Feat/add gas

contracts/gas-service/AxelarGasService.sol

@@ -97,6 +97,28 @@ contract AxelarGasService is Upgradable, IAxelarGasService {
         );
     }
 
+    function addGas(
+        bytes32 txHash,
+        uint256 logIndex,
+        address gasToken,
+        uint256 gasFeeAmount,
+        address refundAddress
+    ) external override {
+        _safeTransferFrom(gasToken, msg.sender, gasFeeAmount);
+
+        emit GasAdded(txHash, logIndex, gasToken, gasFeeAmount, refundAddress);
+    }
+
+    function addNativeGas(
+        bytes32 txHash,
+        uint256 logIndex,
+        address refundAddress
+    ) external payable override {
+        if (msg.value == 0) revert NothingReceived();
+
+        emit NativeGasAdded(txHash, logIndex, msg.value, refundAddress);
+    }
+
     function collectFees(address payable receiver, address[] calldata tokens) external onlyOwner {
         for (uint256 i; i < tokens.length; i++) {
             address token = tokens[i];

contracts/interfaces/IAxelarGasService.sol

@@ -51,6 +51,10 @@ interface IAxelarGasService is IUpgradable {
         address refundAddress
     );
 
+    event GasAdded(bytes32 indexed txHash, uint256 indexed logIndex, address gasToken, uint256 gasFeeAmount, address refundAddress);
+
+    event NativeGasAdded(bytes32 indexed txHash, uint256 indexed logIndex, uint256 gasFeeAmount, address refundAddress);
+
     // This is called on the source chain before calling the gateway to execute a remote contract.
     function payGasForContractCall(
         address sender,
@@ -95,6 +99,20 @@ interface IAxelarGasService is IUpgradable {
         address refundAddress
     ) external payable;
 
+    function addGas(
+        bytes32 txHash,
+        uint256 txIndex,
+        address gasToken,
+        uint256 gasFeeAmount,
+        address refundAddress
+    ) external;
+
+    function addNativeGas(
+        bytes32 txHash,
+        uint256 logIndex,
+        address refundAddress
+    ) external payable;
+
     function collectFees(address payable receiver, address[] calldata tokens) external;
 
     function refund(

test/gmp/AxelarGasService.js

@@ -234,4 +234,25 @@ describe('AxelarGasService', () => {
             await expect(await gasService.owner()).to.be.equal(userWallet.address);
         });
     });
+
+    it('should emit events when gas is added', async () => {
+        const txHash = keccak256(defaultAbiCoder.encode(['string'], ['random tx hash']));
+        const logIndex = 13;
+        const gasToken = testToken.address;
+        const gasFeeAmount = 1000;
+        const nativeGasFeeAmount = parseEther('1.0');
+
+        await testToken.connect(userWallet).approve(gasService.address, 1e6);
+
+        await expect(gasService.connect(userWallet).addGas(txHash, logIndex, gasToken, gasFeeAmount, userWallet.address))
+            .to.emit(gasService, 'GasAdded')
+            .withArgs(txHash, logIndex, gasToken, gasFeeAmount, userWallet.address)
+            .and.to.emit(testToken, 'Transfer')
+            .withArgs(userWallet.address, gasService.address, gasFeeAmount);
+
+        await expect(await gasService.connect(userWallet).addNativeGas(txHash, logIndex, userWallet.address, { value: nativeGasFeeAmount }))
+            .to.emit(gasService, 'NativeGasAdded')
+            .withArgs(txHash, logIndex, nativeGasFeeAmount, userWallet.address)
+            .and.to.changeEtherBalance(gasService, nativeGasFeeAmount);
+    });
 });