From 18b48a81f0a80cff6882cae72c325917252425f7 Mon Sep 17 00:00:00 2001
From: Nacy Dev <hoanle0126@gmail.com>
Date: Mon, 2 Nov 2026 06:47:44 +0700
Subject: [PATCH] fix(types): allow optional error parameter in CallbackSession

---
 types/index.d.ts   |  2 +-
 types/index.tst.ts | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/types/index.d.ts b/types/index.d.ts
index 8e7b89f..1ba59c0 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -27,7 +27,7 @@ type FastifySession = FastifyPluginCallback<fastifySession.FastifySessionOptions
 }
 
 type Callback = (err?: any) => void
-type CallbackSession = (err: any, result?: Fastify.Session | null) => void
+type CallbackSession = (err?: any, result?: Fastify.Session | null) => void
 
 interface ExpressSessionData {
   /** The cookie properties as defined by express-session */
diff --git a/types/index.tst.ts b/types/index.tst.ts
index 2da05aa..9b56b2e 100644
--- a/types/index.tst.ts
+++ b/types/index.tst.ts
@@ -26,6 +26,32 @@ class EmptyStore {
   destroy (_sessionId: string, _callback: Function) {}
 }
 
+const customTypedStore: SessionStore = {
+  set (_sessionStoreId, _session, callback) {
+    callback()
+  },
+  get (_sessionStoreId, callback) {
+    callback()
+    callback(null)
+    callback(null, null)
+    callback(null, undefined)
+    callback(new Error('failed'))
+    callback(new Error('failed'), null)
+    callback(null, {
+      cookie: {
+        originalMaxAge: null
+      },
+      foo: 'bar'
+    })
+  },
+  compareAndSet (_sessionStoreId, _expectedGeneration, _session, callback) {
+    callback()
+  },
+  destroy (_sessionStoreId, callback) {
+    callback()
+  }
+}
+
 declare module 'fastify' {
   interface Session {
     user?: {
@@ -68,6 +94,10 @@ app.register(plugin, {
   secret,
   store: new EmptyStore() as any
 })
+app.register(plugin, {
+  secret,
+  store: customTypedStore
+})
 expect(app.register).type.not.toBeCallableWith(plugin, {
   secret,
   store: new RedisStore({ client: createClient() })