@0x/contracts-erc20: Switch LibERC20Token.approveIfBelowMax() to LibERC20Token.approveIfBelow().

`@0x/contracts-asset-proxy`: Use `LibERC20Token.approveIfBelow()` for bridge approvals.

contracts/asset-proxy/CHANGELOG.json

@@ -3,7 +3,7 @@
         "version": "3.3.0",
         "changes": [
             {
-                "note": "Use `approveIfBelowMax()` in DEX bridges for for approvals.",
+                "note": "Use `LibERC20Token.approveIfBelow()` in DEX bridges for for approvals.",
                 "pr": 2512
             },
             {

contracts/asset-proxy/contracts/src/bridges/CurveBridge.sol

@@ -67,9 +67,9 @@ contract CurveBridge is
 
         address fromTokenAddress = ICurve(data.curveAddress).underlying_coins(data.fromCoinIdx);
         require(toTokenAddress != fromTokenAddress, "CurveBridge/INVALID_PAIR");
-        // Grant an allowance to the exchange to spend `fromTokenAddress` token.
-        LibERC20Token.approveIfBelowMax(fromTokenAddress, data.curveAddress);
         uint256 fromTokenBalance = IERC20Token(fromTokenAddress).balanceOf(address(this));
+        // Grant an allowance to the exchange to spend `fromTokenAddress` token.
+        LibERC20Token.approveIfBelow(fromTokenAddress, data.curveAddress, fromTokenBalance);
 
         // Try to sell all of this contract's `fromTokenAddress` token balance.
         if (data.version == 0) {

contracts/asset-proxy/contracts/src/bridges/Eth2DaiBridge.sol

@@ -57,10 +57,9 @@ contract Eth2DaiBridge is
         (address fromTokenAddress) = abi.decode(bridgeData, (address));
 
         IEth2Dai exchange = IEth2Dai(_getEth2DaiAddress());
-        // Grant an allowance to the exchange to spend `fromTokenAddress` token.
-        LibERC20Token.approveIfBelowMax(fromTokenAddress, address(exchange));
-
         uint256 fromTokenBalance = IERC20Token(fromTokenAddress).balanceOf(address(this));
+        // Grant an allowance to the exchange to spend `fromTokenAddress` token.
+        LibERC20Token.approveIfBelow(fromTokenAddress, address(exchange), fromTokenBalance);
 
         // Try to sell all of this contract's `fromTokenAddress` token balance.
         uint256 boughtAmount = exchange.sellAllAmount(

contracts/asset-proxy/contracts/src/bridges/KyberBridge.sol

@@ -110,7 +110,11 @@ contract KyberBridge is
         } else if (state.fromTokenAddress != address(state.weth)) {
             // If the input token is not WETH, grant an allowance to the exchange
             // to spend them.
-            LibERC20Token.approveIfBelowMax(state.fromTokenAddress, address(state.kyber));
+            LibERC20Token.approveIfBelow(
+                state.fromTokenAddress,
+                address(state.kyber),
+                state.fromTokenBalance
+            );
         } else {
             // If the input token is WETH, unwrap it and attach it to the call.
             state.fromTokenAddress = KYBER_ETH_ADDRESS;

contracts/asset-proxy/contracts/src/bridges/UniswapBridge.sol

@@ -110,7 +110,7 @@ contract UniswapBridge is
         // Convert from a token to WETH.
         } else if (toTokenAddress == address(state.weth)) {
             // Grant the exchange an allowance.
-            _grantExchangeAllowance(state.exchange, fromTokenAddress);
+            _grantExchangeAllowance(state.exchange, fromTokenAddress, state.fromTokenBalance);
             // Buy as much ETH with `fromTokenAddress` token as possible.
             state.boughtAmount = state.exchange.tokenToEthSwapInput(
                 // Sell all tokens we hold.
@@ -128,7 +128,7 @@ contract UniswapBridge is
         // Convert from one token to another.
         } else {
             // Grant the exchange an allowance.
-            _grantExchangeAllowance(state.exchange, fromTokenAddress);
+            _grantExchangeAllowance(state.exchange, fromTokenAddress, state.fromTokenBalance);
             // Buy as much `toTokenAddress` token with `fromTokenAddress` token
             // and transfer it to `to`.
             state.boughtAmount = state.exchange.tokenToTokenTransferInput(
@@ -177,10 +177,19 @@ contract UniswapBridge is
     ///      on behalf of this contract.
     /// @param exchange The Uniswap token exchange.
     /// @param tokenAddress The token address for the exchange.
-    function _grantExchangeAllowance(IUniswapExchange exchange, address tokenAddress)
+    /// @param minimumAllowance The minimum necessary allowance.
+    function _grantExchangeAllowance(
+        IUniswapExchange exchange,
+        address tokenAddress,
+        uint256 minimumAllowance
+    )
         private
     {
-        LibERC20Token.approveIfBelowMax(tokenAddress, address(exchange));
+        LibERC20Token.approveIfBelow(
+            tokenAddress,
+            address(exchange),
+            minimumAllowance
+        );
     }
 
     /// @dev Retrieves the uniswap exchange for a given token pair.

contracts/erc20/CHANGELOG.json

@@ -3,7 +3,7 @@
         "version": "3.2.0",
         "changes": [
             {
-                "note": "Add `LibERC20Token.approveIfBelowMax()`",
+                "note": "Add `LibERC20Token.approveIfBelow()`",
                 "pr": 2512
             }
         ]

contracts/erc20/contracts/src/LibERC20Token.sol

@@ -48,18 +48,20 @@ library LibERC20Token {
     }
 
     /// @dev Calls `IERC20Token(token).approve()` and sets the allowance to the
-    ///      maximum if the current approval is not already set to the maximum.
+    ///      maximum if the current approval is not already >= an amount.
     ///      Reverts if `false` is returned or if the return
     ///      data length is nonzero and not 32 bytes.
     /// @param token The address of the token contract.
     /// @param spender The address that receives an allowance.
-    function approveIfBelowMax(
+    /// @param amount The minimum allowance needed.
+    function approveIfBelow(
         address token,
-        address spender
+        address spender,
+        uint256 amount
     )
         internal
     {
-        if (IERC20Token(token).allowance(address(this), spender) != uint256(-1)) {
+        if (IERC20Token(token).allowance(address(this), spender) < amount) {
             approve(token, spender, uint256(-1));
         }
     }