Pickup CoroutineContext saved by CoWebFilter in coRouter

Closes gh-31793

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/CoRouterFunctionDsl.kt

@@ -27,6 +27,7 @@ import org.springframework.http.HttpMethod
 import org.springframework.http.HttpStatusCode
 import org.springframework.http.MediaType
 import org.springframework.web.reactive.function.server.RouterFunctions.nest
+import org.springframework.web.server.CoWebFilter
 import reactor.core.publisher.Mono
 import java.net.URI
 import kotlin.coroutines.CoroutineContext
@@ -731,7 +732,8 @@ class CoRouterFunctionDsl internal constructor (private val init: (CoRouterFunct
 	) : HandlerFunction<T> {
 
 		override fun handle(request: ServerRequest): Mono<T> {
-			return handle(Dispatchers.Unconfined, request)
+			val context = request.attributes()[CoWebFilter.COROUTINE_CONTEXT_ATTRIBUTE] as CoroutineContext?
+			return handle(context ?: Dispatchers.Unconfined, request)
 		}
 
 		fun handle(context: CoroutineContext, request: ServerRequest) = asMono(request, context) {

spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/server/CoRouterFunctionDslTests.kt

@@ -25,7 +25,11 @@ import org.springframework.http.HttpHeaders.CONTENT_TYPE
 import org.springframework.http.HttpMethod.PATCH
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType.*
+import org.springframework.web.server.CoWebFilter
+import org.springframework.web.server.CoWebFilterChain
+import org.springframework.web.server.ServerWebExchange
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest.*
+import org.springframework.web.testfixture.http.server.reactive.MockServerHttpResponse
 import org.springframework.web.testfixture.server.MockServerWebExchange
 import reactor.test.StepVerifier
 
@@ -204,6 +208,16 @@ class CoRouterFunctionDslTests {
 			.verifyComplete()
 	}
 
+	@Test
+	fun webFilterAndContext() {
+		val strategies = HandlerStrategies.builder().webFilter(MyCoWebFilterWithContext()).build()
+		val httpHandler = RouterFunctions.toHttpHandler(routerWithoutContext, strategies)
+		val mockRequest = get("https://example.com/").build()
+		val mockResponse = MockServerHttpResponse()
+		StepVerifier.create(httpHandler.handle(mockRequest, mockResponse)).verifyComplete()
+		assertThat(mockResponse.headers.getFirst("context")).contains("Filter context")
+	}
+
 	@Test
 	fun multipleContextProviders() {
 		assertThatIllegalStateException().isThrownBy {
@@ -309,6 +323,12 @@ class CoRouterFunctionDslTests {
 		}
 	}
 
+	private val routerWithoutContext = coRouter {
+		GET("/") {
+			ok().header("context", currentCoroutineContext().toString()).buildAndAwait()
+		}
+	}
+
 	private val otherRouter = router {
 		"/other" {
 			ok().build()
@@ -369,3 +389,12 @@ class CoRouterFunctionDslTests {
 
 @Suppress("UNUSED_PARAMETER")
 private suspend fun handle(req: ServerRequest) = ServerResponse.ok().buildAndAwait()
+
+
+private class MyCoWebFilterWithContext : CoWebFilter() {
+	override suspend fun filter(exchange: ServerWebExchange, chain: CoWebFilterChain) {
+		withContext(CoroutineName("Filter context")) {
+			chain.filter(exchange)
+		}
+	}
+}