起因

如题，最近在编写一个使用Fastapi调用Playwright进行网页渲染截图的工具

环境如下：

试图在FastApi路由中运行子进程，但执行结果是 NotImplementedError

原始代码如下

from playwright.async_api import async_playwright,TimeoutError

import asyncio
from typing import Literal
from io import BytesIO
import uvicorn
from fastapi import FastAPI,Form
from fastapi.responses import JSONResponse,StreamingResponse
from asyncio.windows_events import ProactorEventLoop
from uvicorn import Config, Server


app = FastAPI(
    title="Playwright",
    description="Playwright服务",
    version="0.0.2",
    docs_url="/apidoc",
    redoc_url=None
)


async def AsyncPWscreenshot(
    content:str = "",
    url:str = "https://www.baidu.com",
    referer:str = "",
    wait_until:Literal["commit", "domcontentloaded", "load", "networkidle"] = "networkidle",
    timeout:int = 30000,
    viewport_height:int = 1080,
    viewport_width: int = 1920,
    proxy_address:str = "",
    proxy_username:str = "",
    proxy_password:str = "",
    screenshot_quality:int = 100,
    scale: Literal["css", "device"] =  "device",
    format: Literal["png","jpeg"] = "device",
    ifRAW:bool = False
):
    async with async_playwright() as playwright:
        
        try:
            browser = await playwright.firefox.launch(
                headless=True,
                timeout=timeout,
                )
            context = await browser.new_context(
                    viewport={'width': viewport_width, 'height': viewport_height}
                    )
            if proxy_address:
                proxy={
                    "server":proxy_address,
                    "username": proxy_username,
                    "password": proxy_password

                }

                context = await browser.new_context(
                    viewport={'width': viewport_width, 'height': viewport_height},
                    proxy=proxy
                    )

            page = await context.new_page()

            if ifRAW and content:
                return JSONResponse(status_code=200,content={"message":"","result":content})

            if content:
                await page.set_content(content,timeout=timeout,wait_until=wait_until)

            else:
                await page.goto(
                    url,
                    referer=referer,
                    wait_until=wait_until
                    )
                if ifRAW:
                    return JSONResponse(status_code=200,content={"message":"","result":await page.content()})

            if format == "png":
                screenshot_quality = None
            data = await page.screenshot(
                full_page=True,
                scale=scale,
                type=format,
                quality=screenshot_quality
                )
        except TimeoutError:
            return JSONResponse(status_code=502,content={"message":"Time Out","result":None})


        bytes_io = BytesIO(data)
        bytes_io.seek(0)
        return StreamingResponse(content=bytes_io,media_type=f"image/{format}")


@app.post("/playwright",tags=["pw代理"])
async def root(
    content:str = Form("",description="直接使用传入字符串生成"),
    url:str = Form("https://www.baidu.com",description="使用网址生成"),
    referer:str = Form("",description="来源"),
    wait_until:Literal["commit", "domcontentloaded", "load", "networkidle"] = Form("networkidle",description="等待模式"),
    timeout:int = Form(30000,description="超时时间"),
    viewport_height:int = Form(1080,description="浏览器高度"),
    viewport_width: int = Form(1920,description="浏览器宽度"),
    proxy_address:str = Form("",description="代理地址"),
    proxy_username:str = Form("",description="代理账号"),
    proxy_password:str = Form("",description="代理密码"),
    screenshot_quality:int = Form(100,description="图片质量，仅JPEG生效"),
    scale: Literal["css", "device"] =  Form("device",description="scale"),
    format: Literal["png","jpeg"] = Form("png",description="图片格式"),
    ifRAW:bool = Form(False,description="是否仅返回页面源码"),
):  
    return await AsyncPWscreenshot(
        content=content,
        url=url,
        referer=referer,
        wait_until=wait_until,
        timeout=timeout,
        viewport_height=viewport_height,
        viewport_width=viewport_width,
        proxy_address=proxy_address,
        proxy_password=proxy_password,
        proxy_username=proxy_username,
        screenshot_quality=screenshot_quality,
        scale=scale,
        format=format,
        ifRAW=ifRAW
    )

import multiprocessing

if __name__ == '__main__':
    vcpus = multiprocessing.cpu_count()
    workers = int((vcpus*2)+1)
    uvicorn.run(app='pw:app', host="0.0.0.0", port=8003,workers=2,reload=False)

