From 9ee12a84da43ab12d03ae562ae2d693e8f6cdad8 Mon Sep 17 00:00:00 2001
From: arsam <me@asabbagh.com>
Date: Fri, 18 Sep 2026 23:12:28 +0330
Subject: [PATCH] Import source: backend/src/middleware/session

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.
---
 backend/src/middleware/session.ts | 86 +++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 backend/src/middleware/session.ts

diff --git a/backend/src/middleware/session.ts b/backend/src/middleware/session.ts
new file mode 100644
index 0000000..1025087
--- /dev/null
+++ b/backend/src/middleware/session.ts
@@ -0,0 +1,86 @@
+import { randomBytes } from 'node:crypto';
+import type { Request, RequestHandler } from 'express';
+import { sha256 } from '../utils/crypto.js';
+import { env } from '../config/env.js';
+import { store } from '../services/store.js';
+import type { DatabaseShape } from '../types.js';
+
+export const SESSION_COOKIE = 'cshare_sid';
+const ONE_YEAR_MS = 365 * 24 * 60 * 60 * 1000;
+const ROTATION_INTERVAL_MS = 24 * 60 * 60 * 1000; // Rotate session once a day
+
+// Map of sessionId -> { clientHash: string, expiresAt: number }
+const sessionCache = new Map<string, { clientHash: string, expiresAt: number }>();
+
+function getClientFingerprint(req: Request): string {
+  const ip = req.ip ?? req.socket.remoteAddress ?? 'unknown';
+  const ua = req.headers['user-agent'] as string ?? 'unknown';
+  return sha256(`${ip}:${ua}`);
+}
+
+/** Issues a long-lived HTTP-only, SameSite=Strict secure session cookie on first visit, bound to client IP/UA, and rotates periodically. */
+export const sessionMiddleware: RequestHandler = (req, res, next) => {
+  const currentSid = req.cookies?.[SESSION_COOKIE];
+  const clientHash = getClientFingerprint(req);
+  const now = Date.now();
+
+  if (!currentSid) {
+    const sid = randomBytes(32).toString('hex');
+    res.cookie(SESSION_COOKIE, sid, {
+      httpOnly: true,
+      sameSite: 'strict',
+      secure: env.nodeEnv === 'production',
+      maxAge: ONE_YEAR_MS,
+      path: '/',
+    });
+    req.cookies[SESSION_COOKIE] = sid;
+    sessionCache.set(sid, { clientHash, expiresAt: now + ROTATION_INTERVAL_MS });
+  } else {
+    if (!sessionCache.has(currentSid)) {
+      sessionCache.set(currentSid, { clientHash, expiresAt: now + ROTATION_INTERVAL_MS });
+    }
+    const cached = sessionCache.get(currentSid)!;
+    // Bind session to the client's fingerprint to prevent cookie hijacking
+    if (cached.clientHash !== clientHash) {
+      // Fingerprint mismatch — clear cookie, force new session
+      res.clearCookie(SESSION_COOKIE);
+      const sid = randomBytes(32).toString('hex');
+      res.cookie(SESSION_COOKIE, sid, {
+        httpOnly: true,
+        sameSite: 'strict',
+        secure: env.nodeEnv === 'production',
+        maxAge: ONE_YEAR_MS,
+        path: '/',
+      });
+      req.cookies[SESSION_COOKIE] = sid;
+      sessionCache.set(sid, { clientHash, expiresAt: now + ROTATION_INTERVAL_MS });
+    } else if (now > cached.expiresAt) {
+      // Periodic rotation logic: rotate the session cookie value to limit lifetime of any stolen session id
+      sessionCache.delete(currentSid);
+      const newSid = randomBytes(32).toString('hex');
+      res.cookie(SESSION_COOKIE, newSid, {
+        httpOnly: true,
+        sameSite: 'strict',
+        secure: env.nodeEnv === 'production',
+        maxAge: ONE_YEAR_MS,
+        path: '/',
+      });
+      req.cookies[SESSION_COOKIE] = newSid;
+      sessionCache.set(newSid, { clientHash, expiresAt: now + ROTATION_INTERVAL_MS });
+
+      // Migrate file ownership to the new session ID so uploads survive rotation.
+      store.update((db: DatabaseShape) => {
+        for (const file of db.files) {
+          if (file.sessionId === currentSid) {
+            file.sessionId = newSid;
+          }
+        }
+      }).catch(() => {});
+    }
+  }
+  next();
+};
+
+export function getSessionId(req: Request): string {
+  return req.cookies?.[SESSION_COOKIE] ?? '';
+}