Issues with `useSession`: Invariant failed: expected content-type header to be set

[mhsattarian]

Which project does this relate to?

Start

Describe the bug

When implementing a manual authentication procedure from the provided guide in the documentation, several issues arise. Notably, the useSession method is not functioning correctly. Below is the sample code I utilize and the corresponding error:

How session is configured:

// utils/tanstack-session.ts
"use server";

import { useSession } from "@tanstack/react-start/server";

export function useAppSession() {
  return useSession({
    name: "session",
    password:
      "LKMDSM<DCLMSCDKNScjdnskjdfn3434rmn3kj4n3kjrnk3j4nrkj34nrkj3nrkj3n4rkjn", // At least 32 characters
    cookie: {
      secure: false,
      sameSite: "lax",
      httpOnly: true,
      maxAge: 7 * 24 * 60 * 60, // 7 days
    },
  });
}

How is used:

// actions.ts
import { useAppSession } from "./utils/tanstack-session";

export async function getSessionAction() {
  const session = await useAppSession();

  if (!session.data) {
    return null;
  }

  return session.data;
}

here is the error I get:

Error: Invariant failed: expected content-type header to be set

---

There are some other issues with the docs regarding the manual authentication guide:

1. In the "2. Session Management" section, the provided code sample's wont work unless after adding a "use server" directive.

2. In the "3. Authentication Context" section, the usage of useServerFn is incorrect:

Your Example Website or App

https://codesandbox.io/p/devbox/cranky-mayer-pl9r9f

Steps to Reproduce the Bug or Issue

1. Go to "https://codesandbox.io/p/devbox/cranky-mayer-pl9r9f"
2. In the CodeSandBox there's another error that I coud'nt figure out: "globalThis.process.getBuiltinModule is not a function"
3. Download the project and run it locally
4. Open the project, on the main page there's a butto which by clicking on it the action that uses the cookies would run hence causing the error

Expected behavior

This should work as expected and return the cookie, as it did previously.

Screenshots or Videos

Platform

• Router / Start Version: Router: 1.141.2 | Start: 1.141.3
• OS: macOS
• Browser: Chrome
• Browser Version: 143.0.7499.109
• Bundler: vite
• Bundler Version: 7.1.7

Additional context

No response

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🔗 Similar Issues

Related Issues

• Tanstack React Example: Start Basic Auth Broken #3850
• Generic type of useSession (SessionDataT) is not accepted: Expected 0 type arguments, but got 1. #3448

🔗 Related PRs

#5318 - docs: fix import path for useSession in authentication.md [merged]
#5347 - update solid start docs [merged]
#5390 - fix: pass in request when requestMiddleware is used in combination wi… [merged]
#5935 - fix(start-server-core): deserialize tss context when using formdata [merged]
#5978 - test(start): test that multiple Set-Cookie headers are not lost during redirect [merged]

👤 Suggested Assignees

• nick22985
• renomureza
• johnf
• brenelz
• schiller-manuel

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[schiller-manuel]

you must wrap your server function into createServerFn, "use server" is not supported.

[mhsattarian]

right. my bad.
thank you. but the error handling here could be a lot better directing my to find the problem.