make the relayer great again

circuits/withdraw.circom

@@ -31,6 +31,8 @@ template Withdraw(levels, rounds) {
     signal input root;
     signal input nullifierHash;
     signal input receiver; // not taking part in any computations
+    signal input relayer; // not taking part in any computations
+    signal input fee; // not taking part in any computations
 
     signal private input nullifier;
     signal private input secret;
@@ -55,7 +57,11 @@ template Withdraw(levels, rounds) {
     // Most likely it is not required, but it's better to stay on the safe side and it only takes 2 constraints
     // Squares are used to prevent optimizer from removing those constraints
     signal receiverSquare;
+    signal feeSquare;
+    signal relayerSquare;
     receiverSquare <== receiver * receiver;
+    feeSquare <== fee * fee;
+    relayerSquare <== relayer * relayer;
 }
 
 component main = Withdraw(16, 220);

contracts/ETHMixer.sol

@@ -25,86 +25,14 @@ contract ETHMixer is Mixer, GSNRecipient {
   ) Mixer(_verifier, _mixDenomination, _merkleTreeHeight, _emptyElement, _operator) public {
   }
 
-  function _processWithdraw(address payable _receiver) internal {
-    _receiver.transfer(mixDenomination);
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee) internal {
+    _receiver.transfer(mixDenomination - _fee);
+    if (_fee > 0) {
+      _relayer.transfer(_fee);
+    }
   }
 
   function _processDeposit() internal {
     require(msg.value == mixDenomination, "Please send `mixDenomination` ETH along with transaction");
   }
-
-  function withdrawViaRelayer(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[3] memory input) public {
-    uint256 root = input[0];
-    uint256 nullifierHash = input[1];
-    address receiver = address(input[2]);
-    require(!nullifierHashes[nullifierHash], "The note has been already spent");
-
-    require(isKnownRoot(root), "Cannot find your merkle root"); // Make sure to use a recent one
-    require(verifier.verifyProof(a, b, c, input), "Invalid withdraw proof");
-    nullifierHashes[nullifierHash] = true;
-    emit Withdraw(receiver, nullifierHash, tx.origin);
-    // we will process withdraw in postRelayedCall func
-  }
-
-  // gsn related stuff
-  // this func is called by a Relayer via the RelayerHub before sending a tx
-  function acceptRelayedCall(
-    address relay,
-    address from,
-    bytes memory encodedFunction,
-    uint256 transactionFee,
-    uint256 gasPrice,
-    uint256 gasLimit,
-    uint256 nonce,
-    bytes memory approvalData,
-    uint256 maxPossibleCharge
-  ) public view returns (uint256, bytes memory) {
-    // think of a withdraw dry-run
-    if (!compareBytesWithSelector(encodedFunction, this.withdrawViaRelayer.selector)) {
-      return (1, "Only withdrawViaRelayer can be called");
-    }
-    bytes memory recipient;
-    assembly {
-      let dataPointer := add(encodedFunction, 32)
-      let recipientPointer := mload(add(dataPointer, 324)) // 4 + (8 * 32) + (32) + (32) == selector + proof + root + nullifier
-      mstore(recipient, 32) // save array length
-      mstore(add(recipient, 32), recipientPointer) // save recipient address
-    }
-    return (0, recipient);
-  }
-
-  // this func is called by RelayerHub right before calling a target func
-  function preRelayedCall(bytes calldata /*context*/) external returns (bytes32) {}
-
-  event Debug(uint actualCharge, bytes context, address recipient);
-  // this func is called by RelayerHub right after calling a target func
-  function postRelayedCall(bytes memory context, bool /*success*/, uint actualCharge, bytes32 /*preRetVal*/) public {
-    IRelayHub relayHub = IRelayHub(getHubAddr());
-    address payable recipient;
-    assembly {
-      recipient := mload(add(context, 32))
-    }
-    emit Debug(actualCharge, context, recipient);
-
-    recipient.transfer(mixDenomination - actualCharge);
-    relayHub.depositFor.value(actualCharge)(address(this));
-    // or we can send actualCharge somewhere else...
-  }
-
-  function compareBytesWithSelector(bytes memory data, bytes4 sel) internal pure returns (bool) {
-    return data[0] == sel[0]
-        && data[1] == sel[1]
-        && data[2] == sel[2]
-        && data[3] == sel[3];
-  }
-
-  function withdrawFundsFromHub(uint256 amount, address payable dest) external {
-    require(msg.sender == operator, "unauthorized");
-    IRelayHub(getHubAddr()).withdraw(amount, dest);
-  }
-
-  function upgradeRelayHub(address newRelayHub) external {
-    require(msg.sender == operator, "unauthorized");
-    _upgradeRelayHub(newRelayHub);
-  }
 }

