feat: add stable session UUID to MinecraftConnection

api/src/main/java/com/velocitypowered/api/proxy/InboundConnection.java

@@ -12,6 +12,7 @@
 import com.velocitypowered.api.network.ProtocolVersion;
 import java.net.InetSocketAddress;
 import java.util.Optional;
+import java.util.UUID;
 
 /**
  * Represents an incoming connection to the proxy.
@@ -68,4 +69,14 @@ public interface InboundConnection {
    * @return the intent of the connection
    */
   HandshakeIntent getHandshakeIntent();
+
+  /**
+   * Returns the unique, stable session UUID for this connection, generated when
+   * the client initially connects to the proxy. The session id remains consistent
+   * across all login-phase events and all proxy-to-backend connections for the
+   * same player session.
+   *
+   * @return the session UUID, never {@code null}
+   */
+  UUID getSessionId();
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -72,6 +72,7 @@
 import java.util.EnumMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
@@ -87,6 +88,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
 
   private static final Logger logger = LogManager.getLogger(MinecraftConnection.class);
 
+  private final @Nullable UUID sessionId;
   private final Channel channel;
   public boolean pendingConfigurationSwitch = false;
   private SocketAddress remoteAddress;
@@ -105,10 +107,11 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
    * @param channel the channel on the connection
    * @param server  the Velocity instance
    */
-  public MinecraftConnection(Channel channel, VelocityServer server) {
+  public MinecraftConnection(Channel channel, VelocityServer server, @Nullable UUID sessionId) {
     this.channel = channel;
     this.remoteAddress = channel.remoteAddress();
     this.server = server;
+    this.sessionId = sessionId;
     this.state = StateRegistry.HANDSHAKE;
 
     this.sessionHandlers = new EnumMap<>(StateRegistry.class);
@@ -322,6 +325,17 @@ public Channel getChannel() {
     return channel;
   }
 
+  /**
+   * Returns the session UUID for this connection. Client connections have a
+   * unique session UUID; backend connections share the client's session UUID;
+   * ping connections have {@code null}.
+   *
+   * @return the session UUID, or {@code null} for ping connections
+   */
+  public @Nullable UUID getSessionId() {
+    return sessionId;
+  }
+
   public boolean isClosed() {
     return !channel.isActive();
   }

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -105,7 +105,8 @@ public CompletableFuture<Impl> connect() {
         .connect(registeredServer.getServerInfo().getAddress())
         .addListener((ChannelFutureListener) future -> {
           if (future.isSuccess()) {
-            connection = new MinecraftConnection(future.channel(), server);
+            connection = new MinecraftConnection(future.channel(), server,
+                proxyPlayer.getConnection().getSessionId());
             connection.setAssociation(VelocityServerConnection.this);
             future.channel().pipeline().addLast(HANDLER, connection);
 

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -321,6 +321,11 @@ public MinecraftConnection getConnection() {
     return connection;
   }
 
+  @Override
+  public UUID getSessionId() {
+    return connection.getSessionId();
+  }
+
   @Override
   public long getPing() {
     return this.ping;

proxy/src/main/java/com/velocitypowered/proxy/connection/client/LoginInboundConnection.java

@@ -33,6 +33,7 @@
 import java.net.InetSocketAddress;
 import java.util.Optional;
 import java.util.Queue;
+import java.util.UUID;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 import net.kyori.adventure.text.Component;
@@ -183,4 +184,9 @@ public ProtocolState getProtocolState() {
   public HandshakeIntent getHandshakeIntent() {
     return delegate.getHandshakeIntent();
   }
+
+  @Override
+  public UUID getSessionId() {
+    return delegate.getSessionId();
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/util/VelocityInboundConnection.java

@@ -19,11 +19,17 @@
 
 import com.velocitypowered.api.proxy.InboundConnection;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
+import java.util.UUID;
 
 /**
  * Base internal interface for a {@link InboundConnection}.
  */
 public interface VelocityInboundConnection extends InboundConnection {
 
   MinecraftConnection getConnection();
+
+  @Override
+  default UUID getSessionId() {
+    return getConnection().getSessionId();
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/network/ServerChannelInitializer.java

@@ -42,6 +42,7 @@
 import io.netty.channel.ChannelInitializer;
 import io.netty.handler.codec.haproxy.HAProxyMessageDecoder;
 import io.netty.handler.timeout.ReadTimeoutHandler;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -69,7 +70,7 @@ protected void initChannel(final Channel ch) {
         .addLast(MINECRAFT_DECODER, new MinecraftDecoder(ProtocolUtils.Direction.SERVERBOUND))
         .addLast(MINECRAFT_ENCODER, new MinecraftEncoder(ProtocolUtils.Direction.CLIENTBOUND));
 
-    final MinecraftConnection connection = new MinecraftConnection(ch, this.server);
+    final MinecraftConnection connection = new MinecraftConnection(ch, this.server, UUID.randomUUID());
     connection.setActiveSessionHandler(StateRegistry.HANDSHAKE,
         new HandshakeSessionHandler(connection, this.server));
     ch.pipeline().addLast(Connections.HANDLER, connection);

proxy/src/main/java/com/velocitypowered/proxy/server/VelocityRegisteredServer.java

@@ -123,7 +123,7 @@ protected void initChannel(Channel ch) {
             .addLast(MINECRAFT_DECODER, new MinecraftDecoder(ProtocolUtils.Direction.CLIENTBOUND))
             .addLast(MINECRAFT_ENCODER, new MinecraftEncoder(ProtocolUtils.Direction.SERVERBOUND));
 
-        ch.pipeline().addLast(HANDLER, new MinecraftConnection(ch, server));
+        ch.pipeline().addLast(HANDLER, new MinecraftConnection(ch, server, null));
       }
     }).connect(serverInfo.getAddress()).addListener((ChannelFutureListener) future -> {
       if (future.isSuccess()) {