How to log request and response bodies in Spring WebFlux

1078

Koguro :

I want to have centralised logging for requests and responses in my REST API on Spring WebFlux with Kotlin. So far I've tried this approaches

@Bean
fun apiRouter() = router {
    (accept(MediaType.APPLICATION_JSON) and "/api").nest {
        "/user".nest {
            GET("/", userHandler::listUsers)
            POST("/{userId}", userHandler::updateUser)
        }
    }
}.filter { request, next ->
    logger.info { "Processing request $request with body ${request.bodyToMono<String>()}" }
    next.handle(request).doOnSuccess { logger.info { "Handling with response $it" } }
}

Here request method and path log successfully but the body is Mono, so how should I log it? Should it be the other way around and I have to subscribe on request body Mono and log it in the callback? Another problem is that ServerResponse interface here doesn't have access to the response body. How can I get it here?

Another approach I've tried is using WebFilter

@Bean
fun loggingFilter(): WebFilter =
        WebFilter { exchange, chain ->
            val request = exchange.request
            logger.info { "Processing request method=${request.method} path=${request.path.pathWithinApplication()} params=[${request.queryParams}] body=[${request.body}]"  }

            val result = chain.filter(exchange)

            logger.info { "Handling with response ${exchange.response}" }

            return@WebFilter result
        }

Same problem here: request body is Flux and no response body.

Is there a way to access full request and response for logging from some filters? What don't I understand?

Brian Clozel :

This is more or less similar to the situation in Spring MVC.

In Spring MVC, you can use a AbstractRequestLoggingFilter filter and ContentCachingRequestWrapper and/or ContentCachingResponseWrapper. Many tradeoffs here:

if you'd like to access servlet request attributes, you need to actually read and parse the request body
logging the request body means buffering the request body, which can use a significant amount of memory
if you'd like to access the response body, you need to wrap the response and buffer the response body as it's being written, for later retrieval

ContentCaching*Wrapper classes don't exist in WebFlux but you could create similar ones. But keep in mind other points here:

buffering data in memory somehow goes against the reactive stack, since we're trying there to be very efficient with the available resources
you should not tamper with the actual flow of data and flush more/less often than expected, otherwise you'd risk breaking streaming uses cases
at that level, you only have access to DataBuffer instances, which are (roughly) memory-efficient byte arrays. Those belong to buffer pools and are recycled for other exchanges. If those aren't properly retained/released, memory leaks are created (and buffering data for later consumption certainly fits that scenario)
again at that level, it's only bytes and you don't have access to any codec to parse the HTTP body. I'd forget about buffering the content if it's not human-readable in the first place

deixe-me dizer algumas palavras

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How to log request and response bodies in Spring WebFlux

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