如何实现一个实时转发 Stream 流的接口

想写一个实时转发 Stream 流内容的接口，不怎么懂 stream 流相关的知识

之前的接口是

async def index(path: str, request: Request):
    data = await request.json()
    resp = c.send_request(path, data)
    headers = dict(resp.headers)

    async def generate():
        for chunk in resp.iter_lines():
            if chunk:
                yield chunk + b'\n\n'
    return StreamingResponse(generate(), headers=headers)

问题是，这个会等接受完全部的 Stream 流信息，才会转发，想实现的效果是实时转发 stream 流信息，具体一点就是，接收到一行或者指定大小的信息块，就转发出去。

想法是将 resp = c.send_request(path, data)这块改造成异步的，然后实时转发。

目前的代码是

async def index(path: str, request: Request):
    data = await request.json()
    async with httpx.AsyncClient() as client:
        async with client.stream('POST', path, json=data) as response:
            resp_headers = dict(response.headers)
            async def generate():
                async for line in response.aiter_lines():
                    if line:
                        yield line.encode('utf-8') + b'\n\n'
            return StreamingResponse(generate(), headers=resp_headers)

但是会报：

httpx.StreamClosed: Attempted to read or stream content, but the stream has been closed.

不知道怎么改，求赐教