Fix Brigadier command node redirect serialization (#565)

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

@@ -44,17 +44,24 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
     if (varintEnd == -1) {
       // We tried to go beyond the end of the buffer. This is probably a good sign that the
       // buffer was too short to hold a proper varint.
+      if (reader.getResult() == DecodeResult.RUN_OF_ZEROES) {
+        // Special case where the entire packet is just a run of zeroes. We ignore them all.
+        in.clear();
+      }
       return;
     }
 
-    if (reader.getResult() == DecodeResult.SUCCESS) {
+    if (reader.getResult() == DecodeResult.RUN_OF_ZEROES) {
+      // this will return to the point where the next varint starts
+      in.readerIndex(varintEnd);
+    } else if (reader.getResult() == DecodeResult.SUCCESS) {
       int readVarint = reader.getReadVarint();
       int bytesRead = reader.getBytesRead();
       if (readVarint < 0) {
         in.clear();
         throw BAD_LENGTH_CACHED;
       } else if (readVarint == 0) {
-        // skip over the empty packet and ignore it
+        // skip over the empty packet(s) and ignore it
         in.readerIndex(varintEnd + 1);
       } else {
         int minimumRead = bytesRead + readVarint;

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

@@ -27,6 +27,14 @@ class VarintByteDecoder implements ByteProcessor {
 
   @Override
   public boolean process(byte k) {
+    if (k == 0 && bytesRead == 0) {
+      // tentatively say it's invalid, but there's a possibility of redemption
+      result = DecodeResult.RUN_OF_ZEROES;
+      return true;
+    }
+    if (result == DecodeResult.RUN_OF_ZEROES) {
+      return false;
+    }
     readVarint |= (k & 0x7F) << bytesRead++ * 7;
     if (bytesRead > 3) {
       result = DecodeResult.TOO_BIG;
@@ -54,6 +62,7 @@ class VarintByteDecoder implements ByteProcessor {
   public enum DecodeResult {
     SUCCESS,
     TOO_SHORT,
-    TOO_BIG
+    TOO_BIG,
+    RUN_OF_ZEROES
   }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/AvailableCommands.java

@@ -122,6 +122,9 @@ public class AvailableCommands implements MinecraftPacket {
       if (!idMappings.containsKey(child)) {
         idMappings.put(child, idMappings.size());
         childrenQueue.addAll(child.getChildren());
+        if (child.getRedirect() != null) {
+          childrenQueue.add(child.getRedirect());
+        }
       }
     }