change fee structure

contracts/ERC20Mixer.sol

@@ -15,65 +15,37 @@ import "./Mixer.sol";
 
 contract ERC20Mixer is Mixer {
   address public token;
-  // mixed token amount
-  uint256 public tokenDenomination;
   // ether value to cover network fee (for relayer) and to have some ETH on a brand new address
-  uint256 public etherFeeDenomination;
+  uint256 public userEther;
 
   constructor(
     address _verifier,
-    uint256 _etherFeeDenomination,
+    uint256 _userEther,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
     address payable _operator,
     address _token,
-    uint256 _tokenDenomination
-  ) Mixer(_verifier, _merkleTreeHeight, _emptyElement, _operator) public {
+    uint256 _mixDenomination
+  ) Mixer(_verifier, _mixDenomination, _merkleTreeHeight, _emptyElement, _operator) public {
     token = _token;
-    tokenDenomination = _tokenDenomination;
-    etherFeeDenomination = _etherFeeDenomination;
+    userEther = _userEther;
   }
 
-  /**
-    @dev Deposit funds into the mixer. The caller must send ETH value equal to `etherFeeDenomination` of this mixer.
-    The caller also has to have at least `tokenDenomination` amount approved for the mixer.
-    @param commitment the note commitment, which is PedersenHash(nullifier + secret)
-  */
-  function deposit(uint256 commitment) public payable {
-    require(msg.value == etherFeeDenomination, "Please send `etherFeeDenomination` ETH along with transaction");
-    transferFrom(msg.sender, address(this), tokenDenomination);
-    _deposit(commitment);
-
-    emit Deposit(commitment, next_index - 1, block.timestamp);
+  function _processDeposit() internal {
+    require(msg.value == userEther, "Please send `userEther` ETH along with transaction");
+    safeErc20TransferFrom(msg.sender, address(this), mixDenomination);
   }
 
-  /**
-    @dev Withdraw deposit from the mixer. `a`, `b`, and `c` are zkSNARK proof data, and input is an array of circuit public inputs
-    `input` array consists of:
-      - merkle root of all deposits in the mixer
-      - hash of unique deposit nullifier to prevent double spends
-      - 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[4] memory input) public {
-    _withdraw(a, b, c, input);
-    address payable receiver = address(input[2]);
-    uint256 fee = input[3];
-    uint256 nullifierHash = input[1];
+  function _processWithdraw(address payable _receiver, uint256 _fee) internal {
+    _receiver.transfer(userEther);
 
-    require(fee < etherFeeDenomination, "Fee exceeds transfer value");
-    receiver.transfer(etherFeeDenomination - fee);
-
-    if (fee > 0) {
-      operator.transfer(fee);
+    safeErc20Transfer(_receiver, mixDenomination - _fee);
+    if (_fee > 0) {
+      safeErc20Transfer(operator, _fee);
+    }
   }
 
-    transfer(receiver, tokenDenomination);
-
-    emit Withdraw(receiver, nullifierHash, fee);
-  }
-
-  function transferFrom(address from, address to, uint256 amount) internal {
+  function safeErc20TransferFrom(address from, address to, uint256 amount) internal {
     bool success;
     bytes memory data;
     bytes4 transferFromSelector = 0x23b872dd;
@@ -92,7 +64,7 @@ contract ERC20Mixer is Mixer {
     }
   }
 
-  function transfer(address to, uint256 amount) internal {
+  function safeErc20Transfer(address to, uint256 amount) internal {
     bool success;
     bytes memory data;
     bytes4 transferSelector = 0xa9059cbb;

contracts/ETHMixer.sol

@@ -14,49 +14,23 @@ pragma solidity ^0.5.8;
 import "./Mixer.sol";
 
 contract ETHMixer is Mixer {
-  uint256 public etherDenomination;
-
   constructor(
     address _verifier,
-    uint256 _etherDenomination,
+    uint256 _mixDenomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
     address payable _operator
-  ) Mixer(_verifier, _merkleTreeHeight, _emptyElement, _operator) public {
-    etherDenomination = _etherDenomination;
+  ) Mixer(_verifier, _mixDenomination, _merkleTreeHeight, _emptyElement, _operator) public {
   }
 
