Bug Report: Connection Error During Server Transfer

[StarWeizz]

• The FAQ doesn't contain a resolution to my issue

📋 Summary

Mineflayer bots get kicked with the error "An internal error occurred during your connection" when transferring between servers via Velocity Proxy on Minecraft 1.21+.

---

🔍 Problem Description

Observed Behavior

• ✅ Bot successfully connects to Velocity lobby
• ✅ Authentication with /login works
• ✅ Command /joinq <server> is executed
• ❌ Bot is kicked during the destination server's configuration phase

Error Message

An internal error occurred during your connection.

Technical Logs

📦 [CONFIG] Packet received: select_known_packs
   Data: {
     "packs": [
       {
         "namespace": "minecraft",
         "id": "core",
         "version": "1.21.8"
       }
     ]
   }

📦 [CONFIG] Packet received: registry_data
   [... huge amount of data ...]

📦 [CONFIG] Packet received: disconnect
   Data: {
     "reason": "An internal error occurred during your connection."
   }

---

🛠️ Environment

Component	Version
Server	Paper 1.21.8
Proxy	Velocity
Mineflayer	4.33.0
minecraft-protocol	1.62.0
Node.js	v22+
OS	Windows

Server Configuration

• Lobby : Velocity Proxy → ✅ Works
• Server A : Transfer from lobby → ✅ Works with fix
• Server B : Transfer from lobby → ❌ Fails even with fix (custom resource pack)

---

🔬 Technical Analysis

Root Cause

Known Mineflayer bug with Minecraft 1.21+ during Velocity transfers:

• GitHub Issue: Server redirection error #3764
• Problem: Mineflayer sends physics packets during the configuration phase, causing a server-side error

Problematic Packets

1. select_known_packs: Data pack negotiation (new in 1.21)
2. registry_data: Massive registry data transmission
3. Physics packets: Sent during configuration instead of waiting for spawn

---

✅ Partial Solution Applied

Implemented Fix

// In BotFactory.js
const botOptions = {
  username,
  auth: config.bots.auth,
  keepAlive: config.bots.keepAlive,
  hideErrors: false,
  checkTimeoutInterval: 30000,
  closeTimeout: 120000,
  // FIX: Disable physics during configuration
  physicsEnabled: false,  // ← Solution
};

// Re-enable after spawn
bot.once('spawn', async () => {
  setTimeout(() => {
    if (!bot._ended) {
      bot.physicsEnabled = true;  // ← Re-activation
    }
  }, 2000);
  // ...
});

Tested Versions

MC Version	Lobby	Server A	Server B (with resource pack)
1.21.8	✅	❌	❌
1.21.4	✅	❌	❌
1.21.1	✅	✅	❌
1.20.6	✅	❌	❌

---

📊 Results

✅ What Works

• Initial connection to Velocity lobby
• Transfer to servers without custom resource pack (e.g., Server A)
• Authentication and commands

❌ What Doesn't Work

• Transfer to servers with large custom resource packs (e.g., Server B)
• Servers sending large amounts of registry_data during configuration

---

📝 Bug Reproduction

Minimal Test Code

import mineflayer from 'mineflayer';

const bot = mineflayer.createBot({
  host: 'your.server.ip',
  port: 25565,
  username: 'TestBot',
  auth: 'offline',
  version: '1.21.1',
  physicsEnabled: false,  // FIX
});

bot.on('spawn', () => {
  console.log('✅ Spawn successful');

  // Re-enable physics
  setTimeout(() => {
    bot.physicsEnabled = true;
  }, 2000);

  // Attempt transfer
  setTimeout(() => {
    bot.chat('/login password');

    setTimeout(() => {
      bot.chat('/joinq targetserver');  // ← Fails here
    }, 2000);
  }, 3000);
});

bot.on('kicked', (reason) => {
  console.log('❌ Kicked:', reason);
});

Steps to Reproduce

1. Connect to Velocity lobby
2. Execute /login <password>
3. Execute /joinq <server> (server with resource pack)
4. Observe kick with "internal error"

---

🔗 References

• Main GitHub Issue: Server redirection error #3764
• Associated PR: Disable physics during configuration packet #3722

---

Bot Logs During Kick

🔧 select_known_packs packet received!
   Data received: {
  "packs": [
    {
      "namespace": "minecraft",
      "id": "core",
      "version": "1.21.8"
    }
  ]
}
📦 [CONFIG] Packet received: registry_data
   [... 1.6 million characters of data ...]
📦 [CONFIG] Packet received: disconnect
   Data: {
  "reason": {
    "type": "compound",
    "value": {
      "color": {
        "type": "string",
        "value": "red"
      },
      "text": {
        "type": "string",
        "value": "An internal error occurred during your connection."
      }
    }
  }
}
❌ Bot kicked!

[haxmcdev]

This is related to your issue
#3764
Please look for answers next time.