The Aave protocol is migrating from its native LEND token to the AAVE token, as detailed in Aavenomics. The AAVE token is an ERC-20 compatible token with the addition of a snapshot feature (used in governance balance tracking) and integrates EIP 2612 permit function, allowing gas-less transactions and one transaction approval/transfer.

The source code for the AAVE token and migration can be found on Github here.

AAVE Token

• permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s ) external

  使用EIP-2612协议的permit实现了无需花费gas的转账功能

  function permit(
          address owner,
          address spender,
          uint256 value,
          uint256 deadline,
          uint8 v,
          bytes32 r,
          bytes32 s
      ) external {
          require(owner != address(0), "INVALID_OWNER");
          //solium-disable-next-line
          require(block.timestamp <= deadline, "INVALID_EXPIRATION");
          uint256 currentValidNonce = _nonces[owner];
          bytes32 digest = keccak256(
                  abi.encodePacked(
                      "\\x19\\x01",
                      DOMAIN_SEPARATOR,
                      keccak256(
                          abi.encode(PERMIT_TYPEHASH, owner, spender, value, currentValidNonce, deadline))
                      )
          );
  
          require(owner == ecrecover(digest, v, r, s), "INVALID_SIGNATURE");
          _nonces[owner] = currentValidNonce.add(1);
          _approve(owner, spender, value);
      }
  

  import { signTypedData_v4 } from 'eth-sig-util'
  import { fromRpcSig } from 'ethereumjs-util'
  
  // ... other imports
  
  import AaveTokenAbi from "./AaveTokenAbi.json"
  
  // ... setup your web3 provider
  
  const aaveTokenAddress = "AAVE_TOKEN_ADDRESS"
  const aaveTokenContract = new web3.eth.Contract(AaveTokenAbi, aaveTokenAddress)
  
  const privateKey = "YOUR_PRIVATE_KEY_WITHOUT_0x"
  const chainId = 1
  const owner = "OWNER_ADDRESS"
  const spender = "SPENDER_ADDRESS"
  const value = 100 // Amount the spender is permitted
  const nonce = 1 // The next valid nonce, use `_nonces()`
  const deadline = 1600093162
  
  const permitParams = {
    types: {
      EIP712Domain: [
        { name: "name", type: "string" },
        { name: "version", type: "string" },
        { name: "chainId", type: "uint256" },
        { name: "verifyingContract", type: "address" },
      ],
      Permit: [
        { name: "owner", type: "address" },
        { name: "spender", type: "address" },
        { name: "value", type: "uint256" },
        { name: "nonce", type: "uint256" },
        { name: "deadline", type: "uint256" },
      ],
    },
    primaryType: "Permit",
    domain: {
      name: "Aave Token",
      version: "1",
      chainId: chainId,
      verifyingContract: aaveTokenAddress,
    },
    message: {
      owner,
      spender,
      value,
      nonce,
      deadline,
    },
  }
  
  const signature = signTypedData_v4(
    Buffer.from(privateKey, "hex"),
    { data: permitParams }
  )
  
  const { v, r, s } = fromRpcSig(signature)
  
  await aaveTokenContract.methods
      .permit({
        owner,
        spender,
        value,
        deadline,
        v,
        r,
        s
      })
      .send()
      .catch((e) => {
          throw Error(`Error permitting: ${e.message}`)
      })
  

• _nonces()

  Returns the next valid nonce to submit when calling permit()