, deep breaths! If reading through Sarah’s ordeal is already making your head spin, you’re not alone. This is the frustrating reality we’re trying to fix.

Feel free to skim the code breakdown below if you’re already convinced this flow is broken. The real magic starts in Section 2 where we begin unveiling the solutions!

Let’s Look Under the Hood (The Code):

Let’s define our basic contracts first.

// SPDX-License-Identifier: MIT pragma solidity ^0.8.20; import "@openzeppelin/contracts/token/ERC20/ERC20.sol"; import "@openzeppelin/contracts/access/Ownable.sol"; /** * @title PlatformCredits * @dev Basic ERC20 token representing credits on our platform. * Includes a function for the owner (platform) to grant credits. */ contract PlatformCredits is ERC20, Ownable { // Assuming 18 decimals for credits, like ETH. Adjust if needed. constructor(address initialOwner) ERC20("PlatformCredits", "CRED") Ownable(initialOwner) {} /** * @dev Grants credits to a specific address. Only callable by the owner (platform). * Used for simulating the initial free credits grant upon signup. */ function grantCredits(address to, uint256 amount) public onlyOwner { _mint(to, amount); // Internally, granting credits is minting tokens } // Later, we will add ERC2612 permit functionality here! }

How the Frontend Orchestrates the Pain (Interactive Demo):

Even with helpful libraries like viem and wagmi, the frontend code reflects this awkward two-step dance (approve then buyNFT). Let’s see it in action.

Try It Yourself!

Connect your wallet to the Sepolia Testnet. You’ll need some Sepolia ETH for gas fees (try a Sepolia Faucet if you don’t have any - be warned, they can be unreliable!). This demo uses placeholder contract addresses; replace them with actual deployed addresses if you’re following along with your own contracts.

Why This Flow is Broken (The Friction Points):

Let’s hammer this home. This ā€œstandardā€ flow is riddled with problems:

  • The Wallet Mandate: Users need a wallet before they can even receive anything of value.
  • The ETH Tollbooth: Users must acquire and hold ETH, even if your dApp uses other tokens or they received tokens for free. This is often the biggest barrier to actual usage.
  • The Double-Transaction Tax: The approve followed by the actual action (buyNFT) is confusing and requires two separate gas payments.
  • Confusion & Delay: Multiple steps, blockchain confirmations, and unfamiliar concepts (ā€œapproveā€, ā€œgasā€) create a terrible, slow user experience.

This is the baseline we must improve upon if we want Web3 to reach its potential. Now that we’ve truly felt Sarah’s pain, let’s explore the secrets to making it disappear.

2. The First Secret Weapon: Sponsoring Gas with Meta-Transactions

Remember Sarah’s nightmare? Stuck with 100 free CRED tokens but blocked by the dreaded ā€œETH Tollboothā€? She couldn’t even use her free gift without jumping through hoops to buy ETH just for gas. This is where countless potential users drop off, frustrated and confused.

But what if there was a way to make that tollbooth… invisible?

Imagine Sarah clicks ā€œBuy NFTā€ with her credits, and it just… works. No pop-ups demanding ETH, no confusing ā€œgas feeā€ messages. Behind the scenes, someone else handles the network fee. This isn’t magic; it’s the power of Meta-Transactions, our first secret weapon against the onboarding killer.

The Big Idea: The ā€œTrusted Assistantā€ (Relayer)

Think of it like having a trusted assistant. Instead of Sarah going to the blockchain ā€œpost officeā€ herself, filling out complex forms (transactions), and paying the postage (gas fee) with a special currency (ETH) she doesn’t have, she does something much simpler:

  1. Sarah’s Simple Request: Sarah just writes down what she wants to do (ā€œUse 100 CRED to buy NFT #123ā€) and signs it with her unique signature (using her wallet’s private key, but off-chain, costing nothing). This proves she authorized the request.
  2. Handing Off to the Assistant: Her browser (the dApp frontend) sends this signed note to a special service – the ā€œTrusted Assistant,ā€ technically called a Relayer.
  3. The Assistant Does the Work: The Relayer takes Sarah’s signed note. It verifies her signature is valid. Then, it goes to the blockchain post office, fills out the official transaction form, pays the ETH gas fee out of its own pocket, and submits the transaction.
  4. The Contract Listens: The MyNFT smart contract receives the transaction from the Relayer. But how does it know it was Sarah who wanted the NFT, not the Relayer? This is where a standard called EIP-2771  comes in.

EIP-2771: The Standardized ā€œWho’s Asking?ā€ Protocol

EIP-2771 provides a standard way for a contract to know the original sender of a request, even when it’s submitted by a trusted Relayer (often called a ā€œForwarderā€ in EIP-2771 terminology).

EIP2771

Here’s how it works with our contracts:

  • The Forwarder Contract: We need a trusted, on-chain ā€œForwarderā€ contract. The Relayer sends the transaction through this Forwarder. The Forwarder’s job is to verify Sarah’s signature on her original request and then call the actual target contract (MyNFT).
  • Modified MyNFT Contract: Our MyNFT contract needs a small but crucial modification. Instead of checking msg.sender (which would be the Forwarder address), it needs to ask, ā€œWho is the original sender that the trusted Forwarder verified?ā€ OpenZeppelin provides a handy helper contract, ERC2771Context, to make this easy.

Code Transformation: Making MyNFT EIP-2771 Aware

Let’s see how our MyNFT contract changes. We need to:

  1. Import and inherit ERC2771Context from OpenZeppelin.
  2. Add a constructor to store the address of the trustedForwarder contract.
  3. Replace all instances of msg.sender with _msgSender(). The _msgSender() function, provided by ERC2771Context, automatically checks if the call comes from the trusted forwarder and, if so, extracts the original sender’s address (Sarah’s address) from the transaction data. Otherwise, it just returns the normal msg.sender.

Here’s the modified MyNFT contract:

