function amf0decUString(buf) {
  let sLen = buf.readUInt16BE(0);
  return { len: 2 + sLen, value: buf.toString("utf8", 2, 2 + sLen) };
}
AMF0 Decode Untyped (without the type byte) String
@param {Buffer} buf
@returns {{len: *, value: (* | string | string)}}