update fastapi example and documentation

[0x4bs3nt]

Description

The data streaming option when working with the V5 AI SDK seems to not work at all.

I have tried a lot of things and could not get anything working with a FastAPI backend and using useChat with the V5 on the frontend.

It seems to work well when using the text protocol, but the data protocol does not work at all.

From what I found there are 2 examples of how to implement it using FastAPI.
One of those; https://github.com/vercel-labs/ai-sdk-preview-python-streaming, is using the V4, and the other; https://github.com/vercel/ai/tree/main/examples/next-fastapi just doesn't work.

I pulled and tested locally the https://github.com/vercel/ai/tree/main/examples/next-fastapi repository and not only do the Pydantic models not reflect the V5 changes, but when fixing those issues and trying the data protocol, it just doesn't work.

Is this not supported yet, is the documentation lacking, is there any working example of V5 and FastAPI?

AI SDK Version

• ai: "^5.0.0-beta.25"
• @ai-sdk/openai: "^2.0.0-beta.11",
• @ai-sdk/react: "^2.0.0-beta.25",

[neri-rnd]

any updates on this?

[evokelektrique]

Same issue, Any updates? I need help

[imaaditya-stack]

I'm also facing the same issue, suddenly the streaming response for a chat app stopped working after upgrading to V5. I'm using fast-api backend.

    response = llm.stream(prompt)

    def event_stream():
        try:
            for chunk in response:
                if chunk.content:
                    yield "0:{text}\n".format(text=json.dumps(chunk.content))
        except Exception as e:
            yield f"data: ERROR: {str(e)}\n\n"
        finally:
            print("DONE------")

    return StreamingResponse(event_stream(), media_type="text/event-stream")

[0x4bs3nt]

I'm also facing the same issue, suddenly the streaming response for a chat app stopped working after upgrading to V5. I'm using fast-api backend.

    response = llm.stream(prompt)

    def event_stream():
        try:
            for chunk in response:
                if chunk.content:
                    yield "0:{text}\n".format(text=json.dumps(chunk.content))
        except Exception as e:
            yield f"data: ERROR: {str(e)}\n\n"
        finally:
            print("DONE------")

    return StreamingResponse(event_stream(), media_type="text/event-stream")

Yup, seems to work with V4, but doesn't work at all with V5.

[davidroeca]

I tried this out and was having issues. Turns out mine were with my load balancer. But the protocol has also changed and the example hasn't been updated to reflect that. Check the docs here: https://ai-sdk.dev/docs/ai-sdk-ui/stream-protocol#data-stream-protocol

Here's an example of what you have to do now:

import asyncio
import json
import uuid

async def event_stream():
    message_id = f"msg_{uuid.uuid4().hex}"
    
    yield f'data: {json.dumps({"type": "start", "messageId": message_id})}\n\n'
    
    text_id = f"text_{uuid.uuid4().hex}"
    yield f'data: {json.dumps({"type": "text-start", "id": text_id})}\n\n'
    
    chunks = ["This", " is", " a", " test", " response"]
    for chunk in chunks:
        yield f'data: {json.dumps({"type": "text-delta", "id": text_id, "delta": chunk})}\n\n'
        await asyncio.sleep(0.1)
    
    yield f'data: {json.dumps({"type": "text-end", "id": text_id})}\n\n'
    yield f'data: {json.dumps({"type": "finish"})}\n\n'
    yield f'data: [DONE]\n\n'

Took me longer than I would have liked to get this working -- hope this saves someone else some time!

Edit: make sure you add the custom headers: {"x-vercel-ai-ui-message-stream": "v1"} -- won't work without it

[keerthanenr]

Hey everyone - I just gone ahead and raised an MR on that python stre - check it out vercel-labs/ai-sdk-preview-python-streaming#20