在 FastAPI 中返回 StreamingResponse 时出现“AttributeError: encode”

问题描述 投票：0回答：1

我正在使用 Python 3.10 和 FastAPI 

0.92.0
编写服务器发送事件 (SSE) 流 api。这就是 Python 代码的样子：

from fastapi import APIRouter, FastAPI, Header

from src.chat.completions import chat_stream
from fastapi.responses import StreamingResponse

router = APIRouter()

@router.get("/v1/completions",response_class=StreamingResponse)
def stream_chat(q: str, authorization: str = Header(None)):
    auth_mode, auth_token = authorization.split(' ')
    if auth_token is None:
        return "Authorization token is missing"
    answer = chat_stream(q, auth_token)
    return StreamingResponse(answer, media_type="text/event-stream")

这是 

chat_stream
函数：

import openai

def chat_stream(question: str, key: str):
    openai.api_key = key
    # create a completion
    completion = openai.Completion.create(model="text-davinci-003",
                                          prompt=question,
                                          stream=True)
    return completion

当我使用此命令调用 api 时：

curl -N -H "Authorization: Bearer sk-the openai key" https://chat.poemhub.top/v1/completions?q=hello

服务器端显示以下错误：

INFO:     123.146.17.54:0 - "GET /v1/completions?q=hello HTTP/1.0" 200 OK
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/uvicorn/protocols/http/h11_impl.py", line 429, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File "/usr/local/lib/python3.10/dist-packages/uvicorn/middleware/proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/applications.py", line 276, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/applications.py", line 122, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/usr/local/lib/python3.10/dist-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/usr/local/lib/python3.10/dist-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/usr/local/lib/python3.10/dist-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 718, in __call__
    await route.handle(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/routing.py", line 69, in app
    await response(scope, receive, send)
  File "/usr/local/lib/python3.10/dist-packages/starlette/responses.py", line 270, in __call__
    async with anyio.create_task_group() as task_group:
  File "/usr/local/lib/python3.10/dist-packages/anyio/_backends/_asyncio.py", line 662, in __aexit__
    raise exceptions[0]
  File "/usr/local/lib/python3.10/dist-packages/starlette/responses.py", line 273, in wrap
    await func()
  File "/usr/local/lib/python3.10/dist-packages/starlette/responses.py", line 264, in stream_response
    chunk = chunk.encode(self.charset)
  File "/usr/local/lib/python3.10/dist-packages/openai/openai_object.py", line 61, in __getattr__
    raise AttributeError(*err.args)
AttributeError: encode

为什么会出现这个错误？我应该怎么做才能修复它？

python-3.x streaming fastapi server-sent-events openai-api
1个回答
2
投票

如 FastAPI 的文档 中所述，

StreamingResponse
采用 
async
生成器或普通生成器/迭代器并流式传输响应主体。正如 this answer 中所解释的，在任何一种情况下，FastAPI 仍将异步工作——如果传递给 
StreamingResponse
的生成器不是异步的，FastAPI/Starlette 将在单独的线程中运行生成器（参见相关实现这里），使用
iterate_in_threadpool()
，然后将被
await
ed（见
iterate_in_threadpool()
实现）。有关 FastAPI 中 
def
与 
async def
的更多详细信息，以及在 
async def
端点内运行阻塞操作的解决方案，请查看此详细答案。

StreamingResponse
是 
Response
的子类，在 
bytes
中流式传输响应主体。因此，如果通过生成器传递的内容不是 
bytes
格式，FastAPI/Starlette 将尝试将其编码/转换为 
bytes
（使用 default 
utf-8
编码方案）。以下是相关实现的代码片段：

async for chunk in self.body_iterator:
    if not isinstance(chunk, bytes):
        chunk = chunk.encode(self.charset)
    await send({"type": "http.response.body", "body": chunk, "more_body": True})

但是，如果迭代器/生成器中的

chunk
不是可以编码的
str
格式，则会引发
AttributeError
（例如，
AttributeError: ... has no attribute 'encode'
），类似于this answer中描述的内容（见选项 2，注 3）。此外，如果一个块包含 
utf-8
编码范围之外的字符，您还不如面对 
UnicodeEncodeError: ... codec can't encode character
。因此，鉴于您提供的错误回溯中的
AttributeError: encode
，您很可能传递的对象不是
str
.

下面的示例演示了一个普通的生成器（即 

def gen()
），流式传输 JSON 数据，在这种情况下，需要先将 
dict
对象转换为 
str
（使用 
json.dumps()
或任何其他 JSON 编码器，例如
orjson
，请参阅here）然后到相应的字节值（使用
.encode('utf-8')
，如前所述，如果省略，FastAPI/Starlette 将处理）。此外，下面的示例使用了
text/event-stream
媒体类型（也称为MIME 类型），通常用于从服务器发送事件（另请参见event stream format）。如果您确信从服务器发送的数据始终为 JSON 格式，您也可以使用 
application/json
媒体类型。请注意，如 this answer 中所述，使用 
text/plain
媒体类型可能不会立即在浏览器中显示流数据，因为浏览器用于缓冲 
text/plain
对所谓的“MIME 嗅探”的响应（请参阅上面关于如何禁用它的链接答案，如果你想使用
text/plain
）。

工作示例

from fastapi import FastAPI
from fastapi.responses import StreamingResponse
import json
import time

app = FastAPI()


@app.get('/')
def main():
    def gen():
        while True:
            yield (json.dumps({'msg': 'Hello World!'}) + '\n\n').encode('utf-8')
            time.sleep(0.5)

    return StreamingResponse(gen(), media_type='text/event-stream')
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