Exposed fee getters.

contracts/src/bridge/L2/EthereumBridge.sol

@@ -56,8 +56,19 @@ contract EthereumBridge is
         return address(wrappedTokens[wrappedToken]) != address(0x0);
     }
 
+    function erc20Fee() public view returns (uint256) {
+        // receiveAssets selector (4 bytes) + address (20 bytes) + uint256 (32 bytes) + address (20 bytes) = 76 bytes
+        uint256 dataLength = 76;
+        return _messageBus().getMessageFee(dataLength);
+    }
+
+    function valueTransferFee() public view returns (uint256) {
+        return _messageBus().getValueTransferFee();
+    }
+
     function sendNative(address receiver) external payable {
         require(msg.value > 0, "Nothing sent.");
+        require(msg.value >= _messageBus().getValueTransferFee(), "Insufficient funds to publish value transfer");
         _messageBus().sendValueToL2{value: msg.value}(receiver, msg.value);
     }
 
@@ -77,6 +88,8 @@ contract EthereumBridge is
             amount,
             receiver
         );
+
+        require(msg.value >= _messageBus().getMessageFee(data.length), "Insufficient funds to publish message");
         queueMessage(remoteBridgeAddress, data, uint32(Topics.TRANSFER), 0, 0, msg.value);
     }
 

contracts/src/messaging/IMessageBus.sol

@@ -72,4 +72,10 @@ interface IMessageBus {
 
     // This is a testnet function which allows the bridge owner to retrieve all funds from the message bus.
     function retrieveAllFunds(address receiver) external;
+
+    // the fee needed to be paid in msg.value to publish the value transfer
+    function getValueTransferFee() external view returns (uint256);
+
+    // the fee needed to be paid in msg.value to publish a message
+    function getMessageFee(uint256 payloadLength) external view returns (uint256);
 }

contracts/src/messaging/MessageBus.sol

@@ -82,11 +82,11 @@ contract MessageBus is IMessageBus, Initializable, OwnableUpgradeable {
                8; // sequence (uint64)
     }
 
-    function getValueTransferFee() internal view returns (uint256) {
+    function getValueTransferFee() public view returns (uint256) {
         return fees.messageFee(32); //just a hash
     }
 
-    function getMessageFee(uint256 payloadLength) internal view returns (uint256) {
+    function getMessageFee(uint256 payloadLength) public view returns (uint256) {
         return fees.messageFee(payloadLength + getFixedDataLength());
     }