Global Middleware causes serialisation error when throwing redirects via server function

Which project does this relate to?

Start

Describe the bug

When there is a global function middleware present in the start instance created in a start.ts file, and a redirect is thrown by any server function a SerovalUnsupportedTypeError occurs.

Your Example Website or App

https://github.com/mubrik/tanstack-start-middleware-issue

Steps to Reproduce the Bug or Issue

start of using the basic install steps:

npx gitpick TanStack/router/tree/main/examples/react/start-basic start-basic
cd start-basic
npm install
npm run dev

create a start.ts file in the src directory, content:

import { createMiddleware, createStart } from '@tanstack/react-start'

export const fnMw = createMiddleware({ type: 'function' })
  .server(({ next }) => {
    console.log("herrr")
    return next({
      context: {
        fromFnMw: true,
      },
    })
  })

export const startInstance = createStart(() => {
  return {
    defaultSsr: true,
    functionMiddleware: [fnMw],
  }
})

update vite config to match:

export default defineConfig({
  server: {
    port: 3000,
  },
  plugins: [
    tsConfigPaths({
      projects: ['./tsconfig.json'],
    }),
    tanstackStart({
      srcDirectory: 'src',
      start: { entry: './start.ts' },
    }),
    viteReact(),
  ],
})

Add a file with the server function throwing redirect:

import { createServerFn } from '@tanstack/react-start';
import { redirect } from '@tanstack/react-router';

export const redirectTest = createServerFn()
    .handler(async () => {
        throw redirect({ to: "/posts" })
    })

// in a component 
function Home() {
  const redir = useServerFn(redirectTest);

  return (
    <div className="p-2">
      <h3>Welcome Home!!!</h3>
      <button onClick={() => redir()}>test redirect</button>
    </div>
  )
}

Expected behavior

I expected the redirect to be propagated to the client router correctly

Screenshots or Videos

Platform

Router / Start Version: 1.132.38
OS: macOS
Browser: Chrome
Browser Version: 138
Bundler: vite
Bundler Version: 7.1.1

Additional context

No response

also seeing this using just a server function middleware attached with .middleware([myMiddleware]) rather than a global middleware, if it matters

export const authMiddleware = createMiddleware({ type: "function" }).server(
  async ({ next }) => {
    const session = await auth.api.getSession({
      headers: getRequestHeaders(),
    });

    return next({
      context: {
        session,
      },
    });
  },
);

export const myFunction = createServerFn({ method: "POST" })
  .inputValidator(someSchema)
  .middleware([authMiddleware])
  .handler(async ({ data, context }) => {
    throw redirect({ to: '/' });
  });

function useMyMutation() {
  const mutationFn = useServerFn(myFunction);
  return useMutation({
    mutationFn,
    onSuccess: () => toast.success("Success!")
  });
}

Same, also seeing this issue with a normal server function and [non global] middleware. This one is a bit problematic for us and will block our migration over to tanstack/start. Hoping it can be addressed in the next few weeks as stable v1 gets closer. Thanks team!

Found a workaround via discord

import { isRedirect } from "@tanstack/react-router";
import { createMiddleware, createStart } from "@tanstack/react-start";

const tempRedirectMiddleware = createMiddleware({ type: "function" }).server(async ({ next }) => {
  const result = await next();
  if ("error" in result && isRedirect(result.error)) {
    throw result.error;
  }
  return result;
});

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Global Middleware causes serialisation error when throwing redirects via server function #5372

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Global Middleware causes serialisation error when throwing redirects via server function #5372

Description

Which project does this relate to?

Describe the bug

Your Example Website or App

Steps to Reproduce the Bug or Issue

Expected behavior

Screenshots or Videos

Platform

Additional context

Activity

kylekz commented on Oct 20, 2025

willhoney7 commented on Nov 3, 2025

willhoney7 commented on Nov 10, 2025

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