Sesame-Server/Sources/App/Message.swift

import Foundation
import NIOCore

struct Message: Equatable, Hashable {

    struct Content: Equatable, Hashable {

        let time: UInt32

        let id: UInt32

        init(time: UInt32, id: UInt32) {
            self.time = time
            self.id = id
        }

        init<T: Sequence>(decodeFrom data: T) where T.Element == UInt8 {
            self.time = UInt32(data: data.prefix(4))
            self.id = UInt32(data: data.dropFirst(4))
        }

        static var length: Int {
            MemoryLayout<UInt32>.size * 2
        }

        var encoded: Data {
            time.encoded + id.encoded
        }

        var bytes: [UInt8] {
            time.bytes + id.bytes
        }
    }

    let mac: Data

    let content: Content

    init(mac: Data, content: Content) {
        self.mac = mac
        self.content = content
    }

    init?(decodeFrom buffer: ByteBuffer) {
        guard let data = buffer.getBytes(at: 0, length: Message.length) else {
            return nil
        }
        self.init(decodeFrom: data)
    }

    var encoded: Data {
        mac + content.encoded
    }

    var bytes: [UInt8] {
        Array(mac) + content.bytes
    }
}

 extension UInt32 {

     init<T: Sequence>(data: T) where T.Element == UInt8 {
        self = data
            .reversed()
            .enumerated()
            .map { UInt32($0.element) << ($0.offset * 8) }
            .reduce(0, +)
    }

    var encoded: Data {
        .init(bytes)
    }

    var bytes: [UInt8] {
        (0..<4).reversed().map {
            UInt8((self >> ($0*8)) & 0xFF)
        }
    }
}