// SPDX-License-Identifier: MIT pragma solidity ^0.8.20; import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; import "@openzeppelin/contracts/token/ERC20/IERC20.sol"; import "@openzeppelin/contracts/access/Ownable.sol"; // Still Ownable for withdrawal etc. import "@openzeppelin/contracts/utils/Counters.sol"; // Import the EIP-2771 context import "@openzeppelin/contracts/metatx/ERC2771Context.sol"; // <--- Import /** * @title MyNFT (EIP-2771 Enabled) * @dev ERC721 contract allowing NFT purchase with PlatformCredits, * compatible with EIP-2771 meta-transactions. */ // Inherit ERC2771Context contract MyNFT is ERC721, Ownable, ERC2771Context { // <--- Inherit using Counters for Counters.Counter; Counters.Counter private _tokenIdCounter; IERC20 public immutable paymentCredits; uint256 public constant NFT_PRICE_IN_CREDITS = 100 * 10**18; event NFTMinted(address indexed buyer, uint256 indexed tokenId); // Constructor now takes the trusted forwarder address constructor( address initialOwner, address _paymentCreditsAddress, address trustedForwarder // <--- Add trusted forwarder param ) ERC721("MyNFT", "MYNFT") Ownable(initialOwner) ERC2771Context(trustedForwarder) // <--- Initialize ERC2771Context { require(_paymentCreditsAddress != address(0), "MyNFT: Invalid credits token address"); paymentCredits = IERC20(_paymentCreditsAddress); } /** * @dev Mints a new NFT after receiving payment in PlatformCredits. * Requires prior approval of PlatformCredits for this contract. * Uses _msgSender() to identify the original buyer in meta-tx scenarios. */ function buyNFT() public returns (uint256) { uint256 currentPrice = NFT_PRICE_IN_CREDITS; // Use _msgSender() instead of msg.sender address buyer = _msgSender(); // <--- Use _msgSender() // Check allowance for PlatformCredits (still needed!) uint256 allowance = paymentCredits.allowance(buyer, address(this)); require(allowance >= currentPrice, "MyNFT: Check credits allowance"); // Transfer PlatformCredits from buyer to owner/treasury // transferFrom uses the 'buyer' address obtained via _msgSender() bool success = paymentCredits.transferFrom(buyer, owner(), currentPrice); require(success, "MyNFT: Credits transfer failed"); // Mint the NFT to the original buyer _tokenIdCounter.increment(); uint256 newTokenId = _tokenIdCounter.current(); _safeMint(buyer, newTokenId); // Mint to the original buyer emit NFTMinted(buyer, newTokenId); return newTokenId; } /** * @dev Withdraw collected credits. Only callable by the contract owner. * Note: Ownable's owner check uses the real msg.sender, which is fine here, * but the transfer target is the owner address derived potentially * from an initial deployment or transferOwnership call. * If owner actions were meant to be meta-tx compatible, Ownable would * also need adjustment or replacement with an EIP-2771 compatible version. */ function withdrawCredits() public onlyOwner { // onlyOwner uses actual msg.sender uint256 balance = paymentCredits.balanceOf(address(this)); if (balance > 0) { // Transfer to the owner address stored by Ownable bool success = paymentCredits.transfer(owner(), balance); require(success, "MyNFT: Credits withdrawal failed"); } } // --- EIP-2771 Overrides --- // Optional: If you need to override the trusted forwarder later, // you can override the trustedForwarder() function from ERC2771Context. // function trustedForwarder() public view virtual override returns (address) { // // return address(YOUR_NEW_FORWARDER); // return super.trustedForwarder(); // Keep original if not changing // } // The _msgSender() and _msgData() functions are inherited from ERC2771Context. }
The 'Approve' Problem Persists!

Notice a critical limitation here: While the buyNFT call itself can be sponsored via the Relayer, the user (Sarah) still needs to have previously called approve on the PlatformCredits contract, granting spending permission to the MyNFT contract (or technically, the Forwarder acting on its behalf).

That standard approve transaction still costs gas and must be executed by Sarah’s EOA before the meta-transaction for buyNFT can work. This EIP-2771 pattern alone doesn’t make the entire flow gasless. We haven’t solved the initial approval hurdle yet! (Spoiler: That’s what the next patterns address).

Frontend: Talking to the Relayer

The frontend code changes slightly. Instead of preparing and sending a transaction directly to the blockchain using useWriteContract, it now:

  1. Gets the user (Sarah) to sign the intent (the action she wants the Forwarder to execute on her behalf) using useSignTypedData. This signature is specific to the Forwarder’s requirements (EIP-712).
  2. Sends this signed message and the action details to the Relayer’s API endpoint.
  3. Waits for the Relayer to process the request and return a transaction hash.

Here’s the conceptual frontend code again, highlighting the interaction with the Relayer:

import { encodeFunctionData, parseAbi } from 'viem'; import { useAccount, useSignTypedData, useReadContract } from 'wagmi'; // useReadContract for nonce // Assume Forwarder contract address and ABI are known const forwarderAddress = "0x..."; const forwarderABI = parseAbi([ 'function getNonce(address from) view returns (uint256)', // Example EIP-2771 execute function signature (adjust based on actual Forwarder) 'function execute(tuple(address from, address to, uint256 value, uint256 gas, uint256 nonce, bytes data) req, bytes signature) payable', ]); // Assume MyNFT ABI and address are known const myNFTAddress = "0x..."; const myNFTABI = [ /* ... MyNFT ABI including buyNFT ... */ ] as const; // Assume Relayer API endpoint is known const relayerApiEndpoint = '/api/relay'; // Your backend relayer service // EIP-712 Domain and Types specific to YOUR Forwarder contract's execute function // These define the structure the user needs to sign. const domain = { name: "MyForwarder", version: "1", chainId: 1, verifyingContract: forwarderAddress }; // Example const types = { ForwardRequest: [ // Example structure - MUST match your Forwarder's expected struct { name: 'from', type: 'address' }, { name: 'to', type: 'address' }, { name: 'value', type: 'uint256' }, { name: 'gas', type: 'uint256' }, { name: 'nonce', type: 'uint256' }, { name: 'data', type: 'bytes' }, ] } as const; function MetaTxButton() { const { address } = useAccount(); const { signTypedDataAsync, isPending: isSigning } = useSignTypedData(); const [isRelaying, setIsRelaying] = useState(false); const [status, setStatus] = useState(''); // Fetch the current nonce for the user *from the Forwarder* const { data: nonce, isLoading: isLoadingNonce } = useReadContract({ address: forwarderAddress, abi: forwarderABI, functionName: 'getNonce', args: [address!], // Ensure address is not null enabled: !!address, // Only run query if address exists }); const handleMetaTxPurchase = async () => { if (!address || nonce === undefined) { setStatus("Error: Wallet not connected or nonce not loaded."); return; } setIsRelaying(true); setStatus("Preparing meta-transaction..."); // 1. Craft the inner function call data (calling MyNFT.buyNFT()) const targetCallData = encodeFunctionData({ abi: myNFTABI, functionName: 'buyNFT', args: [], }); // 2. Prepare the ForwardRequest message for signing // User signs this structure, authorizing the Forwarder to act const message = { from: address, to: myNFTAddress, // The target contract the Forwarder will call value: 0n, // We are not sending ETH in this inner call gas: 150000n, // Estimate gas needed for MyNFT.buyNFT() (Relayer might adjust) nonce: nonce, // Nonce from the Forwarder to prevent replays data: targetCallData, // The action for the Forwarder to execute }; try { // 3. Sign the typed data (EIP-712 signature) setStatus("Requesting signature from wallet..."); console.log("Signing message:", message); const signature = await signTypedDataAsync({ domain, types, primaryType: 'ForwardRequest', message, }); setStatus("Signature obtained. Sending to Relayer..."); console.log("Signature:", signature); // 4. Send the signed request and signature to YOUR Relayer backend console.log("Sending signed message to relayer API:", relayerApiEndpoint); const response = await fetch(relayerApiEndpoint, { method: 'POST', headers: { 'Content-Type': 'application/json' }, // The body structure depends entirely on YOUR Relayer API design body: JSON.stringify({ forwardRequest: message, // The message that was signed signature: signature, // The signature itself // You might include other info your relayer needs }), }); if (!response.ok) { const errorBody = await response.text(); throw new Error(`Relayer request failed: ${response.status} ${response.statusText} - ${errorBody}`); } const result = await response.json(); // Assuming relayer returns JSON { transactionHash: "0x..." } setStatus(`Relayer accepted! Tx Hash: ${result.transactionHash}. Waiting for confirmation...`); console.log("Relayer response:", result); // You would typically then use the txHash to monitor confirmation status } catch (error: any) { console.error("Meta-transaction failed:", error); setStatus(`Error: ${error.message}`); } finally { setIsRelaying(false); } }; return ( <div> <button onClick={handleMetaTxPurchase} disabled={!address || nonce === undefined || isLoadingNonce || isSigning || isRelaying} > {isLoadingNonce ? 'Loading Nonce...' : isSigning ? 'Waiting for Signature...' : isRelaying ? 'Relaying Transaction...' : 'Buy NFT (Meta-Transaction)'} </button> {status && <p style={{ marginTop: '10px', wordBreak: 'break-word' }}>Status: {status}</p>} </div> ); }
Interactive Demo Skipped for EIP-2771