启动后，Fastapi工作正常，但在请求目标路由的时候，开始报错

INFO:     Started server process [9192]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [21696]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
Task exception was never retrieved
future: <Task finished name='Task-5' coro=<Connection.run() done, defined at D:\Python311\Lib\site-packages\playwright\_impl\_connection.py:240> exception=NotImplementedError()>
Traceback (most recent call last):
  File "D:\Python311\Lib\site-packages\playwright\_impl\_connection.py", line 247, in run
    await self._transport.connect()
  File "D:\Python311\Lib\site-packages\playwright\_impl\_transport.py", line 127, in connect
    raise exc
  File "D:\Python311\Lib\site-packages\playwright\_impl\_transport.py", line 116, in connect
    self._proc = await asyncio.create_subprocess_exec(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\subprocess.py", line 218, in create_subprocess_exec
    transport, protocol = await loop.subprocess_exec(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\base_events.py", line 1688, in subprocess_exec
    transport = await self._make_subprocess_transport(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\base_events.py", line 502, in _make_subprocess_transport
    raise NotImplementedError
NotImplementedError
INFO:     127.0.0.1:58295 - "POST /playwright HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "D:\Python311\Lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 407, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\site-packages\uvicorn\middleware\proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\site-packages\fastapi\applications.py", line 271, in __call__
    await super().__call__(scope, receive, send)
  File "D:\Python311\Lib\site-packages\starlette\applications.py", line 118, in __call__
    await self.middleware_stack(scope, receive, send)
  File "D:\Python311\Lib\site-packages\starlette\middleware\errors.py", line 184, in __call__
    raise exc
  File "D:\Python311\Lib\site-packages\starlette\middleware\errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "D:\Python311\Lib\site-packages\starlette\middleware\exceptions.py", line 79, in __call__
    raise exc
  File "D:\Python311\Lib\site-packages\starlette\middleware\exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "D:\Python311\Lib\site-packages\fastapi\middleware\asyncexitstack.py", line 21, in __call__
    raise e
  File "D:\Python311\Lib\site-packages\fastapi\middleware\asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "D:\Python311\Lib\site-packages\starlette\routing.py", line 706, in __call__
    await route.handle(scope, receive, send)
  File "D:\Python311\Lib\site-packages\starlette\routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "D:\Python311\Lib\site-packages\starlette\routing.py", line 66, in app
    response = await func(request)
               ^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\site-packages\fastapi\routing.py", line 237, in app
    raw_response = await run_endpoint_function(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\site-packages\fastapi\routing.py", line 163, in run_endpoint_function
    return await dependant.call(**values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "e:\Desktop\pw.py", line 112, in root
    return await AsyncPWscreenshot(
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "e:\Desktop\pw.py", line 38, in AsyncPWscreenshot
    async with async_playwright() as playwright:
  File "D:\Python311\Lib\site-packages\playwright\async_api\_context_manager.py", line 46, in __aenter__
    playwright = AsyncPlaywright(next(iter(done)).result())
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\site-packages\playwright\_impl\_transport.py", line 116, in connect
    self._proc = await asyncio.create_subprocess_exec(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\subprocess.py", line 218, in create_subprocess_exec
    transport, protocol = await loop.subprocess_exec(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\base_events.py", line 1688, in subprocess_exec
    transport = await self._make_subprocess_transport(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Python311\Lib\asyncio\base_events.py", line 502, in _make_subprocess_transport
    raise NotImplementedError
NotImplementedError

当我试图使用这样的方法来调用异步的PlaywrightAPI的时候，它提示 create_subprocess 失败

解决

通过询问大佬和查阅相关文档，我注意到这是因为uvicorn默认使用的Loop循环在Windows下会产生很迷惑的问题

因此需要手动对Fastapi指定Loop循环，可以将循环修改为 ProactorEventLoop 并且关闭uvicorn的reload功能，因为这个功能可能会在下一次重载的时候，再次把Loop恢复为默认。

因此需要强制修改循环，部分修改代码如下

import asyncio
from asyncio.windows_events import ProactorEventLoop

from fastapi import FastAPI
from uvicorn import Config, Server

app = FastAPI()


class ProactorServer(Server):
    def run(self, sockets=None):
        loop = ProactorEventLoop()
        asyncio.set_event_loop(loop) # since this is the default in Python 3.10, explicit selection can also be omitted
        asyncio.run(self.serve(sockets=sockets))


config = Config(app=app, host="0.0.0.0", port=8000, reload=True)
server = ProactorServer(config=config)
server.run()

经过这种魔法后的Fastapi就能正常启动Playwright的子进程了。

次魔方仅适用Windows，Linux下经过测试可能不需要此魔法