Upon connection exception, discard all incoming packets instead

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

@@ -16,6 +16,7 @@ import com.velocitypowered.natives.encryption.VelocityCipher;
 import com.velocitypowered.natives.encryption.VelocityCipherFactory;
 import com.velocitypowered.natives.util.Natives;
 import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.network.netty.DiscardHandler;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.netty.MinecraftCipherDecoder;
@@ -144,6 +145,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
         }
       }
 
+      ctx.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
       ctx.close();
     }
   }

proxy/src/main/java/com/velocitypowered/proxy/network/netty/DiscardHandler.java

@@ -0,0 +1,17 @@
+package com.velocitypowered.proxy.network.netty;
+
+import io.netty.channel.ChannelHandler.Sharable;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelInboundHandlerAdapter;
+import io.netty.util.ReferenceCountUtil;
+
+@Sharable
+public class DiscardHandler extends ChannelInboundHandlerAdapter {
+
+  public static final DiscardHandler HANDLER = new DiscardHandler();
+
+  @Override
+  public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
+    ReferenceCountUtil.release(msg);
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftDecoder.java

@@ -2,17 +2,26 @@ package com.velocitypowered.proxy.protocol.netty;
 
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.proxy.network.Connections;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.ProtocolUtils;
 import com.velocitypowered.proxy.protocol.StateRegistry;
+import com.velocitypowered.proxy.util.except.QuietException;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.handler.codec.CorruptedFrameException;
 import io.netty.handler.codec.MessageToMessageDecoder;
+import io.netty.util.ReferenceCountUtil;
 import java.util.List;
 
 public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
 
+  private static final boolean DEBUG = Boolean.getBoolean("velocity.packet-decode-logging");
+  private static final QuietException DECODE_FAILED =
+      new QuietException("A packet did not decode successfully (invalid data). If you are a " +
+          "developer, launch Velocity with -Dvelocity.packet-decode-logging=true to see more.");
+
   private final ProtocolUtils.Direction direction;
   private StateRegistry state;
   private StateRegistry.PacketRegistry.ProtocolRegistry registry;
@@ -46,17 +55,34 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
       try {
         packet.decode(msg, direction, registry.version);
       } catch (Exception e) {
-        throw new CorruptedFrameException(
-            "Error decoding " + packet.getClass() + " " + getExtraConnectionDetail(packetId), e);
+        throw handleDecodeFailure(e, packet, packetId);
       }
+
       if (msg.isReadable()) {
-        throw new CorruptedFrameException("Did not read full packet for " + packet.getClass() + " "
-                + getExtraConnectionDetail(packetId));
+        throw handleNotReadEnough(packet, packetId);
       }
       out.add(packet);
     }
   }
 
+  private Exception handleNotReadEnough(MinecraftPacket packet, int packetId) {
+    if (DEBUG) {
+      return new CorruptedFrameException("Did not read full packet for " + packet.getClass() + " "
+          + getExtraConnectionDetail(packetId));
+    } else {
+      return DECODE_FAILED;
+    }
+  }
+
+  private Exception handleDecodeFailure(Exception cause, MinecraftPacket packet, int packetId) {
+    if (DEBUG) {
+      return new CorruptedFrameException(
+          "Error decoding " + packet.getClass() + " " + getExtraConnectionDetail(packetId), cause);
+    } else {
+      return DECODE_FAILED;
+    }
+  }
+
   private String getExtraConnectionDetail(int packetId) {
     return "Direction " + direction + " Protocol " + registry.version + " State " + state
         + " ID " + Integer.toHexString(packetId);