Upon connection exception, discard all incoming packets instead

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

@@ -5,6 +5,7 @@ import com.velocitypowered.api.network.ProtocolVersion;
 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.handler.codec.CorruptedFrameException;
@@ -13,6 +14,11 @@ 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;
@@ -46,21 +52,39 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
       try {
         packet.decode(msg, direction, registry.version);
       } catch (Exception e) {
-        throw new CorruptedFrameException(
-            "Error decoding " + packet.getClass() + " Direction " + direction
-                + " Protocol " + registry.version + " State " + state + " ID " + Integer
-                .toHexString(packetId), e);
+        throw handleDecodeFailure(e, packet, packetId);
       }
+
       if (msg.isReadable()) {
-        throw new CorruptedFrameException(
-            "Did not read full packet for " + packet.getClass() + " Direction " + direction
-                + " Protocol " + registry.version + " State " + state + " ID " + Integer
-                .toHexString(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);
+  }
+
   public void setProtocolVersion(ProtocolVersion protocolVersion) {
     this.registry = direction.getProtocolRegistry(state, protocolVersion);
   }

proxy/src/main/java/com/velocitypowered/proxy/util/except/QuietException.java

@@ -0,0 +1,17 @@
+package com.velocitypowered.proxy.util.except;
+
+/**
+ * A special-purpose exception thrown when we want to indicate an error condition but do not want
+ * to see a large stack trace in logs.
+ */
+public class QuietException extends RuntimeException {
+
+  public QuietException(String message) {
+    super(message);
+  }
+
+  @Override
+  public synchronized Throwable fillInStackTrace() {
+    return this;
+  }
+}