While EIP-2771 meta-transactions were an important early solution, setting up a full interactive demo requires a dedicated Relayer backend service, which adds significant complexity beyond the scope of this tutorial’s focus on smart contract patterns and frontend interactions.

Furthermore, newer patterns like ERC-2612 Permits (for approvals) and especially ERC-4337 Account Abstraction (for full transaction abstraction) offer more standardized, flexible, and often preferred solutions today.

Therefore, we’ll skip the interactive demo for this specific pattern and focus our interactive efforts on Account Abstraction later in the tutorial, which better represents the current state-of-the-art for gasless experiences.

The Trade-offs: Convenience Comes at a Cost

This ā€œTrusted Assistantā€ model sounds great, right? Sarah gets her NFT without touching ETH! But like any powerful secret, it has important caveats:

  1. The Relayer Dependency (Centralization & Trust): Your entire gasless flow depends on that Relayer service being online, funded, and trustworthy. If the Relayer goes down, your users can’t perform gasless actions. You are essentially trusting and relying on this specific off-chain infrastructure. This is a stark contrast to the ERC-4337 model (which we’ll explore later), where a decentralized network of ā€œBundlersā€ can pick up requests, removing single points of failure. You’re often locked into the specific API and requirements of your chosen Relayer.
  2. Contract Modification Required (No Backwards Compatibility): This pattern only works if the target smart contract (MyNFT in our case) is specifically designed to use EIP-2771 and _msgSender(). You cannot use this method to interact with existing contracts that haven’t been built this way. If you wanted to interact with, say, a standard Uniswap router gaslessly using this pattern, it wouldn’t work because the Uniswap router isn’t EIP-2771 aware.
  3. The approve Problem Still Lingers: Notice that Sarah still needs to have previously called approve on the PlatformCredits contract, granting spending permission to the MyNFT contract (or technically, the Forwarder acting on behalf of MyNFT). That approve transaction itself costs gas! So, while the buyNFT step becomes gasless for Sarah, we haven’t solved the entire flow yet. (Don’t worry, we have secrets for that too!)
  4. Relayer Costs: Someone has to pay the gas. The Relayer service pays the ETH, but they aren’t a charity. They will likely pass this cost back to the dApp provider (you!) potentially with a markup, or implement logic to only relay transactions under certain conditions.
Complexity & Security

Implementing a secure and reliable meta-transaction system involves careful smart contract design (using ERC2771Context correctly, handling nonces) and robust backend infrastructure (the Relayer must validate signatures, manage its own nonces and gas, and protect against spam/replay attacks). It’s a significant undertaking.

Pros:

  • Hides Gas from User: The primary benefit – users with supported wallets (EOAs) don’t need native tokens (ETH) for the sponsored transaction itself.
  • Works with Existing Wallets: Users don’t need a new type of wallet; their standard EOA (like MetaMask) works for signing.

Cons:

  • Relayer Infrastructure: Requires building or relying on a centralized Relayer service (cost, uptime, trust, potential lock-in).
  • Contract Modification: Target contracts must be EIP-2771 compatible (_msgSender()). Not backward compatible with existing, unmodified contracts.
  • Doesn’t Solve approve Gas: The crucial initial token approval (PlatformCredits.approve(...)) still costs the user gas and must be done separately before this meta-transaction flow can be used for the main action.
  • Complexity: Requires careful coordination between frontend, relayer backend, and EIP-2771 aware contracts.

The Gas Station Network (GSN)  was an early, more decentralized attempt at providing shared Relayer infrastructure, but implementing and using it also involves specific contract modifications and understanding its architecture.

Gas station network

Meta-transactions via EIP-2771 were a crucial first step in tackling the gas problem. They showed we could abstract gas away from the user, but the reliance on specific relayers and the need for contract changes highlighted the need for even better solutions, especially for common flows like token approvals and interacting with diverse contracts. Let’s keep digging into our arsenal of secrets!

3. The ā€œMagic Permission Slipā€: Slaying the Approve Dragon with ERC-2612 Permits!

Okay, we unveiled our first secret weapon – Meta-Transactions – and saw how it could sponsor the gas for Sarah’s buyNFT call. Pretty cool, right? But remember that nagging little problem? That annoying, separate approve transaction Sarah still had to make (and pay gas for!) before the meta-transaction could even work?

It’s like giving someone a VIP pass to the theme park (the sponsored buyNFT), but still making them wait in line and pay separately just to get a wristband allowing them to use the pass! It breaks the magic!

What if we could eliminate that approve transaction entirely? What if Sarah could grant permission without touching the blockchain, without spending a single drop of gas on approval?

Enter the Second Secret Weapon: ERC-2612 Permits – The Magic Permission Slip!

This is where things get really elegant. Imagine instead of Sarah having to go to the blockchain post office twice (once to file the ā€œapproveā€ form, once for the actual purchase), she could simply sign a special permission slip off-chain – like signing a piece of paper at her desk.

This ā€œpermission slipā€ is a digitally signed message, created using a secure standard called EIP-712. Think of EIP-712 as the universal template for creating these secure, off-chain agreements. It ensures the message is tamper-proof and clearly states: ā€œI, Sarah (identified by my unique wallet signature), grant permission for the MyNFT contract to spend up to 100 of my CRED tokens, and this permission slip is valid until [specific time].ā€

The Magic: Sarah signs this message in her wallet (like MetaMask). It costs ZERO GAS because it never touches the blockchain directly. It’s just data + signature.

