Decode multiple VarInt-prefixed packets

If the remote server does flush consolidation, Velocity will be able to
frame the packets all at once instead of having to constantly decode
packets. This should provide a modest performance boost for them whilst
not impacting un-optimized servers.

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

@@ -11,36 +11,35 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
 
   @Override
   protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
-    if (!in.isReadable()) {
+    int lastReaderIndex = in.readerIndex();
-      return;
+    find_packets: while (in.isReadable()) {
-    }
-
-    int origReaderIndex = in.readerIndex();
       for (int i = 0; i < 3; i++) {
         if (!in.isReadable()) {
-        in.readerIndex(origReaderIndex);
+          break;
-        return;
         }
 
         byte read = in.readByte();
         if (read >= 0) {
           // Make sure reader index of length buffer is returned to the beginning
-        in.readerIndex(origReaderIndex);
+          in.readerIndex(lastReaderIndex);
           int packetLength = ProtocolUtils.readVarInt(in);
           if (packetLength == 0) {
-          return;
+            break find_packets;
           }
 
           if (in.readableBytes() < packetLength) {
-          in.readerIndex(origReaderIndex);
+            break find_packets;
-          return;
           }
 
           out.add(in.readRetainedSlice(packetLength));
-        return;
+          lastReaderIndex = in.readerIndex();
+          continue find_packets;
         }
       }
 
       throw new CorruptedFrameException("VarInt too big");
     }
+
+    in.readerIndex(lastReaderIndex);
+  }
 }