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contracts/bridge/RootAxelarBridgeAdaptor.sol

@@ -25,8 +25,7 @@ contract RootAxelarBridgeAdaptor is IRootERC20BridgeAdaptor, IAxelarBridgeAdapto
     string public childChain;
     IAxelarGateway public immutable AXELAR_GATEWAY;
     IAxelarGasService public immutable GAS_SERVICE;
-
-    bytes32 public constant MAP_TOKEN_SIG = keccak256("MAP_TOKEN");
+    mapping(uint256 => string) public chainIdToChainName;
 
     constructor(
         address _rootBridge,
@@ -56,23 +55,16 @@ contract RootAxelarBridgeAdaptor is IRootERC20BridgeAdaptor, IAxelarBridgeAdapto
 
     /**
      * @inheritdoc IRootERC20BridgeAdaptor
-     * @dev Send a map token message to the child chain via the Axelar Gateway.
+     * @notice Sends an arbitrary message to the child chain, via the Axelar network.
      */
-    function mapToken(
-        address rootToken,
-        string calldata name,
-        string calldata symbol,
-        uint8 decimals
-    ) external payable override {
+    function sendMessage(bytes calldata payload, address refundRecipient) external payable override {
         if (msg.value == 0) {
             revert NoGas();
         }
         if (msg.sender != ROOT_BRIDGE) {
             revert CallerNotBridge();
         }
 
-        bytes memory payload = abi.encode(MAP_TOKEN_SIG, rootToken, name, symbol, decimals);
-
         // Load from storage.
         string memory _childBridgeAdaptor = childBridgeAdaptor;
         string memory _childChain = childChain;
@@ -83,7 +75,7 @@ contract RootAxelarBridgeAdaptor is IRootERC20BridgeAdaptor, IAxelarBridgeAdapto
             _childChain,
             _childBridgeAdaptor,
             payload,
-            msg.sender
+            refundRecipient
         );
 
         AXELAR_GATEWAY.callContract(_childChain, _childBridgeAdaptor, payload);

contracts/bridge/RootERC20Bridge.sol

@@ -27,6 +27,7 @@ contract RootERC20Bridge is
     IRootERC20BridgeErrors
 {
     using SafeERC20 for IERC20Metadata;
+    bytes32 public constant MAP_TOKEN_SIG = keccak256("MAP_TOKEN");
 
     IRootERC20BridgeAdaptor public bridgeAdaptor;
     /// @dev The address that will be minting tokens on the child chain.
@@ -82,12 +83,14 @@ contract RootERC20Bridge is
 
         rootTokenToChildToken[address(rootToken)] = childToken;
 
-        bridgeAdaptor.mapToken{value: msg.value}(
-            address(rootToken),
+        bytes memory payload = abi.encode(
+            MAP_TOKEN_SIG,
+            rootToken,
             rootToken.name(),
             rootToken.symbol(),
             rootToken.decimals()
         );
+        bridgeAdaptor.sendMessage{value: msg.value}(payload, msg.sender);
 
         emit TokenMapped(address(rootToken), childToken);
         return childToken;

contracts/bridge/interfaces/IAxelarBridgeAdaptor.sol

@@ -6,6 +6,7 @@ interface IAxelarBridgeAdaptorErrors {
     error InvalidChildChain();
     error NoGas();
     error CallerNotBridge();
+    error InvalidArrayLengths();
 }
 
 interface IAxelarBridgeAdaptorEvents {

contracts/bridge/interfaces/IRootERC20BridgeAdaptor.sol

@@ -1,13 +1,13 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.17;
 
