generous-apricot

Build fails when I use a server function middleware with a server function

The middleware reads the user's data from a session cookie. From what I understand, the error is about me trying to run server-only code on the client side (like reading the encrypted session data), but I created my middleware using the server() method, so I'm confused. Reproduction I forked the basic example and added a commit to it to reproduce the issue. Commit: https://github.com/fulopkovacs/tanstack-start-middleware-issue/commit/60d7283c05ab71353d6014f062242f72fd8be12e#diff-6aa551c33ca5fabc618706416b028e5ce253ca1e09a72d61fe0163b09e2bbcae Repo: https://github.com/fulopkovacs/tanstack-start-middleware-issue ❌ This is the error:

✗ Build failed in 825ms

[12:16:35 PM]  ERROR  node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js (2:9): "Readable" is not exported by "__vite-browser-external", imported by "node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js".
file: /Users/fulopkovacs/dev-learning/2025/tanstack-start-weirdness/start-basic/node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js:2:9

1: import { ReadableStream } from "node:stream/web";
2: import { Readable } from "node:stream";
           ^
3: import { createControlledPromise } from "@tanstack/router-core";
4: function transformReadableStreamWithRouter(router, routerStream) {

[see the full error in the attachment]

✗ Build failed in 825ms

[12:16:35 PM]  ERROR  node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js (2:9): "Readable" is not exported by "__vite-browser-external", imported by "node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js".
file: /Users/fulopkovacs/dev-learning/2025/tanstack-start-weirdness/start-basic/node_modules/.pnpm/@tanstack+start-server-core@1.120.10/node_modules/@tanstack/start-server-core/dist/esm/transformStreamWithRouter.js:2:9

1: import { ReadableStream } from "node:stream/web";
2: import { Readable } from "node:stream";
           ^
3: import { createControlledPromise } from "@tanstack/router-core";
4: function transformReadableStreamWithRouter(router, routerStream) {

[see the full error in the attachment]

I started using TanStack Start a week ago and am still a newbie. 😅 Would be really grateful for some help with this! 🙏

GitHub

GitHub - fulopkovacs/tanstack-start-middleware-issue: Repro of an i...

Repro of an issue with server function middlewares. - fulopkovacs/tanstack-start-middleware-issue

GitHub

Build error · fulopkovacs/tanstack-start-middleware-issue@60d7283

5 Replies

generous-apricotOP•4mo ago

@Manuel Schiller [continuing the convo I mistakenly opened in the router channel 😅] so the middleware is defined in src/utils/authMiddleware.ts , and used in src/utils/posts/. Heyy, sorry to ping you again, but do you have any idea what is the problem here?

foreign-sapphire•4mo ago

ah sorry i did not look into it more closely the problem you have here is that you export a function useAppSession from the file where the middleware is also exported when start compiles the middleware, it removes the server part of the middleware but it cannot possible remove stuff that is still being used by exported functions so in your case, dont export anything else but middlewares from that file

generous-apricotOP•4mo ago

Ohhhh wooow. Thank you very much! It does work with your fix. I'm too tired to understand the reasoning now, but I'll reread it tomorrow morning! 🤣

foreign-sapphire•4mo ago

i hope we can provide better error messages for those situations in the future

generous-apricotOP•4mo ago

ngl, that'd be awesome 🤣

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Build fails when I use a server function middleware with a server function

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