test with real DAI and USDT

.env.example

@@ -5,3 +5,12 @@ TOKEN_AMOUNT=100000000000000000
 EMPTY_ELEMENT=1337
 PRIVATE_KEY=
 ERC20_TOKEN=
+
+# DAI mirror in Kovan
+#ERC20_TOKEN=0xd2b1a6b34f4a68425e7c28b4db5a37be3b7a4947
+# block when 0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1 has some DAI is 13146218
+
+# USDT mirror in Kovan
+#ERC20_TOKEN=0xf3e0d7bf58c5d455d31ef1c2d5375904df525105
+#TOKEN_AMOUNT=1000000
+# block when 0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1 has some USDT is 13147586

contracts/ERC20Mixer.sol

@@ -12,10 +12,9 @@
 pragma solidity ^0.5.8;
 
 import "./Mixer.sol";
-import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
 
 contract ERC20Mixer is Mixer {
-  IERC20 public token;
+  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
@@ -27,7 +26,7 @@ contract ERC20Mixer is Mixer {
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
     address payable _operator,
-    IERC20 _token,
+    address _token,
     uint256 _tokenDenomination
   ) Mixer(_verifier, _merkleTreeHeight, _emptyElement, _operator) public {
     token = _token;
@@ -42,7 +41,7 @@ contract ERC20Mixer is Mixer {
   */
   function deposit(uint256 commitment) public payable {
     require(msg.value == etherFeeDenomination, "Please send `etherFeeDenomination` ETH along with transaction");
-    require(token.transferFrom(msg.sender, address(this), tokenDenomination), "Approve before using");
+    transferFrom(msg.sender, address(this), tokenDenomination);
     _deposit(commitment);
 
     emit Deposit(commitment, next_index - 1, block.timestamp);
@@ -69,8 +68,46 @@ contract ERC20Mixer is Mixer {
       operator.transfer(fee);
     }
 
-    token.transfer(receiver, tokenDenomination);
+    transfer(receiver, tokenDenomination);
 
     emit Withdraw(receiver, nullifierHash, fee);
   }
+
+  function transferFrom(address from, address to, uint256 amount) internal {
+    bool success;
+    bytes memory data;
+    bytes4 transferFromSelector = 0x23b872dd;
+    (success, data) = token.call(
+        abi.encodeWithSelector(
+            transferFromSelector,
+            from, to, amount
+        )
+    );
+    require(success, "not enough allowed tokens");
+    if (data.length > 0) {
+      assembly {
+        success := mload(add(data, 0x20))
+      }
+      require(success, "not enough allowed tokens");
+    }
+  }
+
+  function transfer(address to, uint256 amount) internal {
+    bool success;
+    bytes memory data;
+    bytes4 transferSelector = 0xa9059cbb;
+    (success, data) = token.call(
+        abi.encodeWithSelector(
+            transferSelector,
+            to, amount
+        )
+    );
+    require(success, "not enough tokens");
+    if (data.length > 0) {
+      assembly {
+        success := mload(add(data, 0x20))
+      }
+      require(success, "not enough tokens");
+    }
+  }
 }

contracts/Mocks/IUSDT.sol

@@ -0,0 +1,18 @@
+contract ERC20Basic {
+    uint public _totalSupply;
+    function totalSupply() public view returns (uint);
+    function balanceOf(address who) public view returns (uint);
+    function transfer(address to, uint value) public;
+    event Transfer(address indexed from, address indexed to, uint value);
+}
+
+/**
+ * @title ERC20 interface
+ * @dev see https://github.com/ethereum/EIPs/issues/20
+ */
+contract IUSDT is ERC20Basic {
+    function allowance(address owner, address spender) public view returns (uint);
+    function transferFrom(address from, address to, uint value) public;
+    function approve(address spender, uint value) public;
+    event Approval(address indexed owner, address indexed spender, uint value);
+}

