How do you use WebFlux to parse an event stream that does not conform to Server Sent Events? - spring

Question

I am trying to use WebClient to deal with the Docker /events endpoint. However, it does not conform to the text/eventstream contract in that each message is separated by 2 LFs. It just sends it as one JSON document followed by another.
It also sets the MIME type to application/json rather than text/eventstream.
What I am thinking of but not implemented yet is to create a node proxy that will add the required line feed and put that in between but I was hoping to avoid that kind of workaround.

Answer 1

Instead of trying to handle a ServerSentEvent, just receive it as a String. Then attempt to parse it as JSON (ignoring the ones that fail which I am presuming may happen but I haven't hit it myself)
#PostConstruct
public void setUpStreamer() {
final Map<String, List<String>> filters = new HashMap<>();
filters.put("type", Collections.singletonList("service"));
WebClient.create(daemonEndpoint)
.get()
.uri("/events?filters={filters}",
mapper.writeValueAsString(filters))
.retrieve()
.bodyToFlux(String.class)
.flatMap(Mono::justOrEmpty)
.map(s -> {
try {
return mapper.readValue(s, Map.class);
} catch (IOException e) {
log.warn("unable to parse {} as JSON", s);
return null;
}
})
.flatMap(Mono::justOrEmpty)
.subscribe(
event -> {
log.trace("event={}", event);
refreshRoutes();
},
throwable -> log.error("Error on event stream: {}", throwable.getMessage(), throwable),
() -> log.warn("event stream completed")
);
}