KTOR-4849 Routing: Wrong content-type should result in 415

ktor-server/ktor-server-core/jvmAndNix/src/io/ktor/server/routing/RouteSelector.kt

@@ -7,7 +7,6 @@ package io.ktor.server.routing
 import io.ktor.http.*
 import io.ktor.server.plugins.*
 import io.ktor.server.request.*
-import io.ktor.util.*
 
 /**
  * A result of a route evaluation against a call.
@@ -552,8 +551,8 @@ public data class HttpMethodRouteSelector(
 
 /**
  * Evaluates a route against a header in the request.
- * @param name is a name of the header
- * @param value is a value of the header
+ * @param name is the name of the header
+ * @param value is the value of the header
  */
 public data class HttpHeaderRouteSelector(
     val name: String,
@@ -572,6 +571,32 @@ public data class HttpHeaderRouteSelector(
     override fun toString(): String = "(header:$name = $value)"
 }
 
+/**
+ * Evaluates a route against a `Content-Type` in the [HttpHeaders.ContentType] request header.
+ * @param contentType is an instance of [ContentType]
+ */
+internal data class ContentTypeHeaderRouteSelector(
+    val contentType: ContentType
+) : RouteSelector() {
+
+    private val failedEvaluation = RouteSelectorEvaluation.Failure(
+        RouteSelectorEvaluation.qualityFailedParameter,
+        HttpStatusCode.UnsupportedMediaType
+    )
+
+    override fun evaluate(context: RoutingResolveContext, segmentIndex: Int): RouteSelectorEvaluation {
+        val headers = context.call.request.header(HttpHeaders.ContentType)
+        val parsedHeaders = parseAndSortContentTypeHeader(headers)
+
+        val header = parsedHeaders.firstOrNull { ContentType.parse(it.value).match(contentType) }
+            ?: return failedEvaluation
+
+        return RouteSelectorEvaluation.Success(header.quality)
+    }
+
+    override fun toString(): String = "(contentType = $contentType)"
+}
+
 /**
  * Evaluates a route against a `Content-Type` in the [HttpHeaders.Accept] request header.
  * @param contentType is an instance of [ContentType]

ktor-server/ktor-server-core/jvmAndNix/src/io/ktor/server/routing/RoutingBuilder.kt

@@ -96,7 +96,8 @@ public fun Route.accept(contentType: ContentType, build: Route.() -> Unit): Rout
  */
 @KtorDsl
 public fun Route.contentType(contentType: ContentType, build: Route.() -> Unit): Route {
-    return header(HttpHeaders.ContentType, "${contentType.contentType}/${contentType.contentSubtype}", build)
+    val selector = ContentTypeHeaderRouteSelector(contentType)
+    return createChild(selector).apply(build)
 }
 
 /**

ktor-server/ktor-server-tests/jvmAndNix/test/io/ktor/tests/server/routing/RoutingProcessingTest.kt

@@ -510,6 +510,48 @@ class RoutingProcessingTest {
         }
     }
 
+    @Test
+    fun testContentTypeHeaderProcessing() = testApplication {
+        routing {
+            route("/") {
+                contentType(ContentType.Text.Plain) {
+                    handle {
+                        call.respond("OK")
+                    }
+                }
+                contentType(ContentType.Application.Any) {
+                    handle {
+                        call.respondText("{\"status\": \"OK\"}", ContentType.Application.Json)
+                    }
+                }
+            }
+        }
+
+        client.get("/") {
+            header(HttpHeaders.ContentType, "text/plain")
+        }.let {
+            assertEquals("OK", it.bodyAsText())
+        }
+
+        client.get("/") {
+            header(HttpHeaders.ContentType, "application/json")
+        }.let {
+            assertEquals("{\"status\": \"OK\"}", it.bodyAsText())
+        }
+
+        client.get("/") {
+            header(HttpHeaders.ContentType, "application/pdf")
+        }.let {
+            assertEquals("{\"status\": \"OK\"}", it.bodyAsText())
+        }
+
+        client.get("/") {
+            header(HttpHeaders.ContentType, "text/html")
+        }.let {
+            assertEquals(HttpStatusCode.UnsupportedMediaType, it.status)
+        }
+    }
+
     @Test
     fun testTransparentSelectorWithHandler() = withTestApplication {
         application.routing {