Telegraf session中间件报错：Cannot set properties of undefined

添加session()中间件前Bot运行正常，但执行/start命令时触发以下错误：

Error in webhook handler: TypeError: Cannot set properties of undefined (setting 'state')
    at file:///C:/fm-telebot/index.js:134:21
    at C:\fm-telebot\node_modules\telegraf\lib\composer.js:397:28
    at C:\fm-telebot\node_modules\telegraf\lib\composer.js:165:111
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async execute (C:\fm-telebot\node_modules\telegraf\lib\composer.js:518:17)
    at async C:\fm-telebot\node_modules\telegraf\lib\composer.js:519:21
    at async execute (C:\fm-telebot\node_modules\telegraf\lib\composer.js:518:17)
    at async C:\fm-telebot\node_modules\telegraf\lib\composer.js:519:21
    at async C:\fm-telebot\node_modules\telegraf\lib\session.js:104:13
    at async execute (C:\fm-telebot\node_modules\telegraf\lib\composer.js:518:17)

在/start命令中打印ctx.session显示为undefined，错误由expressApp.post()的捕获块捕获。尝试调整session中间件选项无效，需定位问题原因，或获取无需手动初始化会话的解决办法。

相关代码 #

Bot主代码 #

// Using import statements instead of require
import express from "express";
import path, { dirname } from "path";
import { Telegraf, session } from "telegraf";
import { config } from "dotenv";
import { fileURLToPath } from "url";
import { PrismaClient } from "@prisma/client";
import { botSendMessage, sendServState, sendWPT } from "./helper_functions.js";
import ngrok from 'ngrok'

config();
// Using Prisma ORM
const prisma = new PrismaClient();

// Setup __dirname equivalent in ES module scope
const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);

// Initialize Express
const expressApp = express();
const port = process.env.PORT || 3000;

// Middleware to serve static files
expressApp.use(express.static("static"));
expressApp.use(express.json());

// Initialize the bot
const bot = new Telegraf(process.env.BOT_TOKEN,  { telegram: { webhookReply: false } });
bot.use(session())


// Start ngrok and set the webhook
(async function() {
  try {
    // Connect ngrok to the specified port
    const url = await ngrok.connect(port);
    const WEBHOOK_URL = `${url}/telegram-webhook`;
    // Set the webhook for the bot
    await bot.telegram.setWebhook(WEBHOOK_URL);
    console.log(`Webhook set to ${WEBHOOK_URL}`);

    // Webhook handler for incoming Telegram updates
    expressApp.post('/telegram-webhook', (req, res) => {
      bot.handleUpdate(req.body)
      .then(() => {
        if (!res.headersSent) {
          res.sendStatus(200);
        }
      })
      .catch((error) => {
        console.error('Error in webhook handler:', error);
        if (!res.headersSent) {
          res.sendStatus(500);
        }
      });
    });

    // Root endpoint to serve the main page
    expressApp.get("/", (req, res) => {
      res.sendFile(path.join(__dirname, "/index.html"));
    });

    // Start the Express server
    expressApp.listen(port, () => {
      console.log(`Server running on port ${port}`);
    });
  } catch (err) {
    console.error('Error setting up webhook or server:', err);
  }
})();



bot.command("start", (ctx) => {
  console.log(ctx.from);
  console.log(ctx.session);
  ctx.session.state = 'idle'
  ctx.session.cur_command = null
  botSendMessage(bot, ctx, "Hello there! I am the FM helper bot.")
});

botSendMessage函数 #

export function botSendMessage(bot, ctx, message){
  bot.telegram.sendMessage(ctx.chat.id, `@${ctx.from.username}\n${message}`);
}

解决方案 #

核心问题原因 #

手动调用bot.handleUpdate(req.body)时，没有让Telegraf的中间件链完整执行，session中间件的异步初始化逻辑未被正确触发，导致ctx.session未被创建。

修复步骤 #

1. 替换手动Webhook处理为Telegraf内置方法
   将原来的expressApp.post('/telegram-webhook', ...)路由替换为Telegraf提供的webhookCallback，它会自动处理请求上下文，确保中间件链（包括session）按顺序执行：

   // 替换原来的expressApp.post路由
   expressApp.use(bot.webhookCallback('/telegram-webhook'));
   

2. 验证session中间件注册顺序
   确保bot.use(session())在所有命令、监听函数之前注册，你的现有代码已经满足这一点，无需修改。

3. 优化消息发送函数（可选）
   直接使用ctx.reply替代传入bot实例，代码更简洁且符合Telegraf最佳实践：

   export function botSendMessage(ctx, message){
     ctx.reply(`@${ctx.from.username}\n${message}`);
   }
   

   调用时改为：

   botSendMessage(ctx, "Hello there! I am the FM helper bot.")
   

修改后，ctx.session会被session中间件正确初始化，/start命令中的赋值操作不再报错。

内容的提问来源于stack exchange，提问作者Kaiwen Xie