feat(emp): add trimExcess function to send excess tokens

packages/core/contracts/financial-templates/expiring-multiparty/ExpiringMultiPartyCreator.sol

@@ -38,6 +38,7 @@ contract ExpiringMultiPartyCreator is ContractCreator, Testable, Lockable {
         FixedPoint.Unsigned minSponsorTokens;
         uint256 withdrawalLiveness;
         uint256 liquidationLiveness;
+        address excessTokenBeneficiary;
     }
     // - Address of TokenFactory to pass into newly constructed ExpiringMultiParty contracts
     address public tokenFactoryAddress;
@@ -93,6 +94,7 @@ contract ExpiringMultiPartyCreator is ContractCreator, Testable, Lockable {
         require(bytes(params.syntheticSymbol).length != 0, "Missing synthetic symbol");
         require(params.withdrawalLiveness != 0, "Withdrawal liveness cannot be 0");
         require(params.liquidationLiveness != 0, "Liquidation liveness cannot be 0");
+        require(params.excessTokenBeneficiary != address(0), "Token Beneficiary cannot be 0x0");
         require(params.expirationTimestamp > now, "Invalid expiration time");
         _requireWhitelistedCollateral(params.collateralAddress);
 
@@ -117,5 +119,6 @@ contract ExpiringMultiPartyCreator is ContractCreator, Testable, Lockable {
         constructorParams.minSponsorTokens = params.minSponsorTokens;
         constructorParams.withdrawalLiveness = params.withdrawalLiveness;
         constructorParams.liquidationLiveness = params.liquidationLiveness;
+        constructorParams.excessTokenBeneficiary = params.excessTokenBeneficiary;
     }
 }

packages/core/contracts/financial-templates/expiring-multiparty/Liquidatable.sol

@@ -61,6 +61,7 @@ contract Liquidatable is PricelessPositionManager {
         address finderAddress;
         address tokenFactoryAddress;
         address timerAddress;
+        address excessTokenBeneficiary;
         bytes32 priceFeedIdentifier;
         string syntheticName;
         string syntheticSymbol;
@@ -165,7 +166,8 @@ contract Liquidatable is PricelessPositionManager {
             params.syntheticSymbol,
             params.tokenFactoryAddress,
             params.minSponsorTokens,
-            params.timerAddress
+            params.timerAddress,
+            params.excessTokenBeneficiary
         )
         nonReentrant()
     {

packages/core/contracts/financial-templates/expiring-multiparty/PricelessPositionManager.sol

@@ -82,6 +82,9 @@ contract PricelessPositionManager is FeePayer, AdministrateeInterface {
     // The expiry price pulled from the DVM.
     FixedPoint.Unsigned public expiryPrice;
 
+    // The excessTokenBeneficiary of any excess tokens added to the contract.
+    address public excessTokenBeneficiary;
+
     /****************************************
      *                EVENTS                *
      ****************************************/
@@ -149,6 +152,8 @@ contract PricelessPositionManager is FeePayer, AdministrateeInterface {
      * @param _tokenFactoryAddress deployed UMA token factory to create the synthetic token.
      * @param _minSponsorTokens minimum amount of collateral that must exist at any time in a position.
      * @param _timerAddress Contract that stores the current time in a testing environment.
+     * @param _excessTokenBeneficiary Beneficiary to which all excess token balances that accrue in the contract can be
+     * sent.
      * Must be set to 0x0 for production environments that use live time.
      */
     constructor(
@@ -161,7 +166,8 @@ contract PricelessPositionManager is FeePayer, AdministrateeInterface {
         string memory _syntheticSymbol,
         address _tokenFactoryAddress,
         FixedPoint.Unsigned memory _minSponsorTokens,
-        address _timerAddress
+        address _timerAddress,
+        address _excessTokenBeneficiary
     ) public FeePayer(_collateralAddress, _finderAddress, _timerAddress) nonReentrant() {
         require(_expirationTimestamp > getCurrentTime(), "Invalid expiration in future");
         require(_getIdentifierWhitelist().isIdentifierSupported(_priceIdentifier), "Unsupported price identifier");
@@ -172,6 +178,7 @@ contract PricelessPositionManager is FeePayer, AdministrateeInterface {
         tokenCurrency = tf.createToken(_syntheticName, _syntheticSymbol, 18);
         minSponsorTokens = _minSponsorTokens;
         priceIdentifier = _priceIdentifier;
+        excessTokenBeneficiary = _excessTokenBeneficiary;
     }
 
