[Protocol3] add ProtocolFeesUpdated event (#258)

* [Protocol3] add event: ProtocolFeeChanged

* update

Author: kongliangzhong

packages/loopring_v3/contracts/iface/IExchange.sol

@@ -114,6 +114,13 @@ contract IExchange
         uint96          amount
     );
 
+    event ProtocolFeesUpdated(
+        uint8 takerFeeBips,
+        uint8 makerFeeBips,
+        uint8 previousTakerFeeBips,
+        uint8 previousMakerFeeBips
+    );
+
     // -- Settings --
     function getGlobalSettings()
         public

packages/loopring_v3/contracts/impl/libexchange/ExchangeAccounts.sol

@@ -27,7 +27,6 @@ import "./ExchangeData.sol";
 /// @author Brecht Devos - <[email protected]>
 library ExchangeAccounts
 {
-    using AddressUtil       for address payable;
     using MathUint          for uint;
     using ExchangeBalances  for ExchangeData.State;
 

packages/loopring_v3/contracts/impl/libexchange/ExchangeBlocks.sol

@@ -52,6 +52,13 @@ library ExchangeBlocks
         uint    indexed blockIdx
     );
 
+    event ProtocolFeesUpdated(
+        uint8 takerFeeBips,
+        uint8 makerFeeBips,
+        uint8 previousTakerFeeBips,
+        uint8 previousMakerFeeBips
+    );
+
     function commitBlock(
         ExchangeData.State storage S,
         uint8  blockType,
@@ -260,7 +267,7 @@ library ExchangeBlocks
                 "INVALID_TIMESTAMP"
             );
             require(
-                validateProtocolFeeValues(S, protocolTakerFeeBips, protocolMakerFeeBips),
+                validateAndUpdateProtocolFeeValues(S, protocolTakerFeeBips, protocolMakerFeeBips),
                 "INVALID_PROTOCOL_FEES"
             );
         } else if (blockType == ExchangeData.BlockType.DEPOSIT) {
@@ -388,7 +395,7 @@ library ExchangeBlocks
         emit BlockCommitted(S.blocks.length - 1, publicDataHash);
     }
 
-    function validateProtocolFeeValues(
+    function validateAndUpdateProtocolFeeValues(
         ExchangeData.State storage S,
         uint8 takerFeeBips,
         uint8 makerFeeBips
@@ -407,6 +414,18 @@ library ExchangeBlocks
                 S.onchainDataAvailability
             );
             data.timestamp = uint32(now);
+
+            bool feeUpdated = (data.takerFeeBips != data.previousTakerFeeBips) ||
+                (data.makerFeeBips != data.previousMakerFeeBips);
+
+            if (feeUpdated) {
+                emit ProtocolFeesUpdated(
+                    data.takerFeeBips,
+                    data.makerFeeBips,
+                    data.previousTakerFeeBips,
+                    data.previousMakerFeeBips
+                );
+            }
         }
         // The given fee values are valid if they are the current or previous protocol fee values
         return (takerFeeBips == data.takerFeeBips && makerFeeBips == data.makerFeeBips) ||