Simplify and harden Netty handlers

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

@@ -5,10 +5,10 @@ import com.velocitypowered.natives.encryption.VelocityCipher;
 import com.velocitypowered.natives.util.MoreByteBufUtils;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.handler.codec.ByteToMessageDecoder;
+import io.netty.handler.codec.MessageToMessageDecoder;
 import java.util.List;
 
-public class MinecraftCipherDecoder extends ByteToMessageDecoder {
+public class MinecraftCipherDecoder extends MessageToMessageDecoder<ByteBuf> {
 
   private final VelocityCipher cipher;
 
@@ -30,7 +30,7 @@ public class MinecraftCipherDecoder extends ByteToMessageDecoder {
   }
 
   @Override
-  protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception {
+  public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
     cipher.dispose();
   }
 }

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

@@ -13,7 +13,8 @@ import java.util.List;
 
 public class MinecraftCompressDecoder extends MessageToMessageDecoder<ByteBuf> {
 
-  private static final int MAXIMUM_UNCOMPRESSED_SIZE = 2 * 1024 * 1024; // 2MiB
+  private static final int SOFT_MAXIMUM_UNCOMPRESSED_SIZE = 2 * 1024 * 1024; // 2MiB
+  private static final int HARD_MAXIMUM_UNCOMPRESSED_SIZE = 16 * 1024 * 1024; // 16MiB
 
   private final int threshold;
   private final VelocityCompressor compressor;
@@ -25,21 +26,23 @@ public class MinecraftCompressDecoder extends MessageToMessageDecoder<ByteBuf> {
 
   @Override
   protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
-    int expectedSize = ProtocolUtils.readVarInt(in);
-    if (expectedSize == 0) {
+    int claimedUncompressedSize = ProtocolUtils.readVarInt(in);
+    if (claimedUncompressedSize == 0) {
       // Strip the now-useless uncompressed size, this message is already uncompressed.
       out.add(in.retainedSlice());
       in.skipBytes(in.readableBytes());
       return;
     }
 
-    checkFrame(expectedSize >= threshold, "Uncompressed size %s is less than threshold %s",
-        expectedSize, threshold);
-    int initialCapacity = Math.min(expectedSize, MAXIMUM_UNCOMPRESSED_SIZE);
+    checkFrame(claimedUncompressedSize >= threshold, "Uncompressed size %s is less than"
+            + " threshold %s", claimedUncompressedSize, threshold);
+    int allowedMax = Math.min(claimedUncompressedSize, HARD_MAXIMUM_UNCOMPRESSED_SIZE);
+    int initialCapacity = Math.min(claimedUncompressedSize, SOFT_MAXIMUM_UNCOMPRESSED_SIZE);
+
     ByteBuf compatibleIn = ensureCompatible(ctx.alloc(), compressor, in);
     ByteBuf uncompressed = preferredBuffer(ctx.alloc(), compressor, initialCapacity);
     try {
-      compressor.inflate(compatibleIn, uncompressed, expectedSize);
+      compressor.inflate(compatibleIn, uncompressed, allowedMax);
       out.add(uncompressed);
     } catch (Exception e) {
       uncompressed.release();

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

@@ -47,20 +47,21 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
         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);
+            "Error decoding " + packet.getClass() + " " + getExtraConnectionDetail(packetId), e);
       }
       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 new CorruptedFrameException("Did not read full packet for " + packet.getClass() + " "
+                + getExtraConnectionDetail(packetId));
       }
       out.add(packet);
     }
   }
 
+  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/protocol/netty/MinecraftVarintFrameDecoder.java

@@ -27,16 +27,13 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
         // Make sure reader index of length buffer is returned to the beginning
         in.readerIndex(origReaderIndex);
         int packetLength = ProtocolUtils.readVarInt(in);
-        if (packetLength == 0) {
-          return;
-        }
-
-        if (in.readableBytes() < packetLength) {
-          in.readerIndex(origReaderIndex);
-          return;
-        }
 
+        if (in.readableBytes() >= packetLength) {
           out.add(in.readRetainedSlice(packetLength));
+        } else {
+          in.readerIndex(origReaderIndex);
+        }
+
         return;
       }
     }