     /****************************************
@@ -607,6 +614,25 @@ contract PricelessPositionManager is FeePayer, AdministrateeInterface {
         return;
     }
 
+    /**
+     * @notice Drains any excess balance of the provided ERC20 token to a pre-selected beneficiary.
+     * @dev This will drain down to the amount of tracked collateral and drain the full balance of any other token.
+     * @param token address of the ERC20 token whose excess balance should be drained.
+     */
+    function trimExcess(IERC20 token) external fees() nonReentrant() returns (FixedPoint.Unsigned memory amount) {
+        FixedPoint.Unsigned memory balance = FixedPoint.Unsigned(token.balanceOf(address(this)));
+
+        if (address(token) == address(collateralCurrency)) {
+            // If it is the collateral currency, send only the amount that the contract is not tracking.
+            // Note: this could be due to rounding error or balance-changing tokens, like aTokens.
+            amount = balance.sub(_pfc());
+        } else {
+            // If it's not the collateral currency, send the entire balance.
+            amount = balance;
+        }
+        token.safeTransfer(excessTokenBeneficiary, amount.rawValue);
+    }
+
     /**
      * @notice Accessor method for a sponsor's collateral.
      * @dev This is necessary because the struct returned by the positions() method shows

packages/core/scripts/DeploySyntheticTokens.js

@@ -10,6 +10,7 @@ const AddressWhitelist = artifacts.require("AddressWhitelist");
 const ExpiringMultiPartyCreator = artifacts.require("ExpiringMultiPartyCreator");
 const IdentifierWhitelist = artifacts.require("IdentifierWhitelist");
 const Registry = artifacts.require("Registry");
+const Store = artifacts.require("Store");
 
 const collateral = {
   "Kovan DAI": "0x08ae34860fbfe73e223596e65663683973c72dd3"
@@ -65,6 +66,7 @@ const actualDeploy = async inputCsv => {
   const deployer = (await web3.eth.getAccounts())[0];
   const expiringMultiPartyCreator = await ExpiringMultiPartyCreator.deployed();
   const identifierWhitelist = await IdentifierWhitelist.deployed();
+  const store = await Store.deployed();
 
   // Add EMP as a registered financial contract template factory.
   const registry = await Registry.deployed();
@@ -99,7 +101,8 @@ const actualDeploy = async inputCsv => {
       disputeBondPct: percentToFixedPoint(params.disputeBond),
       sponsorDisputeRewardPct: percentToFixedPoint(params.sponsorDisputeReward),
       disputerDisputeRewardPct: percentToFixedPoint(params.disputeReward),
-      minSponsorTokens: percentToFixedPoint(params.minSponsorTokens)
+      minSponsorTokens: percentToFixedPoint(params.minSponsorTokens),
+      excessTokenBeneficiary: store.address
     };
     const address = await expiringMultiPartyCreator.createExpiringMultiParty.call(constructorParams);
     await expiringMultiPartyCreator.createExpiringMultiParty(constructorParams);

packages/core/scripts/local/DeployEMP.js

@@ -35,6 +35,7 @@ const WETH9 = artifacts.require("WETH9");
 const Timer = artifacts.require("Timer");
 const TokenFactory = artifacts.require("TokenFactory");
 const AddressWhitelist = artifacts.require("AddressWhitelist");
+const Store = artifacts.require("Store");
 const argv = require("minimist")(process.argv.slice(), { boolean: ["test"], string: ["identifier"] });
 
 // Contracts we need to interact with.
@@ -44,6 +45,7 @@ let mockOracle;
 let identifierWhitelist;
 let collateralTokenWhitelist;
 let expiringMultiPartyCreator;
+let store;
 
 const empCollateralTokenMap = {
   COMPUSD: TestnetERC20,
@@ -88,6 +90,8 @@ const deployEMP = async callback => {
       console.log("Whitelisted collateral currency");
     }
 
