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()) {
-      return;
-    }
-
-    int origReaderIndex = in.readerIndex();
-    for (int i = 0; i < 3; i++) {
-      if (!in.isReadable()) {
-        in.readerIndex(origReaderIndex);
-        return;
-      }
-
-      byte read = in.readByte();
-      if (read >= 0) {
-        // Make sure reader index of length buffer is returned to the beginning
-        in.readerIndex(origReaderIndex);
-        int packetLength = ProtocolUtils.readVarInt(in);
-        if (packetLength == 0) {
-          return;
+    int lastReaderIndex = in.readerIndex();
+    find_packets: while (in.isReadable()) {
+      for (int i = 0; i < 3; i++) {
+        if (!in.isReadable()) {
+          break;
         }
 
-        if (in.readableBytes() < packetLength) {
-          in.readerIndex(origReaderIndex);
-          return;
-        }
+        byte read = in.readByte();
+        if (read >= 0) {
+          // Make sure reader index of length buffer is returned to the beginning
+          in.readerIndex(lastReaderIndex);
+          int packetLength = ProtocolUtils.readVarInt(in);
+          if (packetLength == 0) {
+            break find_packets;
+          }
 
-        out.add(in.readRetainedSlice(packetLength));
-        return;
+          if (in.readableBytes() < packetLength) {
+            break find_packets;
+          }
+
+          out.add(in.readRetainedSlice(packetLength));
+          lastReaderIndex = in.readerIndex();
+          continue find_packets;
+        }
       }
+
+      throw new CorruptedFrameException("VarInt too big");
     }
 
-    throw new CorruptedFrameException("VarInt too big");
+    in.readerIndex(lastReaderIndex);
   }
 }