Fix: Velocity Kicking Players For Long Commands

by Ahmed Latif 48 views

Introduction

Hey guys! Today, we're diving deep into an issue some of you might have encountered while using Velocity proxy servers: players getting kicked when executing long commands. Specifically, we're talking about commands that exceed a certain character limit, leading to unexpected disconnections and frustration. This article will break down the problem, explore the causes, and offer solutions to ensure your players have a smooth experience on your network. So, let's get started and figure out how to keep those long commands from causing trouble!

The Problem: Long Commands and Unexpected Kicks

So, you've got players on your server, and they're trying to use some pretty lengthy commands – maybe something with a lot of arguments or a complex text input. But then, bam! They get kicked with a cryptic error message. The core issue here is that Velocity, in its default configuration, has a limit on the length of commands it can process. When a player sends a command that goes over this limit, Velocity throws an error and disconnects the player to prevent potential issues. This can be super frustrating for players who are just trying to use in-game features or custom plugins that require longer commands. Understanding why this happens is the first step in fixing it.

The error message typically looks something like this:

[01:19:50 INFO]: [connected player] Gloriosus_0929 (/**.**.**.**:38721) has disconnected: ζ‚¨ηš„θΏžζŽ₯ε‘η”Ÿε†…ιƒ¨ι”™θ――γ€‚
[01:19:50 ERROR]: [connected player] Gloriosus_0929 (/**.**.**.**:38721): exception encountered in com.velocitypowered.proxy.connection.client.ClientPlaySession
Handler@b379af5
com.velocitypowered.proxy.util.except.QuietRuntimeException: A packet did not decode successfully (invalid data). For more information, launch Velocity with -Dvelocity.packet-decode-logging=true to see more.

This error indicates that Velocity couldn't process the incoming command packet due to its size or format. The QuietRuntimeException suggests that the issue is related to the decoding of the packet, which is a common symptom of exceeding the command length limit. The message "A packet did not decode successfully (invalid data)" further confirms that the command is likely too long for Velocity to handle by default. By recognizing this error, server administrators can start to investigate the cause and implement solutions to prevent these disconnects. The -Dvelocity.packet-decode-logging=true flag can provide more detailed information, but in many cases, simply knowing that long commands are the culprit is enough to guide troubleshooting efforts.

Why Does This Happen? Diving into the Technical Details

Okay, so why does Velocity even have this limit in the first place? Well, it comes down to a few key reasons, mainly related to security and performance. Security is a big one; allowing extremely long commands could potentially open the door to exploits or denial-of-service (DoS) attacks. Imagine someone sending a command that's several megabytes long – that could really bog down the server! Performance is another factor. Processing very large commands takes up server resources, and if multiple players are doing it at the same time, it can lead to lag and a bad experience for everyone. Think of it like trying to fit too much information through a small pipe – eventually, things get clogged.

Velocity, being a proxy, sits between the players and the actual game servers. This means it has to handle all the data flowing back and forth, including commands. To prevent abuse and maintain stability, Velocity imposes certain limits on the size of packets it will accept and process. These limits are in place to ensure that the server can handle the load and that malicious actors can't exploit the system. The command length limit is just one of these safeguards, designed to keep the server running smoothly and securely. By setting a maximum command length, Velocity can efficiently process commands without risking performance degradation or security vulnerabilities. This is especially crucial in a proxy environment where the server must handle multiple connections and requests simultaneously.

When a command exceeds the configured limit, Velocity's packet handling mechanism rejects the oversized packet. This rejection is not just a simple refusal to execute the command; it often leads to a disconnection because the client and server states become inconsistent. The client might still be waiting for a response to the command, while the server has already discarded it and closed the connection. This inconsistency triggers the error message and the subsequent kick. Understanding the underlying reasons for these limits helps in making informed decisions about how to address the issue, balancing the need for player freedom with the imperative of server security and performance.

Diagnosing the Issue: Is It Really the Command Length?

Before we jump to conclusions, let's make sure a long command is actually the problem. Sometimes, disconnects can be caused by other things, like network issues, plugin conflicts, or even bugs in the server software itself. A good first step is to try to replicate the issue with a shorter command. If short commands work fine, but the kicks only happen with long ones, that's a strong indicator that you've found the culprit. Another useful test is to try the same long command directly on the backend server, bypassing Velocity. If the command works there, it further confirms that Velocity's command length limit is the issue.

To effectively diagnose the problem, gather as much information as possible. Talk to the player who experienced the kick and get the exact command they were trying to use. Check the Velocity logs for any error messages or warnings that coincide with the disconnection. The error message we discussed earlier, indicating a packet decoding failure, is a key piece of evidence. Also, consider the context in which the command was used. Was it part of a plugin interaction, a custom command, or a vanilla Minecraft feature? Knowing the context can help narrow down the potential sources of the problem.

Examining your plugin list is another important step. Certain plugins might generate longer commands or interact with Velocity in ways that exceed its limits. If you suspect a particular plugin, try disabling it temporarily to see if the issue resolves. Remember, the goal is to isolate the problem. By systematically eliminating potential causes, you can confidently determine if the command length is the true source of the disconnects. Once you've confirmed the issue, you can move on to exploring solutions to accommodate longer commands without compromising server stability.

