code: public static int getContentLengthValue(H2HeaderField header) {
          if ("content-length".equalsIgnoreCase(header.getName())) {
              return Integer.parseInt(header.getValue());
          }
          return -1;
      }
docs: Get the content length value from a header, if one exists
  
  @param H2HeaderField
  @return the content-length value, or -1 if no content-length is found