service fee handling

.env.example

@@ -3,5 +3,7 @@ RPC_URL=https://kovan.infura.io/v3/a3f4d001c1fc4a359ea70dd27fd9cb51
 PRIVATE_KEY=
 ETH_MIXER_ADDRESS=0x1Cea940cA15a303A0E01B7F8589F39fF34308DB2
 DAI_MIXER_ADDRESS=0x7ed3fC8042e18db889A0466F49c438bB1410b3c7
+# 25 means 2.5%
+RELAYER_FEE=25
 
 APP_PORT=8000

config.js

@@ -1,20 +1,23 @@
 require('dotenv').config()
 
 module.exports = {
-  netId: process.env.NET_ID || 42,
+  netId: Number(process.env.NET_ID) || 42,
   rpcUrl: process.env.RPC_URL || 'https://kovan.infura.io/v3/a3f4d001c1fc4a359ea70dd27fd9cb51',
   privateKey: process.env.PRIVATE_KEY,
   mixers: [ { 
     address: process.env.ETH_MIXER_ADDRESS,
-    currency: 'eth' 
+    currency: 'eth',
+    amount: '0.1'
   }, 
   { 
     address: process.env.DAI_MIXER_ADDRESS,
-    currency: 'dai' 
+    currency: 'dai',
+    amount: '100'
   } ],
   defaultGasPrice: 2,
   gasOracleUrls: ['https://www.etherchain.org/api/gasPriceOracle', 'https://gasprice.poa.network/'],
   port: process.env.APP_PORT,
   //dai
-  tokens: ['0x6b175474e89094c44da98b954eedeac495271d0f']
+  tokens: ['0x6b175474e89094c44da98b954eedeac495271d0f'],
+  relayerServiceFee: process.env.RELAYER_FEE
 }

src/index.js

@@ -1,5 +1,5 @@
 const express = require('express')
-const { netId, mixers, port } = require('../config')
+const { netId, mixers, port, relayerServiceFee } = require('../config')
 const relayController = require('./relayController')
 const { fetcher, web3 } = require('./instances')
 
@@ -28,7 +28,7 @@ app.get('/', function (req, res) {
 
 app.get('/status', function (req, res) {
   const { ethPrices, gasPrices } = fetcher
-  res.json({ relayerAddress: web3.eth.defaultAccount, mixers, gasPrices, netId, ethPrices })
+  res.json({ relayerAddress: web3.eth.defaultAccount, mixers, gasPrices, netId, ethPrices, relayerServiceFee })
 })
 
 app.post('/relay', relayController)
@@ -44,3 +44,4 @@ console.log(`mixers: ${JSON.stringify(mixers)}`)
 console.log(`gasPrices: ${JSON.stringify(fetcher.gasPrices)}`)
 console.log(`netId: ${netId}`)
 console.log(`ethPrices: ${JSON.stringify(fetcher.ethPrices)}`)
+console.log(`Service fee: ${relayerServiceFee / 10}%`)

src/relayController.js

@@ -21,8 +21,8 @@ async function relay (req, resp) {
     return resp.status(400).json({ error: 'Withdraw arguments are invalid' })
   }
 
-  let currency
-  ( { valid, currency } = isKnownContract(contract))
+  let currency, amount
+  ( { valid, currency, amount } = isKnownContract(contract))
   if (!valid) {
     console.log('Contract does not exist:', contract)
     return resp.status(400).json({ error: 'This relayer does not support the token' })
@@ -73,7 +73,7 @@ async function relay (req, resp) {
 
     gas += 50000
     const ethPrices = fetcher.ethPrices
-    const { isEnough, reason } = isEnoughFee({ gas, gasPrices, currency, refund, ethPrices, fee })
+    const { isEnough, reason } = isEnoughFee({ gas, gasPrices, currency, amount, refund, ethPrices, fee })
     if (!isEnough) {
       console.log(`Wrong fee: ${reason}`)
       return resp.status(400).json({ error: reason })

src/utils.js

@@ -1,5 +1,5 @@
 const { isHexStrict, toBN, toWei } = require('web3-utils')
-const { mixers } = require('../config')
+const { mixers, relayerServiceFee } = require('../config')
 
 function isValidProof(proof) {
   // validator expects `websnarkUtils.toSolidityInput(proof)` output
@@ -46,7 +46,7 @@ function isValidArgs(args) {
 function isKnownContract(contract) {
   for (let i = 0; i < mixers.length; i++) {
     if (mixers[i].address === contract) {
-      return { valid: true, currency: mixers[i].currency }
+      return { valid: true, currency: mixers[i].currency, amount: mixers[i].amount }
     }
   }
   return { valid: false }
@@ -56,12 +56,14 @@ function sleep(ms) {
   return new Promise(resolve => setTimeout(resolve, ms))
 }
 
-function isEnoughFee({ gas, gasPrices, currency, refund, ethPrices, fee }) {
+function isEnoughFee({ gas, gasPrices, currency, amount, refund, ethPrices, fee }) {
+  // TODO tokens can have less then 18 decimals
+  const feePercent = toBN(toWei(amount)).mul(toBN(relayerServiceFee)).div(toBN('1000'))
   const expense = toBN(toWei(gasPrices.fast.toString(), 'gwei')).mul(toBN(gas))
   let desiredFee
   switch (currency) {
     case 'eth': {
-      desiredFee = expense
+      desiredFee = expense.add(feePercent)
       break
     }
     case 'dai': {
@@ -69,10 +71,11 @@ function isEnoughFee({ gas, gasPrices, currency, refund, ethPrices, fee }) {
         expense.add(refund)
           .mul(toBN(10 ** 18))
           .div(toBN(ethPrices.dai))
+      desiredFee = desiredFee.add(feePercent)
       break
     }
   }
-  console.log('desired fee', desiredFee.toString())
+  console.log('desired fee, feePercent', desiredFee.toString(), feePercent.toString())
   if (fee.lt(desiredFee)) {
     return { isEnough: false, reason: 'Not enough fee' }
   }