How the Magic Works On-Chain:

  1. Sarah Signs the Slip: Sarah clicks ā€œBuy NFTā€. The dApp prepares the EIP-712 ā€œPermitā€ message and asks her to sign it. Click, sign, done. No gas.
  2. Frontend Bundles the Request: The dApp now takes Sarah’s main request (ā€œBuy the NFT!ā€) and attaches this signed permission slip (the permit signature) to it.
  3. One Transaction to Rule Them All: The dApp sends one single transaction to the MyNFT contract. This transaction calls a new function we’ll add, let’s call it buyNFTWithPermit.
  4. The Contract Uses the Slip: Inside the buyNFTWithPermit function, the first thing the MyNFT contract does is take Sarah’s signed permission slip and present it to the PlatformCredits contract by calling its special permit() function.
  5. PlatformCredits Verifies: The PlatformCredits contract (which we’ll upgrade slightly) looks at the signed slip. Using the magic of cryptography (specifically ecrecover on the EIP-712 signature), it verifies:
    • Was this really signed by Sarah?
    • Has this specific permission slip been used before (checking a ā€˜nonce’)?
    • Is it still valid (checking the ā€˜deadline’)?
    • If everything checks out, the PlatformCredits contract says, ā€œOkay, permission granted!ā€ and internally updates the allowance for the MyNFT contract without needing a separate transaction from Sarah.
  6. Purchase Proceeds: Now that the allowance is set within the same transaction, the rest of the buyNFTWithPermit function in MyNFT can proceed immediately. It calls transferFrom on PlatformCredits (which now succeeds!) and mints the NFT to Sarah.

One transaction. Zero gas spent by Sarah on approval. The annoying approve step? Obliterated!

Code Transformation: Giving Our Contracts Permit Power

This requires two key changes:

  1. Upgrade PlatformCredits.sol: It needs the ability to understand and process these magic permission slips. Thankfully, OpenZeppelin makes this easy! We just need to inherit their ERC20Permit contract.

    // SPDX-License-Identifier: MIT pragma solidity ^0.8.20; import "@openzeppelin/contracts/token/ERC20/ERC20.sol"; import "@openzeppelin/contracts/access/Ownable.sol"; // Import ERC20Permit import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol"; // <--- Import /** * @title PlatformCredits (with Permit) * @dev ERC20 token now including ERC-2612 permit functionality. */ // Inherit ERC20Permit contract PlatformCredits is ERC20, Ownable, ERC20Permit { // <--- Inherit constructor(address initialOwner) ERC20("PlatformCredits", "CRED") Ownable(initialOwner) // Initialize ERC20Permit with the token name (must match ERC20 name) ERC20Permit("PlatformCredits") // <--- Initialize Permit {} function grantCredits(address to, uint256 amount) public onlyOwner { _mint(to, amount); } // The permit() function and nonce tracking are inherited from ERC20Permit! }
  2. Add buyNFTWithPermit to MyNFT.sol: We add a new function that accepts the permit signature components (v, r, s, deadline) along with the purchase request.

    // Inside MyNFT contract... /** * @dev Mints a new NFT using PlatformCredits, leveraging ERC2612 permit. * Allows purchase without a prior separate 'approve' transaction. * @param deadline The permit deadline timestamp. * @param v The recovery byte of the permit signature. * @param r The r value of the permit signature. * @param s The s value of the permit signature. */ function buyNFTWithPermit( uint256 deadline, uint8 v, bytes32 r, bytes32 s ) public returns (uint256) { uint256 currentPrice = NFT_PRICE_IN_CREDITS; address buyer = msg.sender; // The user sending this transaction // Step 1: Call permit on the PlatformCredits contract // This grants allowance if the signature is valid // It will revert if the signature is invalid, expired, or already used. paymentCredits.permit(buyer, address(this), currentPrice, deadline, v, r, s); // Step 2: Allowance is now set, proceed with transferFrom bool success = paymentCredits.transferFrom(buyer, owner(), currentPrice); require(success, "MyNFT: Credits transfer failed after permit"); // Step 3: Mint the NFT _tokenIdCounter.increment(); uint256 newTokenId = _tokenIdCounter.current(); _safeMint(buyer, newTokenId); emit NFTMinted(buyer, newTokenId); return newTokenId; }

Frontend: The Slight Shift

The frontend now needs to:

  1. Prepare the EIP-712 Permit message.
  2. Get the user to sign it using signTypedDataAsync.
  3. Split the signature into v, r, s components.
  4. Call the new buyNFTWithPermit function via useWriteContract, passing the signature components and deadline.
Try Signing a Permit!

Connect your wallet to the Sepolia Testnet. This demo lets you sign the EIP-712 Permit message off-chain (no gas cost). You’ll see the parameters used and the resulting signature. Note that this only creates the signature; it doesn’t submit it to the blockchain. You’ll need to replace the placeholder contract addresses in the component code with actual deployed addresses for the nonce fetching and domain separator to work correctly.

The Result? Pure Elegance!

With ERC-2612 Permits, we’ve eliminated one of the most confusing and costly steps in the standard flow. Sarah signs one message off-chain (free!), then submits one transaction on-chain. It’s smoother, cheaper, and feels much more like the seamless Web2 experiences users expect.

Pros:

  • Eliminates approve Gas: The biggest win! Saves users one transaction fee.
  • Better UX: Reduces the number of steps and confusing pop-ups.
  • Standardized: EIP-2612 is a widely adopted standard for many tokens.
  • Atomic: Approval and action happen within the same transaction.

Cons:

  • Token Must Support It: The PlatformCredits token must implement ERC20Permit. You can’t use this on tokens that don’t have the permit function.
  • Main Transaction Still Costs Gas: While approval is gasless, the buyNFTWithPermit transaction itself still requires gas paid by the user (Sarah, in this case).

We’ve slain the approve dragon, a massive victory! But Sarah still needs that pesky ETH in her wallet to pay gas for the main purchase. Can we do better? Can we make the entire thing gasless? Oh yes… the next secrets await!

4. Solution Pattern 3: Direct EIP-712 Signature + Permit (Gas Sponsorship)

Concept: Instead of relying on a generic Forwarder contract (like in Pattern 1), we can build the signature verification logic directly into our target contract (MyNFT). This pattern combines an off-chain signature for the main action (buyNFT using credits) with an embedded ERC-2612 permit signature for the PlatformCredits transfer, allowing a relayer to submit the transaction.

How it Works:

  1. User:
    • Signs an ERC-2612 permit message for PlatformCredits, granting allowance to the MyNFT contract (off-chain, no gas).
    • Signs an EIP-712 typed data message authorizing the MyNFT contract to perform the buyNFT action on their behalf using credits. This message includes details like the function to call, parameters, a nonce, and potentially the permit signature components (v, r, s, deadline).
  2. Frontend: Sends the action signature and the permit signature (or the combined signed message structure) to a Relayer backend API.
  3. Relayer:
    • Verifies both signatures off-chain against the user’s address. Checks the nonce for replay protection.
    • Constructs an Ethereum transaction calling a specific function on MyNFT (e.g., buyNFTWithSignatureAndPermit).
    • Passes the user’s address, action details, permit signature components, and the action signature as arguments to the contract function.
    • Pays the gas fee using its own ETH.
    • Submits the transaction to the network.
  4. Smart Contract (MyNFT):
    • Needs a new function (e.g., buyNFTWithSignatureAndPermit).
    • Implements EIP-712 domain separation and signature verification logic to validate the action signature against the provided user address and nonce.
    • Calls permit() on the PlatformCredits contract using the provided permit signature components (v, r, s, deadline).
    • If both signatures are valid and the nonce is correct, it executes the buyNFT logic (calling transferFrom on PlatformCredits which now succeeds due to the permit, and minting the NFT) on behalf of the original user. It must manage nonces for the action signature.

