docs: private String makeBoundary() {
          StringBuffer s = new StringBuffer();
          int length = 32;
          int base = 97; //a..z
          int range = 26;
          while (length-- > 0) {
              char c = (char) (int) (Math.random() * range + base);
              s.append(c);
          }
          return s.toString();
      }