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Nuxt•2mo ago
Byte

Nuxt Auth Utils

I have a server middleware. If the user isn't authorised I want to store the requested url in the session and redirect to the login page. On successful login I want to redirect to the requested url. In my server middleware I'm trying to call setUserSession however I'm seeing the error message ERROR [unhandledRejection] Cannot set headers after they are sent to the client 10:53:55 AM at ServerResponse.setHeader (node:_http_outgoing:659:11) at setCookie (node_modules/.pnpm/h3@1.15.3/node_modules/h3/dist/index.mjs:610:20) at updateSession (node_modules/.pnpm/h3@1.15.3/node_modules/h3/dist/index.mjs:1424:5) at async Object.update (node_modules/.pnpm/h3@1.15.3/node_modules/h3/dist/index.mjs:1338:7) at async setUserSession (.nuxt/dev/index.mjs:2548:3)
2 Replies
kapa.ai
kapa.ai•2mo ago
Hi @Byte. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave: ---------------------- The error message "Cannot set headers after they are sent to the client" occurs when you attempt to modify the response (such as setting cookies or headers) after the response has already started being sent to the client. In the context of Nuxt server middleware and session handling, this typically means that setUserSession (which sets a cookie) is being called too late in the request lifecycle. Key points from the knowledge sources: - Middleware handlers in Nuxt server middleware should not return anything or close/respond to the request; they are meant to inspect or extend the request context or throw an error, not to send a response themselves. If you attempt to set headers after the response has started, you'll get this error.
Docs: Server Middleware - If you want to perform a redirect and set session data, you must ensure both actions happen before the response is sent. For example, in an API handler, you can set the session and then send a redirect response using a 302 status and Location header, but you must not write to the response after it has been sent.
Stack Overflow: Nuxt 3, navigate to login on 401 - The Nuxt Auth Utils recipe shows that session data is set using setUserSession in the API handler before returning a response.
Docs: Sessions and Authentication How to fix: - Make sure you call setUserSession and perform the redirect before any part of the response is sent. - In server middleware, if you need to redirect, you should throw an error or handle the redirect by writing the headers and ending the response immediately after setting the session. Example approach: 
// server/middleware/auth.ts
export default defineEventHandler(async (event) => {
  const isAuthenticated = /* your auth check logic */;
  if (!isAuthenticated) {
    // Store the requested URL in the session
    await setUserSession(event, {
      redirectTo: getRequestURL(event)
    });
    // Redirect to login before sending any response
    event.node.res.writeHead(302, { Location: '/login' });
    event.node.res.end();
  }
});
// server/middleware/auth.ts
export default defineEventHandler(async (event) => {
  const isAuthenticated = /* your auth check logic */;
  if (!isAuthenticated) {
    // Store the requested URL in the session
    await setUserSession(event, {
      redirectTo: getRequestURL(event)
    });
    // Redirect to login before sending any response
    event.node.res.writeHead(302, { Location: '/login' });
    event.node.res.end();
  }
});
Make sure this logic is the first thing that happens in the request, before any response is sent. If you try to set the session or headers after the response has started, you'll get the error you described. Summary:
You must set the session and perform the redirect before the response is sent. If you see "Cannot set headers after they are sent to the client," it means you're trying to modify the response too late in the lifecycle. Move your setUserSession and redirect logic earlier, and ensure nothing else has written to the response yet.
Docs: Server Middleware
Stack Overflow: Nuxt 3, navigate to login on 401 ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------
kapa.ai
kapa.ai•2mo ago
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