+// TODO: This is likely able to become a generic bridge adaptor, not just for ERC20 tokens.
 interface IRootERC20BridgeAdaptor {
     /**
-     * @notice Send a map token message to the child chain via the message passing protocol.
-     * @param rootToken The address of the token on the root chain.
-     * @param name The name of the token.
-     * @param symbol The symbol of the token.
-     * @param decimals The decimals of the token.
+     * @notice Send an arbitrary message to the child chain via the message passing protocol.
+     * @param payload The message to send, encoded in a `bytes` array.
+     * @param refundRecipient Used if the message passing protocol requires fees & pays back excess to a refund recipient.
+     * @dev `payable` because the message passing protocol may require a fee to be paid.
      */
-    function mapToken(address rootToken, string calldata name, string calldata symbol, uint8 decimals) external payable;
+    function sendMessage(bytes calldata payload, address refundRecipient) external payable;
 }

contracts/bridge/test/MockAdaptor.sol

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+// @dev A contract for ensuring the Axelar Bridge Adaptor is called correctly during unit tests.
+contract MockAdaptor {
+    function sendMessage(bytes calldata , address) external payable{}
+}

test/bridge/integration/RootERC20Bridge.t.sol

@@ -51,7 +51,7 @@ contract RootERC20BridgeIntegrationTest is Test, IRootERC20BridgeEvents, IAxelar
             address(axelarAdaptor),
             mapTokenFee,
             abi.encodeWithSelector(
-                axelarAdaptor.mapToken.selector, address(token), token.name(), token.symbol(), token.decimals()
+                axelarAdaptor.sendMessage.selector, payload, address(this)
             )
         );
 
@@ -65,7 +65,7 @@ contract RootERC20BridgeIntegrationTest is Test, IRootERC20BridgeEvents, IAxelar
                 CHILD_CHAIN_NAME,
                 Strings.toHexString(CHILD_BRIDGE_ADAPTOR),
                 payload,
-                address(rootBridge)
+                address(this)
             )
         );
 
@@ -80,8 +80,16 @@ contract RootERC20BridgeIntegrationTest is Test, IRootERC20BridgeEvents, IAxelar
             )
         );
 
+        // Check that we pay mapTokenFee to the axelarGasService.
+        uint256 thisPreBal = address(this).balance;
+        uint256 axelarGasServicePreBal = address(axelarGasService).balance;
+
         rootBridge.mapToken{value: mapTokenFee}(token);
 
+        // Should update ETH balances as gas payment for message.
+        assertEq(address(this).balance, thisPreBal - mapTokenFee);
+        assertEq(address(axelarGasService).balance, axelarGasServicePreBal + mapTokenFee);
+
         assertEq(rootBridge.rootTokenToChildToken(address(token)), childToken);
     }
 }

test/bridge/unit/RootAxelarBridgeAdaptor.t.sol

@@ -65,7 +65,8 @@ contract RootAxelarBridgeAdaptorTest is Test, IAxelarBridgeAdaptorEvents, IAxela
     }
 
     /// @dev For this unit test we just want to make sure the correct functions are called on the Axelar Gateway and Gas Service.
-    function test_mapToken() public {
+    function test_sendMessage_CallsGasService() public {
+        address refundRecipient = address(123);
         bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
         uint256 callValue = 300;
 
@@ -78,10 +79,17 @@ contract RootAxelarBridgeAdaptorTest is Test, IAxelarBridgeAdaptorEvents, IAxela
                 CHILD_CHAIN_NAME,
                 Strings.toHexString(CHILD_BRIDGE_ADAPTOR),
                 payload,
-                address(this)
+                refundRecipient
             )
         );
 
+        axelarAdaptor.sendMessage{value: callValue}(payload, refundRecipient);
+    }
+
+    function test_sendMessage_CallsGateway() public {
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
+        uint256 callValue = 300;
+
         vm.expectCall(
             address(mockAxelarGateway),
             abi.encodeWithSelector(
@@ -92,31 +100,71 @@ contract RootAxelarBridgeAdaptorTest is Test, IAxelarBridgeAdaptorEvents, IAxela
             )
         );
 
+        axelarAdaptor.sendMessage{value: callValue}(payload, address(123));
+    }
+
+    function test_sendMessage_EmitsMapTokenAxelarMessageEvent() public {
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
+        uint256 callValue = 300;
+
         vm.expectEmit(true, true, true, false, address(axelarAdaptor));
         emit MapTokenAxelarMessage(CHILD_CHAIN_NAME, Strings.toHexString(CHILD_BRIDGE_ADAPTOR), payload);
 
