main.py

from fastapi import FastAPI
from linebot import LineBotApi, WebhookHandler
from linebot.exceptions import InvalidSignatureError
from linebot.models import MessageEvent, TextMessage
from starlette.exceptions import HTTPException
import os
 
app = FastAPI()
line_bot_api = LineBotApi(os.environ["LINE_CHANNEL_ACCESS_TOKEN"])
handler = WebhookHandler(os.environ["LINE_CHANNEL_SECRET"])
 
@app.get("/")
def root():
    return {"title": "Echo Bot"}
     
@app.post("/callback")
async def callback(
    request: Request,
    background_tasks: BackgroundTasks,
    x_line_signature=Header(None),
):
    body = await request.body()

    try:
        background_tasks.add_task(
            handler.handle, body.decode("utf-8"), x_line_signature
        )
    except InvalidSignatureError:
         raise HTTPException(status_code=400, detail="Invalid signature")
 
    return "ok"
 
@handler.add(MessageEvent)
def handle_message(event):
    if event.type != "message" or event.message.type != "text":
        return
    message = TextMessage(text=event.message.text)
    line_bot_api.reply_message(event.reply_token, message)