migrations/5_deploy_erc20_mixer.js

@@ -13,7 +13,7 @@ module.exports = function(deployer, network, accounts) {
     const miMC = await MiMC.deployed()
     await ERC20Mixer.link(MiMC, miMC.address)
     let token = ERC20_TOKEN
-    if(deployer.network !== 'mainnet') {
+    if(token === '') {
       const tokenInstance = await deployer.deploy(ERC20Mock)
       token = tokenInstance.address
     }

test/ERC20Mixer.test.js

@@ -10,7 +10,8 @@ const { takeSnapshot, revertSnapshot } = require('../lib/ganacheHelper')
 
 const Mixer = artifacts.require('./ERC20Mixer.sol')
 const Token = artifacts.require('./ERC20Mock.sol')
-const { ETH_AMOUNT, TOKEN_AMOUNT, MERKLE_TREE_HEIGHT, EMPTY_ELEMENT } = process.env
+const USDTToken = artifacts.require('./IUSDT.sol')
+const { ETH_AMOUNT, TOKEN_AMOUNT, MERKLE_TREE_HEIGHT, EMPTY_ELEMENT, ERC20_TOKEN } = process.env
 
 const websnarkUtils = require('websnark/src/utils')
 const buildGroth16 = require('websnark/src/groth16')
@@ -45,11 +46,12 @@ function getRandomReceiver() {
 contract('ERC20Mixer', accounts => {
   let mixer
   let token
+  let usdtToken
   const sender = accounts[0]
   const operator = accounts[0]
   const levels = MERKLE_TREE_HEIGHT || 16
   const zeroValue = EMPTY_ELEMENT || 1337
-  const tokenDenomination = TOKEN_AMOUNT || '1000000000000000000' // 1 ether
+  let tokenDenomination = TOKEN_AMOUNT || '1000000000000000000' // 1 ether
   const value = ETH_AMOUNT || '1000000000000000000' // 1 ether
   let snapshotId
   let prefix = 'test'
@@ -69,8 +71,13 @@ contract('ERC20Mixer', accounts => {
       prefix,
     )
     mixer = await Mixer.deployed()
-    token = await Token.deployed()
+    if (ERC20_TOKEN) {
-    await token.mint(sender, tokenDenomination)
+      token = await Token.at(ERC20_TOKEN)
+      usdtToken = await USDTToken.at(ERC20_TOKEN)
+    } else {
+      token = await Token.deployed()
+      await token.mint(sender, tokenDenomination)
+    }
     snapshotId = await takeSnapshot()
     groth16 = await buildGroth16()
     circuit = require('../build/circuits/withdraw.json')
@@ -161,6 +168,167 @@ contract('ERC20Mixer', accounts => {
       ethBalanceRecieverAfter.should.be.eq.BN(toBN(ethBalanceRecieverBefore).add(toBN(value)).sub(feeBN))
 