+    store = await Store.deployed();
+
     // Create a new EMP
     const constructorParams = {
       expirationTimestamp: "1601503200", // 09/30/2020 @ 10:00pm (UTC)
@@ -101,7 +105,8 @@ const deployEMP = async callback => {
       disputerDisputeRewardPct: { rawValue: toWei("0.2") },
       minSponsorTokens: { rawValue: toWei("100") },
       liquidationLiveness: 7200,
-      withdrawalLiveness: 7200
+      withdrawalLiveness: 7200,
+      excessTokenBeneficiary: store.address
     };
 
     let _emp = await expiringMultiPartyCreator.createExpiringMultiParty.call(constructorParams, { from: deployer });

packages/core/test/financial-templates/ExpiringMultiParty.js

@@ -37,7 +37,8 @@ contract("ExpiringMultiParty", function(accounts) {
       sponsorDisputeRewardPct: { rawValue: toWei("0.1") },
       disputerDisputeRewardPct: { rawValue: toWei("0.1") },
       minSponsorTokens: { rawValue: toWei("1") },
-      timerAddress: timer.address
+      timerAddress: timer.address,
+      excessTokenBeneficiary: accounts[0]
     };
 
     identifierWhitelist = await IdentifierWhitelist.deployed();

packages/core/test/financial-templates/ExpiringMultiPartyCreator.js

@@ -1,5 +1,5 @@
 const { toWei, hexToUtf8, toBN } = web3.utils;
-const { didContractThrow, MAX_UINT_VAL } = require("@uma/common");
+const { didContractThrow, MAX_UINT_VAL, ZERO_ADDRESS } = require("@uma/common");
 const truffleAssert = require("truffle-assertions");
 
 // Tested Contract
@@ -12,8 +12,7 @@ const Registry = artifacts.require("Registry");
 const ExpiringMultiParty = artifacts.require("ExpiringMultiParty");
 const IdentifierWhitelist = artifacts.require("IdentifierWhitelist");
 const AddressWhitelist = artifacts.require("AddressWhitelist");
-const Timer = artifacts.require("Timer");
-const Finder = artifacts.require("Finder");
+const Store = artifacts.require("Store");
 
 contract("ExpiringMultiPartyCreator", function(accounts) {
   let contractCreator = accounts[0];
@@ -23,6 +22,7 @@ contract("ExpiringMultiPartyCreator", function(accounts) {
   let expiringMultiPartyCreator;
   let registry;
   let collateralTokenWhitelist;
+  let store;
 
   // Re-used variables
   let constructorParams;
@@ -36,6 +36,8 @@ contract("ExpiringMultiPartyCreator", function(accounts) {
     collateralTokenWhitelist = await AddressWhitelist.deployed();
     await collateralTokenWhitelist.addToWhitelist(collateralToken.address, { from: contractCreator });
 
+    store = await Store.deployed();
+
     constructorParams = {
       expirationTimestamp: "1898918401", // 2030-03-05T05:20:01.000Z
       collateralAddress: collateralToken.address,
@@ -48,7 +50,8 @@ contract("ExpiringMultiPartyCreator", function(accounts) {
       disputerDisputeRewardPct: { rawValue: toWei("0.1") },
       minSponsorTokens: { rawValue: toWei("1") },
       liquidationLiveness: 7200,
-      withdrawalLiveness: 7200
+      withdrawalLiveness: 7200,
+      excessTokenBeneficiary: store.address
     };
 
     identifierWhitelist = await IdentifierWhitelist.deployed();
@@ -160,6 +163,18 @@ contract("ExpiringMultiPartyCreator", function(accounts) {
     );
   });
 
+  it("Beneficiary cannot be 0x0", async function() {
+    // Change only the beneficiary address.
+    constructorParams.excessTokenBeneficiary = ZERO_ADDRESS;
+    assert(
+      await didContractThrow(
+        expiringMultiPartyCreator.createExpiringMultiParty(constructorParams, {
+          from: contractCreator
+        })
+      )
+    );
+  });
+
   it("Can create new instances of ExpiringMultiParty", async function() {
     // Use `.call` to get the returned value from the function.
     let functionReturnedAddress = await expiringMultiPartyCreator.createExpiringMultiParty.call(constructorParams, {