Merge pull request openocean-finance#1 from openocean-finance/main

updata example

OpenOcean-Contract Call-Example/APIproxy.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity 0.6.9;
+pragma experimental ABIEncoderV2;
+
+// need 
+
+contract APIproxy {
+    using SafeERC20 for IERC20;
+
+    address constant _ETH_ADDRESS_ = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
+
+
+    receive() external payable {}
+
+    //Compatible with ETH=>ERC20, ERC20=>ETH
+    function useAPIData(
+        address fromToken, //fromTokenaddress
+        address toToken, //toTokenaddress
+        uint256 fromAmount, //inamout with dicimals
+        address OOApprove, // 0x6352a56caadc4f1e25cd6c75970fa768a3304e64
+        address OOProxy, // 0x6352a56caadc4f1e25cd6c75970fa768a3304e64
+        bytes memory OOApiData // data param from swap_quote API 
+    )
+        external
+        payable
+    {
+        if (fromToken != _ETH_ADDRESS_) {
+            IERC20(fromToken).transferFrom(msg.sender, address(this), fromAmount);
+            _approveMax(fromToken, OOApprove, fromAmount);
+        } else {
+            require(fromAmount == msg.value);
+        }
+
+        (bool success, bytes memory result ) = OOProxy.call{value: fromToken == _ETH_ADDRESS_ ? fromAmount : 0}(OOApiData);
+        require(success, "API_SWAP_FAILED");
+
+        uint256 returnAmount = _balanceOf(toToken, address(this));
+
+        _transfer(toToken, msg.sender, returnAmount);
+    }
+
+
+    function _approveMax(
+        address token,
+        address to,
+        uint256 amount
+    ) internal {
+        uint256 allowance = IERC20(token).allowance(address(this), to);
+        if (allowance < amount) {
+            if (allowance > 0) {
+                IERC20(token).safeApprove(to, 0);
+            }
+            IERC20(token).safeApprove(to, uint256(-1));
+        }
+    }
+
+    function _transfer(
+        address token,
+        address payable to,
+        uint256 amount
+    ) internal {
+        if (amount > 0) {
+            if (token == _ETH_ADDRESS_) {
+                to.transfer(amount);
+            } else {
+                IERC20(token).safeTransfer(to, amount);
+            }
+        }
+    }
+
+    function _balanceOf(
+        address token, 
+        address who
+    ) internal view returns (uint256) {
+        if (token == _ETH_ADDRESS_ ) {
+            return who.balance;
+        } else {
+            return IERC20(token).balanceOf(who);
+        }
+    }
+
+}

OpenOcean-Contract Call-Example/README.md

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+In case there are certain users request in our community asking about how to use our API directly in their contract. So we provide code example for developers to quick intergrate our API and contract.
+
+Here is the file for contran intergration [APIProxy](./APIproxy.sol)