CS2 Plugin Bug: Garbled Chinese Chat Messages?

Hey guys! Ever run into a weird issue where your plugin messes up Chinese characters in Counter-Strike 2? I recently stumbled upon a tricky problem while developing a plugin that intercepts chat messages. Let me walk you through it, and maybe we can all learn something new!

The Mystery of the Garbled Text

So, I was building this plugin that uses the UserMessage hook for SayText2 (ID 118) to catch chat messages. Everything seemed fine and dandy until players started sending longer Chinese messages. That's when things got funky. Short messages with a few Chinese characters (like, up to 5, which is about 15 bytes in UTF-8) worked perfectly. But when the messages got longer, the ReadString function started spitting out garbled text after the first few characters. It was like the plugin was choking on the UTF-8 encoding. This was happening before I even touched the message, which pointed to a potential issue in how the framework itself was decoding the text from the game engine.

Diving Deep into the Issue

The core problem lies in how the UserMessage.ReadString function handles multi-byte characters, specifically those in the UTF-8 encoding used for Chinese characters. When a long string of Chinese characters is sent, the function seems to misinterpret the byte stream, leading to corruption. This isn't just a minor inconvenience; it can severely impact plugins that rely on accurate chat message processing, such as those for moderation, translation, or even gameplay mechanics. To really understand the scope of the issue, we need to look at a reproducible example and analyze the expected versus actual behavior.

When dealing with multi-byte characters, especially in a real-time environment like a game, encoding and decoding become critical. UTF-8 is designed to handle a wide range of characters, but it requires careful handling of byte sequences. The ReadString function likely has a buffer or a logic flaw that causes it to misinterpret the byte boundaries when processing longer strings. This can lead to a cascade of errors, where a single misread character throws off the entire sequence, resulting in the dreaded garbled text. This issue highlights the importance of thorough testing with various character sets and string lengths when developing plugins that handle text input.

Furthermore, the problem isn't isolated to just displaying incorrect characters. In many cases, the corrupted strings can lead to unexpected behavior in other parts of the plugin. For example, if the plugin is designed to parse commands from chat messages, a corrupted string can prevent the commands from being recognized, leading to frustrating user experiences. The debugging process becomes even more challenging because the corruption occurs at a low level, within the framework's decoding mechanism. This means that developers need to carefully examine the input and output at each stage of the process to pinpoint the exact moment when the corruption occurs.

The Importance of Proper UTF-8 Handling

UTF-8 is a variable-width character encoding capable of encoding all possible Unicode code points. Because of its design, UTF-8 is backward compatible with ASCII, making it a popular choice for text representation in computer systems. However, the variable-width nature of UTF-8 means that each character can be represented by one to four bytes. This flexibility comes with the cost of complexity in processing, as the code needs to correctly interpret the byte sequences to identify character boundaries.

The issue with UserMessage.ReadString suggests a potential flaw in how the function handles these variable-length byte sequences. It might be incorrectly calculating the length of the string or misinterpreting the start and end points of multi-byte characters. This can result in partial characters being read, leading to the corruption observed in the chat messages. A proper UTF-8 decoder needs to carefully analyze the byte stream, checking for continuation bytes to determine the length of each character. If the decoder encounters an invalid byte sequence, it should either skip it or replace it with a placeholder character, rather than attempting to interpret it as part of a valid character.

Steps to Reproduce the Issue

To show you exactly what I mean, I've put together a simple way to reproduce this bug. It's super easy, trust me!

1. First things first: Create a basic plugin with the OnMessage handler (I'll show you the code in a sec).
2. Load it up: Pop that plugin onto your Counter-Strike 2 server.
3. Get chatty: Jump into the game as a client and open the chat box.
4. Type it out: Type a long Chinese message. Something like 这是一个超过五个汉字的测试消息 should do the trick.
5. Witness the chaos: Hit send and watch the chat output. You'll probably see some garbled text.

The Minimal Reproducible Example

I even made a super-simplified OnMessage handler to really nail down the problem. This code reads the message, slaps a "[Diagnosis]" tag in front, and sends it back. No fancy stuff, just the basics:

public HookResult OnMessage(UserMessage um)
{
    // Check who's talking
    if (Utilities.GetPlayerFromIndex(um.ReadInt("entityindex")) is not CCSPlayerController player || player.IsBot)
        return HookResult.Continue;

    // Grab the message
    string originalMessage = um.ReadString("param2");

    if (string.IsNullOrEmpty(originalMessage))
        return HookResult.Handled;

    // Add a tag for debugging
    string debugMessage = "[Diagnosis] " + originalMessage;
    um.SetString("param2", debugMessage);

    // Let the server know we tweaked it
    return HookResult.Changed;
}

This code snip is crucial because it isolates the issue. The corruption happens within the `um.ReadString(