Spring cloud gateway with Spring cache and caffeine - spring

Question

I have a spring cloud gateway which forwards the API rest requests to some microservices.
I would like to cache the response for specific requests.
For this reason I wrote this Filter
#Component
#Slf4j
public class CacheResponseGatewayFilterFactory extends AbstractGatewayFilterFactory<CacheResponseGatewayFilterFactory.Config> {
private final CacheManager cacheManager;
public CacheResponseGatewayFilterFactory(CacheManager cacheManager) {
super(CacheResponseGatewayFilterFactory.Config.class);
this.cacheManager = cacheManager;
}
#Override
public GatewayFilter apply(CacheResponseGatewayFilterFactory.Config config) {
final var cache = cacheManager.getCache("MyCache");
return (exchange, chain) -> {
final var path = exchange.getRequest().getPath();
if (nonNull(cache.get(path))) {
log.info("Return cached response for request: {}", path);
final var response = cache.get(path, ServerHttpResponse.class);
final var mutatedExchange = exchange.mutate().response(response).build();
return mutatedExchange.getResponse().setComplete();
}
return chain.filter(exchange).doOnSuccess(aVoid -> {
cache.put(path, exchange.getResponse());
});
};
}
When I call my rest endpoint, the first time I receive the right json, the second time I got an empty body.
What am I doing wrong?
EDIT
This is a screenshot of the exchange.getRequest() just before doing cache.put()

Answer 1

I solved it creating a GlobalFilter and a ServerHttpResponseDecorator. This code is caching all the responses regardless (it can be easily improved to cache only specific responses).
This is the code. However I think it can be improved. In case let me know.
#Slf4j
#Component
public class CacheFilter implements GlobalFilter, Ordered {
private final CacheManager cacheManager;
public CacheFilter(CacheManager cacheManager) {
this.cacheManager = cacheManager;
}
#Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
final var cache = cacheManager.getCache("MyCache");
final var cachedRequest = getCachedRequest(exchange.getRequest());
if (nonNull(cache.get(cachedRequest))) {
log.info("Return cached response for request: {}", cachedRequest);
final var cachedResponse = cache.get(cachedRequest, CachedResponse.class);
final var serverHttpResponse = exchange.getResponse();
serverHttpResponse.setStatusCode(cachedResponse.httpStatus);
serverHttpResponse.getHeaders().addAll(cachedResponse.headers);
final var buffer = exchange.getResponse().bufferFactory().wrap(cachedResponse.body);
return exchange.getResponse().writeWith(Flux.just(buffer));
}
final var mutatedHttpResponse = getServerHttpResponse(exchange, cache, cachedRequest);
return chain.filter(exchange.mutate().response(mutatedHttpResponse).build());
}
private ServerHttpResponse getServerHttpResponse(ServerWebExchange exchange, Cache cache, CachedRequest cachedRequest) {
final var originalResponse = exchange.getResponse();
final var dataBufferFactory = originalResponse.bufferFactory();
return new ServerHttpResponseDecorator(originalResponse) {
#NonNull
#Override
public Mono<Void> writeWith(#NonNull Publisher<? extends DataBuffer> body) {
if (body instanceof Flux) {
final var flux = (Flux<? extends DataBuffer>) body;
return super.writeWith(flux.buffer().map(dataBuffers -> {
final var outputStream = new ByteArrayOutputStream();
dataBuffers.forEach(dataBuffer -> {
final var responseContent = new byte[dataBuffer.readableByteCount()];
dataBuffer.read(responseContent);
try {
outputStream.write(responseContent);
} catch (IOException e) {
throw new RuntimeException("Error while reading response stream", e);
}
});
if (Objects.requireNonNull(getStatusCode()).is2xxSuccessful()) {
final var cachedResponse = new CachedResponse(getStatusCode(), getHeaders(), outputStream.toByteArray());
log.debug("Request {} Cached response {}", cacheKey.getPath(), new String(cachedResponse.getBody(), UTF_8));
cache.put(cacheKey, cachedResponse);
}
return dataBufferFactory.wrap(outputStream.toByteArray());
}));
}
return super.writeWith(body);
}
};
}
#Override
public int getOrder() {
return -2;
}
private CachedRequest getCachedRequest(ServerHttpRequest request) {
return CachedRequest.builder()
.method(request.getMethod())
.path(request.getPath())
.queryParams(request.getQueryParams())
.build();
}
#Value
#Builder
private static class CachedRequest {
RequestPath path;
HttpMethod method;
MultiValueMap<String, String> queryParams;
}
#Value
private static class CachedResponse {
HttpStatus httpStatus;
HttpHeaders headers;
byte[] body;
}
}