Update EIP-6909: Update reference implementation to specification

EIPS/eip-6909.md

@@ -510,46 +510,52 @@ contract ERC6909 {
     /// @param receiver The address of the receiver.
     /// @param id The id of the token.
     /// @param amount The amount of the token.
-    function transfer(address receiver, uint256 id, uint256 amount) public {
+    function transfer(address receiver, uint256 id, uint256 amount) public returns (bool) {
         if (balanceOf[msg.sender][id] < amount) revert InsufficientBalance(msg.sender, id);
         balanceOf[msg.sender][id] -= amount;
         balanceOf[receiver][id] += amount;
         emit Transfer(msg.sender, receiver, id, amount);
+        return true;
     }
 
     /// @notice Transfers an amount of an id from a sender to a receiver.
     /// @param sender The address of the sender.
     /// @param receiver The address of the receiver.
     /// @param id The id of the token.
     /// @param amount The amount of the token.
-    function transferFrom(address sender, address receiver, uint256 id, uint256 amount) public {
+    function transferFrom(address sender, address receiver, uint256 id, uint256 amount) public returns (bool) {
         if (sender != msg.sender && !isOperator[sender][msg.sender]) {
-            if (allowance[sender][msg.sender][id] < amount) {
-                revert InsufficientPermission(msg.sender, id);
+            uint256 senderAllowance = allowance[sender][msg.sender][id];
+            if (senderAllowance < amount) revert InsufficientPermission(msg.sender, id);
+            if (senderAllowance != type(uint256).max) {
+                allowance[sender][msg.sender][id] = senderAllowance - amount;
             }
-            allowance[sender][msg.sender][id] -= amount;
         }
         if (balanceOf[sender][id] < amount) revert InsufficientBalance(sender, id);
         balanceOf[sender][id] -= amount;
         balanceOf[receiver][id] += amount;
         emit Transfer(sender, receiver, id, amount);
+        return true;
     }
 
     /// @notice Approves an amount of an id to a spender.
     /// @param spender The address of the spender.
     /// @param id The id of the token.
     /// @param amount The amount of the token.
-    function approve(address spender, uint256 id, uint256 amount) public {
+    function approve(address spender, uint256 id, uint256 amount) public returns (bool) {
         allowance[msg.sender][spender][id] = amount;
         emit Approval(msg.sender, spender, id, amount);
+        return true;
     }
 
+
     /// @notice Sets or removes a spender as an operator for the caller.
     /// @param spender The address of the spender.
     /// @param approved The approval status.
-    function setOperator(address spender, bool approved) public {
+    function setOperator(address spender, bool approved) public returns (bool) {
         isOperator[msg.sender][spender] = approved;
         emit OperatorSet(msg.sender, spender, approved);
+        return true;
     }
 
     /// @notice Checks if a contract implements an interface.