Pass-through API / Preserve backend headers in Spring Webflux - spring-boot

Question

I am building an application to call a back-end which responds with a mime-type response.
#Override
public Mono<String> getDocument() {
return webClient.get()
.uri(path)
.retrieve()
.bodyToMono(String.class);
}
From this request, I need to preserve the response headers and pass it through as the response. This is mostly because the response headers contain the dynamic content type of the file. I need to forward these headers (all as received) to the API response. For example :
Content-Type : application/pdf
Content-Disposition: attachment; filename="test.pdf"
Following is my handler.
public Mono<ServerResponse> getDocument(ServerRequest request) {
return ServerResponse
.ok()
.contentType(MediaType.APPLICATION_PDF)
.header("Content-Disposition", "attachment; filename=\"test.pdf\"")
.body(BodyInserters.fromPublisher(documentService.getDocument(), String.class));
}
The file is coming through from the API as an attachment as expected, but I do not want to hard code the content-type header. How can I achieve this?
Update with the handler code :
public Mono<ServerResponse> getDocument(ServerRequest request) {
return ServerResponse
.ok()
.contentType(MediaType.APPLICATION_JSON)
.body(BodyInserters.fromPublisher(documentService.getDocument(), String.class));
}

Answer 1

I was able to resolve the problem by returning a ResponseEntity from the service instead of the body and using that to construct the ServerResponse in the handler.
Service :
public Mono<ResponseEntity<String>> getDocument() {
return webClient.get()
.uri(path)
.retrieve()
.toEntity(String.class);
}
Handler :
public Mono<ServerResponse> getDocument(ServerRequest request) {
return documentService
.getDocument()
.flatMap(r -> ServerResponse
.ok()
.headers(httpHeaders -> httpHeaders.addAll(r.getHeaders()))
.body(BodyInserters.fromValue(r.getBody()))
);
}