ZIP-0029: Gasless Transactions for Conservation

Abstract

This proposal defines a meta-transaction relay system that sponsors gas fees for conservation-related actions on Zoo Network. Users performing donations, citizen science submissions, grant milestone reports, and impact data contributions can interact with the network without holding ZOO tokens for gas. The Foundation operates a relay network funded by a dedicated gas sponsorship pool, with EIP-2771 compliant forwarding contracts.

Motivation

Gas fees are the primary barrier to conservation participation on blockchain networks:

Donor onboarding: Donors who want to contribute should not need to first acquire gas tokens
Citizen scientists: Researchers submitting species observations should not bear transaction costs
Global access: Users in developing countries where even small gas fees are prohibitive need free access
Mission priority: Conservation actions are the core purpose of Zoo Network and should be frictionless
Nonprofit obligation: As a 501(c)(3), Zoo should minimize barriers to charitable participation

Specification

Action	Sponsored	Daily Limit per User
Conservation donation	Yes	10 transactions
Citizen science data submission	Yes	50 transactions
Grant milestone report	Yes	5 transactions
Impact oracle data submission	Yes	20 transactions
Governance vote	Yes	5 transactions
ZNS registration (conservation projects)	Yes	1 transaction
Token transfers	No	-
DeFi operations	No	-
NFT trading	No	-

Meta-Transaction Architecture

┌──────────┐    sign     ┌──────────┐    relay    ┌──────────────┐
│  User    │────────────►│  Relay   │────────────►│  Forwarder   │
│ (no gas) │  (EIP-712)  │  Server  │  (pays gas) │  Contract    │
└──────────┘             └──────────┘             └──────┬───────┘
                                                         │
                                                         ▼
                                                  ┌──────────────┐
                                                  │  Target      │
                                                  │  Contract    │
                                                  │ (trusts fwd) │
                                                  └──────────────┘

EIP-2771 Forwarder Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract ZooForwarder {
    struct ForwardRequest {
        address from;
        address to;
        uint256 value;
        uint256 gas;
        uint256 nonce;
        uint48 deadline;
        bytes data;
    }

    mapping(address => uint256) public nonces;
    mapping(bytes32 => bool) public sponsoredActions;

    event MetaTransactionExecuted(
        address indexed from,
        address indexed to,
        bytes32 actionType,
        bool success
    );

    function execute(
        ForwardRequest calldata req,
        bytes calldata signature
    ) external payable returns (bool success, bytes memory result) {
        require(block.timestamp <= req.deadline, "expired");
        require(nonces[req.from] == req.nonce, "invalid nonce");

        // Verify action is sponsored
        bytes32 actionType = getActionType(req.to, req.data);
        require(sponsoredActions[actionType], "not sponsored");

        // Verify signature (EIP-712)
        address signer = recoverSigner(req, signature);
        require(signer == req.from, "invalid signature");

        nonces[req.from]++;

        // Execute with sender appended (EIP-2771)
        (success, result) = req.to.call{gas: req.gas, value: req.value}(
            abi.encodePacked(req.data, req.from)
        );

        emit MetaTransactionExecuted(req.from, req.to, actionType, success);
    }
}

Target Contract Integration

Contracts that accept meta-transactions must inherit ERC2771Context:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/metatx/ERC2771Context.sol";

contract ConservationDonation is ERC2771Context {
    constructor(address trustedForwarder) ERC2771Context(trustedForwarder) {}

    function donate(bytes32 projectId) external payable {
        address donor = _msgSender(); // Returns actual sender, not relay
        // Process donation from donor
    }
}

Gas Sponsorship Pool

sponsorship_pool:
  source: 5% of transaction fees collected on Zoo Network
  replenishment: automatic per epoch
  monthly_budget: 500,000 ZOO
  per_user_daily_limit:
    gas_value: 0.1 ZOO equivalent
    transactions: varies by action type (see table above)
  reserve: 3 months operating buffer

Relay Network

relay_network:
  operators:
    minimum: 3
    selection: permissionless (any address can relay)
    reimbursement: from sponsorship pool + 10% premium
  availability:
    target: 99.9% uptime
    fallback: users can submit transactions directly (with gas)
  rate_limiting:
    per_user: enforced at forwarder contract level
    per_relay: 1000 transactions/minute
    global: 10000 transactions/minute

Anti-Abuse Measures

Measure	Implementation
Daily transaction limits	Per-user nonce tracking in forwarder
Action type whitelist	Only conservation-related actions are sponsored
Proof of humanity	Optional World ID or Gitcoin Passport for higher limits
IP rate limiting	Relay-level, not on-chain
Reputation gating	Users with ZOO-REP (ZIP-0026) get 2x daily limits

User Experience Flow

User connects wallet (no ZOO balance needed)
User signs an EIP-712 typed data message (gasless signature)
Relay server validates the request and submits on behalf of user
Target contract processes the action using _msgSender() to identify the real user
Relay is reimbursed from the sponsorship pool

SDK Integration

The Zoo SDK (ZIP-0028) transparently handles meta-transactions:

const client = new ZooClient({
  rpcUrl: "https://api.zoo.network/ext/bc/zoo/rpc",
  relayUrl: "https://relay.zoo.network",  // Meta-transaction relay
  gasless: true,  // Enable gasless mode for sponsored actions
});

// This donation is automatically relayed (user pays no gas)
await client.conservation.donate({
  projectId: "borneo-orangutan",
  amount: parseEther("100"),
});

Rationale

EIP-2771 is chosen over EIP-4337 (account abstraction) because it requires no changes to user wallets and works with existing EOAs. Conservation donors likely have standard wallets (MetaMask, etc.) and should not need to deploy smart contract wallets.

Limiting sponsorship to conservation actions (not DeFi or trading) ensures the gas pool is used for mission-aligned activities. This is both economically sustainable and consistent with the Foundation's 501(c)(3) charitable purpose.

The 10% relay premium above gas cost ensures relaying is economically viable for third-party operators, creating a competitive relay market rather than Foundation-only infrastructure.

Security Considerations

Replay attacks: Nonce tracking in the forwarder contract prevents transaction replay
Relay censorship: Multiple independent relays ensure no single operator can censor transactions; users can always fall back to direct submission
Sponsorship pool drain: Daily per-user limits and action-type whitelist prevent rapid pool depletion
Forwarder trust: Target contracts must only trust the canonical Zoo Forwarder address; a compromised forwarder could impersonate any user
Signature malleability: EIP-712 structured signing prevents signature manipulation attacks
Relay griefing: Relays validate transactions locally before submission to avoid wasting gas on guaranteed-to-fail transactions

Gasless Transactions for Conservation