Error Fetching Discord Channel in FastAPI and discord.py Integration: '_MissingSentinel' object has no attribute 'is_set

[MaTwickenham]

Issue Description:

I am integrating discord.py with FastAPI, and both the FastAPI server and the Discord bot (client) start correctly, triggering the on_ready() method as expected. However, when the forward_via_channel() method is triggered, it raises the following exception:

'_MissingSentinel' object has no attribute 'is_set'

This happens when attempting to fetch a channel using channel = await self.client.fetch_channel(channel_id) in forward_via_channel (). I cannot retrieve the channel and need assistance resolving this issue.

Can anyone help me figure out how to fix this problem?

main.py

import asyncio
import uvicorn
from fastapi import FastAPI
from src.routers.relay_router import router as relay_router
from src.services.relay_service import RelayService
from contextlib import asynccontextmanager

relay_service = RelayService("/path/to/config.toml")

def get_relay_service() -> RelayService:
    return relay_service

@asynccontextmanager
async def lifespan(app: FastAPI):
    bot_tasks = []
    for sender in relay_service.senders.values():
        bot_task = asyncio.create_task(sender.client.start(sender.token))
        bot_tasks.append(bot_task)
    
    await asyncio.sleep(4)
    print(f"All bots are connected to Discord!")
    
    yield
    
    for task in bot_tasks:
        task.cancel()
    await asyncio.gather(*bot_tasks, return_exceptions=True)

app = FastAPI(lifespan=lifespan)
app.include_router(relay_router, prefix="/relay", tags=["relay"])

if __name__ == "__main__":
    uvicorn.run(app, host="localhost", port=8000)

discord_sender_service.py

import discord
from io import BytesIO
import requests
from discord.ext import commands
import asyncio

class DiscordSenderService:
    def __init__(self, token: str, service_name: str):
        self.token = token
        self.service_name = service_name
        intents = discord.Intents.default()
        intents.message_content = True
        self.client = commands.Bot(command_prefix="!", intents=intents)

        @self.client.event
        async def on_ready():
            print(f"Logged in as {self.client.user.name} - {self.client.user.id}")

    def forward_via_webhook(self, payload) -> None:
        try:
            headers = {"Content-Type": "application/json"}
            response = requests.post(payload["webhook_url"], json=payload, headers=headers)

            if response.status_code == 204:
                print("Message forwarded via Webhook successfully")
            else:
                print(f"Webhook forward failed: {response.status_code}, {response.text}")
        except requests.exceptions.RequestException as e:
            print(f"Error during Webhook forwarding: {e}")

    async def forward_via_channel(self, channel_id, content, embeds, attachments, username=None, avatar_url=None, thread=None) -> None:
        try:
            channel = await self.client.fetch_channel(channel_id)
            if not channel:
                print(f"Could not find Discord channel: {channel_id}")
                return

            ...

            print(f"Message successfully sent to channel {channel_id}")
        except Exception as e:
            print(f"Error sending message to channel {channel_id}: {e}")

    async def process_message(self, message_data) -> None:
        try:
            ...

            if send_method == "webhook" and webhook_url:
                ...
                self.forward_via_webhook(payload)

            elif send_method == "channel":
				...
                username = message_data.get("username", None)
                avatar_url = message_data.get("avatar_url", None)
                thread = message_data.get("thread", None)
                asyncio.create_task(self.forward_via_channel(
                    target_channel_id, content, embeds, attachments, username, avatar_url, thread
                ))

            else:
                print(f"Unsupported send method: {send_method}")

        except Exception as e:
            print(f"Error processing message: {e}")

[mikeshardmind]

The client is an async context manager, your issue here comes from not using it as one.

See the example on customizing client startup here