Spring webclient exchangeToFlux() not making HTTP request - spring

Question

I'm using Spring WebFlux 5.3.6's WebClient to stream a response from a REST endpoint that generates text/csv content.
I can use retrieve() and responseSpec.bodyToFlux to stream the body only like this:
WebClient.ResponseSpec responseSpec = headersSpec.retrieve();
Flux<DataBuffer> dataBufferFlux = responseSpec.bodyToFlux(DataBuffer.class);
DataBufferUtils
.write(dataBufferFlux, outputStream)
.blockLast(Duration.of(20, ChronoUnit.SECONDS));
but I want to get hold of the content-type header and validate it as part of the test. The above code provides access to the response body only, and not the headers.
I've tried to instead use exchangeToFlux() to get more control, and access to the response headers, but what I'm seeing is that the HTTP request is never made. If I add a breakpoint to myResponse.setStatus(clientResponse.rawStatusCode()); it is never hit.
A fuller code sample is below. I've struggled to find any examples of exchangeToFlux that use DataBuffer to stream the result back.
HttpClient httpClient = HttpClient.create()
.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 5000)
.responseTimeout(Duration.ofMillis(5000))
.doOnConnected(conn ->
conn.addHandlerLast(new ReadTimeoutHandler(5000, TimeUnit.MILLISECONDS))
.addHandlerLast(new WriteTimeoutHandler(5000, TimeUnit.MILLISECONDS)));
WebClient webClient = WebClient.builder()
.clientConnector(new ReactorClientHttpConnector(httpClient))
.build();
WebClient.RequestHeadersSpec<?> headersSpec = webClient
.get()
.uri("http://localhost:8080/v1/users")
.header(CONTENT_TYPE, "text/csv");
MyResponse<T> myResponse = new MyResponse<>();
CountDownLatch latch = new CountDownLatch(1);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
headersSpec.exchangeToFlux(clientResponse -> {
// Never enters here!
myResponse.setStatus(clientResponse.rawStatusCode());
myResponse.setContentType(clientResponse.headers().contentType());
latch.countDown();
if (clientResponse.statusCode() == HttpStatus.OK) {
Flux<DataBuffer> dataBufferFlux = clientResponse.bodyToFlux(DataBuffer.class);
DataBufferUtils
.write(dataBufferFlux, outputStream)
.blockLast(Duration.of(20, ChronoUnit.SECONDS));
return dataBufferFlux;
}
return Flux.empty();
});
latch.await();
return myResponse;

Answer 1

Seem's like you are not subscribing to the Flux returned from headersSpec.exchangeToFlux.
headersSpec.exchangeToFlux(clientResponse -> {
// Never enters here!
myResponse.setStatus(clientResponse.rawStatusCode());
myResponse.setContentType(clientResponse.headers().contentType());
latch.countDown();
if (clientResponse.statusCode() == HttpStatus.OK) {
Flux<DataBuffer> dataBufferFlux = clientResponse.bodyToFlux(DataBuffer.class);
DataBufferUtils
.write(dataBufferFlux, outputStream)
.blockLast(Duration.of(20, ChronoUnit.SECONDS));
return dataBufferFlux;
}
return Flux.empty();
})
.subscribe(); // <- Subscribe is missing.