code: static StringBuilder appendQuotedString(StringBuilder target, String key) {
          target.append('"');
          for (int i = 0, len = key.length(); i < len; i++) {
              char ch = key.charAt(i);
              switch (ch) {
                  case '\n':
                      target.append("%0A");
                      break;
                  case '\r':
                      target.append("%0D");
                      break;
                  case '"':
                      target.append("%22");
                      break;
                  default:
                      target.append(ch);
                      break;
              }
          }
          target.append('"');
          return target;
      }
docs: Appends a quoted-string to a StringBuilder.
  
  <p>RFC 2388 is rather vague about how one should escape special characters in form-data
  parameters, and as it turns out Firefox and Chrome actually do rather different things, and
  both say in their comments that they're not really sure what the right approach is. We go with
  Chrome's behavior (which also experimentally seems to match what IE does), but if you actually
  want to have a good chance of things working, please avoid double-quotes, newlines, percent
  signs, and the like in your field names.