fix: SSR invariant dehydration errors with bun

[Cyenoch]

Related: https://github.com/TanStack/router/issues/3989

The script assigned to __TSR_SSR__.dehydrated appears outside the </html> tag. When the entry script /_build/assets/client-BJoNZ2zg.js is cached locally by the browser, even if the entry script is async, the script outside the html may still be executed after the entry script.

https://github.com/TanStack/router/blob/72ffeb4d4ae23a30859b9c7b8a3164535d5f2b85/packages/start-server-core/src/transformStreamWithRouter.ts#L171

Problems occur when text is complete HTML

https://github.com/TanStack/router/blob/72ffeb4d4ae23a30859b9c7b8a3164535d5f2b85/packages/start-server-core/src/transformStreamWithRouter.ts#L174-L175

https://github.com/TanStack/router/blob/72ffeb4d4ae23a30859b9c7b8a3164535d5f2b85/packages/start-server-core/src/transformStreamWithRouter.ts#L190

bodyEndMatch is assigned before the !headStarted branch processes chunkString.

https://github.com/TanStack/router/blob/72ffeb4d4ae23a30859b9c7b8a3164535d5f2b85/packages/start-server-core/src/transformStreamWithRouter.ts#L216

The length of bodyEndIndex obtained here will exceed the length of the modified chunkString, resulting in <script> being appended after </html>

The solution is make sure hydrate is executed after TSR_SSR.dehydrated is assigned a value by other means.

[nx-cloud[bot]]

View your CI Pipeline Execution ↗ for commit 846bf44fa7ca506adbd31ae9e8e8fbd1e0a287b8.

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---

☁️ Nx Cloud last updated this comment at 2025-05-25 09:36:29 UTC

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commit: 846bf44

[Cyenoch]

I think it would be better if ensure that all tsr-once is before the entry script

[schiller-manuel]

I think it would be better if ensure that all tsr-once is before the entry script

that's not possible as values might stream in later

[schiller-manuel]

how can I reproduce the issue locally?

[Cyenoch]

how can I reproduce the issue locally?

For example:

cd example/react/start-material-ui

Update app.config.ts set server.preset = 'bun'

pnpm build

bun run .output/server/index.mjs

Open "localhost:3000" and enter F12 to switch the throttling to 3G

Tap reload button on browser navigation bar, after reloading for about a dozen times (client entry scripts cached in memory), Invariant failed started to appear.

[Cyenoch]

Even if tsr-once is in html, Invariant failed will still appear. So I think if this script is before client entry script, the problem should be solved. Or the other way to make sure hydrate is executed after __TSR_SSR__.dehydrated is assigned a value by other means.

[Cyenoch]

Change script loading attribute from async to defer seems to solve this problem

[schiller-manuel]

i found the issue, a synchronization error when injecting the scripts. I'll fix this as part of a rewrite of this section.

[Cyenoch]

very thankful