hyperlane-monorepo/solidity/abacus-xapps/contracts/xapp-template/MessageTemplate.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.6.11;

import "@summa-tx/memview-sol/contracts/TypedMemView.sol";

/*
============ Overview: xApp Message Library ============
Messages are the actual data passed between chains.
We define messages as a byte vector in memory.

To make sure that messages are compact and chain agnostic,
we recommend a simple, custom serialization format (rather than ABI encoding).

TypedMemView is a library for working with memory in Solidity.
We use TypedMemView to create a custom serialization format for xApp messages.
We use a 1-byte type tag on the front of the message.
(The typed tag is optional if the user is familiar with writing wire protocols)

Message Flow Between xApps:
1. xApp Router A receives a command on chain A
2. xApp Router A encodes (formats) the information into a message
2. xApp Router A sends the message to xApp Router B on chain B via Abacus
3. xApp Router B receives the message via Abacus
4. xApp Router B decodes (gets) the information from the message and acts on it

The Message Library should contain the following for each type of message:
1. Formatter: a function which takes information as Solidity arguments and
   encodes it as a byte vector in a defined format, producing the message

2. Identifier: a function which takes a byte vector and returns TRUE
   if the vector is matches the expected format of this message type

3. Getter(s): function(s) which parse the information stored in the message
   and return them in the form of Solidity arguments
*/
library Message {
    using TypedMemView for bytes;
    using TypedMemView for bytes29;

    enum Types {
        Invalid, // 0
        A // 1 - a message which contains a single number
    }

    // ============ Formatters ============

    /**
     * @notice Given the information needed for a message TypeA
     * (in this example case, the information is just a single number)
     * format a bytes message encoding the information
     * @param _number The number to be included in the TypeA message
     * @return The encoded bytes message
     */
    function formatTypeA(uint256 _number) internal pure returns (bytes memory) {
        return abi.encodePacked(uint8(Types.A), _number);
    }

    // ============ Identifiers ============

    /**
     * @notice Get the type that the TypedMemView is cast to
     * @param _view The message
     * @return _type The type of the message (one of the enum Types)
     */
    function messageType(bytes29 _view) internal pure returns (Types _type) {
        _type = Types(uint8(_view.typeOf()));
    }

    /**
     * @notice Determine whether the message is a message TypeA
     * @param _view The message
     * @return _isTypeA True if the message is TypeA
     */
    function isTypeA(bytes29 _view) internal pure returns (bool _isTypeA) {
        _isTypeA = messageType(_view) == Types.A;
    }

    // ============ Getters ============

    /**
     * @notice Parse the number sent within a TypeA message
     * @param _view The message
     * @return _number The number encoded in the message
     */
    function number(bytes29 _view) internal pure returns (uint256 _number) {
        require(
            isTypeA(_view),
            "MessageTemplate/number: view must be of type A"
        );
        _number = uint256(_view.index(0, 32));
    }
}