Add interaction of Teleporter and fallback function (#206)

add interaction of Teleporter and fallback function

contracts/src/Teleporter/README.md

@@ -5,7 +5,9 @@
   - [Data Flow](#data-flow)
   - [Properties](#properties)
   - [Fees](#fees)
+    - [Message Receipts and Fee Redemption](#message-receipts-and-fee-redemption)
   - [Required Interface](#required-interface)
+  - [Teleporter Contract Deployment](#teleporter-contract-deployment)
   - [Message Delivery and Execution](#message-delivery-and-execution)
 
 
@@ -19,6 +21,8 @@ The `ITeleporterMessenger` interface provides two primary methods:
 The `ITeleporterReceiver` interface provides a single method. All contracts that wish to receive Teleporter messages on the destination chain must implement this interface:
 - `receiveTeleporterMessage`: called by the Teleporter contract on the destination chain to deliver a message to the destination contract.
 
+> Note: If a contract does not implement `ITeleporterReceiver`, but instead implements [fallback](https://docs.soliditylang.org/en/latest/contracts.html#fallback-function), the fallback function will be called when Teleporter attempts to perform message execution. The message execution is marked as failed if the fallback function reverts, otherwise it is marked as successfully executed.
+
 ## Data Flow
 <div align="center">
   <img src="../../../resources/TeleporterDataFlowDiagram.png?raw=true"/>

contracts/src/Teleporter/TeleporterMessenger.sol

@@ -357,6 +357,8 @@ contract TeleporterMessenger is ITeleporterMessenger, ReentrancyGuards {
 
         // Re-encode the payload by ABI encoding a call to the {receiveTeleporterMessage} function
         // defined by the {ITeleporterReceiver} interface.
+        // If the destination address does not implement {receiveTeleporterMessage}, but does implement
+        // a fallback function, then the fallback function will be called instead.
         bytes memory payload = abi.encodeCall(
             ITeleporterReceiver.receiveTeleporterMessage,
             (originBlockchainID, message.senderAddress, message.message)

