Support multiple CoWebFilter changing the context

This commit ensures CoWebFilter merges the exchange
CoroutineContext with the filter one if needed.

Closes gh-31792

Author: sdeleuze

spring-web/src/main/kotlin/org/springframework/web/server/CoWebFilter.kt

@@ -22,6 +22,7 @@ import kotlinx.coroutines.currentCoroutineContext
 import kotlinx.coroutines.reactor.awaitSingleOrNull
 import kotlinx.coroutines.reactor.mono
 import reactor.core.publisher.Mono
+import kotlin.coroutines.CoroutineContext
 
 /**
  * Kotlin-specific implementation of the [WebFilter] interface that allows for
@@ -34,7 +35,8 @@ import reactor.core.publisher.Mono
 abstract class CoWebFilter : WebFilter {
 
 	final override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> {
-		return mono(Dispatchers.Unconfined) {
+		val context = exchange.attributes[COROUTINE_CONTEXT_ATTRIBUTE] as CoroutineContext?
+		return mono(context ?: Dispatchers.Unconfined) {
 			filter(exchange, object : CoWebFilterChain {
 				override suspend fun filter(exchange: ServerWebExchange) {
 					exchange.attributes[COROUTINE_CONTEXT_ATTRIBUTE] = currentCoroutineContext().minusKey(Job.Key)

spring-web/src/test/kotlin/org/springframework/web/server/CoWebFilterTests.kt

@@ -26,6 +26,7 @@ import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRe
 import org.springframework.web.testfixture.server.MockServerWebExchange
 import reactor.core.publisher.Mono
 import reactor.test.StepVerifier
+import kotlin.coroutines.AbstractCoroutineContextElement
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -44,10 +45,24 @@ class CoWebFilterTests {
 		val filter = MyCoWebFilter()
 		val result = filter.filter(exchange, chain)
 
-		StepVerifier.create(result)
-			.verifyComplete()
+		StepVerifier.create(result).verifyComplete()
+
+		assertThat(exchange.attributes["foo"]).isEqualTo("bar")
+	}
+
+	@Test
+	fun multipleFilters() {
+		val exchange = MockServerWebExchange.from(MockServerHttpRequest.get("https://example.com"))
+
+		val chain = Mockito.mock(WebFilterChain::class.java)
+		given(chain.filter(exchange)).willAnswer { MyOtherCoWebFilter().filter(exchange,chain) }.willReturn(Mono.empty())
+
+		val result = MyCoWebFilter().filter(exchange, chain)
+
+		StepVerifier.create(result).verifyComplete()
 
 		assertThat(exchange.attributes["foo"]).isEqualTo("bar")
+		assertThat(exchange.attributes["foofoo"]).isEqualTo("barbar")
 	}
 
 	@Test
@@ -69,6 +84,28 @@ class CoWebFilterTests {
 		assertThat(coroutineName.name).isEqualTo("foo")
 	}
 
+	@Test
+	fun multipleFiltersWithContext() {
+		val exchange = MockServerWebExchange.from(MockServerHttpRequest.get("https://example.com"))
+
+		val chain = Mockito.mock(WebFilterChain::class.java)
+		given(chain.filter(exchange)).willAnswer { MyOtherCoWebFilterWithContext().filter(exchange,chain) }.willReturn(Mono.empty())
+
+		val filter = MyCoWebFilterWithContext()
+		val result = filter.filter(exchange, chain)
+
+		StepVerifier.create(result).verifyComplete()
+
+		val context = exchange.attributes[CoWebFilter.COROUTINE_CONTEXT_ATTRIBUTE] as CoroutineContext
+		assertThat(context).isNotNull()
+		val coroutineName = context[CoroutineName.Key] as CoroutineName
+		assertThat(coroutineName).isNotNull()
+		assertThat(coroutineName.name).isEqualTo("foo")
+		val coroutineDescription = context[CoroutineDescription.Key] as CoroutineDescription
+		assertThat(coroutineDescription).isNotNull()
+		assertThat(coroutineDescription.description).isEqualTo("foofoo")
+	}
+
 }
 
 
@@ -79,10 +116,33 @@ private class MyCoWebFilter : CoWebFilter() {
 	}
 }
 
+private class MyOtherCoWebFilter : CoWebFilter() {
+	override suspend fun filter(exchange: ServerWebExchange, chain: CoWebFilterChain) {
+		exchange.attributes["foofoo"] = "barbar"
+		chain.filter(exchange)
+	}
+}
+
 private class MyCoWebFilterWithContext : CoWebFilter() {
 	override suspend fun filter(exchange: ServerWebExchange, chain: CoWebFilterChain) {
 		withContext(CoroutineName("foo")) {
 			chain.filter(exchange)
 		}
 	}
 }
+
+private class MyOtherCoWebFilterWithContext : CoWebFilter() {
+	override suspend fun filter(exchange: ServerWebExchange, chain: CoWebFilterChain) {
+		withContext(CoroutineDescription("foofoo")) {
+			chain.filter(exchange)
+		}
+	}
+}
+
+data class CoroutineDescription(val description: String) : AbstractCoroutineContextElement(CoroutineDescription) {
+
+	companion object Key : CoroutineContext.Key<CoroutineDescription>
+
+	override fun toString(): String = "CoroutineDescription($description)"
+}
+