Solutions: What Can We Do About It?

Alright, so you've confirmed that long commands are the cause of the kicks. What can you do about it? Luckily, there are a few approaches you can take. One option is to adjust Velocity's configuration to increase the maximum command length. This is a straightforward solution, but it's important to do it cautiously. Increasing the limit too much could potentially expose your server to the security and performance issues we talked about earlier. You'll want to find a balance that allows for legitimate long commands without opening the floodgates to abuse.

Another approach is to optimize the commands themselves. Can the plugin or feature that's generating the long commands be modified to use shorter commands or a different method of communication? Sometimes, a simple change in how a command is structured can significantly reduce its length. For example, instead of sending a single command with a large amount of data, you could break it down into multiple smaller commands. This approach requires more effort, but it can be a more sustainable solution in the long run.

Finally, you might consider using alternative methods for players to interact with the server. For instance, instead of typing long commands, players could use a graphical user interface (GUI) or a chat-based system that doesn't rely on commands. This approach is particularly useful for complex interactions that involve a lot of data. For example, a plugin could provide a menu system that allows players to configure settings without typing long strings of text. Each of these solutions has its own set of trade-offs, so you'll need to consider your specific needs and circumstances when choosing the best approach.

Adjusting Velocity's Configuration

To adjust Velocity's configuration, you'll need to access the velocity.toml file, which is the main configuration file for Velocity. Within this file, you can modify various settings, including the maximum command length. The specific setting you're looking for is usually related to the maximum packet size or command buffer size. Unfortunately, there isn't a single, universally named setting for this, as it can vary slightly depending on the Velocity version and any installed plugins. However, you should look for settings that mention packet size, buffer size, or command length limits.

Once you've found the relevant setting, you can increase the value to allow for longer commands. It's crucial to do this incrementally and test the changes thoroughly. Start by increasing the value by a small amount and see if it resolves the issue without causing any negative side effects. Monitor your server's performance and stability after each adjustment. If you notice any lag or other issues, you might need to reduce the value or explore alternative solutions. Remember, increasing the limit too much can make your server more vulnerable to attacks, so it's best to err on the side of caution.

Before making any changes to the configuration file, it's always a good idea to back up the original file. This way, if something goes wrong, you can easily revert to the previous configuration. Also, be sure to restart Velocity after making changes to the velocity.toml file for the new settings to take effect. Finally, document any changes you make to the configuration so that you can easily track what you've done and why. This will be helpful if you need to troubleshoot issues in the future.

Optimizing Commands

Optimizing commands involves modifying the way commands are structured or processed to reduce their length. This can be a more complex solution, but it can also be more sustainable in the long run. If a specific plugin is generating the long commands, consider reaching out to the plugin developer to see if they can optimize the plugin's command handling. Often, plugin developers are aware of the command length limits and can provide updates or configuration options to address the issue.

One common optimization technique is to break long commands into smaller, more manageable chunks. For example, if a command involves setting multiple properties or values, you could split it into multiple commands, each setting a single property. This reduces the overall length of any single command and makes it easier for Velocity to process. Another approach is to use shorthand notations or abbreviations for command arguments. This can significantly reduce the length of commands without sacrificing functionality.

In some cases, you might be able to use a different method of communication altogether. For example, instead of using a command to transfer a large amount of data, you could use a file transfer or a database interaction. These alternative methods can bypass the command length limits and provide a more efficient way to handle large data transfers. Optimizing commands often requires a deep understanding of the specific commands and the underlying systems involved. However, the effort can be well worth it, as it can lead to a more stable and efficient server environment.

Alternative Methods: GUIs and Chat-Based Systems

Using alternative methods like GUIs and chat-based systems can be a great way to bypass the command length issue entirely. GUIs, in particular, provide a user-friendly way for players to interact with server features without typing long commands. Plugins can create custom GUIs that allow players to click buttons and select options, effectively replacing complex commands with simple interactions. This approach is especially useful for tasks that involve a lot of configuration or data input.

Chat-based systems offer another alternative. Instead of typing commands directly, players can interact with a bot or a chat interface that processes their requests. The bot can then translate the chat input into a series of shorter commands or use other methods to accomplish the desired task. This approach can be particularly useful for features that involve natural language processing or complex decision-making.

Implementing GUIs and chat-based systems requires some development effort, but it can significantly improve the player experience. Players no longer need to memorize long commands or worry about syntax errors. They can simply use a visual interface or a natural language input to interact with the server. This not only eliminates the command length issue but also makes the server more accessible and user-friendly. When choosing an alternative method, consider the specific needs of your players and the complexity of the features you want to provide. GUIs are generally better for tasks that involve a lot of configuration or data input, while chat-based systems are well-suited for natural language interactions and complex decision-making.

Real-World Examples and Use Cases

Let's look at some real-world examples of how these solutions can be applied. Imagine you have a plugin that allows players to create custom signs with a lot of text. If players try to use a long command to set the sign text, they might get kicked. In this case, you could either increase Velocity's command length limit slightly or, even better, implement a GUI that allows players to type the text into a text box and preview it before applying it to the sign. This not only avoids the command length issue but also provides a better user experience.

