Velocity b582+ support (#230)

* Log about writability changes if enabled
* Velocity b582+ support

Author: UserNugget

plugin/src/main/java/net/elytrium/limboapi/LimboAPI.java

@@ -40,6 +40,7 @@
 import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.netty.MinecraftCompressDecoder;
 import com.velocitypowered.proxy.protocol.netty.MinecraftCompressorAndLengthEncoder;
+import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
 import com.velocitypowered.proxy.protocol.netty.MinecraftEncoder;
 import com.velocitypowered.proxy.protocol.netty.MinecraftVarintLengthEncoder;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
@@ -49,6 +50,8 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
 import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -137,6 +140,8 @@ public class LimboAPI implements LimboFactory {
 
   public static final ConcurrentHashMap<Player, UUID> INITIAL_ID = new ConcurrentHashMap<>();
 
+  private static final MethodHandle STATE_FIELD;
+
   private final VelocityServer server;
   private final Metrics.Factory metricsFactory;
   private final File configFile;
@@ -443,12 +448,14 @@ public void inject3rdParty(Player player, MinecraftConnection connection, Channe
   public void setState(MinecraftConnection connection, StateRegistry stateRegistry) {
     connection.setState(stateRegistry);
     this.setEncoderState(connection, stateRegistry);
+    this.fixDecoderState(connection, stateRegistry);
   }
 
   public void setActiveSessionHandler(MinecraftConnection connection, StateRegistry stateRegistry,
                                       MinecraftSessionHandler sessionHandler) {
     connection.setActiveSessionHandler(stateRegistry, sessionHandler);
     this.setEncoderState(connection, stateRegistry);
+    this.fixDecoderState(connection, stateRegistry);
   }
 
   public void setEncoderState(MinecraftConnection connection, StateRegistry state) {
@@ -474,6 +481,20 @@ public void setEncoderState(MinecraftConnection connection, StateRegistry state)
     }
   }
 
+  public void fixDecoderState(MinecraftConnection connection, StateRegistry state) {
+    if (state.name() == null) { // custom state
+      MinecraftDecoder decoder = connection.getChannel().pipeline().get(MinecraftDecoder.class);
+      if (decoder != null) {
+        try {
+          // Let decoder know what we're in PLAY state, or it will kick the player.
+          STATE_FIELD.invokeExact(decoder, StateRegistry.PLAY);
+        } catch (Throwable throwable) {
+          LimboAPI.getLogger().error("Failed to fixup decoder", throwable);
+        }
+      }
+    }
+  }
+
   public void deject3rdParty(ChannelPipeline pipeline) {
     this.preparedPacketFactory.deject(pipeline);
   }
@@ -693,4 +714,13 @@ private static void setSerializer(Serializer serializer) {
   public static Serializer getSerializer() {
     return SERIALIZER;
   }
+
+  static {
+    try {
+      STATE_FIELD = MethodHandles.privateLookupIn(MinecraftDecoder.class, MethodHandles.lookup())
+          .findSetter(MinecraftDecoder.class, "state", StateRegistry.class);
+    } catch (NoSuchFieldException | IllegalAccessException e) {
+      throw new RuntimeException(e);
+    }
+  }
 }

plugin/src/main/java/net/elytrium/limboapi/injection/login/confirmation/LoginConfirmHandler.java

@@ -37,6 +37,9 @@
 
 public class LoginConfirmHandler implements MinecraftSessionHandler {
 
+  private static final boolean BACKPRESSURE_LOG =
+      Boolean.getBoolean("velocity.log-server-backpressure");
+
   private static final MethodHandle TEARDOWN_METHOD;
 
   private final LimboAPI plugin;
@@ -108,6 +111,17 @@ public void handleUnknown(ByteBuf buf) {
     this.connection.close(true);
   }
 
+  @Override
+  public void writabilityChanged() {
+    if (BACKPRESSURE_LOG) {
+      if (this.connection.getChannel().isWritable()) {
+        LimboAPI.getLogger().info("{} is writable, will auto-read", this.player);
+      } else {
+        LimboAPI.getLogger().info("{} is not writable, not auto-reading", this.player);
+      }
+    }
+  }
+
   @Override
   public void disconnected() {
     try {

plugin/src/main/java/net/elytrium/limboapi/server/LimboSessionHandlerImpl.java

@@ -68,6 +68,9 @@
 
 public class LimboSessionHandlerImpl implements MinecraftSessionHandler {
 
+  private static final boolean BACKPRESSURE_LOG =
+      Boolean.getBoolean("velocity.log-server-backpressure");
+
   private static final MethodHandle TEARDOWN_METHOD;
 
   private final LimboAPI plugin;
@@ -380,6 +383,17 @@ public void handleGeneric(MinecraftPacket packet) {
     this.callback.onGeneric(packet);
   }
 
+  @Override
+  public void writabilityChanged() {
+    if (BACKPRESSURE_LOG) {
+      if (this.player.getConnection().getChannel().isWritable()) {
+        LimboAPI.getLogger().info("{} is writable, will auto-read", this.player);
+      } else {
+        LimboAPI.getLogger().info("{} is not writable, not auto-reading", this.player);
+      }
+    }
+  }
+
   private void kickTooBigPacket(String type, int length) {
     this.player.getConnection().closeWith(this.plugin.getPackets().getTooBigPacket());