String encode(String value) {
  // Map each code unit from the given value to a base-2 representation of this
  // code unit, adding zeroes to the left until the string has length 8, and join
  // each code unit representation to a single string using spaces
  return value.codeUnits.map((v) => v.toRadixString(2).padLeft(8, '0')).join(" ");
}
String decode(String value) {
  // Split the given value on spaces, parse each base-2 representation string to
  // an integer and return a new string from the corresponding code units
  return String.fromCharCodes(value.split(" ").map((v) => int.parse(v, radix: 2)));
}
void main() {
  print(encode("Hey"));    // Output: 01001000 01100101 01111001
  print(decode("01001000 01100101 01111001"));    // Output: Hey
}