Connector Server Mixin Fix

Connector Server Mixin Fix

A tiny server-side library that fixes dedicated-server crashes caused by Sinytra Connector not removing client-only members from Fabric mixin classes.

Just drop it in your server’s mods/ folder next to Connector and the crash is gone. It does nothing on clients, so it’s safe to ship in the same pack.

Symptoms it fixes

If a Fabric mod loaded through Connector has a mixin with a client-only method, your dedicated server crashes during startup with something like:

MixinPreProcessorException: Attach error for .mixins.json:SomeMixin
  -> INVOKESTATIC net/minecraft/client/Minecraft::getInstance
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.Minecraft

Note the key detail: no crash report is generated (it dies during class loading), so all you get is this stack trace in the console, which is exactly what this mod prevents.

Why it happens

Connector correctly strips Fabric @Environment(CLIENT) members from regular classes, but it skips this step for mixin classes. A common mixin carrying a client-only method (correctly annotated by the mod author) therefore survives on the server, and the mixin processor later tries to resolve a net.minecraft.client.* class that doesn’t exist server-side → crash.

This is a Connector limitation, not a bug in the affected mod, the mod works fine in singleplayer and on native Fabric servers.

What it does

Runs just before the mixin processor reads each mixin class and removes any @Mixin member marked @Environment(CLIENT) on a dedicated server, exactly like the Fabric loader does natively. It’s generic: it fixes every Fabric mod hitting this pattern, not one specific mod.

You’ll see this line on server startup confirming it’s active:

[ConnectorEnvStrip/]: Registered 'connector_env_strip' launch plugin

ℹ️ This is a low-level library, so it does not appear in the in-game mod list. Check the startup log line above to confirm it loaded.

Requirements

• Minecraft 1.21.1, NeoForge 21.1.x
• Sinytra Connector (without it, this mod simply does nothing)
• Server-side only (harmless on clients)