Implementation Changes:

  • PlatformCredits.sol: Must implement ERC20Permit (EIP-2612).
  • MyNFT.sol:
    • Needs to implement EIP-712 utilities (domain separator, struct hashing, ecrecover). OpenZeppelin’s EIP712 utility contract is helpful here.
    • Needs a new function like buyNFTWithSignatureAndPermit(address user, /* permit params */, /* action params */, bytes memory actionSignature).
    • Needs state to track used nonces for the action signature to prevent replays.

Frontend Interaction (Conceptual JS using viem & wagmi):

import { useAccount, useSignTypedData, useReadContract } from 'wagmi'; import { encodeFunctionData, parseAbi, recoverTypedDataAddress } from 'viem'; // For verification maybe import { ethers } from 'ethers'; // For signature splitting (or use viem utils) // Assume PlatformCredits and MyNFT ABIs, addresses are known const platformCreditsAddress = "0x..."; const myNFTAddress = "0x..."; const nftPriceInCredits = parseEther("100"); // Assume Relayer API endpoint is known: const relayerApiEndpoint = '/api/relay-direct-sig'; // EIP-712 Domain/Types for PlatformCredits permit const permitDomain = { /* ... EIP712 domain for PlatformCredits ... */ }; const permitTypes = { Permit: [ /* ... Permit fields ... */ ] }; // EIP-712 Domain/Types for MyNFT action signature const nftActionDomain = { /* ... EIP712 domain for MyNFT contract ... */ }; const nftActionTypes = { BuyNFTAction: [ /* ... Fields like user, nonce, etc. ... */ ] }; function DirectSigButton() { const { address } = useAccount(); const { signTypedDataAsync } = useSignTypedData(); // Fetch nonces if needed (permit nonce from token, action nonce from NFT contract) // const { data: permitNonce } = useReadContract({...}); // const { data: actionNonce } = useReadContract({...}); // NFT contract needs a nonce getter const handleDirectSigPurchase = async () => { if (!address /* || permitNonce === undefined || actionNonce === undefined */) { console.error("Wallet not connected or nonces not loaded"); return; } const currentActionNonce = 0n; // Replace with actual fetched actionNonce const currentPermitNonce = 0n; // Replace with actual fetched permitNonce const deadline = BigInt(Math.floor(Date.now() / 1000) + 3600); // 1 hour try { // 1. Sign Permit message for PlatformCredits const permitMessage = { owner: address, spender: myNFTAddress, // NFT contract needs allowance value: nftPriceInCredits, // Use the price in credits nonce: currentPermitNonce, deadline: deadline, }; console.log("Requesting permit signature..."); const permitSignature = await signTypedDataAsync({ domain: permitDomain, types: permitTypes, primaryType: 'Permit', message: permitMessage, }); const { v: permitV, r: permitR, s: permitS } = ethers.Signature.from(permitSignature); // Or viem equivalent // 2. Sign Action message const actionMessage = { user: address, nftContract: myNFTAddress, // Could include relevant details nonce: currentActionNonce, // Include other relevant parameters if needed by the contract verification }; console.log("Requesting action signature..."); const actionSignature = await signTypedDataAsync({ domain: nftActionDomain, types: nftActionTypes, primaryType: 'BuyNFTAction', message: actionMessage, }); // 3. Send to Relayer console.log("Sending signatures to relayer..."); const response = await fetch(relayerApiEndpoint, { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ userAddress: address, permit: { value: nftPriceInCredits.toString(), deadline: deadline.toString(), v: permitV, r: permitR, s: permitS }, action: { nonce: currentActionNonce.toString() /* ... other params ... */ }, actionSignature: actionSignature, }), }); if (!response.ok) { throw new Error(`Relayer request failed: ${response.statusText}`); } const result = await response.json(); console.log("Relayer response:", result); // Should contain tx hash } catch (error) { console.error("Direct Signature Purchase failed:", error); } }; return ( <button onClick={handleDirectSigPurchase} disabled={!address}> Buy NFT (Direct Signature) </button> ); }
Contract Complexity

Implementing EIP-712 verification correctly (domain separator, struct hashing, nonce management, signature recovery) adds significant complexity and potential security risks to the target smart contract (MyNFT). Thorough testing and audits are crucial.

Pros:

  • User doesn’t need ETH (if Relayer pays).
  • Eliminates the separate approve transaction.
  • Avoids the need for a generic, potentially complex Forwarder contract.
  • Works with existing EOAs.

Cons:

  • Requires Relayer infrastructure (centralization risk, cost).
  • Requires significant modification and complexity within the target smart contract (MyNFT).
  • User typically needs to sign two messages (permit + action), although UX can sometimes combine this.
  • Less standardized than EIP-2771 or ERC-4337 approaches; signature verification logic is bespoke to the contract.

This pattern offers an alternative to generic meta-transactions when you want gas sponsorship but prefer to keep the verification logic tightly coupled with the target contract. However, the increased contract complexity is a major trade-off compared to using ERC-2612 alone or leveraging ERC-4337/EIP-7702 infrastructure.

5. Solution Pattern 4: ERC-4337 Account Abstraction

Concept: Instead of users interacting directly via their Externally Owned Accounts (EOAs), they use Smart Contract Wallets (SCWs). These SCWs act as their primary account, initiating transactions through a special mechanism defined by ERC-4337 . This standard introduces a way to achieve account abstraction without requiring consensus-layer protocol changes.

Key Components:

  • Smart Contract Wallet (SCW): The user’s account, implemented as a smart contract (e.g., Safe, Kernel). It defines its own validation logic (how transactions are authorized, e.g., owner signature, multi-sig, social recovery).
  • UserOperation: A data structure representing the user’s intent to perform an action (e.g., call MyNFT.buyNFT). It includes sender (SCW address), target, call data, gas limits, nonce, and potentially paymaster data. It’s like a pseudo-transaction.
  • Bundler: An off-chain actor (service) that gathers UserOperation objects from users via a dedicated mempool. Bundlers package multiple UserOperations into a single standard Ethereum transaction and send it to the EntryPoint contract.
  • EntryPoint: A global singleton smart contract that orchestrates the execution of UserOperations. It verifies signatures, manages gas payments, and calls the appropriate SCW to execute the transaction.
  • Paymaster: An optional smart contract that can agree to pay for a user’s UserOperation gas fees, enabling sponsored transactions. Paymasters define their own sponsorship policies (e.g., free for certain actions, pay with platform credits).
Caveat: Paying Gas with Platform Credits (ERC20)

While the concept of users paying gas fees directly with ERC20 tokens (like our PlatformCredits) via a Paymaster is a goal of Account Abstraction, the current reality (as of early 2025) is often different. Most Paymaster implementations work like this:

  1. The Paymaster (or its sponsoring dApp) must be pre-funded with the native token (e.g., ETH) required by the Bundler.
  2. The Paymaster pays the Bundler in the native token.
  3. If the user is meant to pay in PlatformCredits, the Paymaster’s validatePaymasterUserOp function verifies the user can pay (e.g., has sufficient CRED balance and has approved the Paymaster).
  4. The actual CRED transfer from the user to the Paymaster (or sponsor) happens after validation, often within the postOp function of the Paymaster or even embedded within the execution logic of the UserOperation itself (e.g., the MyNFT.buyNFT function could be modified to transfer an extra amount of CRED to the sponsor).

