bug: [webflux] ServerRequest.bodyToMono returns empty

[kdby-io]

Expected behavior

ServerRequest.bodyToMono returns its body.

Actual behavior

ServeRequest.bodyToMono returns Mono.empty().

Steps to reproduce

1. Use graphql-dgs-example-java-webflux example.
2. Modify MyContextBuilder.build() as below

    public Mono<MyContext> build(@Nullable Map<String, ?> extensions, @Nullable HttpHeaders headers, @Nullable ServerRequest serverRequest) {
        assert serverRequest != null;
        return Mono.just(new MyContext())
                .doOnNext(body -> System.out.println("before bodyToMono"))
                .flatMap(c -> serverRequest.bodyToMono(String.class))
                .doOnNext(System.out::println)
                .doOnNext(body -> System.out.println("after bodyToMono"))
                .map(body -> new MyContext());
    }

3. Run its server
4. Request with { usingContext } query in localhost:8080/graphiql
5. See only before bodyToMono is printed

[srinivasankavitha]

Thanks for reporting!

[kilink]

The request body is already consumed in DefaultDgsWebfluxHttpHandler by the time your context builder is run, so the bodyToMono call is returning an empty Mono. I think this is expected behavior, as it's necessary for the body to get consumed by the HTTP handler, and unfortunately I don't think there is much that DGS itself can do about it. I think you'd need to implement a WebFilter and cache the request somehow.