code: async function readToEnd(input, concat) {
    if (isStream(input)) {
      return getReader(input).readToEnd(concat);
    }
    return input;
  }
docs: Read a stream to the end and return its contents, concatenated by the concat function (defaults to concat).
  @param {ReadableStream|Uint8array|String} input
  @param {Function} concat
  @returns {Promise<Uint8array|String|Any>} the return value of concat()
  @async