contracts/Mixer.sol

@@ -14,7 +14,7 @@ pragma solidity ^0.5.8;
 import "./MerkleTreeWithHistory.sol";
 
 contract IVerifier {
-  function verifyProof(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[3] memory input) public returns(bool);
+  function verifyProof(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[5] memory input) public returns(bool);
 }
 
 contract Mixer is MerkleTreeWithHistory {
@@ -29,7 +29,7 @@ contract Mixer is MerkleTreeWithHistory {
   uint256 public mixDenomination;
 
   event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
-  event Withdraw(address to, uint256 nullifierHash, address indexed relayer);
+  event Withdraw(address to, uint256 nullifierHash, address indexed relayer, uint fee);
 
   /**
     @dev The constructor
@@ -75,17 +75,20 @@ contract Mixer is MerkleTreeWithHistory {
       - the receiver of funds
       - optional fee that goes to the transaction sender (usually a relay)
   */
-  function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[3] memory input) public {
+  function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[5] memory input) public {
     uint256 root = input[0];
     uint256 nullifierHash = input[1];
     address payable receiver = address(input[2]);
+    address payable relayer = address(input[3]);
+    uint256 fee = input[4];
+    require(fee < mixDenomination, "Fee exceeds transfer value");
     require(!nullifierHashes[nullifierHash], "The note has been already spent");
 
     require(isKnownRoot(root), "Cannot find your merkle root"); // Make sure to use a recent one
     require(verifier.verifyProof(a, b, c, input), "Invalid withdraw proof");
     nullifierHashes[nullifierHash] = true;
-    _processWithdraw(receiver);
-    emit Withdraw(receiver, nullifierHash, receiver);
+    _processWithdraw(receiver, relayer, fee);
+    emit Withdraw(receiver, nullifierHash, relayer, fee);
   }
 
   function toggleDeposits() external {
@@ -103,5 +106,5 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   function _processDeposit() internal {}
-  function _processWithdraw(address payable _receiver) internal {}
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee) internal {}
 }

migrations/4_deploy_eth_mixer.js

@@ -13,6 +13,6 @@ module.exports = function(deployer, network, accounts) {
     await ETHMixer.link(MiMC, miMC.address)
     const mixer = await deployer.deploy(ETHMixer, verifier.address, ETH_AMOUNT, MERKLE_TREE_HEIGHT, EMPTY_ELEMENT, accounts[0])
     console.log('ETHMixer\'s address ', mixer.address)
-    const tx = await mixer.initialize()
+    // const tx = await mixer.initialize()
   })
 }

package.json

@@ -33,9 +33,9 @@
     "eslint": "^6.2.2",
     "ganache-cli": "^6.4.5",
     "snarkjs": "^0.1.16",
-    "truffle": "^5.0.27",
-    "truffle-artifactor": "^4.0.23",
-    "truffle-contract": "^4.0.24",
+    "truffle": "^5.0.37",
+    "truffle-artifactor": "^4.0.30",
+    "truffle-contract": "^4.0.31",
     "truffle-hdwallet-provider": "^1.0.14",
     "web3": "^1.0.0-beta.55",
     "web3-utils": "^1.0.0-beta.55",

test/GSNsupport.test.js

@@ -45,7 +45,7 @@ function getRandomReceiver() {
   return receiver
 }
 
-contract('GSN support', accounts => {
+contract.skip('GSN support', accounts => {
   let mixer
   let gsnMixer
   let relayHubAddress
@@ -93,7 +93,7 @@ contract('GSN support', accounts => {
   })
 
   describe('#withdrawViaRelayer', () => {
-    it.only('should work', async () => {
+    it('should work', async () => {
       const gasPrice = toBN('20000000000')
       const relayerTxFee = 10 // 20%
       const deposit = generateDeposit()