Callback for app layer to aware the message dispatch result (#99)

* on message delivery

* fix

* rename

* increase timeout

* add some doc

contracts/bridge/contracts/common/message/OutboundLane.sol

@@ -18,6 +18,7 @@ pragma experimental ABIEncoderV2;
 import "@openzeppelin/contracts/access/AccessControl.sol";
 import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
 import "../../interfaces/IOutboundLane.sol";
+import "../../interfaces/IOnMessageDelivered.sol";
 import "./MessageVerifier.sol";
 import "./TargetChain.sol";
 import "./SourceChain.sol";
@@ -29,8 +30,10 @@ contract OutboundLane is IOutboundLane, MessageVerifier, TargetChain, SourceChai
     event MessagePruned(uint64 oldest_unpruned_nonce);
     event MessageFeeIncreased(uint64 nonce, uint256 fee);
     event RelayerReward(address relayer, uint256 reward);
+    event CallbackMessageDelivered(uint64 nonce, bool result);
 
     bytes32 internal constant OUTBOUND_ROLE = keccak256("OUTBOUND_ROLE");
+    uint256 internal constant MAX_GAS_PER_MESSAGE = 100000;
     uint64 internal constant MAX_PENDING_MESSAGES = 50;
     uint64 internal constant MAX_PRUNE_MESSAGES_ATONCE = 10;
 
@@ -79,7 +82,13 @@ contract OutboundLane is IOutboundLane, MessageVerifier, TargetChain, SourceChai
         _setupRole(DEFAULT_ADMIN_ROLE, msg.sender);
     }
 
-    // Send message over lane.
+    /**
+     * @notice Send message over lane.
+     * Submitter could be a contract or just an EOA address.
+     * At the beginning of the launch, submmiter is permission, after the system is stable it will be permissionless.
+     * @param targetContract The target contract address which you would send cross chain message to
+     * @param encoded The calldata which encoded by ABI Encoding
+     */
     function send_message(address targetContract, bytes calldata encoded) external payable override nonReentrant returns (uint64) {
         require(hasRole(OUTBOUND_ROLE, msg.sender), "Lane: NotAuthorized");
         require(outboundLaneNonce.latest_generated_nonce - outboundLaneNonce.latest_received_nonce <= MAX_PENDING_MESSAGES, "Lane: TooManyPendingMessages");
@@ -135,7 +144,7 @@ contract OutboundLane is IOutboundLane, MessageVerifier, TargetChain, SourceChai
     ) public nonReentrant {
         verify_lane_data_proof(hash(inboundLaneData), messagesProof);
         DeliveredMessages memory confirmed_messages = confirm_delivery(inboundLaneData);
-        // TODO: callback `on_messages_delivered`
+        on_messages_delivered(confirmed_messages);
         pay_relayers_rewards(inboundLaneData.relayers, confirmed_messages.begin, confirmed_messages.end);
         commit();
     }
@@ -245,6 +254,22 @@ contract OutboundLane is IOutboundLane, MessageVerifier, TargetChain, SourceChai
         }
     }
 
+    function on_messages_delivered(DeliveredMessages memory confirmed_messages) internal {
+        for (uint64 nonce = confirmed_messages.begin; nonce <= confirmed_messages.end; nonce ++) {
+            uint256 offset = nonce - confirmed_messages.begin;
+            bool dispatch_result = ((confirmed_messages.dispatch_results >> offset) & 1) > 0;
+            // Submitter could be a contract or just an EOA address.
+            address submitter = messages[nonce].payload.sourceAccount;
+            bytes memory deliveredCallbackData = abi.encodeWithSelector(
+                IOnMessageDelivered.on_messages_delivered.selector,
+                nonce,
+                dispatch_result
+            );
+            (bool ok,) = submitter.call{value: 0, gas: MAX_GAS_PER_MESSAGE}(deliveredCallbackData);
+            emit CallbackMessageDelivered(nonce, ok);
+        }
+    }
+
 	/// Prune at most `max_messages_to_prune` already received messages.
 	///
 	/// Returns number of pruned messages.

contracts/bridge/contracts/interfaces/ICrossChainFilter.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.7.0;
+pragma solidity >=0.6.0;
 
 /**
  * @title A interface for message layer to filter unsafe message

contracts/bridge/contracts/interfaces/IOnMessageDelivered.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.6.0;
+
+/**
+ * @title A interface for app layer to get message dispatch result
+ * @author echo
+ * @notice The app layer could implement the interface `IOnMessageDelivered` to receive message dispatch result (optionally)
+ */
+interface IOnMessageDelivered {
+    /**
+     * @notice Message delivered callback
+     * @param nonce Nonce of the callback message
+     * @param dispatch_result Dispatch result of cross chain message
+     */
+    function on_messages_delivered(uint64 nonce, bool dispatch_result) external;
+}

contracts/bridge/test/v1/2_test_light_client_gas.js

@@ -86,7 +86,7 @@ describe("Light Client Gas Usage", function () {
   for (const testCase of testCases) {
     it(`runs full flow with ${testCase.totalNumberOfValidators} validators and ${testCase.totalNumberOfSignatures} signers with the complete transaction succeeding`,
       async function () {
-        this.timeout(1000 * 100);
+        this.timeout(1000 * 200);
         await runFlow(testCase.totalNumberOfValidators, testCase.totalNumberOfSignatures)
       });
   }

contracts/bridge/test/v2/test_sync_message_layer.js

@@ -47,6 +47,11 @@ const receive_messages_delivery_proof = async (begin, end) => {
     await expect(tx)
       .to.emit(outbound, "MessagesDelivered")
       .withArgs(begin, end, 0)
+    for (let i = begin; i<=end; i++) {
+      await expect(tx)
+        .to.emit(outbound, "CallbackMessageDelivered")
+        .withArgs(i, true)
+    }
     await logNonce()
 }