-  /**
-    @dev Deposit funds into mixer. The caller must send value equal to `etherDenomination` of this mixer.
-    @param commitment the note commitment, which is PedersenHash(nullifier + secret)
-  */
-  function deposit(uint256 commitment) public payable {
-    require(msg.value == etherDenomination, "Please send `etherDenomination` ETH along with transaction");
-    _deposit(commitment);
-
-    emit Deposit(commitment, next_index - 1, block.timestamp);
+  function _processWithdraw(address payable _receiver, uint256 _fee) internal {
+    _receiver.transfer(mixDenomination - _fee);
+    if (_fee > 0) {
+      operator.transfer(_fee);
+    }
   }
 
-  /**
-    @dev Withdraw deposit from the mixer. `a`, `b`, and `c` are zkSNARK proof data, and input is an array of circuit public inputs
-    `input` array consists of:
-      - merkle root of all deposits in the mixer
-      - hash of unique deposit nullifier to prevent double spends
-      - 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[4] memory input) public {
-    _withdraw(a, b, c, input);
-    address payable receiver = address(input[2]);
-    uint256 fee = input[3];
-    uint256 nullifierHash = input[1];
-
-    require(fee < etherDenomination, "Fee exceeds transfer value");
-    receiver.transfer(etherDenomination - fee);
-    if (fee > 0) {
-      operator.transfer(fee);
-    }
-
-    emit Withdraw(receiver, nullifierHash, fee);
+  function _processDeposit() internal {
+    require(msg.value == mixDenomination, "Please send `mixDenomination` ETH along with transaction");
   }
 }

contracts/Mixer.sol

@@ -26,6 +26,7 @@ contract Mixer is MerkleTreeWithHistory {
   // we store all commitments just to prevent accidental deposits with the same commitment
   mapping(uint256 => bool) public commitments;
   IVerifier public verifier;
+  uint256 public mixDenomination;
 
   event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
   event Withdraw(address to, uint256 nullifierHash, uint256 fee);
@@ -39,31 +40,54 @@ contract Mixer is MerkleTreeWithHistory {
   */
   constructor(
     address _verifier,
+    uint256 _mixDenomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
     address payable _operator
   ) MerkleTreeWithHistory(_merkleTreeHeight, _emptyElement) public {
     verifier = IVerifier(_verifier);
     operator = _operator;
+    mixDenomination = _mixDenomination;
   }
-
-  function _deposit(uint256 commitment) internal {
+  /**
+    @dev Deposit funds into mixer. The caller must send value equal to `mixDenomination` of this mixer.
+    @param commitment the note commitment, which is PedersenHash(nullifier + secret)
+  */
+  /**
+    @dev Deposit funds into the mixer. The caller must send ETH value equal to `userEther` of this mixer.
+    The caller also has to have at least `mixDenomination` amount approved for the mixer.
+    @param commitment the note commitment, which is PedersenHash(nullifier + secret)
+  */
+  function deposit(uint256 commitment) public payable {
     require(isDepositsEnabled, "deposits disabled");
     require(!commitments[commitment], "The commitment has been submitted");
+    _processDeposit();
     _insert(commitment);
     commitments[commitment] = true;
-  }
 
