Description:
I am developing a Spring WebFlux application that integrates with a third-party API. This API returns data in the text/event-stream format, specifically for streaming chat messages. I have set up an endpoint in my application to forward requests to this API using WebClient and handle the SSE responses.

Problem:

Despite receiving data from the third-party API when testing with tools like Postman and cURL, my Spring WebFlux endpoint (/v1/api/bot-manager/chat-messages) does not return any data to the client. I have verified that the third-party API responds correctly with the expected SSE data format when called directly.

Code Snippets:

Below are relevant parts of my Spring WebFlux application:

1. Service Layer (BotManagerService):

   @Override
   public Flux<String> chatMessages(ChatMessageRequest model) {
       BotInfo botInfo = botInfoRepository.findById(model.getBotId()).orElse(null);
       if (botInfo != null) {
           HttpHeaders headers = new HttpHeaders();
           headers.setBearerAuth(botInfo.getBotKey());
           headers.setContentType(MediaType.APPLICATION_JSON);
           return webClient.post()
                   .uri("/chat-messages")
                   .headers(httpHeaders -> httpHeaders.addAll(headers))
                   .body(BodyInserters.fromValue(model))
                   .accept(MediaType.TEXT_EVENT_STREAM, MediaType.APPLICATION_OCTET_STREAM, MediaType.APPLICATION_JSON)
                   .acceptCharset(StandardCharsets.UTF_8)
                   .retrieve()
                   .bodyToFlux(String.class)
                   .doOnNext(chatResponse -> {
                       System.out.println(gson.toJson(chatResponse));
                   })
                   .log();
       }
       throw new RuntimeException("Bot info not found");
   }
   

2. Controller Layer (BotManagerController):

   @PostMapping(value = "/chat-messages", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
   public Flux<String> chatMessages(@RequestBody ChatMessageRequest model) {
       return botManagerService.chatMessages(model);
   }
   

Additional Information:

• The third-party API returns data continuously in the text/event-stream format.
• I have confirmed that the webClient setup and headers are correct since I can log the responses in my service layer.
• Despite successful logs in the service layer, the controller endpoint does not transmit any data back to the client.

Question:

What could be causing my Spring WebFlux endpoint /v1/api/bot-manager/chat-messages to not transmit the received Server-Sent Events (SSE) data to the client? Is there a configuration issue or an error in my approach?