modifyResponseBodyFilterFactory for some reason not executing

[dreamstar-enterprises]

Hi, I'm not sure why the rewrite function here simply won't execute.

/**
 * Gateway filter that enriches the /user-info endpoint response with session timing information.
 *
 * Process flow:
 * 1. Intercepts responses from the /user-info endpoint
 * 2. Attempts to retrieve session creation time from Redis session hash
 * 3. If successful, adds session timing information to the JSON response:
 *    - sessionCreatedAt: When the session was created
 *    - sessionExpiresAt: When the session will expire (xx mins after creation)
 *
 * Error handling:
 * - If Redis access fails: Logs error and continues without session timing info
 * - If session key not found: Continues without session timing info
 * - Non-user-info endpoints: Passes through unmodified
 *
 * The filter maintains the original response integrity even when Redis operations fail,
 * ensuring the user-info endpoint remains functional with or without the additional
 * session timing data.
 *
 * @property redisTemplate For accessing Redis session data
 * @property sessionProperties Configuration for Redis session namespacing
 * @property serverProperties Server configuration including endpoint prefixes
 * @property modifyResponseBodyFilterFactory Factory for response body modification
 */
@Component
internal class SessionInfoResponseFilter(
    private val redisTemplate: ReactiveRedisTemplate<String, Any>,
    private val sessionProperties: SessionProperties,
    private val serverProperties: ServerProperties,
    private val modifyResponseBodyFilterFactory: ModifyResponseBodyGatewayFilterFactory
) : AbstractGatewayFilterFactory<SessionInfoResponseFilter.Config>() {

    /** Configuration class for the session info response filter */
    class Config

    private val logger = LoggerFactory.getLogger(SessionInfoResponseFilter::class.java)

    /**
     * Applies the filter to add session timing information to /me responses.
     *
     * @param config Filter configuration (unused in this implementation)
     * @return GatewayFilter that enriches /user-info responses with session data
     */
    override fun apply(config: Config): GatewayFilter = GatewayFilter { exchange, chain ->

        // only modify /user-info endpoint responses
        if (exchange.request.path.value() != "${serverProperties.resourceServerPrefix}/me") {
            logger.debug("request did not match me endpoint")
            chain.filter(exchange)
        } else {
            chain.filter(exchange).then(
                exchange.session.flatMap { session ->
                    logger.debug("request did match me endpoint")
                    val sessionId = session.id
                    val sessionKey = "${sessionProperties.redis?.sessionNamespace}:sessions:$sessionId"

                    redisTemplate.opsForHash<String, Any>()
                        .get(sessionKey, "creationTime")
                        .doOnNext { creationTime ->
                            logger.debug("3. Found creation time in Redis: {}", creationTime)
                        }
                        .flatMap { creationTime ->

                            val created = Instant.ofEpochMilli(creationTime.toString().toLong())
                            logger.debug("4. Converted to Instant: {}", created)

                            // Define the RewriteFunction separately
                            val rewriteFunction = RewriteFunction<String, String> { _, originalResponse ->
                                logger.debug("Entering RewriteFunction with body: {}", originalResponse)

                                if (originalResponse.isNullOrEmpty()) {
                                    logger.warn("Response body is empty or null")
                                    return@RewriteFunction Mono.just(originalResponse)
                                }

                                return@RewriteFunction try {
                                    val jsonNode = JSONUtilities.objectMapper.readTree(originalResponse)
                                    logger.debug("Parsed JSON node: {}", jsonNode)

                                    (jsonNode as ObjectNode).apply {
                                        put("sessionCreatedAt", created.toString())
                                        put("sessionExpiresAt", created.plusSeconds(sessionProperties.timeout.toLong()).toString())
                                    }

                                    val modifiedResponse = JSONUtilities.objectMapper.writeValueAsString(jsonNode)
                                    logger.debug("Modified response body: {}", modifiedResponse)

                                    Mono.just(modifiedResponse)
                                } catch (ex: Exception) {
                                    logger.error("Failed to process response body", ex)
                                    Mono.error(ex)
                                }
                            }

                            val modifyConfig = ModifyResponseBodyGatewayFilterFactory.Config().apply {
                                logger.debug("Setting up rewrite function")
                                setInClass(String::class.java)
                                setOutClass(String::class.java)
                                setRewriteFunction(String::class.java, String::class.java, rewriteFunction)
                            }

                            // Apply modification filter first, then the chain
                            modifyResponseBodyFilterFactory.apply(modifyConfig).filter(exchange, chain)
                            
                        }
                        .onErrorResume { error ->
                            // log the Redis error but allow the chain to continue
                            logger.error("Failed to get session timing from Redis", error)
                            Mono.empty()
                        }
                }
            )
        }
    }
}

In the logs all I can see is:

2025-01-15T21:21:43.302Z DEBUG 35283 --- [BFFApplication] [ctor-http-nio-4] c.v.b.r.s.SessionInfoResponseFilter      : request did match userinfo endpoint
2025-01-15T21:21:43.316Z DEBUG 35283 --- [BFFApplication] [xecutorLoop-3-5] c.v.b.r.s.SessionInfoResponseFilter      : 3. Found creation time in Redis: 1736971305338
2025-01-15T21:21:43.317Z DEBUG 35283 --- [BFFApplication] [xecutorLoop-3-5] c.v.b.r.s.SessionInfoResponseFilter      : 4. Converted to Instant: 2025-01-15T20:01:45.338Z
2025-01-15T21:21:43.317Z DEBUG 35283 --- [BFFApplication] [xecutorLoop-3-5] c.v.b.r.s.SessionInfoResponseFilter      : Setting up rewrite function

I've spent 3 hours going over the internet trying to find a solution, but am getting stuck.

Would appreciate if anyone could help