How to Validate a Specific Value in the Request Body of a Multipart POST Request in Spring Cloud Gateway MVC?

Hi,

In our Spring Cloud Gateway MVC project, we need to validate a specific value in the request body of a multipart POST request before routing it to a downstream microservice.

Currently, we're reading the request in a before() filter, but this causes the body to appear empty when the RestClient forwards the request to the backend service. It seems this happens because the multipart stream is consumed and not cached.

From our understanding, a solution would require a version of GatewayMultipartHttpServletRequest that supports caching of the full multipart request.

Questions:

• Will support for multipart request caching be added in a future release?
• Is there a recommended workaround in the meantime?
• Is there a more elegant or idiomatic way to perform this kind of validation in Spring Cloud Gateway MVC?

Thanks in advance for your help!

Router configuration example

    return route()
        .POST(
            “path”
            https())
        .before(validate())
        .build();

Before filter example

public static Function<ServerRequest, ServerRequest> validate() {

  return request -> {

    var servletRequest = request.servletRequest();

    if (servletRequest instanceof MultipartHttpServletRequest multipartRequest) {
      try {
        var data = multipartRequest.getPart("data");
        if (data != null) {
           // Validation logic based on data part of multipart request
        }
      } catch (IOException | ServletException e) {
        throw new RuntimeException(e);
      }
    }
  };
}

Start with the MVC before() filter path, GatewayMultipartHttpServletRequest, and the RestClient forwarding behavior shown in the issue. Determine whether multipart request caching is supported or needs a workaround, and document or implement the recommended idiomatic validation approach without leaving the forwarded request body empty.