Start: page route returns 500 when Accept excludes HTML

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
85/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
react, typescript
Domain
api, backend

Research direction

Start at packages/start-server-core/src/createStartHandler.ts around lines 558-561, then reproduce the issue with the provided curl commands and Accept headers. Done means non-HTML Accept values return 406 Not Acceptable, while /, browser Accept headers, and an absent header continue returning 200.

Written by the indexing model from the issue text.

Description

Which project does this relate to?

Start

Describe the bug

createStartHandler refuses to render a page route when the request's Accept
header does not allow HTML, and reports that refusal as 500:

https://github.com/TanStack/router/blob/179d9b9b5eec50dc7833b4e2ef91b735d34bbc07/packages/start-server-core/src/createStartHandler.ts#L558-L561

A failed content negotiation is a client-side condition, so this should be
406 Not Acceptable. 500 says the server malfunctioned, and nothing did.

Complete minimal reproducer

reproduction doesn't need any custom code

Steps to Reproduce the Bug

Against any Start app, on any page (non-server) route:

  curl -i -H 'Accept: application/json' https://example.com/
  curl -i -H 'Accept: image/webp'       https://example.com/

Both return 500 {"error":"Only HTML requests are supported here"}. Accept: /, a browser Accept, and an absent header all return 200.

Expected behavior

Should return 406 Not Acceptable instead of 500 Server Error.

Screenshots or Videos

No response

Platform
  • @tanstack/react-start 1.168.32
  • @tanstack/start-server-core 1.169.17 (current latest)
Additional context

No response

Dominant language
TypeScript
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