Hello, I’m following <this> approach in order to g...

# spring

[André Martins]

Hello, I’m following this approach in order to get coroutine wrappers for Webflux WebFilters and I’m now trying to propagate MDC context in order to have it on my controllers. Im using withContext(MDCContext()) whenever I put something in MDC, also using Mono contextWrite(Context.of(coroutineContext[MDCContext.Key]?.contextMap ?: emptyMap())) when calling WebFilter base chain Although this is not working and I suspect that is due to passing the coroutine context to the ReactorContext somehow I’m not doing it right

[André Martins]

Figured it out!

[André Martins]

Basically I have this code in order to add filters using coroutines

interface CoWebFilter : WebFilter {
    override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> = mono(MDCContext()) {
        coFilter(exchange, chain)
        null
    }

    suspend fun coFilter(exchange: ServerWebExchange, chain: WebFilterChain)
}

const val MDC_REACTOR_CONTEXT_KEY = "MDCReactorContextKey"

suspend fun WebFilterChain.coFilter(exchange: ServerWebExchange) {
    val mdcContextMap = coroutineContext[MDCContext.Key]?.contextMap ?: emptyMap()
    filter(exchange)
        .contextWrite(Context.of(MDC_REACTOR_CONTEXT_KEY, mdcContextMap))
        .awaitSingleOrNull()
}

on the controller you simply can obtain that mdc context via coroutine context since reactor fills that in for you from reactor context

coroutineContext[ReactorContext.Key]?.context?.getOrDefault<MDCContextMap>(MDC_REACTOR_CONTEXT_KEY, emptyMap())

This last snippet just gets the passed MDCContext from by the filter, then you simply just wrap that inside a withContext and tada 💪

[Richard Gomez]

There's also: https://github.com/Kotlin/kotlinx.coroutines/tree/master/integration/kotlinx-coroutines-slf4j