Telegraf Crashes When replyWithPhoto Is Used with Webhook

Context

• Telegraf.js Version: 3.21.2
• Node.js Version: v10.3.0
• Operating System: Ubuntu 18.04 LTS

Expected Behavior

I have a simple bot, which replies with image to any text received. Basically, everything it does is

bot.on('text', ctx => {
  ...
  ctx.replyWithPhoto({source: fs.createReadStream(somePath)}, {caption: someCaption})
  ...
})

Everything works just fine when the bot is configured to use polling, but crashes if I set up webhook.

Current Behavior

When I configure the bot to use webhook, it crashes when I try to send a photo with ctx.replyWithPhoto. If I modify the code above to:

bot.on('text', ctx => {
  ...
  ctx.reply(someMessage)
  ctx.replyWithPhoto({source: fs.createReadStream(somePath)}, {caption: someCaption})
  ...
})

everything works. So basically, telegraf crashes when photo is being sent with answerToWebhook.

Failure Information (for bugs)

Failure Logs

telegraf:client HTTP call setWebhook { url:
   'https://HOST/SECRETADDRESS' } +0ms
  telegraf:client Call via webhook sendPhoto { chat_id: 94968010,
  photo:
   { source:
      ReadStream {
        _readableState: [ReadableState],
        readable: true,
        _events: [Object],
        _eventsCount: 1,
        _maxListeners: undefined,
        path: '/tmp/tmp-8281XUbvvO3XH1A4.tmp',
        fd: null,
        flags: 'r',
        mode: 438,
        start: undefined,
        end: Infinity,
        autoClose: true,
        pos: undefined,
        bytesRead: 0,
        closed: false } },
  caption: 'test caption' } +3s
events.js:167
      throw er; // Unhandled 'error' event
      ^

Error [ERR_STREAM_WRITE_AFTER_END]: write after end
    at write_ (_http_outgoing.js:580:17)
    at ServerResponse.write (_http_outgoing.js:575:10)
    at MultipartStream.ondata (_stream_readable.js:672:20)
    at MultipartStream.emit (events.js:182:13)
    at MultipartStream.Readable.read (_stream_readable.js:492:10)
    at flow (_stream_readable.js:920:34)
    at resume_ (_stream_readable.js:902:3)
    at process._tickCallback (internal/process/next_tick.js:63:19)
Emitted 'error' event at:
    at ServerResponse.onerror (_stream_readable.js:696:12)
    at ServerResponse.emit (events.js:182:13)
    at writeAfterEndNT (_http_outgoing.js:639:7)
    at process._tickCallback (internal/process/next_tick.js:63:19)

[r2axz]

OK, finally it looks like I found the cause for the issue.

The solution is to simply change the code:

bot.on('text', async (ctx) => {
  ctx.replyWithPhoto({source: fs.createReadStream('/some/existing/image.png')})
})

to:

bot.on('text', async (ctx) => {
  return ctx.replyWithPhoto({source: fs.createReadStream('/some/existing/image.png')})
})

There is a perfectly valid reason for this change, though. The code in webhook.ls expects a Promise. When the Promise is resolved, the response is ended. If return is omitted, no promise to wait is received and the response is ended before the response body is fully written.

Basically, the bug is in my code. However, I do think that there is a documentation issue. If you take a look at the Working with files section from which I copied the code, there is no return in the example there. On the other hand, return is used in other parts of documentation. So the documentation kinda sends mixed messages 😃 I believe it should be clearly stated somewhere in the documentation that using return is a must.

[r2axz]

There is a complete script, which illustrates the problem:

'use strict';
const fs = require('fs')
const Telegraf = require('telegraf')

const bot = new Telegraf(process.env.BOT_TOKEN, { webhookReply: false })
bot.telegram.setWebhook(WEBHOOK_ADDRESS)

bot.start((ctx) => {
  ctx.reply('Hi!')
})

bot.on('text', async (ctx) => {
  ctx.replyWithPhoto({source: fs.createReadStream('/some/existing/image.png')})
})

bot.startWebhook(WEBHOOK_ADDRESS, null, 5000)

When I send /start everything works just fine. When I send any text, bot crashes with the following output:

events.js:167
      throw er; // Unhandled 'error' event
      ^

Error [ERR_STREAM_WRITE_AFTER_END]: write after end
    at write_ (_http_outgoing.js:580:17)
    at ServerResponse.write (_http_outgoing.js:575:10)
    at MultipartStream.ondata (_stream_readable.js:672:20)
    at MultipartStream.emit (events.js:182:13)
    at MultipartStream.Readable.read (_stream_readable.js:492:10)
    at flow (_stream_readable.js:920:34)
    at resume_ (_stream_readable.js:902:3)
    at process._tickCallback (internal/process/next_tick.js:63:19)
Emitted 'error' event at:
    at writeAfterEndNT (_http_outgoing.js:639:7)
    at process._tickCallback (internal/process/next_tick.js:63:19)