runtime/runtime_impl_jetty12/src/main/java/com/google/apphosting/runtime/jetty/ee8/FileSender.java [125:162]:
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  public boolean checkIfUnmodified(
      HttpServletRequest request, HttpServletResponse response, Resource resource)
      throws IOException {
    if (!request.getMethod().equals(HttpMethod.HEAD.asString())) {
      String ifms = request.getHeader(HttpHeader.IF_MODIFIED_SINCE.asString());
      if (ifms != null) {
        long ifmsl = -1;
        try {
          ifmsl = request.getDateHeader(HttpHeader.IF_MODIFIED_SINCE.asString());
        } catch (IllegalArgumentException e) {
          // Ignore bad date formats.
        }
        if (ifmsl != -1) {
          if (resource.lastModified().toEpochMilli() <= ifmsl) {
            response.reset();
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.flushBuffer();
            return true;
          }
        }
      }

      // Parse the if[un]modified dates and compare to resource
      long date = -1;
      try {
        date = request.getDateHeader(HttpHeader.IF_UNMODIFIED_SINCE.asString());
      } catch (IllegalArgumentException e) {
        // Ignore bad date formats.
      }
      if (date != -1) {
        if (resource.lastModified().toEpochMilli() > date) {
          response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
          return true;
        }
      }
    }
    return false;
  }
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runtime/runtime_impl_jetty12/src/main/java/com/google/apphosting/runtime/jetty/ee10/FileSender.java [125:162]:
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  public boolean checkIfUnmodified(
      HttpServletRequest request, HttpServletResponse response, Resource resource)
      throws IOException {
    if (!request.getMethod().equals(HttpMethod.HEAD.asString())) {
      String ifms = request.getHeader(HttpHeader.IF_MODIFIED_SINCE.asString());
      if (ifms != null) {
        long ifmsl = -1;
        try {
          ifmsl = request.getDateHeader(HttpHeader.IF_MODIFIED_SINCE.asString());
        } catch (IllegalArgumentException e) {
          // Ignore bad date formats.
        }
        if (ifmsl != -1) {
          if (resource.lastModified().toEpochMilli() <= ifmsl) {
            response.reset();
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.flushBuffer();
            return true;
          }
        }
      }

      // Parse the if[un]modified dates and compare to resource
      long date = -1;
      try {
        date = request.getDateHeader(HttpHeader.IF_UNMODIFIED_SINCE.asString());
      } catch (IllegalArgumentException e) {
        // Ignore bad date formats.
      }
      if (date != -1) {
        if (resource.lastModified().toEpochMilli() > date) {
          response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
          return true;
        }
      }
    }
    return false;
  }
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