contracts/src/Teleporter/tests/FallbackReceiveTests.t.sol

@@ -0,0 +1,148 @@
+// (c) 2023, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+// SPDX-License-Identifier: Ecosystem
+
+pragma solidity 0.8.18;
+
+import {
+    TeleporterMessengerTest,
+    TeleporterMessage,
+    WarpMessage,
+    TeleporterMessageReceipt
+} from "./TeleporterMessengerTest.t.sol";
+
+enum FallbackReceiveAction {
+    Fail,
+    Succeed
+}
+
+contract FallbackReceiveApp {
+    bytes32 public originChainID;
+    address public originSenderAddress;
+    uint256 public nonce;
+
+    constructor(bytes32 originChainID_, address originSenderAddress_) {
+        originChainID = originChainID_;
+        originSenderAddress = originSenderAddress_;
+    }
+
+    // solhint-disable-next-line no-complex-fallback, payable-fallback
+    fallback(bytes calldata data) external returns (bytes memory) {
+        bytes4 selector = bytes4(data[:4]);
+        // Check that the function selector was for receiveTeleporterMessage.
+        require(
+            selector == bytes4(keccak256("receiveTeleporterMessage(bytes32,address,bytes)")),
+            "FallbackReceiveApp: Invalid selector"
+        );
+
+        (bytes32 originChainID_, address originSenderAddress_, bytes memory message) =
+            abi.decode(data[4:], (bytes32, address, bytes));
+
+        require(originChainID == originChainID_, "FallbackReceiveApp: Invalid origin chain ID");
+        require(
+            originSenderAddress == originSenderAddress_,
+            "FallbackReceiveApp: Invalid origin sender address"
+        );
+
+        FallbackReceiveAction action = abi.decode(message, (FallbackReceiveAction));
+
+        if (action == FallbackReceiveAction.Fail) {
+            require(false, "FallbackReceiveApp: Fallback failed");
+        } else if (action == FallbackReceiveAction.Succeed) {
+            nonce++;
+        } else {
+            revert("FallbackReceiveApp: Invalid action");
+        }
+
+        return abi.encode(nonce);
+    }
+}
+
+contract FallbackReceiveTest is TeleporterMessengerTest {
+    FallbackReceiveApp public destinationContract;
+
+    function setUp() public virtual override {
+        TeleporterMessengerTest.setUp();
+        destinationContract = new FallbackReceiveApp(
+            DEFAULT_ORIGIN_CHAIN_ID,
+            address(this)
+        );
+    }
+
+    function testFallbackSuccess() public {
+        uint256 nonce = destinationContract.nonce();
+
+        // Construct the mock message to be received.
+        TeleporterMessage memory messageToReceive = TeleporterMessage({
+            messageID: 1,
+            senderAddress: address(this),
+            destinationBlockchainID: DEFAULT_DESTINATION_CHAIN_ID,
+            destinationAddress: address(destinationContract),
+            requiredGasLimit: DEFAULT_REQUIRED_GAS_LIMIT,
+            allowedRelayerAddresses: new address[](0),
+            receipts: new TeleporterMessageReceipt[](0),
+            message: abi.encode(FallbackReceiveAction.Succeed)
+        });
+        WarpMessage memory warpMessage =
+            _createDefaultWarpMessage(DEFAULT_ORIGIN_CHAIN_ID, abi.encode(messageToReceive));
+
+        // Mock the call to the warp precompile to get the message.
+        _setUpSuccessGetVerifiedWarpMessageMock(0, warpMessage);
+
+        // Receive the message and check that message execution was successful.
+        vm.expectEmit(true, true, true, true, address(teleporterMessenger));
+        emit MessageExecuted(DEFAULT_ORIGIN_CHAIN_ID, messageToReceive.messageID);
+        vm.expectEmit(true, true, true, true, address(teleporterMessenger));
+        emit ReceiveCrossChainMessage(
+            warpMessage.sourceChainID,
+            messageToReceive.messageID,
+            address(this),
+            DEFAULT_RELAYER_REWARD_ADDRESS,
+            messageToReceive
+        );
+        teleporterMessenger.receiveCrossChainMessage(0, DEFAULT_RELAYER_REWARD_ADDRESS);
+
+        // Check that the nonce was incremented.
+        assertEq(destinationContract.nonce(), nonce + 1);
+    }
+
+    function testFallbackFail() public {
+        uint256 nonce = destinationContract.nonce();
+
+        // Construct the mock message to be received.
+        TeleporterMessage memory messageToReceive = TeleporterMessage({
+            messageID: 1,
+            senderAddress: address(this),
+            destinationBlockchainID: DEFAULT_DESTINATION_CHAIN_ID,
+            destinationAddress: address(destinationContract),
+            requiredGasLimit: DEFAULT_REQUIRED_GAS_LIMIT,
+            allowedRelayerAddresses: new address[](0),
+            receipts: new TeleporterMessageReceipt[](0),
+            message: abi.encode(FallbackReceiveAction.Fail)
+        });
+        WarpMessage memory warpMessage =
+            _createDefaultWarpMessage(DEFAULT_ORIGIN_CHAIN_ID, abi.encode(messageToReceive));
+
+        // Mock the call to the warp precompile to get the message.
+        _setUpSuccessGetVerifiedWarpMessageMock(0, warpMessage);
+
+        // Receive the message and check that message execution was successful.
+        vm.expectEmit(true, true, true, true, address(teleporterMessenger));
+        emit MessageExecutionFailed(
+            DEFAULT_ORIGIN_CHAIN_ID, messageToReceive.messageID, messageToReceive
+        );
+        vm.expectEmit(true, true, true, true, address(teleporterMessenger));
+        emit ReceiveCrossChainMessage(
+            warpMessage.sourceChainID,
+            messageToReceive.messageID,
+            address(this),
+            DEFAULT_RELAYER_REWARD_ADDRESS,
+            messageToReceive
+        );
+        teleporterMessenger.receiveCrossChainMessage(0, DEFAULT_RELAYER_REWARD_ADDRESS);
+
+        // Check that the nonce was not changed.
+        assertEq(destinationContract.nonce(), nonce);
+    }
+}