From ab897bf901a76fa783908f9ca6dbfc43ad46df5f Mon Sep 17 00:00:00 2001
From: Mohammed Sohail <sohailsameja@gmail.com>
Date: Thu, 21 Mar 2024 16:57:06 +0800
Subject: [PATCH] fix: apply fee after quote. Exclude fees from public
 liquidity

---
 .gitignore            |  1 +
 solidity/SwapPool.sol | 21 +++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/.gitignore b/.gitignore
index e8f80ec..cc41cdf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ build/
 dist/
 solidity/*.json
 solidity/*.bin
+.venv
\ No newline at end of file
diff --git a/solidity/SwapPool.sol b/solidity/SwapPool.sol
index 6df6a21..457332e 100644
--- a/solidity/SwapPool.sol
+++ b/solidity/SwapPool.sol
@@ -137,22 +137,30 @@ contract SwapPool {
 	function withdraw(address _outToken, address _inToken, uint256 _value) public {
 		bool r;
 		bytes memory v;
-		uint256 netValue;
 		uint256 balance;
 		uint256 fee;
+		uint256 outValue;
+		uint256 trueBalance;
 
-		fee = getFee(_value);
-		netValue = _value - fee;
-		netValue = getQuote(_outToken, _inToken, netValue);
+		outValue = getQuote(_outToken, _inToken, _value);
 
 		(r, v) = _outToken.call(abi.encodeWithSignature("balanceOf(address)", this));
 		require(r, "ERR_TOKEN");
 		balance = abi.decode(v, (uint256));
-		require(balance >= netValue + fee, "ERR_BALANCE");
+
+		// unwithdrawn fees should remain untouched
+		trueBalance = balance - fees[_outToken];
+
+		// deduct the fees from the quoted outValue
+		fee = getFee(outValue);
+		outValue -= fee;
+
+		// pool should have enough balance to cover the final outValue (fees already deducted)
+		require(balance >= outValue, "ERR_BALANCE");
 
 		deposit(_inToken, _value);
 
-		(r, v) = _outToken.call(abi.encodeWithSignature('transfer(address,uint256)', msg.sender, netValue));
+		(r, v) = _outToken.call(abi.encodeWithSignature('transfer(address,uint256)', msg.sender, outValue));
 		require(r, "ERR_TOKEN");
 		r = abi.decode(v, (bool));
 		require(r, "ERR_TRANSFER");
@@ -235,3 +243,4 @@ contract SwapPool {
 		return false;
 	}
 }
+