-        axelarAdaptor.mapToken{value: callValue}(address(token), token.name(), token.symbol(), token.decimals());
+        axelarAdaptor.sendMessage{value: callValue}(payload, address(123));
+    }
+
+    function testFuzz_sendMessage_PaysGasToGasService(uint256 callValue) public {
+        vm.assume(callValue < address(this).balance);
+        vm.assume(callValue > 0);
+
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
+
+        uint256 thisPreBal = address(this).balance;
+        uint256 axelarGasServicePreBal = address(axelarGasService).balance;
+
+        axelarAdaptor.sendMessage{value: callValue}(payload, address(123));
+
+        assertEq(address(this).balance, thisPreBal - callValue);
+        assertEq(address(axelarGasService).balance, axelarGasServicePreBal + callValue);
+    }
+
+    function test_sendMessage_GivesCorrectRefundRecipient() public {
+        address refundRecipient = address(0x3333);
+        uint256 callValue = 300;
+
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
+
+        vm.expectCall(
+            address(axelarGasService),
+            callValue,
+            abi.encodeWithSelector(
+                axelarGasService.payNativeGasForContractCall.selector,
+                address(axelarAdaptor),
+                CHILD_CHAIN_NAME,
+                Strings.toHexString(CHILD_BRIDGE_ADAPTOR),
+                payload,
+                refundRecipient
+            )
+        );
+
+        axelarAdaptor.sendMessage{value: callValue}(payload, refundRecipient);
     }
 
     function test_RevertsIf_mapTokenCalledByNonRootBridge() public {
         address payable prankster = payable(address(0x33));
         uint256 value = 300;
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
 
         // Have to call these above so the expectRevert works on the call to mapToken.
-        string memory name = token.name();
-        string memory symbol = token.symbol();
-        uint8 decimals = token.decimals();
         prankster.transfer(value);
         vm.prank(prankster);
         vm.expectRevert(CallerNotBridge.selector);
-        axelarAdaptor.mapToken{value: value}(address(token), name, symbol, decimals);
+        axelarAdaptor.sendMessage{value: value}(payload, address(123));
     }
 
     function test_RevertsIf_mapTokenCalledWithNoValue() public {
-        string memory name = token.name();
-        string memory symbol = token.symbol();
-        uint8 decimals = token.decimals();
+        bytes memory payload = abi.encode(MAP_TOKEN_SIG, address(token), token.name(), token.symbol(), token.decimals());
         vm.expectRevert(NoGas.selector);
-        axelarAdaptor.mapToken{value: 0}(address(token), name, symbol, decimals);
+        axelarAdaptor.sendMessage{value: 0}(payload, address(123));
     }
 }

test/bridge/unit/RootERC20Bridge.t.sol

@@ -8,7 +8,7 @@ import {Strings} from "@openzeppelin/contracts/utils/Strings.sol";
 import {MockAxelarGateway} from "../../../contracts/bridge/test/MockAxelarGateway.sol";
 import {MockAxelarGasService} from "../../../contracts/bridge/test/MockAxelarGasService.sol";
 import {RootERC20Bridge, IRootERC20BridgeEvents, IERC20Metadata, IRootERC20BridgeErrors } from "../../../contracts/bridge/RootERC20Bridge.sol";
-import {MockRootAxelarBridgeAdaptor} from "../../../contracts/bridge/test/MockRootAxelarBridgeAdaptor.sol";
+import {MockAdaptor} from "../../../contracts/bridge/test/MockAdaptor.sol";
 
 contract RootERC20BridgeUnitTest is Test, IRootERC20BridgeEvents, IRootERC20BridgeErrors {
     address constant CHILD_BRIDGE = address(3);
@@ -17,7 +17,7 @@ contract RootERC20BridgeUnitTest is Test, IRootERC20BridgeEvents, IRootERC20Brid
 
