code: private static void setContentLength(HttpRequest req, HttpHeaders headers, int contentLength) {
          // https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.4
          // prohibits to send message body for below cases.
          // and in those cases, content should be empty.
          if (req.method() == HttpMethod.HEAD || ArmeriaHttpUtil.isContentAlwaysEmpty(headers.status())) {
              return;
          }
          headers.setInt(HttpHeaderNames.CONTENT_LENGTH, contentLength);
      }
docs: Sets the 'content-length' header to the response.