fix #119

src/UserConfig.sol

@@ -40,6 +40,10 @@ contract UserConfig {
     /// @param oracle Oracle which the user application choose.
     /// @param relayer Relayer which the user application choose.
     event AppConfigUpdated(address indexed ua, address oracle, address relayer);
+    /// @dev Notifies an observer that the setter is changed.
+    /// @param oldSetter Old setter address.
+    /// @param newSetter New setter address.
+    event SetterChanged(address indexed oldSetter, address indexed newSetter);
 
     modifier onlySetter() {
         require(msg.sender == setter, "!auth");
@@ -52,9 +56,11 @@ contract UserConfig {
 
     /// @dev Change setter.
     /// @notice Only current setter could call.
-    /// @param setter_ New setter.
-    function changeSetter(address setter_) external onlySetter {
-        setter = setter_;
+    /// @param newSetter New setter.
+    function changeSetter(address newSetter) external onlySetter {
+        address oldSetter = setter;
+        setter = newSetter;
+        emit SetterChanged(oldSetter, newSetter);
     }
 
     /// @dev Set default user config for all user application.

src/eco/Relayer.sol

@@ -24,6 +24,7 @@ contract Relayer {
     event SetDstPrice(uint256 indexed chainId, uint128 dstPriceRatio, uint128 dstGasPriceInWei);
     event SetDstConfig(uint256 indexed chainId, uint64 baseGas, uint64 gasPerByte);
     event SetApproved(address operator, bool approve);
+    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
 
     struct DstPrice {
         uint128 dstPriceRatio; // dstPrice / localPrice * 10^10
@@ -69,8 +70,10 @@ contract Relayer {
         return approvedOf[operator];
     }
 
-    function changeOwner(address owner_) external onlyOwner {
-        owner = owner_;
+    function changeOwner(address newOwner) external onlyOwner {
+        address oldOwner = owner;
+        owner = newOwner;
+        emit OwnershipTransferred(oldOwner, newOwner);
     }
 
     function setApproved(address operator, bool approve) public onlyOwner {