Merge branch 'feature/V2' of github.com:DODOEX/contractV2 into feature/V2

contracts/lib/GasPriceSource.sol

@@ -0,0 +1,29 @@
+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+pragma experimental ABIEncoderV2;
+
+import {Ownable} from "./Ownable.sol";
+
+interface IGasPriceSource {
+    function setGasPrice(uint256) external;
+
+    function getGasPrice() external view returns (uint256);
+}
+
+contract GasPriceSource is IGasPriceSource, Ownable {
+    uint256 public _GAS_PRICE_;
+
+    function setGasPrice(uint256 gasPrice) external override {
+        _GAS_PRICE_ = gasPrice;
+    }
+
+    function getGasPrice() external override view returns (uint256) {
+        return _GAS_PRICE_;
+    }
+}

contracts/lib/UniversalERC20.sol

@@ -12,18 +12,26 @@ import {IERC20} from "../intf/IERC20.sol";
 import {SafeERC20} from "./SafeERC20.sol";
 
 library UniversalERC20 {
-
     using SafeMath for uint256;
     using SafeERC20 for IERC20;
 
     IERC20 private constant ZERO_ADDRESS = IERC20(0x0000000000000000000000000000000000000000);
     IERC20 private constant ETH_ADDRESS = IERC20(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);
 
-    function universalTransfer(IERC20 token, address to, uint256 amount) internal {
+    function universalTransfer(
+        IERC20 token,
+        address to,
+        uint256 amount
+    ) internal {
         universalTransfer(token, to, amount, false);
     }
 
-    function universalTransfer(IERC20 token, address to, uint256 amount, bool mayFail) internal returns(bool) {
+    function universalTransfer(
+        IERC20 token,
+        address to,
+        uint256 amount,
+        bool mayFail
+    ) internal returns (bool) {
         if (amount == 0) {
             return true;
         }
@@ -41,13 +49,33 @@ library UniversalERC20 {
         }
     }
 
-    function universalApprove(IERC20 token, address to, uint256 amount) internal {
+    function universalApprove(
+        IERC20 token,
+        address to,
+        uint256 amount
+    ) internal {
         if (token != ZERO_ADDRESS && token != ETH_ADDRESS) {
-            token.safeApprove(to, amount);
+            if (amount == 0) {
+                token.safeApprove(to, 0);
+                return;
+            }
+
+            uint256 allowance = token.allowance(address(this), to);
+            if (allowance < amount) {
+                if (allowance > 0) {
+                    token.safeApprove(to, 0);
+                }
+                token.safeApprove(to, amount);
+            }
         }
     }
 
-    function universalTransferFrom(IERC20 token, address from, address to, uint256 amount) internal {
+    function universalTransferFrom(
+        IERC20 token,
+        address from,
+        address to,
+        uint256 amount
+    ) internal {
         if (amount == 0) {
             return;
         }
@@ -72,4 +100,4 @@ library UniversalERC20 {
             return token.balanceOf(who);
         }
     }
-}
+}