Crash/Freeze When Kicking Player: Causes & Fixes

Oct 14, 2025 by ADMIN 49 views

Kicking a Player Causes Client Crash or Freeze: Discussion and Solutions

Have you ever experienced a frustrating client crash or a frozen connection when trying to kick a player from your server? It's a common issue in multiplayer environments, and this article dives deep into the causes and potential solutions. We'll explore a specific case from Vintage Story, dissecting the problem and offering insights that can help both players and server administrators.

Understanding the Problem: Client Crashes and Freezes

When dealing with multiplayer games, kicking a player might seem like a straightforward task. However, the process involves intricate server-client communication. If not handled correctly, this can lead to some frustrating issues, specifically client crashes or freezes. A client crash abruptly closes the game application, while a frozen connection leaves the player stuck, unable to interact with the game. Both scenarios disrupt the gameplay experience and need to be addressed for a smoother multiplayer experience.

The key here is understanding the communication process. When a server kicks a player, it needs to send a signal to the client to disconnect. If this signal is not properly received or processed by the client, it can lead to instability. Factors such as network latency, server load, and client-side processing power can all play a role in whether a kick results in a clean disconnect or a crash/freeze. To fully grasp this, we'll examine a real-world scenario from Vintage Story, a sandbox survival game known for its detailed mechanics and active community. We'll look at a specific situation where a developer identified a bug related to player disconnection, and how they investigated and addressed the problem. This will give us a practical understanding of the underlying issues and how they can be resolved.

A Real-World Case: Vintage Story Issue

In the Vintage Story game, version v1.21.4, a player reported that kicking a player while they were connected to the server would lead to a client crash or a frozen connection. This issue was observed in both local and remote servers, suggesting it wasn't solely a matter of connection speed. Let's break down the details of the report:

Game Version: v1.21.4
Platform: Not specified, implying it affected multiple platforms.
Modded: Vanilla (no mods), ruling out mod conflicts.
SP/MP: Multiplayer, highlighting the server-side nature of the problem.
Description: The core issue was identified in the server-side code. A method called DisconnectPlayer was being used during the OnPlayerJoin event. This meant that if a player was disconnected immediately after joining, it could trigger the crash or freeze. The reporter provided a code snippet demonstrating how the disconnection was being initiated:
```
private void OnPlayerJoin(IServerPlayer player)
{
        if (sapi.World is ServerMain serverMain && serverMain.Clients.TryGetValue(player.ClientId, out var targetClient))
        {
                serverMain.DisconnectPlayer(targetClient, null, "test");
        }
}
```
This code attempts to disconnect a player as soon as they join the server, which, while perhaps intended for testing or specific scenarios, exposed a flaw in the disconnection process. On a local server, the client would crash outright. On a remote server, where network latency is a factor, the connection would typically freeze instead. The same behavior was observed when using the /kick NAME reason command during the player's connection phase, further pinpointing the issue to the immediate disconnection process. This observation is critical, as it points to a timing-related problem. The server and client might not be fully synchronized during the initial connection phase, and attempting to disconnect a player at this point could disrupt the expected communication flow.

Diving Deeper: The Root Cause

The key to understanding why this happens lies in the timing of the disconnection. When a player connects to a server, there's an initial handshake process. The server and client exchange information to establish a stable connection. If you interrupt this process by kicking the player too soon, the client might not be ready to handle the disconnection gracefully.

Think of it like this: imagine trying to hang up a phone call before the other person has even said hello. The call hasn't been properly established, so the disconnect signal is unexpected and can cause issues. In the Vintage Story example, the DisconnectPlayer method was being called within the OnPlayerJoin event. This is essentially kicking the player almost immediately after they connect. The client, still in the process of establishing the connection, is hit with a disconnection signal it's not prepared for. This can lead to various issues, including:

Data corruption: The client might be in the middle of writing or reading data related to the connection process. An abrupt disconnection can interrupt this, leading to corrupted data and a crash.
Resource leaks: The client might have allocated resources (memory, network sockets, etc.) in anticipation of a full connection. If disconnected prematurely, these resources might not be properly released, leading to a memory leak or other stability issues.
Race conditions: The server and client might be operating on different timelines. The server might think the connection is established, while the client is still in the initial handshake phase. This can create race conditions where the disconnection signal arrives at an unexpected time, causing the client to crash or freeze.

Potential Solutions and Workarounds

So, how can we fix this issue? There are several approaches, depending on the specific game and the server-side architecture:

Delay the Disconnection: The most straightforward solution is to avoid disconnecting players immediately after they join. Introduce a small delay before calling the DisconnectPlayer method. This gives the client time to fully establish the connection and handle the disconnection signal more gracefully.

For example, you could implement a timer that waits a few seconds after the OnPlayerJoin event before allowing a disconnection. This simple change can often resolve the issue, as it avoids interrupting the critical handshake process.
Implement a Proper Disconnection Handshake: A more robust solution is to implement a proper disconnection handshake. This involves a series of messages exchanged between the server and client to ensure a clean disconnection.

The server sends a disconnection request, and the client acknowledges it. The client then closes its connection and releases resources. This approach ensures that both the server and client are on the same page and can handle the disconnection without causing crashes or freezes. This is a more involved solution but provides a more reliable and stable disconnection process.
Error Handling and Fallbacks: Implement proper error handling in the client code. If the client receives an unexpected disconnection signal, it should attempt to handle it gracefully. This might involve displaying an error message to the user, cleaning up resources, and attempting to reconnect.

A well-designed error handling system can prevent a crash by intercepting the error and taking appropriate action. This is a defensive programming approach that can improve the overall stability of the client.
Rate Limiting Disconnections: If you're disconnecting players frequently, consider implementing rate limiting. This prevents the server from sending too many disconnection signals in a short period, which can overwhelm the client.

Rate limiting can help prevent denial-of-service (DoS) attacks and other issues caused by excessive network traffic. This is particularly important in scenarios where players are being kicked for violating rules or exhibiting disruptive behavior.

In the context of the Vintage Story issue, the developers would likely need to adjust the timing of the DisconnectPlayer call or implement a more robust disconnection handshake. By carefully managing the disconnection process, they can prevent the client crashes and freezes that players were experiencing.

Lessons Learned and Best Practices

This issue highlights the importance of careful server-client communication in multiplayer games. Here are some key takeaways:

Timing is Crucial: The timing of events, especially during the connection and disconnection phases, can significantly impact stability. Avoid interrupting critical processes with premature disconnections.
Handshakes are Essential: Implement proper handshakes for both connection and disconnection. This ensures that the server and client are synchronized and can handle events gracefully.
Error Handling is Key: Robust error handling can prevent crashes and freezes by intercepting unexpected events and taking appropriate action.
Testing is Vital: Thoroughly test your disconnection logic in various scenarios, including local and remote servers, to identify potential issues.

By following these best practices, developers can create more stable and enjoyable multiplayer experiences. Addressing issues like client crashes and freezes is crucial for maintaining a healthy and engaged player base.

Conclusion: A Smoother Multiplayer Experience

Client crashes and freezes when kicking players can be a major headache for both players and server administrators. By understanding the underlying causes and implementing the right solutions, we can create smoother and more stable multiplayer experiences. Whether it's delaying disconnections, implementing handshakes, or improving error handling, the key is to prioritize clear and robust server-client communication. So, the next time you're managing a server, remember these tips and ensure that kicking a player doesn't lead to a game-breaking crash!