From 3d284aead3f4be0042211f8277c57f81e9a9c3a3 Mon Sep 17 00:00:00 2001
From: gergokee <55487440+gergokee@users.noreply.github.com>
Date: Wed, 1 Apr 2026 22:19:48 +0200
Subject: [PATCH] feat: support async serialize/deserialize in
 CacheValueSerializer
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Widen CacheValueSerializer.serialize and .deserialize return types from
sync-only to string | Promise<string> and CacheHandlerValue | null |
Promise<CacheHandlerValue | null> respectively, and add await at both
call sites in redis-strings.ts.

This allows users to replace blocking sync codecs (e.g. brotliCompressSync)
with non-blocking async variants (e.g. brotliCompress) without blocking
the Node.js event loop under load. Existing sync implementations continue
to work unchanged — await on a non-Promise is a no-op in JavaScript.
---
 .../src/handlers/redis-strings.ts                    |  4 ++--
 .../src/handlers/redis-strings.types.ts              | 12 ++++++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/packages/nextjs-cache-handler/src/handlers/redis-strings.ts b/packages/nextjs-cache-handler/src/handlers/redis-strings.ts
index 0662064..4a90322 100644
--- a/packages/nextjs-cache-handler/src/handlers/redis-strings.ts
+++ b/packages/nextjs-cache-handler/src/handlers/redis-strings.ts
@@ -193,7 +193,7 @@ export default function createHandler({
         return null;
       }
 
-      const cacheValue = valueSerializer.deserialize(result);
+      const cacheValue = await valueSerializer.deserialize(result);
 
       if (!cacheValue) {
         return null;
@@ -254,7 +254,7 @@ export default function createHandler({
         parseBuffersToStrings({ ...cacheHandlerValue, value: valueForStorage });
       }
 
-      const serializedValue = valueSerializer.serialize({
+      const serializedValue = await valueSerializer.serialize({
         ...cacheHandlerValue,
         value: valueForStorage,
       });
diff --git a/packages/nextjs-cache-handler/src/handlers/redis-strings.types.ts b/packages/nextjs-cache-handler/src/handlers/redis-strings.types.ts
index 65e1106..9af95c1 100644
--- a/packages/nextjs-cache-handler/src/handlers/redis-strings.types.ts
+++ b/packages/nextjs-cache-handler/src/handlers/redis-strings.types.ts
@@ -5,10 +5,14 @@ import type { CacheHandlerValue } from "./cache-handler.types";
 /**
  * Pluggable wire-format codec for Redis string values (JSON, compression, encryption, etc.).
  * Default behavior is JSON.stringify / JSON.parse (see `jsonCacheValueSerializer` export).
+ *
+ * Both methods may return a `Promise`, enabling non-blocking async codecs such as
+ * stream-based compression (`zlib.brotliCompress`) or encryption (`crypto.subtle`).
+ * Synchronous implementations continue to work unchanged — `await` on a plain value is a no-op.
  */
 export type CacheValueSerializer = {
-  serialize(value: CacheHandlerValue): string;
-  deserialize(stored: string): CacheHandlerValue | null;
+  serialize(value: CacheHandlerValue): string | Promise<string>;
+  deserialize(stored: string): CacheHandlerValue | null | Promise<CacheHandlerValue | null>;
 };
 
 export type RedisCompliantCachedRouteValue = {
@@ -86,6 +90,10 @@ export type CreateRedisStringsHandlerOptions<
    * Optional codec for values stored in Redis (`SET`/`GET`).
    * Implement compression, encryption, or custom formats in your app; this package stays dependency-free.
    *
+   * Both `serialize` and `deserialize` may return a `Promise`, enabling non-blocking async codecs
+   * (e.g. `zlib.brotliCompress` / `zlib.brotliDecompress`) that avoid blocking the Node.js event loop.
+   * Synchronous implementations continue to work unchanged.
+   *
    * @default JSON.stringify / JSON.parse (same as previous releases)
    */
   valueSerializer?: CacheValueSerializer;