     ERC20PresetMinterPauser public token;
     RootERC20Bridge public rootBridge;
-    MockRootAxelarBridgeAdaptor public mockAxelarAdaptor;
+    MockAdaptor public mockAxelarAdaptor;
     MockAxelarGateway public mockAxelarGateway;
     MockAxelarGasService public axelarGasService;
 
@@ -28,7 +28,7 @@ contract RootERC20BridgeUnitTest is Test, IRootERC20BridgeEvents, IRootERC20Brid
         mockAxelarGateway = new MockAxelarGateway();
         axelarGasService = new MockAxelarGasService();
 
-        mockAxelarAdaptor = new MockRootAxelarBridgeAdaptor();
+        mockAxelarAdaptor = new MockAdaptor();
 
         // The specific ERC20 token template does not matter for these unit tests
         rootBridge.initialize(address(mockAxelarAdaptor), CHILD_BRIDGE, address(token));
@@ -51,26 +51,64 @@ contract RootERC20BridgeUnitTest is Test, IRootERC20BridgeEvents, IRootERC20Brid
         bridge.initialize(address(0), address(0), address(0));
     }
 
-    function test_mapToken() public {
+    function test_mapToken_EmitsTokenMappedEvent() public {
         uint256 mapTokenFee = 300;
         address childToken =
             Clones.predictDeterministicAddress(address(token), keccak256(abi.encodePacked(token)), CHILD_BRIDGE);
 
         vm.expectEmit(true, true, false, false, address(rootBridge));
         emit TokenMapped(address(token), childToken);
+
+        rootBridge.mapToken{value: mapTokenFee}(token);
+
+    }
+
+    function test_mapToken_CallsAdaptor() public {
+        uint256 mapTokenFee = 300;
+
+        bytes memory payload = abi.encode(rootBridge.MAP_TOKEN_SIG(), token, token.name(), token.symbol(), token.decimals());
+
         vm.expectCall(
             address(mockAxelarAdaptor),
             mapTokenFee,
             abi.encodeWithSelector(
-                mockAxelarAdaptor.mapToken.selector, address(token), token.name(), token.symbol(), token.decimals()
+                mockAxelarAdaptor.sendMessage.selector, payload, address(this)
             )
         );
 
         rootBridge.mapToken{value: mapTokenFee}(token);
+    }
+
+    function test_mapToken_SetsTokenMapping() public {
+        uint256 mapTokenFee = 300;
+        address childToken =
+            Clones.predictDeterministicAddress(address(token), keccak256(abi.encodePacked(token)), CHILD_BRIDGE);
+
+        rootBridge.mapToken{value: mapTokenFee}(token);
 
         assertEq(rootBridge.rootTokenToChildToken(address(token)), childToken);
     }
 
+    function testFuzz_mapToken_UpdatesEthBalance(uint256 mapTokenFee) public {
+        vm.assume(mapTokenFee < address(this).balance);
+        vm.assume(mapTokenFee > 0);
+        uint256 thisPreBal = address(this).balance;
+        uint256 rootBridgePreBal = address(rootBridge).balance;
+        uint256 adaptorPreBal = address(mockAxelarAdaptor).balance;
+
+        rootBridge.mapToken{value: mapTokenFee}(token);
+
+        /*
+         * Because this is a unit test, the adaptor is mocked. This adaptor would typically
+         * pay the ETH to the gas service, but in this mocked case it will keep the ETH.
+         */
+
+        // User pays
+        assertEq(address(this).balance, thisPreBal - mapTokenFee);
+        assertEq(address(mockAxelarAdaptor).balance, adaptorPreBal + mapTokenFee);
+        assertEq(address(rootBridge).balance, rootBridgePreBal);
+    }
+
     function test_RevertsIf_mapTokenCalledWithZeroAddress() public {
         vm.expectRevert(ZeroAddress.selector);
         rootBridge.mapToken{value: 300}(IERC20Metadata(address(0)));