Shared via Pony Playground (https://playground.ponylang.io/?gist=18be3e4c6b091c064de4cb70c9685920)

main.pony

use "buffered"

actor Main
  new create(env: Env) =>
    
    let reader = Reader
    
    while true do
      reader.append(data_from_somewhere)
      if reader.u128_available() then
        let u: U128 = reader.u128()
        // ... more ...
      end
    end