From f56bb25261be94a39f5e48f2402d8c8856095822 Mon Sep 17 00:00:00 2001
From: rsinukov <rxsinukov@gmail.com>
Date: Mon, 17 Oct 2022 17:45:04 +0200
Subject: [PATCH] KTOR-4990 Fix duplication of default headers

---
 .../plugins/defaultheaders/DefaultHeaders.kt      |  7 +++++--
 .../io/ktor/tests/plugins/DefaultHeadersTest.kt   | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/src/io/ktor/server/plugins/defaultheaders/DefaultHeaders.kt b/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/src/io/ktor/server/plugins/defaultheaders/DefaultHeaders.kt
index 03912581ac6..e1927f14a15 100644
--- a/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/src/io/ktor/server/plugins/defaultheaders/DefaultHeaders.kt
+++ b/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/src/io/ktor/server/plugins/defaultheaders/DefaultHeaders.kt
@@ -6,6 +6,7 @@ package io.ktor.server.plugins.defaultheaders
 
 import io.ktor.http.*
 import io.ktor.server.application.*
+import io.ktor.server.plugins.defaultheaders.DefaultHeadersConfig.*
 import io.ktor.server.response.*
 import io.ktor.util.*
 import io.ktor.util.date.*
@@ -94,13 +95,15 @@ public val DefaultHeaders: RouteScopedPlugin<DefaultHeadersConfig> = createRoute
 
     val serverHeader = "Ktor/$ktorPackageVersion"
     onCallRespond { call, _ ->
-        headers.forEach { name, value -> value.forEach { call.response.header(name, it) } }
+        headers.forEach { name, value ->
+            if (!call.response.headers.contains(name)) value.forEach { call.response.header(name, it) }
+        }
 
         if (!call.response.headers.contains(HttpHeaders.Date)) {
             call.response.header(HttpHeaders.Date, calculateDateHeader())
         }
         if (!call.response.headers.contains(HttpHeaders.Server)) {
-            call.response.headers.append(HttpHeaders.Server, serverHeader)
+            call.response.header(HttpHeaders.Server, serverHeader)
         }
     }
 }
diff --git a/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/test/io/ktor/tests/plugins/DefaultHeadersTest.kt b/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/test/io/ktor/tests/plugins/DefaultHeadersTest.kt
index 2c45f7ab249..ba9bae4827e 100644
--- a/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/test/io/ktor/tests/plugins/DefaultHeadersTest.kt
+++ b/ktor-server/ktor-server-plugins/ktor-server-default-headers/jvm/test/io/ktor/tests/plugins/DefaultHeadersTest.kt
@@ -7,6 +7,7 @@ package io.ktor.tests.plugins
 import io.ktor.client.request.*
 import io.ktor.http.*
 import io.ktor.server.application.*
+import io.ktor.server.application.hooks.*
 import io.ktor.server.plugins.defaultheaders.*
 import io.ktor.server.response.*
 import io.ktor.server.routing.*
@@ -117,4 +118,18 @@ class DefaultHeadersTest {
 
         assertEquals("MyServer", client.get("/").headers[HttpHeaders.Server])
     }
+
+    @Test
+    fun testCustomServerHeaderDoesntDuplicate(): Unit = testApplication {
+        install(createApplicationPlugin("test") {
+            on(CallSetup) {
+                it.response.header(HttpHeaders.Server, "MyServer")
+            }
+        })
+        install(DefaultHeaders) {
+            header(HttpHeaders.Server, "MyServer1")
+        }
+
+        assertEquals(listOf("MyServer"), client.get("/").headers.getAll(HttpHeaders.Server))
+    }
 }