 
+      logs[0].event.should.be.equal('Withdraw')
+      logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.fee.should.be.eq.BN(feeBN)
+      isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
+      isSpent.should.be.equal(true)
+    })
+
+    it.skip('should work with REAL USDT', async () => {
+      // dont forget to specify your token in .env
+      // USDT decimals is 6, so TOKEN_AMOUNT=1000000
+      // and sent `tokenDenomination` to accounts[0] (0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1)
+      // run ganache as
+      // ganache-cli --fork https://kovan.infura.io/v3/27a9649f826b4e31a83e07ae09a87448@13147586  -d --keepAliveTimeout 20
+      const deposit = generateDeposit()
+      const user = accounts[4]
+      const userBal = await usdtToken.balanceOf(user)
+      console.log('userBal', userBal.toString())
+      const senderBal = await usdtToken.balanceOf(sender)
+      console.log('senderBal', senderBal.toString())
+      await tree.insert(deposit.commitment)
+      await usdtToken.transfer(user, tokenDenomination, { from: sender })
+      console.log('transfer done')
+
+      const balanceUserBefore = await usdtToken.balanceOf(user)
+      console.log('balanceUserBefore', balanceUserBefore.toString())
+      await usdtToken.approve(mixer.address, tokenDenomination, { from: user })
+      console.log('approve done')
+      const allowanceUser = await usdtToken.allowance(user, mixer.address)
+      console.log('allowanceUser', allowanceUser.toString())
+      await mixer.deposit(toBN(deposit.commitment.toString()), { value, from: user, gasPrice: '0' })
+      console.log('deposit done')
+
+      const balanceUserAfter = await usdtToken.balanceOf(user)
+      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
+        root,
+        nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        receiver,
+        fee,
+
+        // private
+        nullifier: deposit.nullifier,
+        secret: deposit.secret,
+        pathElements: path_elements,
+        pathIndex: path_index,
+      })
+
+
+      const proof = await websnarkUtils.genWitnessAndProve(groth16, input, circuit, proving_key)
+      const { pi_a, pi_b, pi_c, publicSignals } = websnarkUtils.toSolidityInput(proof)
+
+      const balanceMixerBefore = await usdtToken.balanceOf(mixer.address)
+      const balanceRelayerBefore = await usdtToken.balanceOf(relayer)
+      const ethBalanceOperatorBefore = await web3.eth.getBalance(operator)
+      const balanceRecieverBefore = await usdtToken.balanceOf(toHex(receiver.toString()))
+      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)
+      const { logs } = await mixer.withdraw(pi_a, pi_b, pi_c, publicSignals, { from: relayer, gasPrice: '0' })
+
+      const balanceMixerAfter = await usdtToken.balanceOf(mixer.address)
+      const balanceRelayerAfter = await usdtToken.balanceOf(relayer)
+      const ethBalanceOperatorAfter = await web3.eth.getBalance(operator)
+      const balanceRecieverAfter = await usdtToken.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)))
+      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))
+
+
+      logs[0].event.should.be.equal('Withdraw')
+      logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
+      logs[0].args.fee.should.be.eq.BN(feeBN)
+      isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
+      isSpent.should.be.equal(true)
+    })
+    it.skip('should work with REAL DAI', async () => {
+      // dont forget to specify your token in .env
+      // and sent `tokenDenomination` to accounts[0] (0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1)
+      // run ganache as
+      // 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)
+      console.log('userBal', userBal.toString())
+      const senderBal = await token.balanceOf(sender)
+      console.log('senderBal', senderBal.toString())
+      await tree.insert(deposit.commitment)
+      await token.transfer(user, tokenDenomination, { from: sender })
+      console.log('transfer done')
+
+      const balanceUserBefore = await token.balanceOf(user)
+      console.log('balanceUserBefore', balanceUserBefore.toString())
+      await token.approve(mixer.address, tokenDenomination, { from: user })
+      console.log('approve done')
+      await mixer.deposit(toBN(deposit.commitment.toString()), { value, from: user, gasPrice: '0' })
+      console.log('deposit done')
+
+      const balanceUserAfter = await token.balanceOf(user)
+      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
+        root,
+        nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
+        receiver,
+        fee,
+
+        // private
+        nullifier: deposit.nullifier,
+        secret: deposit.secret,
+        pathElements: path_elements,
+        pathIndex: path_index,
+      })
+
+
+      const proof = await websnarkUtils.genWitnessAndProve(groth16, input, circuit, proving_key)
+      const { pi_a, pi_b, pi_c, publicSignals } = websnarkUtils.toSolidityInput(proof)
+
+      const balanceMixerBefore = await token.balanceOf(mixer.address)
+      const balanceRelayerBefore = await token.balanceOf(relayer)
+      const ethBalanceOperatorBefore = await web3.eth.getBalance(operator)
+      const balanceRecieverBefore = await token.balanceOf(toHex(receiver.toString()))
+      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)
+      const { logs } = await mixer.withdraw(pi_a, pi_b, pi_c, publicSignals, { from: relayer, gasPrice: '0' })
+      console.log('withdraw done')
+
+      const balanceMixerAfter = await token.balanceOf(mixer.address)
+      const balanceRelayerAfter = await token.balanceOf(relayer)
+      const ethBalanceOperatorAfter = await web3.eth.getBalance(operator)
+      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)))
+      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))
+
+
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
       logs[0].args.fee.should.be.eq.BN(feeBN)