-  function _withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) internal {
+    emit Deposit(commitment, next_index - 1, block.timestamp);
+  }
+  /**
+    @dev Withdraw deposit from the mixer. `a`, `b`, and `c` are zkSNARK proof data, and input is an array of circuit public inputs
+    `input` array consists of:
+      - merkle root of all deposits in the mixer
+      - hash of unique deposit nullifier to prevent double spends
+      - 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[4] memory input) public {
     uint256 root = input[0];
     uint256 nullifierHash = input[1];
-
+    address payable receiver = address(input[2]);
+    uint256 fee = input[3];
+    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, fee);
+    emit Withdraw(receiver, nullifierHash, fee);
   }
 
   function toggleDeposits() external {
@@ -79,4 +103,8 @@ contract Mixer is MerkleTreeWithHistory {
   function isSpent(uint256 nullifier) public view returns(bool) {
     return nullifierHashes[nullifier];
   }
+
+  function _processDeposit() internal {}
+  function _processWithdraw(address payable _receiver, uint256 _fee) internal {}
+
 }

test/ERC20Mixer.test.js

@@ -122,7 +122,6 @@ contract('ERC20Mixer', accounts => {
       balanceUserAfter.should.be.eq.BN(toBN(balanceUserBefore).sub(toBN(tokenDenomination)))
 
       const { root, path_elements, path_index } = await tree.path(0)
-
       // Circuit input
       const input = stringifyBigInts({
         // public
@@ -149,7 +148,6 @@ contract('ERC20Mixer', accounts => {
       const ethBalanceRecieverBefore = await web3.eth.getBalance(toHex(receiver.toString()))
       let isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(false)
-
       // Uncomment to measure gas usage
       // gas = await mixer.withdraw.estimateGas(pi_a, pi_b, pi_c, publicSignals, { from: relayer, gasPrice: '0' })
       // console.log('withdraw gas:', gas)
@@ -161,12 +159,11 @@ contract('ERC20Mixer', accounts => {
       const balanceRecieverAfter = await token.balanceOf(toHex(receiver.toString()))
       const ethBalanceRecieverAfter = await web3.eth.getBalance(toHex(receiver.toString()))
       const feeBN = toBN(fee.toString())
-      balanceMixerAfter.should.be.eq.BN(toBN(balanceMixerBefore).sub(toBN(tokenDenomination)))
+      balanceMixerAfter.should.be.eq.BN(toBN(balanceMixerBefore).sub(toBN(value)))
       balanceRelayerAfter.should.be.eq.BN(toBN(balanceRelayerBefore))
-      ethBalanceOperatorAfter.should.be.eq.BN(toBN(ethBalanceOperatorBefore).add(feeBN))
-      balanceRecieverAfter.should.be.eq.BN(toBN(balanceRecieverBefore).add(toBN(tokenDenomination)))
-      ethBalanceRecieverAfter.should.be.eq.BN(toBN(ethBalanceRecieverBefore).add(toBN(value)).sub(feeBN))
-
+      ethBalanceOperatorAfter.should.be.eq.BN(toBN(ethBalanceOperatorBefore))
+      balanceRecieverAfter.should.be.eq.BN(toBN(balanceRecieverBefore).add(toBN(tokenDenomination).sub(feeBN)))
+      ethBalanceRecieverAfter.should.be.eq.BN(toBN(ethBalanceRecieverBefore).add(toBN(value)))
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
@@ -258,9 +255,9 @@ contract('ERC20Mixer', accounts => {
     })
     it.skip('should work with REAL DAI', async () => {
       // dont forget to specify your token in .env
-      // and sent `tokenDenomination` to accounts[0] (0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1)
+      // and send `tokenDenomination` to accounts[0] (0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1)
       // run ganache as
-      // ganache-cli --fork https://kovan.infura.io/v3/27a9649f826b4e31a83e07ae09a87448@13146218 -d --keepAliveTimeout 20
+      // npx ganache-cli --fork https://kovan.infura.io/v3/27a9649f826b4e31a83e07ae09a87448@13146218 -d --keepAliveTimeout 20
       const deposit = generateDeposit()
       const user = accounts[4]
       const userBal = await token.balanceOf(user)

test/ETHMixer.test.js

@@ -90,7 +90,7 @@ contract('ETHMixer', accounts => {
 
   describe('#constructor', () => {
     it('should initialize', async () => {
-      const etherDenomination = await mixer.etherDenomination()
+      const etherDenomination = await mixer.mixDenomination()
       etherDenomination.should.be.eq.BN(toBN(value))
     })
   })