Direct, atomic swaps (e.g., CRED -> ETH) within the Paymaster validation logic to cover gas are complex due to potential atomicity issues and MEV risks, and are not yet widely standardized or implemented. So, ā€œpaying with creditsā€ usually means the Paymaster facilitates it by accepting the credits off-chain or in a separate step, while still paying the Bundler in ETH.

How it Works (Sponsored Flow):

  1. User (via dApp): Wants to execute an action (e.g., buyNFT). The dApp helps construct a UserOperation specifying the target (MyNFT), call data, and gas parameters.
  2. dApp/SDK: Sends the UserOperation to a Paymaster service to request sponsorship.
  3. Paymaster Service: Checks its policy. If sponsorship is granted, it returns paymasterAndData (including its signature agreeing to pay) to be added to the UserOperation.
  4. User: Signs the UserOperation hash using their EOA (which owns the SCW).
  5. dApp/SDK: Sends the signed UserOperation (now including paymasterAndData and the user’s signature) to a Bundler.
  6. Bundler: Verifies the UserOperation, bundles it with others, and submits it to the EntryPoint contract in a single Ethereum transaction.
  7. EntryPoint Contract:
    • Verifies the Paymaster’s stake and signature.
    • Verifies the SCW’s signature (by calling validateUserOp on the SCW).
    • Calls the SCW to execute the action (MyNFT.buyNFT()).
    • If successful, compensates the Bundler for gas (paid by the Paymaster).
ERC-4337 Infra as a Relayer for EOAs

While the primary model for ERC-4337 involves the SCW being the user’s main account, the infrastructure (Bundler, Paymaster, SCW) can also function as a sophisticated relayer system for users who still primarily identify with their EOA.

Imagine combining Pattern 3 (Direct EIP-712 Signature + Permit) with ERC-4337:

  1. The user signs the necessary off-chain messages (permit, action authorization) with their EOA.
  2. Instead of a simple relayer, the frontend interacts with an ERC-4337 SDK.
  3. The SDK prepares a UserOperation where the sender is the user’s SCW (which might be counterfactually deployed or pre-existing).
  4. The callData within the UserOperation instructs the SCW to call a special function on the MyNFT contract, e.g., buyNFTWithSignaturesFor(eoaAddress, permitSig, actionSig).
  5. This buyNFTWithSignaturesFor function on MyNFT would perform the EIP-712 signature verifications (as in Pattern 3) against the eoaAddress and then mint the NFT directly to the eoaAddress.
  6. The UserOperation itself is sponsored by a Paymaster, making the entire flow gasless for the user’s EOA.

In this scenario, the SCW acts purely as a temporary, gas-sponsored execution environment controlled by the EOA’s signature, leveraging the robust Bundler/Paymaster network. The EOA remains the ultimate owner of the asset. This highlights the flexibility of ERC-4337, although it’s arguably not the most common or intended use case compared to using the SCW as the primary account. The advent of EIP-7702 might offer a more direct way to achieve similar EOA-centric sponsored transactions in the future.

Implementation Sketch (React Component using Candide SDK, viem, wagmi):

This example assumes you have a standard RainbowKit/Wagmi/Viem setup and want to use Candide’s SDK and infrastructure for Account Abstraction.

Dependencies

You’ll need to install the Candide Provider SDK:

npm install @candide/provider viem wagmi

Or using yarn:

yarn add @candide/provider viem wagmi
import React, { useState, useEffect } from 'react'; import { useAccount, useWalletClient } from 'wagmi'; import { encodeFunctionData, parseEther, Hex } from 'viem'; import { sepolia } from 'viem/chains'; // Or your target chain import { CandideAccount, createCandideProvider } from "@candide/provider"; // ABIs (ensure they are in viem format) const platformCreditsABI = [ /* ... ERC20 ABI ... */ ] as const; // Needed if SCW needs to interact directly const myNFTABI = [ /* ... MyNFT ABI including buyNFT ... */ ] as const; // Contract Addresses and Config (Replace with your actual values) const platformCreditsAddress = "0x..."; // Deployed PlatformCredits address const myNFTAddress = "0x..."; // Deployed MyNFT address const nftPriceInCredits = parseEther("100"); // Price in CRED (assuming 18 decimals) const chain = sepolia; // Your target chain // Candide Infrastructure URLs (Replace with actual Candide URLs for your chain) const candideBundlerUrl = "https://bundler-sepolia.candide.dev"; // Example for Sepolia const candidePaymasterUrl = "https://paymaster-sepolia.candide.dev"; // Example for Sepolia const entryPointAddress = "0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789"; // Standard EntryPoint v0.6 function GaslessCandideAAPurchaseButton() { const { address: eoaAddress, chain: connectedChain } = useAccount(); const { data: walletClient } = useWalletClient(); const [candideProvider, setCandideProvider] = useState<any>(null); // Type from SDK if available const [smartAccount, setSmartAccount] = useState<CandideAccount | null>(null); const [isInitializing, setIsInitializing] = useState(false); const [isActing, setIsActing] = useState(false); const [status, setStatus] = useState(''); // Initialize Candide Provider useEffect(() => { const initCandide = async () => { // Ensure walletClient, connectedChain exist and match our target chain if (walletClient && connectedChain && connectedChain.id === chain.id && !candideProvider && !isInitializing) { setIsInitializing(true); setStatus("Initializing Candide Provider..."); console.log("Initializing Candide Provider..."); try { const provider = await createCandideProvider({ // Pass the viem WalletClient obtained from wagmi walletClient: walletClient, chain: chain, // Ensure this matches the connected chain entryPointAddress: entryPointAddress, accountAbstractionSalt: "my_unique_salt_for_user", // Important: Use a unique, deterministic salt per user/app bundlerUrl: candideBundlerUrl, paymasterUrl: candidePaymasterUrl, // Provide Paymaster URL for sponsorship }); setCandideProvider(provider); setSmartAccount(provider.account); // Access the initialized smart account setStatus(`Candide Provider Initialized. SCW Address: ${provider.account.address}`); console.log("Candide Provider Initialized. SCW Address:", provider.account.address); } catch (error) { console.error("Failed to initialize Candide Provider:", error); setStatus(`Error initializing Candide: ${error.message}`); } finally { setIsInitializing(false); } } else if (connectedChain && connectedChain.id !== chain.id) { setStatus(`Please connect to the ${chain.name} network.`); } }; initCandide(); }, [walletClient, connectedChain, candideProvider, isInitializing]); const handlePurchase = async () => { if (!smartAccount || !candideProvider) { setStatus("Error: Candide Smart Account not initialized."); return; } setIsActing(true); setStatus("Preparing UserOperation..."); try { // 1. Encode the call data for MyNFT.buyNFT() // Note: The Candide SCW (likely a Safe) must hold PlatformCredits (CRED). // The `prepareUserOperation` below bundles this into the SCW's execution call. // The SCW's internal logic (e.g., Safe's execTransaction) handles the CRED transfer. const callData = encodeFunctionData({ abi: myNFTABI, functionName: 'buyNFT', args: [], // buyNFT takes no arguments in our example }); // 2. Prepare the UserOperation using Candide SDK // This handles nonce, gas estimation (via bundler), etc. // It assumes the SCW's execute function will handle the MyToken transfer internally. const userOperation = await smartAccount.prepareUserOperation({ target: myNFTAddress, // The contract the SCW should call data: callData, // The data for the call value: 0n, // Not sending ETH directly // Options for gas estimation multipliers can be added here if needed // e.g., { maxFeePerGasPercentageMultiplier: 130 } }); setStatus("Sending UserOperation via Candide..."); // 3. Send the UserOperation (Candide SDK handles Paymaster interaction if URL provided) // The SDK internally gets the user's signature on the userOp hash const userOperationResponse = await smartAccount.sendUserOperation(userOperation); setStatus(`UserOperation sent: ${userOperationResponse.userOperationHash}. Waiting for confirmation...`); console.log("UserOperation Hash:", userOperationResponse.userOperationHash); // 4. Wait for the transaction receipt const userOperationReceiptResult = await userOperationResponse.wait(); // Candide SDK helper if (userOperationReceiptResult.success) { setStatus(`NFT Purchased! Transaction Hash: ${userOperationReceiptResult.receipt.transactionHash}`); console.log("Transaction Receipt:", userOperationReceiptResult.receipt); } else { setStatus(`UserOperation failed. Reason: ${userOperationReceiptResult.receipt.revertReason || 'Unknown'}`); console.error("UserOperation failed:", userOperationReceiptResult); } } catch (error: any) { console.error("Candide AA Purchase failed:", error); setStatus(`Error: ${error.message || 'Candide AA Purchase failed.'}`); } finally { setIsActing(false); } }; return ( <div> <button onClick={handlePurchase} disabled={!smartAccount || isInitializing || isActing} > {isInitializing ? 'Initializing...' : isActing ? 'Processing...' : 'Buy NFT (Gasless via Candide AA)'} </button> {status && <p style={{ marginTop: '10px', wordBreak: 'break-word' }}>Status: {status}</p>} {smartAccount && <p>SCW Address: {smartAccount.address}</p>} </div> ); }
Candide SDK & Safe Wallets

