feat(protocol): add readonly functions isMessageFailed & isMessageReceived to Bridge

packages/protocol/contracts/bridge/Bridge.sol

@@ -369,7 +369,8 @@ contract Bridge is EssentialContract, IBridge {
         });
     }
 
-    /// @notice Checks if a msgHash has failed on its destination chain.
+    /// @notice Checks if a msgHash has failed on its destination chain and caches cross-chain data
+    /// if requested.
     /// @param _message The message.
     /// @param _proof The merkle inclusion proof.
     /// @return true if the message has failed, false otherwise.
@@ -390,7 +391,8 @@ contract Bridge is EssentialContract, IBridge {
         );
     }
 
-    /// @notice Checks if a msgHash has failed on its destination chain.
+    /// @notice Checks if a msgHash has failed on its destination chain and caches cross-chain data
+    /// if requested.
     /// @param _message The message.
     /// @param _proof The merkle inclusion proof.
     /// @return true if the message has failed, false otherwise.
@@ -407,6 +409,48 @@ contract Bridge is EssentialContract, IBridge {
         );
     }
 
+    /// @notice Checks if a msgHash has failed on its destination chain.
+    /// This is the 'readonly' version of proveMessageFailed.
+    /// @param _message The message.
+    /// @param _proof The merkle inclusion proof.
+    /// @return true if the message has failed, false otherwise.
+    function isMessageFailed(
+        Message calldata _message,
+        bytes calldata _proof
+    )
+        external
+        view
+        returns (bool)
+    {
+        if (_message.srcChainId != block.chainid) return false;
+
+        return _isSignalReceived(
+            resolve("signal_service", false),
+            signalForFailedMessage(hashMessage(_message)),
+            _message.destChainId,
+            _proof
+        );
+    }
+
+    /// @notice Checks if a msgHash has failed on its destination chain.
+    /// This is the 'readonly' version of proveMessageReceived.
+    /// @param _message The message.
+    /// @param _proof The merkle inclusion proof.
+    /// @return true if the message has failed, false otherwise.
+    function isMessageReceived(
+        Message calldata _message,
+        bytes calldata _proof
+    )
+        external
+        view
+        returns (bool)
+    {
+        if (_message.destChainId != block.chainid) return false;
+        return _isSignalReceived(
+            resolve("signal_service", false), hashMessage(_message), _message.srcChainId, _proof
+        );
+    }
+
     /// @notice Checks if the destination chain is enabled.
     /// @param _chainId The destination chain ID.
     /// @return enabled_ True if the destination chain is enabled.
@@ -575,7 +619,7 @@ contract Bridge is EssentialContract, IBridge {
         }
     }
 
-    /// @notice Checks if the signal was received.
+    /// @notice Checks if the signal was received and caches cross-chain data if requested.
     /// @param _signalService The signal service address.
     /// @param _signal The signal.
     /// @param _chainId The ID of the chain the signal is stored on.
@@ -598,4 +642,30 @@ contract Bridge is EssentialContract, IBridge {
             return false;
         }
     }
+
+    /// @notice Checks if the signal was received.
+    /// This is the 'readonly' version of _proveSignalReceived.
+    /// @param _signalService The signal service address.
+    /// @param _signal The signal.
+    /// @param _chainId The ID of the chain the signal is stored on.
+    /// @param _proof The merkle inclusion proof.
+    /// @return true if the message was received.
+    function _isSignalReceived(
+        address _signalService,
+        bytes32 _signal,
+        uint64 _chainId,
+        bytes calldata _proof
+    )
+        private
+        view
+        returns (bool)
+    {
+        try ISignalService(_signalService).verifySignalReceived(
+            _chainId, resolve(_chainId, "bridge", false), _signal, _proof
+        ) {
+            return true;
+        } catch {
+            return false;
+        }
+    }
 }

packages/protocol/contracts/bridge/IBridge.sol

@@ -104,7 +104,7 @@ interface IBridge {
     event AddressBanned(address indexed addr, bool banned);
 
     /// @notice Sends a message to the destination chain and takes custody
-    /// of Ether required in this contract. All extra Ether will be refunded.
+    /// of Ether required in this contract.
     /// @param _message The message to be sent.
     /// @return msgHash_ The hash of the sent message.
     /// @return message_ The updated message sent.

packages/protocol/contracts/signal/ISignalService.sol

@@ -114,7 +114,7 @@ interface ISignalService {
     /// @param _signal The signal (message) to send.
     /// @param _proof Merkle proof that the signal was persisted on the
     /// source chain.
-    function isSignalReceived(
+    function verifySignalReceived(
         uint64 _chainId,
         address _app,
         bytes32 _signal,

packages/protocol/contracts/signal/SignalService.sol

@@ -134,13 +134,13 @@ contract SignalService is EssentialContract, ISignalService {
 
     /// @inheritdoc ISignalService
     /// @dev This function may revert.
-    function isSignalReceived(
+    function verifySignalReceived(
         uint64 _chainId,
         address _app,
         bytes32 _signal,
         bytes calldata _proof
     )
-        public
+        external
         view
         validSender(_app)
         nonZeroValue(_signal)