Does SkyWalking Support Tracing for WebFlux WebClient Streaming (SSE) Calls? TID is Lost in Event Logs

[chenbihao]

I flipped through https://skywalking.apache.org/docs/skywalking-java/latest/en/setup/service-agent/java-agent/application-toolkit-trace-cross-thread/ as well https://skywalking.apache.org/docs/skywalking-java/latest/en/setup/service-agent/java-agent/application-toolkit-webflux/, the scenario doesn't seem to match very well and wonders if there is a way to do this, for example:

I use WebClientfor SSE streaming calls and log at different points in the response stream.

return webClientBuilder.build()
        .post().uri(url)
        .header(HttpHeaders.ACCEPT, MediaType.TEXT_EVENT_STREAM_VALUE)
        .retrieve()
        .bodyToFlux(MyDataClass.class)
        .doOnNext(dataChunk -> {
            // Goal: Log the correct TID here
            log.info("【SSE Data Chunk】: {}", dataChunk); // TID is N/A here
        })
        .doOnComplete(() -> {
            log.info("【SSE Stream Completed】"); // TID is N/A here too
        })
        .doOnError(error -> {
            log.error("【SSE Stream Error】", error);
        });

I tried using WebFluxSkyWalkingOperators.continueTracingas per the official docs:

.doOnEach(WebFluxSkyWalkingOperators.continueTracing(SignalType.ON_NEXT, () -> 
    log.info("Test log with tid")))

However, this results in an error during application startup or request processing: java.lang.IllegalStateException: No primary or single unique constructor found for interface org.springframework.web.server.ServerWebExchange. This error suggests that within the context of the stream processing, the continueTracingmethod internally cannot properly construct a ServerWebExchangeobject.

Specific Questions:
Does SkyWalking officially support tracing for streaming calls (like SSE) with WebFlux WebClient?
If supported, what is the correct way to implement it in my code scenario? Where did I go wrong with the continueTracingattempt?
If not supported, are there any known workarounds (e.g., manually propagating context using filters , or utilizing Spring's log id) to correlate TID in logs for streaming calls?
What are the best practices for ensuring trace context propagation across asynchronous stream operators in the reactive programming model?

[wu-sheng]

I think we don't have a plugin to support that. Only gRPC streaming is supported so far.
Personally, I don't have experience with this. But in general, you need a proper plugin to propagate tracing context with this streaming style APIs.

[chenbihao]

I found that Trace Cross Thread can do what I want, and it seems that a Wrapper can only be called once, so manual processing only once in doFinally is fine