KotlinProxy

KotlinProxy is a standalone Minecraft proxy that lets players join servers running almost any Minecraft version, from Classic to the latest release. It is a Kotlin rewrite of ViaProxy and uses SpongePowered Mixin for runtime patches.

Features

• Connects clients and servers on different Minecraft versions
• Supports Java Edition, Bedrock Edition and legacy Classic servers
• Runs as a GUI, a CLI, or from a YAML configuration file
• Loads plugins from the plugins directory
• Works with servers in offline mode
• Ships a Java 8 compatible build

KotlinProxy is a protocol proxy. It does not modify the client or the server. It applies its patches with the SpongePowered Mixin runtime from a child-first class loader, so no -javaagent flag or launcher wrapper is required.

Requirements

• Java 17 or newer to run the regular build
• Java 8 or newer to run the +java8 build
• A writable working directory

Usage

java -jar KotlinProxy.jar
java -jar KotlinProxy.jar config <config file>
java -jar KotlinProxy.jar cli --help

A small CLI session that forwards a 1.8 client to a 26.3 server:

java -jar KotlinProxy.jar cli \
  --bind-address 0.0.0.0:25568 \
  --target-address 127.0.0.1:25565 \
  --target-version 26.3 \
  --auth-method NONE \
  --proxy-online-mode false

Set target-version to Auto Detect (1.7+ servers) to let the proxy detect the server version.

Plugins

Plugins are JAR files in the plugins folder. Each plugin contains a viaproxy.yml with name, author, version, main, and optional depends. Plugin classes can listen to the events in net.raphimc.viaproxy.plugins.events.

Runtime patches use SpongePowered Mixin. A plugin that needs to patch proxy or ViaVersion classes can ship a standard mixin configuration and register it from its plugin entry point.

Building

./gradlew build

The build produces build/libs/KotlinProxy-<version>.jar and build/libs/KotlinProxy-<version>+java8.jar, a variant downgraded to Java 8 bytecode. Both variants apply the same mixins.

Differences from ViaProxy

• All source files are Kotlin.
• Runtime patches are applied by the SpongePowered Mixin runtime instead of ClassTransform.
• The plugin loader uses plain URL class loaders. Plugins that relied on ClassTransform transformers must provide a Mixin configuration instead.

License

KotlinProxy is licensed under the GNU General Public License v3.0. It is derived from ViaProxy, copyright RK_01/RaphiMC and contributors.