main.py

from fastapi import FastAPI, WebSocket
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import HTMLResponse
import subprocess
import asyncio

from threading import Thread
from queue import Queue, Empty

def enqueue_output(out, queue):
    for line in iter(out.readline, b''):
        queue.put(line)
    out.close()

class EngineChess:
    def __init__(self, path_engine):
        self._stockfish = subprocess.Popen(
            path_engine,
            universal_newlines=True,
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
        )
        self.queueOutput = Queue()
        self.thread = Thread(target=enqueue_output, args=(self._stockfish.stdout, self.queueOutput))
        self.thread.daemon = True # thread dies with the program
        self.thread.start()
        
        self._has_quit_command_been_sent = False
        self._debug_view = False

    def _put(self, command):
        if not self._stockfish.stdin:
            raise BrokenPipeError()
        if self._stockfish.poll() is None and not self._has_quit_command_been_sent:
            if self._debug_view:
                print(f">>> {command}\n")
            self._stockfish.stdin.write(f"{command}\n")
            self._stockfish.stdin.flush()
            if command == "quit":
                self._has_quit_command_been_sent = True
    
    def _read_line(self) -> str:
        if not self._stockfish.stdout:
            raise BrokenPipeError()
        if self._stockfish.poll() is not None:
            raise StockfishException("The Stockfish process has crashed")
            
        try:
            line = self.queueOutput.get_nowait() # or q.get(timeout=.1)
        except Empty:
            return ""
        
        if self._debug_view:
            print(line.strip())
        return line.strip()
    
    def _is_ready(self) -> None:
        self._put("isready")
        while self._read_line() != "readyok":
            pass
    
    def put(self, cmd):
        return self._put(cmd)
        
    def read_line(self) -> str:
        return self._read_line()

app = FastAPI()

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

@app.websocket("/stockfish-{version}")
async def websocket_endpoint(websocket: WebSocket, version: str):
    await websocket.accept()
    
    stockfish = EngineChess(f"engines/stockfish-{version}-uci")

    async def read_from_socket(websocket: WebSocket):
        async for data in websocket.iter_text():
            print(f"Client: {data}")
            stockfish.put(data)
                    
    asyncio.create_task(read_from_socket(websocket))

    while True:
        while True:
            res = stockfish.read_line()
            if res != "":
                await websocket.send_text(f"{res}")
            else:
                break
        await asyncio.sleep(0.1)