Facing io.netty.handler.timeout.ReadTimeoutException: null while consuming server sent events

In the Mozilla description for server sent events there is a note:

A colon as the first character of a line is in essence a comment, and is ignored. Note: The comment line can be used to prevent connections from timing out; a server can send a comment periodically to keep the connection alive.

So periodically sending comments can keep the connection alive. So how do we send a comment?

Well spring has the class ServerSentEvent that has the function ServerSentEvent#comment. So if we use this class in combination with for instance Flux#interval we can merge in events containing only the comments keep alive.

Here is an example from a project i built a while back

@Bean
public RouterFunction<ServerResponse> foobars() {
    return route()
            .path("/api", builder -> builder
                .GET("/foobar/{id}", accept(TEXT_EVENT_STREAM), request -> ok()
                        .contentType(MediaType.TEXT_EVENT_STREAM)
                        .header("Cache-Control", "no-transform")
                        .body(Flux.merge(foobarHandler.stream(request.pathVariable("id")),
                                Flux.interval(Duration.ofSeconds(15)).map(aLong -> ServerSentEvent.<List<FoobarResponse>>builder()
                                        .comment("keep alive").build())), new ParameterizedTypeReference<ServerSentEvent<List<FoobarResponse>>>(){}))
            .build();
}