CHANGELOG updated, custom error messages added to ERC20, ERC721 and E…

…RC777 for subtraction related exceptions.
OpenZeppelin · Jul 24, 2019 · 3eec22d · 3eec22d
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -8,6 +8,8 @@
 ### Improvements:
  * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
 
+ * `SafeMath`: added support for custom error messages. `ERC20`, `ERC721` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828)) 
+
 ### Bugfixes
 
 ## 2.3.0 (2019-05-27)

diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
@@ -96,7 +96,7 @@ contract ERC20 is IERC20 {
      */
     function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
         _transfer(sender, recipient, amount);
-        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount));
+        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer of tokens exceeding allowance"));
         return true;
     }
 
@@ -132,7 +132,7 @@ contract ERC20 is IERC20 {
      * `subtractedValue`.
      */
     function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
-        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
+        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue, "ERC20: decrease of higher allowance than granted"));
         return true;
     }
 
@@ -154,7 +154,7 @@ contract ERC20 is IERC20 {
         require(sender != address(0), "ERC20: transfer from the zero address");
         require(recipient != address(0), "ERC20: transfer to the zero address");
 
-        _balances[sender] = _balances[sender].sub(amount);
+        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer of tokens exceeding balance");
         _balances[recipient] = _balances[recipient].add(amount);
         emit Transfer(sender, recipient, amount);
     }
@@ -190,8 +190,8 @@ contract ERC20 is IERC20 {
     function _burn(address account, uint256 value) internal {
         require(account != address(0), "ERC20: burn from the zero address");
 
-        _totalSupply = _totalSupply.sub(value);
-        _balances[account] = _balances[account].sub(value);
+        _totalSupply = _totalSupply.sub(value, "ERC20: burn of tokens exceeding balance");
+        _balances[account] = _balances[account].sub(value, "ERC20: burn of tokens exceeding balance");
         emit Transfer(account, address(0), value);
     }
 
@@ -224,6 +224,6 @@ contract ERC20 is IERC20 {
      */
     function _burnFrom(address account, uint256 amount) internal {
         _burn(account, amount);
-        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount));
+        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount, "ERC20: burn of tokens exceeding allowance"));
     }
 }
diff --git a/contracts/token/ERC20/SafeERC20.sol b/contracts/token/ERC20/SafeERC20.sol
@@ -42,7 +42,7 @@ library SafeERC20 {
     }
 
     function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
-        uint256 newAllowance = token.allowance(address(this), spender).sub(value);
+        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decrease of higher allowance than granted");
         callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
     }
 

diff --git a/contracts/token/ERC777/ERC777.sol b/contracts/token/ERC777/ERC777.sol
@@ -285,7 +285,7 @@ contract ERC777 is IERC777, IERC20 {
         _callTokensToSend(spender, holder, recipient, amount, "", "");
 
         _move(spender, holder, recipient, amount, "", "");
-        _approve(holder, spender, _allowances[holder][spender].sub(amount));
+        _approve(holder, spender, _allowances[holder][spender].sub(amount, "ERC777: transfer of tokens exceeding allowance"));
 
         _callTokensReceived(spender, holder, recipient, amount, "", "", false);
 
@@ -383,8 +383,8 @@ contract ERC777 is IERC777, IERC20 {
         _callTokensToSend(operator, from, address(0), amount, data, operatorData);
 
         // Update state variables
-        _totalSupply = _totalSupply.sub(amount);
-        _balances[from] = _balances[from].sub(amount);
+        _totalSupply = _totalSupply.sub(amount, "ERC777: burn of tokens exceeding balance");
+        _balances[from] = _balances[from].sub(amount, "ERC777: burn of tokens exceeding balance");
 
         emit Burned(operator, from, amount, data, operatorData);
         emit Transfer(from, address(0), amount);
@@ -400,7 +400,7 @@ contract ERC777 is IERC777, IERC20 {
     )
         private
     {
-        _balances[from] = _balances[from].sub(amount);
+        _balances[from] = _balances[from].sub(amount, "ERC777: transfer of tokens exceeding balance");
         _balances[to] = _balances[to].add(amount);
 
         emit Sent(operator, from, to, amount, userData, operatorData);