code: function findToken(message, token, offset=0, maxSearchLength) {
    let searchLength = message.length;
    if (maxSearchLength) {
      searchLength = Math.min(offset + maxSearchLength, message.length);
    }
  
    for (let i = offset; i < searchLength; i++) {
      // If the first value of the message matches
      // the first value of the token, check if
      // this is the full token.
      if (message[i] === token[0]) {
        if (containsToken(message, token, i)) {
          return i;
        }
      }
    }
  
    return -1;
  }
docs: Finds a given token in a message at a given offset.
  @param {Uint8Array} message message content
  @param {Uint8Array} token substring that should be found
  @param {String} offset message body offset from where search should start
  @returns {Boolean} whether message has a part at given offset or not