In-Order Delivery
Here is an example that sends and receives cross-chain messages with guaranteed in-order delivery.
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// a simple example to enforce in-order message delivery
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contract MsgExampleInOrder is MessageApp {
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event MessageReceived(
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address srcContract,
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uint64 srcChainId,
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address sender,
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uint64 seq,
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bytes message
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);
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// map at source chain. (dstChainId, dstContract) -> seq
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mapping(uint64 => mapping(address => uint64)) public sendSeq;
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// map at destination chain (srcChainId, srcContract) -> seq
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mapping(uint64 => mapping(address => uint64)) public recvSeq;
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constructor(address _messageBus) MessageApp(_messageBus) {}
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// called by user on source chain to send cross-chain message
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function sendMessage(
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address _dstContract,
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uint64 _dstChainId,
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bytes calldata _message
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) external payable {
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uint64 seq = sendSeq[_dstChainId][_dstContract];
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bytes memory message = abi.encode(msg.sender, seq, _message);
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sendMessage(_dstContract, _dstChainId, message, msg.value);
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sendSeq[_dstChainId][_dstContract] += 1;
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}
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// called by MessageBus on destination chain to receive message
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function executeMessage(
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address _srcContract,
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uint64 _srcChainId,
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bytes calldata _message,
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address // executor
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) external payable override onlyMessageBus returns (ExecutionStatus) {
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(address sender, uint64 seq, bytes memory message) = abi.decode(
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(_message),
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(address, uint64, bytes)
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);
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uint64 expectedSeq = recvSeq[_srcChainId][_srcContract];
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if (seq != expectedSeq) {
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// sequence number not expected, let executor retry.
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// Note: cannot revert here, because once a message execute tx is
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// reverted, it cannot be retried later.
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return ExecutionStatus.Retry;
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}
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emit MessageReceived(_srcContract, _srcChainId, sender, seq, message);
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recvSeq[_srcChainId][_srcContract] += 1;
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return ExecutionStatus.Success;
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}
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}
Last modified 1yr ago