Merge pull request #254 from defi-wonderland/feat/execute-message-hash

Adding messageHash to ExecutingMessage

specs/interop/predeploys.md

@@ -94,19 +94,20 @@ The `ExecutingMessage` event represents an executing message. It MUST be emitted
 to `executeMessage`.
 
 ```solidity
-event ExecutingMessage(bytes,bytes);
+event ExecutingMessage(bytes32 indexed msgHash, Identifier identifier);
 ```
 
-The data encoded in the event contains the `Identifier` and the `msg`.
+The data encoded in the event contains the keccak hash of the `msg` and the `Identifier`.
 The following pseudocode shows the deserialization:
 
 ```solidity
-(bytes memory identifier, bytes memory log) = abi.decode(log.data, (bytes, bytes));
-Identifier id = abi.decode(identifier, (Identifier));
+bytes32 msgHash = log.topics[1];
+Identifier identifier = abi.decode(log.data, (Identifier));
 ```
 
-It is not possible to use solidity structs directly in events, which is why it is ABI encoded
-into `bytes` first.
+Emitting the hash of the message is more efficient than emitting the
+message in its entirety. Equality with the initiating message can be handled off-chain through
+hash comparison.
 
 ### Reference implementation
 
@@ -133,7 +134,7 @@ function executeMessage(Identifier calldata _id, address _target, bytes calldata
 
     require(success);
 
-    emit ExecutingMessage(abi.encode(_id), _msg);
+    emit ExecutingMessage(keccak256(_msg), _id);
 }
 ```
 

specs/interop/sequencer.md

@@ -103,7 +103,8 @@ if not success:
 
 for log in receipt.logs:
   if is_executing_message(log):
-      id, message = abi.decode(log.data)
+      id = abi.decode(log.data)
+      messageHash = log.topics[1]
 
       # assumes there is a client for each chain in the dependency set
       eth = clients[id.chainid]
@@ -116,7 +117,7 @@ for log in receipt.logs:
       if len(log) == 0:
         return False
 
-      if message != encode(log[0]):
+      if messageHash != hash(encode(log[0])):
         return False
 
       block = eth.getBlockByNumber(id.blocknumber)