The @candide/provider SDK abstracts the complexities of ERC-4337. It handles creating the Smart Contract Wallet instance (often a Safe wallet, formerly Gnosis Safe, deployed behind the scenes), preparing the UserOperation (fetching nonces, estimating gas via the Bundler), interacting with the Paymaster for sponsorship (if configured), obtaining the user’s signature, and sending the operation to the Bundler.

It’s worth noting that Safe wallets created this way (or independently) can often be managed through sophisticated interfaces like the official one at safe.global , offering features like multi-sig configurations, asset management, and transaction history viewing directly for the SCW.

Refer to the official Candide documentation for the latest API details and configuration options specific to their SDK.

Pros:

  • True Gasless Experience: Users don’t need ETH if a Paymaster sponsors the transaction.
  • Enhanced UX: Enables features like batching multiple actions into one transaction, social recovery, spending limits, etc., defined at the wallet level.
  • Standardized: ERC-4337 provides a common interface for SCWs, Bundlers, and Paymasters, fostering a growing ecosystem.
  • No Protocol Change: Works on existing EVM chains.

Cons:

  • Infrastructure Reliance: Depends on reliable Bundler and Paymaster services (though these can be decentralized).
  • Potential Cost: While users might not pay gas, the dApp/Paymaster bears the cost. Base gas costs for UserOperations can sometimes be slightly higher than simple EOA transactions due to verification overhead.
  • Adoption Curve: Requires users to have or deploy an SCW. While deployment can be counterfactual (address exists before deployment) and sponsored, it’s still a different model than traditional EOAs.

ERC-4337 represents a major step towards making Web3 more user-friendly by abstracting away gas complexities and enabling richer wallet functionalities.

6. Solution Pattern 5: EIP-7702 - Empowering EOAs

Concept: A new transaction type (0x04) allows an EOA to temporarily delegate its execution logic to a smart contract for a single transaction. This enables EOA batching and sponsorship.

How it Works (Simplified):

  1. User: Still uses their regular EOA (e.g., MetaMask).
  2. Frontend (using an EIP-7702 compatible SDK/library):
    • Identifies the user wants to perform an action (e.g., buyNFT).
    • Needs a Delegate Contract: A pre-deployed contract designed to perform the required actions (e.g., call PlatformCredits.permit then MyNFT.buyNFT). This contract contains the logic the EOA will temporarily adopt.
    • Constructs an EIP-7702 transaction (type 0x04). This involves:
      • Specifying the delegate contract address.
      • The actual call data intended for the delegate contract.
      • Getting an authorization signature from the user’s EOA for this specific delegation + nonce (using a new eth_signTransaction mode or similar).
    • Sends this structured EIP-7702 transaction request to a Sponsor/Relayer service (similar to Bundlers/Paymasters but for EIP-7702).
  3. Sponsor/Relayer Service:
    • Verifies the authorization and potentially checks sponsorship rules.
    • Submits the valid EIP-7702 transaction (type 0x04) to the network, paying the gas.
  4. On-Chain Execution (Post-Pectra Hardfork):
    • The EVM recognizes the EIP-7702 transaction.
    • It verifies the user’s authorization signature.
    • It temporarily sets the user’s EOA code pointer to the delegate contract.
    • The transaction’s to field likely calls the EOA itself (or the delegate directly).
    • The delegate contract’s code executes in the context of the user’s EOA. It performs the batch (permit + buyNFT).
    • The EOA’s code pointer reverts after the transaction.

Implementation Sketch (Conceptual JS using wagmi & viem - EIP-7702):

