From c0415fdfadba1b401883b133b58f462cf71e44d7 Mon Sep 17 00:00:00 2001
From: PJ Fanning <pjfanning@users.noreply.github.com>
Date: Mon, 24 Aug 2026 11:59:30 +0100
Subject: [PATCH] fix: use root locale when looking up a response header by
 name in RouteTest

Motivation:
`RouteTest#header(name: String)` lowercased the given header name with the
JVM default locale before comparing it to `HttpHeader#lowercaseName`, which
is built with `toRootLowerCase`. Under a Turkish locale `"If-Match".toLowerCase`
yields a dotless i, so the lookup silently returned `None` for any header name
containing a capital `I`. The javadsl equivalent (`TestRouteResult`) already
uses `toRootLowerCase`.

Modification:
Use `pekko.util.Helpers.toRootLowerCase` in `RouteTest#header(name)`.

Result:
Header lookup by name in the Scala testkit is locale independent and matches
the javadsl behaviour.

Tests:
- sbt "http-testkit / Test / testOnly org.apache.pekko.http.scaladsl.testkit.ScalatestRouteTestSpec" - passes with the fix; the new test fails without it
- scalafmt --mode diff-ref=origin/main - clean
- sbt +mimaReportBinaryIssues - not run; method body change only, no API or binary shape change

References:
None - found while auditing the code base for locale sensitive lowercasing
---
 .../http/scaladsl/testkit/RouteTest.scala     |  3 ++-
 .../testkit/ScalatestRouteTestSpec.scala      | 21 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/http-testkit/src/main/scala/org/apache/pekko/http/scaladsl/testkit/RouteTest.scala b/http-testkit/src/main/scala/org/apache/pekko/http/scaladsl/testkit/RouteTest.scala
index 8fa833417d..38d85309df 100644
--- a/http-testkit/src/main/scala/org/apache/pekko/http/scaladsl/testkit/RouteTest.scala
+++ b/http-testkit/src/main/scala/org/apache/pekko/http/scaladsl/testkit/RouteTest.scala
@@ -36,6 +36,7 @@ import pekko.stream.{ Materializer, SystemMaterializer }
 import pekko.stream.scaladsl.Source
 import pekko.testkit.TestKit
 import pekko.util.ConstantFun
+import pekko.util.Helpers.toRootLowerCase
 
 import com.typesafe.config.{ Config, ConfigFactory }
 
@@ -96,7 +97,7 @@ trait RouteTest extends RequestBuilding with WSTestRequestBuilding with RouteTes
   def charset: HttpCharset = charsetOption.getOrElse(sys.error("Binary entity does not have charset"))
   def headers: immutable.Seq[HttpHeader] = rawResponse.headers
   def header[T >: Null <: HttpHeader: ClassTag]: Option[T] = rawResponse.header[T](implicitly[ClassTag[T]])
-  def header(name: String): Option[HttpHeader] = rawResponse.headers.find(_.is(name.toLowerCase))
+  def header(name: String): Option[HttpHeader] = rawResponse.headers.find(_.is(toRootLowerCase(name)))
   def status: StatusCode = rawResponse.status
 
   def closingExtension: String = chunks.lastOption match {
diff --git a/http-testkit/src/test/scala/org/apache/pekko/http/scaladsl/testkit/ScalatestRouteTestSpec.scala b/http-testkit/src/test/scala/org/apache/pekko/http/scaladsl/testkit/ScalatestRouteTestSpec.scala
index 18310caa18..c17b49def6 100644
--- a/http-testkit/src/test/scala/org/apache/pekko/http/scaladsl/testkit/ScalatestRouteTestSpec.scala
+++ b/http-testkit/src/test/scala/org/apache/pekko/http/scaladsl/testkit/ScalatestRouteTestSpec.scala
@@ -13,6 +13,8 @@
 
 package org.apache.pekko.http.scaladsl.testkit
 
+import java.util.Locale
+
 import scala.concurrent.Await
 import scala.concurrent.Future
 import scala.concurrent.duration._
@@ -57,6 +59,25 @@ class ScalatestRouteTestSpec extends AnyFreeSpec with Matchers with ScalatestRou
       }
     }
 
+    "a header lookup by name that is unaffected by the turkish-i problem" in {
+      val previousLocale = Locale.getDefault
+      try {
+        Locale.setDefault(new Locale("tr", "TR"))
+        // in the turkish locale 'I'.toLowerCase is a dotless i, so a default-locale
+        // lowercasing of 'If-Match' would not match the header's lowercaseName
+        val ifMatchHeader = RawHeader("If-Match", "\"xyzzy\"")
+        Get() ~> {
+          respondWithHeader(ifMatchHeader) {
+            complete("abc")
+          }
+        } ~> check {
+          header("If-Match") shouldEqual Some(ifMatchHeader)
+        }
+      } finally {
+        Locale.setDefault(previousLocale)
+      }
+    }
+
     "a test using ~!> and some checks" in {
       // raw here, should have been parsed into modelled header when going through an actual server when using `~!>`
       val extraHeader = RawHeader("X-Forwarded-Proto", "abc")