KTOR-7194 Use system property for deferred sessions

ktor-server/ktor-server-plugins/ktor-server-auth/common/test/io/ktor/tests/auth/SessionAuthTest.kt

@@ -18,7 +18,7 @@ import kotlinx.serialization.Serializable
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
-class SessionAuthTest {
+open class SessionAuthTest {
     @Test
     fun testSessionOnly() = testApplication {
         install(Sessions) {

ktor-server/ktor-server-plugins/ktor-server-auth/jvm/test/io/ktor/tests/auth/SessionAuthJvmTest.kt → ktor-server/ktor-server-plugins/ktor-server-auth/jvm/test/io/ktor/tests/auth/SessionAuthDeferredTest.kt

@@ -4,34 +4,30 @@
 
 package io.ktor.tests.auth
 
-import io.ktor.client.request.HttpRequestBuilder
-import io.ktor.client.request.get
-import io.ktor.client.request.header
-import io.ktor.client.request.post
-import io.ktor.http.HttpStatusCode
-import io.ktor.server.application.install
-import io.ktor.server.auth.Authentication
-import io.ktor.server.auth.authenticate
-import io.ktor.server.auth.session
-import io.ktor.server.response.respondText
-import io.ktor.server.routing.get
-import io.ktor.server.routing.post
-import io.ktor.server.routing.routing
-import io.ktor.server.sessions.SessionStorage
-import io.ktor.server.sessions.Sessions
-import io.ktor.server.sessions.cookie
-import io.ktor.server.sessions.defaultSessionSerializer
-import io.ktor.server.sessions.serialization.KotlinxSessionSerializer
-import io.ktor.server.sessions.sessions
-import io.ktor.server.sessions.set
-import io.ktor.server.testing.testApplication
+import io.ktor.client.request.*
+import io.ktor.http.*
+import io.ktor.server.application.*
+import io.ktor.server.auth.*
+import io.ktor.server.response.*
+import io.ktor.server.routing.*
+import io.ktor.server.sessions.*
+import io.ktor.server.sessions.serialization.*
+import io.ktor.server.testing.*
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.Json
-import kotlin.test.Test
-import kotlin.test.assertEquals
-import kotlin.test.assertFailsWith
+import kotlin.test.*
 
-class SessionAuthJvmTest {
+class SessionAuthDeferredTest: SessionAuthTest() {
+
+    @BeforeTest
+    fun setProperty() {
+        System.setProperty("io.ktor.server.sessions.deferred", "true")
+    }
+
+    @AfterTest
+    fun clearProperty() {
+        System.clearProperty("io.ktor.server.sessions.deferred")
+    }
 
     @Test
     fun sessionIgnoredForNonPublicEndpoints() = testApplication {
@@ -45,7 +41,6 @@ class SessionAuthJvmTest {
                 cookie<MySession>("S", storage = brokenStorage) {
                     serializer = KotlinxSessionSerializer(Json.Default)
                 }
-                deferred = true
             }
             install(Authentication.Companion) {
                 session<MySession> {

ktor-server/ktor-server-plugins/ktor-server-sessions/common/src/io/ktor/server/sessions/SessionDeferral.kt

@@ -6,7 +6,12 @@ package io.ktor.server.sessions
 
 import io.ktor.server.application.ApplicationCall
 
+internal const val SESSIONS_DEFERRED_FLAG = "io.ktor.server.sessions.deferred"
+
+internal expect fun isDeferredSessionsEnabled(): Boolean
+
 /**
  * Creates a lazy loading session from the given providers.
  */
 internal expect fun createDeferredSession(call: ApplicationCall, providers: List<SessionProvider<*>>): StatefulSession
+

ktor-server/ktor-server-plugins/ktor-server-sessions/common/src/io/ktor/server/sessions/Sessions.kt

@@ -27,7 +27,7 @@ internal val LOGGER = KtorSimpleLogger("io.ktor.server.sessions.Sessions")
 public val Sessions: RouteScopedPlugin<SessionsConfig> = createRouteScopedPlugin("Sessions", ::SessionsConfig) {
     val providers = pluginConfig.providers.toList()
     val sessionSupplier: suspend (ApplicationCall, List<SessionProvider<*>>) -> StatefulSession =
-        if (pluginConfig.deferred) {
+        if (isDeferredSessionsEnabled()) {
             ::createDeferredSession
         } else {
             ::createSession

ktor-server/ktor-server-plugins/ktor-server-sessions/common/src/io/ktor/server/sessions/SessionsConfig.kt

@@ -18,13 +18,6 @@ public class SessionsConfig {
      */
     public val providers: List<SessionProvider<*>> get() = registered.toList()
 
-    /**
-     * When set to true, sessions will be lazily retrieved from storage.
-     *
-     * Note: this is only available for JVM in Ktor 3.0
-     */
-    public var deferred: Boolean = false
-
     /**
      * Registers a session [provider].
      */

ktor-server/ktor-server-plugins/ktor-server-sessions/jsAndWasmShared/src/io/ktor/server/sessions/SessionDeferral.jsAndWasmShared.kt

@@ -6,5 +6,7 @@ package io.ktor.server.sessions
 
 import io.ktor.server.application.ApplicationCall
 
+internal actual fun isDeferredSessionsEnabled(): Boolean = false
+
 internal actual fun createDeferredSession(call: ApplicationCall, providers: List<SessionProvider<*>>): StatefulSession =
     TODO("Deferred session retrieval is currently only available for JVM")

ktor-server/ktor-server-plugins/ktor-server-sessions/jvm/src/io/ktor/server/sessions/SessionDeferral.jvm.kt

@@ -0,0 +1,8 @@
+/*
+ * Copyright 2014-2025 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package io.ktor.server.sessions
+
+internal actual fun isDeferredSessionsEnabled(): Boolean =
+    System.getProperty(SESSIONS_DEFERRED_FLAG)?.toBoolean() == true

ktor-server/ktor-server-plugins/ktor-server-sessions/posix/src/io/ktor/server/sessions/SessionDeferral.posix.kt

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2014-2025 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package io.ktor.server.sessions
+import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.toKString
+import platform.posix.*
+
+@OptIn(ExperimentalForeignApi::class)
+internal actual fun isDeferredSessionsEnabled(): Boolean =
+    getenv(SESSIONS_DEFERRED_FLAG)?.toKString()?.toBoolean() == true