// NOTE: This is highly conceptual as EIP-7702 SDKs/Wallet support are still emerging. import { sepolia } from 'viem/chains'; import { encodeFunctionData, parseAbi, parseEther, Hex } from 'viem'; import { useAccount, useWalletClient, useSignTypedData } from 'wagmi'; import { ethers } from 'ethers'; // For signature splitting (or use viem utils) // Assume an EIP-7702 compatible SDK/Relayer client exists // import { sendEip7702Transaction } from 'your-eip7702-sdk'; // Address of the pre-deployed Delegate Contract (must be trusted) const delegateContractAddress = "0x..."; // Replace with actual address // ABI of the Delegate Contract const delegateABI = parseAbi([ // Example: Function expects permit signature components 'function executePermitAndBuy(address creditsToken, address nftContract, uint256 price, uint256 deadline, uint8 v, bytes32 r, bytes32 s)', ]); // Assume PlatformCredits implements permit const platformCreditsAddress = "0x..."; // Replace with actual address const myNFTAddress = "0x..."; // Replace with actual address const nftPriceInCredits = parseEther("100"); // Example price in CRED // EIP-712 Domain/Types for PlatformCredits permit signature const permitDomain = { /* ... EIP712 domain for PlatformCredits ... */ }; // Replace with actual domain const permitTypes = { Permit: [ /* ... Permit fields ... */ ] }; // Replace with actual types function GaslessEip7702Button() { const { address } = useAccount(); const { data: walletClient } = useWalletClient(); // Needed for signing EIP-7702 auth const { signTypedDataAsync } = useSignTypedData(); // For signing the permit const handleEip7702Purchase = async () => { if (!address || !walletClient) { console.error("Wallet not connected"); return; } console.log("Starting gasless EIP-7702 NFT purchase..."); try { // --- Step 1: Get Permit Signature for PlatformCredits (Off-chain) --- const deadline = BigInt(Math.floor(Date.now() / 1000) + 3600); // 1 hour // Fetch actual permit nonce from PlatformCredits contract using viem/wagmi readContract const permitNonce = 0n; // Replace with actual fetched nonce const permitMessage = { owner: address, spender: delegateContractAddress, // The delegate contract needs the allowance value: nftPriceInCredits, // Use price in credits nonce: permitNonce, // Use actual nonce deadline: deadline, }; console.log("Requesting permit signature..."); const permitSignature = await signTypedDataAsync({ domain: permitDomain, types: permitTypes, primaryType: 'Permit', message: permitMessage, }); console.log("Permit signature obtained:", permitSignature); // Split signature using viem/ethers utility const { v, r, s } = ethers.Signature.from(permitSignature); // Replace with viem equivalent if preferred // --- Step 2: Prepare the Delegate Call Data --- const delegateCallData = encodeFunctionData({ abi: delegateABI, functionName: 'executePermitAndBuy', args: [ platformCreditsAddress, myNFTAddress, nftPriceInCredits, deadline, v, // Pass signature components r, s, ], }); // --- Step 3: Construct and Send EIP-7702 Transaction via Sponsor/Relayer --- // This part is highly dependent on wallet support and SDKs which are TBD. // It would involve: // 1. Getting an authorization signature from the user via walletClient (e.g., a modified eth_signTransaction) // that approves delegating to `delegateContractAddress` for this specific call (`delegateCallData`). // 2. Sending the transaction details (delegateAddress, delegateCallData, authorization) // to a Sponsor/Relayer service. console.log("Constructing EIP-7702 transaction (Conceptual)..."); // const authorizationSignature = await walletClient.signEip7702Authorization(...) // Speculative // Use an SDK function to send via relayer (API is speculative) // const relayerResponse = await sendEip7702Transaction({ // delegateAddress: delegateContractAddress, // delegateCallData: delegateCallData, // authorization: authorizationSignature, // Speculative // // Potentially other params like nonce, gas limits for the relayer // }); // console.log("EIP-7702 Transaction submitted via Relayer, Hash:", relayerResponse.transactionHash); // Speculative // // Wait for confirmation (SDK might provide a helper) // const receipt = await relayerResponse.wait(); // Speculative // console.log("EIP-7702 Transaction confirmed:", receipt.transactionHash); // Speculative console.log("Conceptual EIP-7702 flow complete. NFT Purchase initiated (if infra existed)."); alert("EIP-7702 flow is conceptual. Transaction not actually sent."); } catch (error) { console.error("EIP-7702 Purchase failed:", error); alert(`Error: ${error.message}`); } }; return ( <button onClick={handleEip7702Purchase} disabled={!address || !walletClient}> Buy NFT (EIP-7702 - Conceptual) </button> ); }
EIP-7702 is New!

EIP-7702 is currently included in the upcoming Pectra hardfork (expected late 2024/early 2025). Wallet support (for the new authorization signing), SDK implementations, relayer infrastructure, and security best practices for delegate contracts are still under development. The code above is highly conceptual and will not work until the ecosystem matures post-hardfork.

Pros:

  • Works directly with existing EOAs (massive user base).
  • Enables native EOA batching and sponsorship.
  • Potentially simpler migration path for dApps compared to full AA.
  • Designed for forward compatibility with ERC-4337.

Cons:

  • Very new, requires Pectra hardfork inclusion and widespread infra/wallet adoption.
  • Security of delegate contracts is paramount.
  • Introduces new complexities around transaction validity and state changes for EOAs.

7. Comparison and Choosing the Right Approach

FeatureMeta-Transactions (Relayer)ERC-2612 PermitsDirect Sig + PermitERC-4337 (AA)EIP-7702
Primary GoalGas SponsorshipGasless ApproveGas SponsorshipFull AA / Gasless TxEOA Batch/Sponsor
Account TypeEOAEOAEOASCWEOA
Needs ETH? (User)No (if Relayer pays)Yes (for main tx)No (if Relayer pays)No (if Paymaster)No (if Sponsor)
BatchingComplexNoYes (in Contract)Yes (Native in SCW)Yes (via Delegate)
Requires Contract Mod?Yes (EIP-2771)Yes (Token+Target)Yes (Target Contract)Yes (SCW logic)Yes (Delegate Contract)
InfrastructureRelayer BackendNoneRelayer BackendBundler, PaymasterSponsor/Relayer (7702)
StandardizationCustom / EIP-2771EIP-2612CustomERC-4337EIP-7702
MaturityMature ConceptMatureCustom / Less CommonGrowingNew / Future

When to Use What:

  • Simple ERC20 approve removal (for PlatformCredits): Use ERC-2612 if the PlatformCredits token supports it. It’s clean and standard.
  • Gas sponsorship for specific contract actions (EOA using credits): Consider Direct Signature + Permit if you control the target contract and prefer embedding logic there over a generic forwarder. Be mindful of complexity.
  • Full gas sponsorship & advanced features (new dApp): Go with ERC-4337. Build with Account Abstraction from the start using SDKs like Candide’s.
  • Need to support existing EOA users with batching/sponsorship: EIP-7702 (once available and supported) offers a powerful bridge. Requires careful delegate design.
  • Basic gas sponsorship for EOAs (generic): Traditional Meta-Transactions (EIP-2771) might still be viable, especially if using existing infrastructure, but compare overhead with AA SDKs.

Conclusion: The Path to Seamless Web3

The journey from clunky, gas-heavy interactions (even for using free credits!) to smooth, potentially gasless flows is well underway. While traditional transactions remain the foundation, solutions like ERC-2612, ERC-4337, and the promising EIP-7702 provide developers with powerful tools to drastically improve the user onboarding experience.

  • ERC-2612 tackles the common approve pain point for tokens like PlatformCredits.
  • ERC-4337 offers a flexible, future-proof framework for gas abstraction and advanced wallet features via Smart Contract Wallets, allowing users to spend their credits without needing ETH.
  • EIP-7702 aims to bring batching and sponsorship capabilities directly to the vast number of existing EOAs.

By understanding and implementing these patterns, we can build dApps that are not just powerful, but also accessible and welcoming to the next wave of Web3 users. Choose the right tool for your specific needs, prioritize user experience, and help build a more seamless decentralized future!

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