Accessing trace ID within reactive WebFilter #30470
Description
Affects: 6.0.8 (spring-webflux)
I have a simple filter that should just inject current trace ID to the response:
package some.controller;
import io.micrometer.tracing.Span;
import io.micrometer.tracing.Tracer;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.Ordered;
import org.springframework.http.HttpHeaders;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Mono;
import java.util.UUID;
@Slf4j
@Component
public class AddResponseHeaderWebFilter implements WebFilter, Ordered {
private final Tracer tracer;
public AddResponseHeaderWebFilter(
final Tracer tracer
) {
this.tracer = tracer;
}
@SuppressWarnings("NullableProblems")
@Override
public Mono<Void> filter(final ServerWebExchange exchange, final WebFilterChain chain) {
return chain.filter(withCallback(exchange));
}
private ServerWebExchange withCallback(final ServerWebExchange exchange) {
exchange
.getResponse()
.beforeCommit(() -> {
HttpHeaders httpHeaders = exchange.getResponse().getHeaders();
httpHeaders.add("trace-id", callId());
return Mono.empty();
});
return exchange;
}
private static String fallbackValue() {
String fallbackValue = UUID.randomUUID().toString();
log.warn("Could not use trace ID; generated dummy UUID for tracking purposes: {}", fallbackValue);
return fallbackValue;
}
private String callId() {
Span currentSpan = this.tracer.currentSpan();
return currentSpan == null
? fallbackValue()
: currentSpan.context().traceId();
}
@Override
public int getOrder() {
return Ordered.HIGHEST_PRECEDENCE;
}
}it works well if my controller returns Mono<List> or Mono but always falls into "fallback" when controller returns Flux;
I am not sure if it is a known limitation now, or some additional configuration / code change is needed on my end?