[KTOR-8970] Lowercase varyKeys keys when deserializing from file storage

ktor-client/ktor-client-core/jvm/src/io/ktor/client/plugins/cache/storage/FileCacheStorage.kt

@@ -222,7 +222,7 @@ private class FileCacheStorage(
         val varyKeysCount = channel.readInt()
         val varyKeys = buildMap {
             for (j in 0 until varyKeysCount) {
-                val key = channel.readUTF8Line()!!
+                val key = channel.readUTF8Line()!!.lowercase()
                 val value = channel.readUTF8Line()!!
                 put(key, value)
             }

ktor-client/ktor-client-core/jvm/test/FileStorageTest.kt

@@ -38,7 +38,8 @@ class FileStorageTest {
         val storage = FileStorage(tempDirectory)
 
         storage.store(Url("http://example.com"), data())
-        storage.store(Url("http://example.com"), data(mapOf("key" to "value")))
+        // Use an uppercase key to test case insensitivity
+        storage.store(Url("http://example.com"), data(mapOf("Key" to "value")))
 
         assertNotNull(storage.find(Url("http://example.com"), mapOf("key" to "value")))
     }

ktor-client/ktor-client-tests/jvm/test/io/ktor/client/tests/FileCacheTest.kt

@@ -11,6 +11,8 @@ import io.ktor.client.request.*
 import io.ktor.client.statement.*
 import io.ktor.client.test.base.*
 import io.ktor.http.*
+import io.ktor.util.date.GMTDate
+import io.ktor.utils.io.core.toByteArray
 import java.nio.file.Files
 import kotlin.test.Test
 import kotlin.test.assertEquals
@@ -134,4 +136,46 @@ class FileCacheTest : ClientLoader() {
             assertEquals("abc", second.bodyAsText())
         }
     }
+
+    @Test
+    fun testUpgradeOldCacheVersionWithCaseSensitiveVary() = clientTests {
+        val file = Files.createTempDirectory("cache-test-public-upgrade").toFile()
+        val publicStorage = FileStorage(file)
+        config {
+            install(HttpCache) {
+                publicStorage(publicStorage)
+            }
+        }
+
+        test { client ->
+            val url = Url("$TEST_SERVER/cache/vary-header-not-modified")
+
+            // Prepopulate the cache with an entry that uses a capitalized "Accept-Language" vary key.
+            val now = GMTDate()
+            publicStorage.store(
+                url,
+                CachedResponseData(
+                    url = url,
+                    statusCode = HttpStatusCode.OK,
+                    requestTime = now,
+                    responseTime = now,
+                    version = HttpProtocolVersion.HTTP_1_1,
+                    expires = now,
+                    headers = headers {
+                        append(HttpHeaders.Vary, HttpHeaders.AcceptLanguage)
+                    },
+                    varyKeys = mapOf(
+                        HttpHeaders.AcceptLanguage to "en-US"
+                    ),
+                    body = "OK".toByteArray(),
+                )
+            )
+
+            val response = client.get(url) {
+                header(HttpHeaders.AcceptLanguage, "en-US")
+            }.bodyAsText()
+
+            assertEquals("OK", response)
+        }
+    }
 }

ktor-test-server/src/main/kotlin/test/server/tests/Cache.kt

@@ -149,6 +149,11 @@ internal fun Application.cacheTestServer() {
                     else -> error("Should not be invoked")
                 }
             }
+
+            get("/vary-header-not-modified") {
+                call.response.header(HttpHeaders.Vary, HttpHeaders.AcceptLanguage)
+                call.respond(HttpStatusCode.NotModified)
+            }
         }
     }
 }