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22 changes: 6 additions & 16 deletions example/backend/routes/chat.py
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,8 @@

Pattern:
1. Create a ``StreamContext`` at the start of the request.
2. Spin up a background asyncio task that calls llm_service.chat().
2. Call ``await ctx.run(...)`` to schedule the background work with
automatic finish/error handling.
3. Return ``StreamingResponse(ctx.stream(), ...)`` immediately so the
client starts receiving SSE events as they are produced.

Expand All @@ -18,8 +19,6 @@

from __future__ import annotations

import asyncio

from fastapi import APIRouter
from fastapi.responses import StreamingResponse
from pydantic import BaseModel
Expand All @@ -29,7 +28,6 @@
from ..services import llm_service

router = APIRouter()
_background_tasks: set[asyncio.Task] = set()


class ChatMessage(BaseModel):
Expand All @@ -51,19 +49,11 @@ async def chat(request: ChatRequest) -> StreamingResponse:
"""
ctx = StreamContext()

async def _work() -> None:
try:
messages = [m.model_dump() for m in request.messages]
await llm_service.chat(messages, ctx=ctx)
except Exception as exc:
await ctx.write_text(f"\n\n_(Error: {exc})_")
finally:
await ctx.finish()

_task = asyncio.create_task(_work())
_background_tasks.add(_task)
_task.add_done_callback(_background_tasks.discard)
async def _work(c: StreamContext) -> None:
messages = [m.model_dump() for m in request.messages]
await llm_service.chat(messages, ctx=c)

await ctx.run(_work)
return StreamingResponse(
ctx.stream(),
media_type="text/event-stream",
Expand Down
12 changes: 4 additions & 8 deletions src/ai_sdk_stream_python/__init__.py
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,6 @@
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
from ai_sdk_stream_python import StreamContext
import asyncio

app = FastAPI()

Expand All @@ -27,14 +26,11 @@
async def chat():
ctx = StreamContext()

async def _work():
try:
await ctx.write_text("Hello ")
await ctx.write_text("world!")
finally:
await ctx.finish()
async def _work(c: StreamContext) -> None:
await c.write_text("Hello ")
await c.write_text("world!")

asyncio.create_task(_work())
await ctx.run(_work)
return StreamingResponse(
ctx.stream(),
media_type="text/event-stream",
Expand Down
17 changes: 7 additions & 10 deletions src/ai_sdk_stream_python/context.py
Original file line number Diff line number Diff line change
Expand Up @@ -34,15 +34,12 @@
async def chat(request: ChatRequest):
ctx = StreamContext()

async def _work():
try:
await ctx.store.set("query", request.message)
async for chunk in my_llm.stream(request.message):
await ctx.write_text(chunk)
finally:
await ctx.finish()
async def _work(c: StreamContext) -> None:
await c.store.set("query", request.message)
async for chunk in my_llm.stream(request.message):
await c.write_text(chunk)

asyncio.create_task(_work())
await ctx.run(_work)
return StreamingResponse(
ctx.stream(),
media_type="text/event-stream",
Expand Down Expand Up @@ -117,8 +114,8 @@ class StreamContext(Generic[_InfoT]):
A stateful context for producing a Vercel AI SDK v6 UIMessageStream.

One ``StreamContext`` maps to one assistant message. Create it at the
start of a request, spin up a background task that writes events through
the helpers, and pass ``ctx.stream()`` to ``StreamingResponse``.
start of a request, use ``ctx.run()`` to schedule the background work,
and pass ``ctx.stream()`` to ``StreamingResponse``.

Attributes
----------
Expand Down