BufferLoader

BufferLoader.swift

struct BufferLoader {
    var buffer: UnsafeRawBufferPointer
    var byteOffset: Int = 0
    
    mutating func loadUnaligned<T>(as type: T.Type) -> T {
        defer { byteOffset += MemoryLayout<T>.size }
        return buffer.loadUnaligned(fromByteOffset: byteOffset, as: T.self)
    }
}
extension UnsafeRawBufferPointer {
    func load<Result>(_ block: (inout BufferLoader) throws -> Result) rethrows -> Result {
        var loader = BufferLoader(buffer: self)
        return try block(&loader)
    }
}

to store, just append to ContiguousArray

var bytes = ContiguousArray<UInt8>()
bytes.reserveCapacity(MemoryLayout<UInt8>.size + MemoryLayout<UInt32>.size)
Swift.withUnsafeBytes(of: level.bigEndian, bytes.append)
Swift.withUnsafeBytes(of: key.bigEndian, bytes.append)
return try bytes.withUnsafeBytes(body)