Another example could be a plugin that allows players to send messages to multiple recipients at once. If a player tries to send a message to a very large group of players, the resulting command could be too long. In this scenario, you could optimize the plugin to send multiple shorter commands, each addressing a smaller group of players. Alternatively, you could implement a chat-based system that allows players to send messages to groups using a more natural language interface.

Consider a scenario where players are using a command to configure a complex set of settings. For instance, a command to set the properties of a custom item might require numerous arguments and values, resulting in a very long command string. Instead of relying on a single command, a plugin developer could create a GUI with interactive elements such as sliders, checkboxes, and text fields. Players can adjust these elements to configure the item, and the plugin can then translate these inputs into a series of smaller, more manageable commands or database updates. This approach simplifies the configuration process and avoids the limitations of command length.

Another use case involves moderation tools. Moderators might need to use lengthy commands to ban players, set permissions, or manage server settings. These commands often include details such as player names, IP addresses, and ban durations, which can add to the length of the command. A well-designed GUI can streamline these tasks by providing a form-based interface. Moderators can fill in the necessary fields, and the GUI can generate the appropriate commands in the background, ensuring that they stay within the acceptable length limits. By considering these real-world examples, you can see how different solutions can be applied to address the long command issue in various situations. The key is to understand the underlying problem and choose the solution that best fits your specific needs.

Conclusion: Keeping Your Players Connected

Dealing with long commands in Velocity can be a bit of a headache, but with the right approach, you can keep your players connected and happy. Remember, the key is to balance player freedom with server stability and security. Whether you choose to adjust Velocity's configuration, optimize commands, or use alternative methods, the goal is to create a smooth and enjoyable experience for everyone on your server. By understanding the causes of the issue and the available solutions, you can confidently address the problem and ensure that long commands don't lead to unexpected kicks. So go forth, optimize, and keep those players connected!

By understanding the causes of disconnects due to long commands and implementing the solutions discussed, you can create a more stable and enjoyable experience for your players. Remember, a little troubleshooting and optimization can go a long way in keeping your server running smoothly.

Troubleshooting Long Command Issues in Velocity

Issue Summary

Players are unexpectedly kicked from the Velocity proxy server when executing commands that exceed a certain length. The error message typically indicates a failure to decode the packet due to invalid data. This problem does not occur when connecting directly to the backend server, suggesting the issue lies within Velocity's command processing.

Environment

  • Proxy Server: Velocity 3.4.0-SNAPSHOT
  • Backend Server: PaperMC (Folia downstream)
  • Plugins: Velocity (floodgate, geyser, multilogin), PaperMC (LightAntiCheat, ViaBackwards, ViaRewind, ViaVersion, voicechat, WorldEdit)

Steps to Reproduce

  1. Connect to the server through Velocity.
  2. Execute a command with a length of approximately 1000 words or more (e.g., using the /dialog command callback).
  3. Observe that the player is disconnected from the server.

Expected Behavior

The player should be able to execute long commands without being disconnected from the server.

Actual Behavior

The player is kicked from the server with the following error message:

[01:19:50 INFO]: [connected player] Gloriosus_0929 (/**.**.**.**:38721) has disconnected: ζ‚¨ηš„θΏžζŽ₯ε‘η”Ÿε†…ιƒ¨ι”™θ――γ€‚
[01:19:50 ERROR]: [connected player] Gloriosus_0929 (/**.**.**.**:38721): exception encountered in com.velocitypowered.proxy.connection.client.ClientPlaySession
Handler@b379af5
com.velocitypowered.proxy.util.except.QuietRuntimeException: A packet did not decode successfully (invalid data). For more information, launch Velocity with -Dvelocity.packet-decode-logging=true to see more.

Root Cause Analysis

The root cause of this issue is that Velocity has a limit on the maximum length of commands it can process. When a player sends a command that exceeds this limit, Velocity fails to decode the packet, resulting in a QuietRuntimeException and the player being disconnected. This limit is in place to prevent potential security vulnerabilities and performance issues associated with processing excessively long commands.

Solutions Implemented

  1. Adjusting Velocity's Configuration:
  • Access the velocity.toml file.
  • Look for settings related to packet size or command buffer size.
  • Increase the value incrementally, testing after each adjustment.
  1. Optimizing Commands:
  • If a specific plugin generates the long commands, contact the developer for optimizations.
  • Break long commands into smaller chunks or use shorthand notations.
  1. Alternative Methods:
  • Implement GUIs for complex interactions.
  • Use chat-based systems to process natural language input.

Additional Notes

  • It is confirmed that this issue does not exist with server-side direct connection only.
  • The issue persists even without Velocity plugins enabled, indicating it is a core Velocity behavior.

Plugin List

Velocity

  • velocity
  • floodgate
  • geyser
  • multilogin

Server (Lophine: downstream of folia)

  • LightAntiCheat
  • ViaBackwards
  • ViaRewind
  • ViaVersion
  • voicechat
  • WorldEdit

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