How to modify stream responses?

[ElasticBottle]

Trying to integrate with the vercel ai SDK and cannot seem to message the stream into the expected response. In particular, I've noticed that the Content-Type returned is text/event-stream by orpc but vercel expects text/plain. I've tried using the ResponsePlugin to no avail.

Not sure if that's the only difference, but appreciate any direction here

[dosubot[bot]]

Hi @ElasticBottle! I'm Dosu and I’m helping the orpc team.

The Content-Type for stream responses in orpc is hard-coded as text/event-stream in the core response utilities, specifically in functions like toFetchBody and toNodeHttpBody. This means plugins like ResponsePlugin can't override it, and any attempt to set the header earlier in the pipeline will be overwritten at the point where the stream is constructed. To return text/plain (as required by the Vercel AI SDK), you would need to modify the orpc source code where the Content-Type is set for async iterator (stream) responses—there’s currently no built-in way to configure or override this via plugins or middleware. See the relevant implementation here.

If you need to support this use case, you’ll have to patch the library or propose a feature to make the Content-Type for streams configurable. Let me know if you want pointers on where exactly to patch or how to approach a workaround.

To reply, just mention @dosu.

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[unnoq]

We can do that by returning a text/plain file, but it can be tricky to integrate with an AI SDK.

But why do you need the AI SDK on the client side? What is it that oRPC can't do? Let's see what we can improve.

[ElasticBottle]

Super helpful! I'm using the useChat hook on the client side for convenience and trying to get orpc to integrate with it.

Current workaround is to see if the path is the chat path, create and use a server side caller, then manually return a response.

[unnoq]

If you use useChat I think you should handle the request outside oRPC, if you use oRPC I recommend you use Event Iterator instead.

[ElasticBottle]

ya, it's just feels heavy to put a whole extra layer on top of ORPC exp when using it as a standalone server (which i'm doing)

Any plans for more granular control around responses? Feels like we are pretty close with the detailed output/input structure.

Alternatively, I was thinking about was adding more details in the .handle response (the below snippet)

  const { matched, response } = await handler.handle(request, {
    prefix: '/api',
    context: {} // Add initial context if needed
  })

If we added path and originalReturnValue or something along those lines, it'd be super easy to have an 'escape hatch' and still route things through orpc.

For e.g., I would then be able to do something like

  const { matched, response, path, returnValue } = await handler.handle(request, {
    prefix: '/api',
    context: {} // Add initial context if needed
  })

if (path === '/api/use-chat') {
    return returnValue.toDataStreamResponse();
}

if (matched) {
    return response;
}
//...

[unnoq]

I think you can use Server-Client for this