Add TTL interception for external conditional TTL handling

index.ts

@@ -21,7 +21,7 @@ interface RedisStoreOptions {
   prefix?: string
   scanCount?: number
   serializer?: Serializer
-  ttl?: number
+  ttl?: number | {(sess: SessionData): number}
   disableTTL?: boolean
   disableTouch?: boolean
 }
@@ -31,7 +31,7 @@ class RedisStore extends Store {
   prefix: string
   scanCount: number
   serializer: Serializer
-  ttl: number
+  ttl: number | {(sess: SessionData): number}
   disableTTL: boolean
   disableTouch: boolean
 
@@ -181,6 +181,10 @@ class RedisStore extends Store {
   }
 
   private _getTTL(sess: SessionData) {
+    if (typeof this.ttl === "function") {
+      return this.ttl(sess)
+    }
+
     let ttl
     if (sess && sess.cookie && sess.cookie.expires) {
       let ms = Number(new Date(sess.cookie.expires)) - Date.now()

readme.md

@@ -89,6 +89,15 @@ If the session cookie has a `expires` date, `connect-redis` will use it as the T
 
 Otherwise, it will expire the session using the `ttl` option (default: `86400` seconds or one day).
 
+```ts
+interface RedisStoreOptions {
+  ...
+  ttl?: number | {(sess: SessionData): number}
+}
+```
+
+`ttl` also has external callback support. You can use it for dynamic TTL generation. It has access to `session` data.
+
 **Note**: The TTL is reset every time a user interacts with the server. You can disable this behavior in _some_ instances by using `disableTouch`.
 
 **Note**: `express-session` does not update `expires` until the end of the request life cycle. _Calling `session.save()` manually beforehand will have the previous value_.