Use client version to roughly determine known packs

Author: valaphee

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java

@@ -58,6 +58,8 @@
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import java.io.IOException;
 import java.net.InetSocketAddress;
+import java.util.Arrays;
+import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
@@ -301,7 +303,8 @@ public boolean handle(TransferPacket packet) {
   public boolean handle(KnownPacksPacket packet) {
     // Server expects us to reply to this packet
     if (serverConn.getPlayer().getConnection().getState() != StateRegistry.CONFIG) {
-      serverConn.ensureConnected().write(new KnownPacksPacket());
+      List<KnownPacksPacket.KnownPack> clientPacks = List.of(new KnownPacksPacket.KnownPack("minecraft", "core", serverConn.getPlayer().getProtocolVersion().getVersionIntroducedIn()));
+      serverConn.ensureConnected().write(new KnownPacksPacket(Arrays.stream(packet.getPacks()).distinct().filter(clientPacks::contains).toArray(KnownPacksPacket.KnownPack[]::new)));
       return true;
     }
     return false; // forward

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/config/KnownPacksPacket.java

@@ -24,6 +24,9 @@
 import com.velocitypowered.proxy.util.except.QuietDecoderException;
 import io.netty.buffer.ByteBuf;
 
+import java.util.Arrays;
+import java.util.Objects;
+
 public class KnownPacksPacket implements MinecraftPacket {
 
     private static final int MAX_LENGTH_PACKS = Integer.getInteger("velocity.max-known-packs", 64);
@@ -36,6 +39,10 @@ public KnownPacksPacket() {
         packs = new KnownPack[0];
     }
 
+    public KnownPacksPacket(KnownPack[] packs) {
+        this.packs = packs;
+    }
+
     @Override
     public void decode(ByteBuf buf, ProtocolUtils.Direction direction,
                        ProtocolVersion protocolVersion) {
@@ -68,6 +75,17 @@ public boolean handle(MinecraftSessionHandler handler) {
         return handler.handle(this);
     }
 
+    public KnownPack[] getPacks() {
+        return packs;
+    }
+
+    @Override
+    public String toString() {
+        return "KnownPacksPacket{" +
+                "packs=" + Arrays.toString(packs) +
+                '}';
+    }
+
     public record KnownPack(String namespace, String id, String version) {
         private static KnownPack read(ByteBuf buf) {
             return new KnownPack(ProtocolUtils.readString(buf), ProtocolUtils.readString(buf), ProtocolUtils.readString(buf));
@@ -78,5 +96,26 @@ private void write(ByteBuf buf) {
             ProtocolUtils.writeString(buf, id);
             ProtocolUtils.writeString(buf, version);
         }
+
+        @Override
+        public boolean equals(Object o) {
+            if (o == null || getClass() != o.getClass()) return false;
+            KnownPack knownPack = (KnownPack) o;
+            return Objects.equals(id, knownPack.id) && Objects.equals(version, knownPack.version) && Objects.equals(namespace, knownPack.namespace);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(namespace, id, version);
+        }
+
+        @Override
+        public String toString() {
+            return "KnownPack{" +
+                    "namespace='" + namespace + '\'' +
+                    ", id='" + id + '\'' +
+                    ", version='" + version + '\'' +
+                    '}';
+        }
     }
 }