[Start] v1.143.3 breaks both dev and production - Buffer is not defined + attachRouterServerSsrUtils is not defined

[Andresuito]

Which project does this relate to?

Start

Describe the bug

After upgrading to v1.143.3, TanStack Start has two critical bugs:

1. Development mode: ReferenceError: Buffer is not defined

• Database client (postgres/pg) is bundled and executed in the browser
• Occurs even though database is ONLY imported in .server.ts files
• Error location: node_modules/postgres/src/bytes.js

2. Production mode: ReferenceError: attachRouterServerSsrUtils is not defined

• Build succeeds but server crashes on startup
• Error location: .output/server/chunks/_/server-FFq0J1Wz.mjs:594:3
• Makes production deployment completely broken

Both issues suggest v1.143.3 has broken changes in:

• Server/client code splitting (dev)
• SSR utilities bundling (prod)

Your Example Website or App

none

Steps to Reproduce the Bug or Issue

1. Create a TanStack Start project with database integration

2. Install dependencies: bun add drizzle-orm postgres

3. Create database client in src/lib/db/index.ts:

   import { drizzle } from "drizzle-orm/postgres-js";
   import postgres from "postgres";
   
   const connection = postgres(process.env.DATABASE_URL!);
   export const db = drizzle(connection);

Create server function in src/services/users.server.ts:

import { createServerFn } from "@tanstack/react-start";
import { db } from "@/lib/db";

export const getUsers = createServerFn({ method: "GET" })
.handler(async () => {
return await db.query.user.findMany();
});

Update package.json to v1.143.3:

"@tanstack/react-router": "^1.143.3",
"@tanstack/react-router-devtools": "^1.143.3",
"@tanstack/react-router-ssr-query": "^1.143.3",
"@tanstack/react-start": "^1.143.3",
"@tanstack/router-plugin": "^1.143.3"

Open browser at http://localhost:3000/
Check console → Error: ReferenceError: Buffer is not defined at node_modules/postgres/src/bytes.js
Note: Database is ONLY imported in .server.ts files but gets bundled in browser anyway.

Expected behavior

Server-only code (.server.ts files) and their dependencies (like postgres, pg, drizzle-orm) should be completely excluded from the client bundle and never execute in the browser.

Screenshots or Videos

buffer.error.mp4

Platform

• Router / Start Version: 1.143.3
• OS: macOS
• Browser: Chrome
• Bundler: Vite
• Database: PostgreSQL with Drizzle ORM
• Packages affected: Both postgres@3.4.7 and pg@8.x exhibit the same issue

Additional context

No response

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🔗 Similar Issues

Possible Duplicates

• Some server-side modules incorrectly bundled into the client? #5738

Related Issues

• No HTTPEvent found in AsyncLocalStorage #4408

🔗 Related PRs

#5215 - fix: various fixes [merged]
#5284 - tests(start): update spa mode e2e to use production build [merged]
#5647 - test(solid-start): fix dev server for suspense transition [merged]
#5896 - fix: memory leaks [merged]
#5903 - fix(solid-start): fix hydration regression in 1.136.9 [merged]

👤 Suggested Assignees

• schiller-manuel
• birkskyum
• elvc
• wobsoriano
• nlynzaad

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[schiller-manuel]

please provide a complete example project as a git repo

[Andresuito]

It happens to me in this project - Link

[schiller-manuel]

i cannot get your project to run and to reproduce your error:

1. git clone
2. bun i
3. added a fake .env

DATABASE_URL=postgres://user:password@localhost:5432/mydatabase
RESEND_API_KEY=your_resend_api_key_here

4. bun dev

then i got this error:

 ERROR  Worker error: A provided trusted origin is invalid, make sure your trusted origins list is properly defined.                 10:21:03 PM


10:21:03 PM [vite] Internal server error: fetch failed
      at node:internal/deps/undici/undici:13510:13
      at async fetchAddress (file:///private/tmp/real-state/node_modules/nitro/dist/_dev.mjs:77:9)
      at async nitroDevMiddleware (file:///private/tmp/real-state/node_modules/nitro/dist/_build/vite.plugin.mjs:279:19)

[Andresuito]

Sorry, I had the plugins in the wrong order in vite.config.ts.

[joshymcd]

@Andresuito whats your correct order? im having the same issue

[Andresuito]

@joshymcd This

import { defineConfig } from 'vite'
import { devtools } from '@tanstack/devtools-vite'
import { tanstackStart } from '@tanstack/react-start/plugin/vite'
import viteReact from '@vitejs/plugin-react'
import viteTsConfigPaths from 'vite-tsconfig-paths'
import tailwindcss from '@tailwindcss/vite'
import { nitro } from 'nitro/vite'

const config = defineConfig({
  plugins: [
    viteTsConfigPaths({
      projects: ['./tsconfig.json'],
    }),
    tanstackStart(),
    nitro(),
    devtools(),
    tailwindcss(),
    viteReact(),
  ],
})

export default config

[nick-cheatwood7]

@joshymcd This

import { defineConfig } from 'vite'
import { devtools } from '@tanstack/devtools-vite'
import { tanstackStart } from '@tanstack/react-start/plugin/vite'
import viteReact from '@vitejs/plugin-react'
import viteTsConfigPaths from 'vite-tsconfig-paths'
import tailwindcss from '@tailwindcss/vite'
import { nitro } from 'nitro/vite'

const config = defineConfig({
plugins: [
viteTsConfigPaths({
projects: ['./tsconfig.json'],
}),
tanstackStart(),
nitro(),
devtools(),
tailwindcss(),
viteReact(),
],
})

export default config

I was facing the exact same issue (with kysely instead of drizzle), and this fixed it for me, too. Thanks!