Attempt to support ViaVersion on the proxy by looking up player version from the data version

src/main/java/com/moulberry/axiom/AxiomPaper.java

@@ -17,6 +17,7 @@ import io.papermc.paper.event.world.WorldGameRuleChangeEvent;
 import io.papermc.paper.network.ChannelInitializeListener;
 import io.papermc.paper.network.ChannelInitializeListenerHolder;
 import net.kyori.adventure.key.Key;
+import net.minecraft.SharedConstants;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.IdMapper;
 import net.minecraft.network.Connection;
@@ -42,7 +43,6 @@ import org.incendo.cloud.execution.ExecutionCoordinator;
 import org.incendo.cloud.paper.LegacyPaperCommandManager;
 import org.jetbrains.annotations.Nullable;
 
-import java.io.FileReader;
 import java.io.IOException;
 import java.lang.ref.WeakReference;
 import java.nio.file.Files;
@@ -58,7 +58,7 @@ public class AxiomPaper extends JavaPlugin implements Listener {
     public final Map<UUID, RateLimiter> playerBlockBufferRateLimiters = new ConcurrentHashMap<>();
     public final Map<UUID, Restrictions> playerRestrictions = new ConcurrentHashMap<>();
     public final Map<UUID, IdMapper<BlockState>> playerBlockRegistry = new ConcurrentHashMap<>();
-    public final Set<UUID> mismatchedDataVersionUsingViaVersion = Collections.newSetFromMap(new ConcurrentHashMap<>());
+    public final Map<UUID, Integer> playerProtocolVersion = new ConcurrentHashMap<>();
     public Configuration configuration;
 
     public IdMapper<BlockState> allowedBlockRegistry = null;
@@ -273,7 +273,7 @@ public class AxiomPaper extends JavaPlugin implements Listener {
             playerBlockBufferRateLimiters.keySet().retainAll(stillActiveAxiomPlayers);
             playerRestrictions.keySet().retainAll(stillActiveAxiomPlayers);
             playerBlockRegistry.keySet().retainAll(stillActiveAxiomPlayers);
-            mismatchedDataVersionUsingViaVersion.retainAll(stillActiveAxiomPlayers);
+            playerProtocolVersion.keySet().retainAll(stillActiveAxiomPlayers);
         }, 20, 20);
 
         boolean sendMarkers = configuration.getBoolean("send-markers");
@@ -336,7 +336,11 @@ public class AxiomPaper extends JavaPlugin implements Listener {
     }
 
     public boolean isMismatchedDataVersion(UUID uuid) {
-        return this.mismatchedDataVersionUsingViaVersion.contains(uuid);
+        return this.playerProtocolVersion.containsKey(uuid);
+    }
+
+    public int getProtocolVersionFor(UUID uuid) {
+        return this.playerProtocolVersion.getOrDefault(uuid, SharedConstants.getProtocolVersion());
     }
 
     public IdMapper<BlockState> getBlockRegistry(UUID uuid) {

src/main/java/com/moulberry/axiom/packet/HelloPacketListener.java

@@ -64,19 +64,39 @@ public class HelloPacketListener implements PluginMessageListener {
             String incompatibleDataVersion = plugin.configuration.getString("incompatible-data-version");
             if (incompatibleDataVersion == null) incompatibleDataVersion = "warn";
 
-            if (!Bukkit.getPluginManager().isPluginEnabled("ViaVersion")) {
+            Component incompatibleWarning = Component.text("Axiom: Incompatible data version detected (client " + dataVersion +
-                Component text = Component.text("Axiom: Incompatible data version detected (client " + dataVersion +
                 ", server " + serverDataVersion  + ")");
 
+            if (!Bukkit.getPluginManager().isPluginEnabled("ViaVersion")) {
                 if (incompatibleDataVersion.equals("warn")) {
-                    player.sendMessage(text.color(NamedTextColor.RED));
+                    player.sendMessage(incompatibleWarning.color(NamedTextColor.RED));
                     return;
                 } else if (!incompatibleDataVersion.equals("ignore")) {
-                    player.kick(text);
+                    player.kick(incompatibleWarning);
                     return;
                 }
             } else {
                 int playerVersion = Via.getAPI().getPlayerVersion(player.getUniqueId());
+                if (playerVersion == SharedConstants.getProtocolVersion()) {
+                    // Likely using via on the proxy, try to get protocol version from data version
+                    if (dataVersion < 3337) {
+                        player.sendMessage(incompatibleWarning.color(NamedTextColor.RED));
+                        return;
+                    } else if (dataVersion == 3337) {
+                        playerVersion = 762; // 1.19.4
+                    } else if (dataVersion <= 3465) {
+                        playerVersion = 763; // 1.20.1
+                    } else if (dataVersion <= 3578) {
+                        playerVersion = 764; // 1.20.2
+                    } else if (dataVersion <= 3700) {
+                        playerVersion = 765; // 1.20.3 / 1.20.4
+                    } else if (dataVersion <= 3837) {
+                        playerVersion = 766; // 1.20.3 / 1.20.4
+                    } else {
+                        player.sendMessage(incompatibleWarning.color(NamedTextColor.RED));
+                        return;
+                    }
+                }
 
                 IdMapper<BlockState> mapper;
                 try {
@@ -96,7 +116,7 @@ public class HelloPacketListener implements PluginMessageListener {
                 }
 
                 this.plugin.playerBlockRegistry.put(player.getUniqueId(), mapper);
-                this.plugin.mismatchedDataVersionUsingViaVersion.add(player.getUniqueId());
+                this.plugin.playerProtocolVersion.put(player.getUniqueId(), playerVersion);
 
                 Component text = Component.text("Axiom: Warning, client and server versions don't match. " +
                         "Axiom will try to use ViaVersion conversions, but this process may cause problems");

src/main/java/com/moulberry/axiom/viaversion/ViaVersionHelper.java

@@ -97,7 +97,7 @@ public class ViaVersionHelper {
     private static final int UNNAMED_COMPOUND_TAG_CHANGE_VERSION = 764; // 1.20.2
 
     public static void skipTagViaVersion(FriendlyByteBuf friendlyByteBuf, Player player) throws Exception {
-        skipTagViaVersion(friendlyByteBuf, Via.getAPI().getPlayerVersion(player.getUniqueId()));
+        skipTagViaVersion(friendlyByteBuf, AxiomPaper.PLUGIN.getProtocolVersionFor(player.getUniqueId()));
     }
 
     public static void skipTagViaVersion(FriendlyByteBuf friendlyByteBuf, int playerVersion) throws Exception {
@@ -105,7 +105,7 @@ public class ViaVersionHelper {
     }
 
     public static CompoundTag readTagViaVersion(FriendlyByteBuf friendlyByteBuf, Player player) throws Exception {
-        return readTagViaVersion(friendlyByteBuf, Via.getAPI().getPlayerVersion(player.getUniqueId()));
+        return readTagViaVersion(friendlyByteBuf, AxiomPaper.PLUGIN.getProtocolVersionFor(player.getUniqueId()));
     }
 
     public static CompoundTag readTagViaVersion(FriendlyByteBuf friendlyByteBuf, int playerVersion) throws Exception {