Fix flight state between world teleports (#6012)

Thanks to @electronicboy for the general fix.

Fixes #4325 for Paper only :)

Co-authored-by: Shane Freeder <theboyetronic@gmail.com>

Essentials/src/main/java/com/earth2me/essentials/Essentials.java

@@ -93,6 +93,7 @@ import net.ess3.provider.providers.PaperMaterialTagProvider;
 import net.ess3.provider.providers.PaperRecipeBookListener;
 import net.ess3.provider.providers.PaperSerializationProvider;
 import net.ess3.provider.providers.PaperServerStateProvider;
+import net.ess3.provider.providers.PaperTickCountProvider;
 import net.ess3.provider.providers.PrehistoricPotionMetaProvider;
 import net.essentialsx.api.v2.services.BalanceTop;
 import net.essentialsx.api.v2.services.mail.MailService;
@@ -421,6 +422,9 @@ public class Essentials extends JavaPlugin implements net.ess3.api.IEssentials {
             // Biome Key Provider
             providerFactory.registerProvider(PaperBiomeKeyProvider.class);
 
+            // Tick Count Provider
+            providerFactory.registerProvider(PaperTickCountProvider.class);
+
             providerFactory.finalizeRegistration();
 
             // Event Providers

Essentials/src/main/java/com/earth2me/essentials/EssentialsPlayerListener.java

@@ -20,6 +20,7 @@ import net.ess3.provider.CommandSendListenerProvider;
 import net.ess3.provider.FormattedCommandAliasProvider;
 import net.ess3.provider.InventoryViewProvider;
 import net.ess3.provider.KnownCommandsProvider;
+import net.ess3.provider.TickCountProvider;
 import net.ess3.provider.providers.BukkitCommandSendListenerProvider;
 import net.ess3.provider.providers.PaperCommandSendListenerProvider;
 import net.essentialsx.api.v2.events.AsyncUserDataLoadEvent;
@@ -588,6 +589,17 @@ public class EssentialsPlayerListener implements Listener, FakeAccessor {
         if (ess.getSettings().isTeleportInvulnerability()) {
             user.enableInvulnerabilityAfterTeleport();
         }
+
+        // Mitigation for https://github.com/EssentialsX/Essentials/issues/4325
+        final TickCountProvider tickCountProvider = ess.provider(TickCountProvider.class);
+        if (tickCountProvider != null && ess.getSettings().isWorldChangePreserveFlying() && VersionUtil.getServerBukkitVersion().isHigherThanOrEqualTo(VersionUtil.v1_17_R01)) {
+            if (user.isAuthorized("essentials.fly")) {
+                //noinspection DataFlowIssue - not real
+                if (event.getFrom().getWorld() != event.getTo().getWorld() && player.isFlying()) {
+                    user.setFlightTick(tickCountProvider.getTickCount());
+                }
+            }
+        }
     }
 
     @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
@@ -741,8 +753,7 @@ public class EssentialsPlayerListener implements Listener, FakeAccessor {
 
         if (ess.getSettings().isWorldChangeFlyResetEnabled()) {
             if (user.getBase().getGameMode() != GameMode.CREATIVE
-                // COMPAT: String compare for 1.7.10
-                && !user.getBase().getGameMode().name().equals("SPECTATOR")
+                && user.getBase().getGameMode() != GameMode.SPECTATOR
                 && !user.isAuthorized("essentials.fly")) {
                 user.getBase().setFallDistance(0f);
                 user.getBase().setAllowFlight(false);
@@ -765,6 +776,13 @@ public class EssentialsPlayerListener implements Listener, FakeAccessor {
                 }
             }
         }
+
+        final TickCountProvider tickCountProvider = ess.provider(TickCountProvider.class);
+        if (tickCountProvider != null && user.getFlightTick() == tickCountProvider.getTickCount()) {
+            user.getBase().setAllowFlight(true);
+            user.getBase().setFlying(true);
+        }
+        user.setFlightTick(-1);
     }
 
     @EventHandler(priority = EventPriority.MONITOR)

Essentials/src/main/java/com/earth2me/essentials/ISettings.java

@@ -344,6 +344,8 @@ public interface ISettings extends IConf {
 
     boolean isWorldChangeFlyResetEnabled();
 
+    boolean isWorldChangePreserveFlying();
+
     boolean isWorldChangeSpeedResetEnabled();
 
     long getCommandCooldownMs(String label);

Essentials/src/main/java/com/earth2me/essentials/Settings.java

@@ -1919,6 +1919,11 @@ public class Settings implements net.ess3.api.ISettings {
         return config.getBoolean("world-change-fly-reset", true);
     }
 
+    @Override
+    public boolean isWorldChangePreserveFlying() {
+        return config.getBoolean("world-change-preserve-flying", true);
+    }
+
     @Override
     public boolean isWorldChangeSpeedResetEnabled() {
         return config.getBoolean("world-change-speed-reset", true);

Essentials/src/main/java/com/earth2me/essentials/User.java

@@ -102,6 +102,7 @@ public class User extends UserData implements Comparable<User>, IMessageRecipien
     // Misc
     private transient final List<String> signCopy = Lists.newArrayList("", "", "", "");
     private transient long lastVanishTime = System.currentTimeMillis();
+    private transient int flightTick = -1;
     private String lastLocaleString;
     private Locale playerLocale;
 
@@ -1299,4 +1300,12 @@ public class User extends UserData implements Comparable<User>, IMessageRecipien
         }
         return toggleShout == null ? toggleShout = ess.getSettings().isShoutDefault() : toggleShout;
     }
+
+    public int getFlightTick() {
+        return flightTick;
+    }
+
+    public void setFlightTick(int flightTick) {
+        this.flightTick = flightTick;
+    }
 }

Essentials/src/main/resources/config.yml

@@ -224,6 +224,11 @@ socialspy-uses-displaynames: true
 # This will disable flight if the player does not have essentials.fly.
 world-change-fly-reset: true
 
+# Starting in 1.17, Minecraft no longer preserves the abilities of a player when they change worlds.
+# Setting this to true will make EssentialsX preserve if users flying when they change worlds.
+# This will only work if the player has the essentials.fly permission.
+world-change-preserve-flying: true
+
 # When a player changes world, should we reset their speed according to their permissions?
 # This resets the player's speed to the default if they don't have essentials.speed.
 # If the player doesn't have essentials.speed.bypass, this resets their speed to the maximum specified above.

providers/BaseProviders/src/main/java/net/ess3/provider/TickCountProvider.java

@@ -0,0 +1,8 @@
+package net.ess3.provider;
+
+import net.essentialsx.providers.NullableProvider;
+
+@NullableProvider
+public interface TickCountProvider extends Provider {
+    int getTickCount();
+}

providers/PaperProvider/src/main/java/net/ess3/provider/providers/PaperTickCountProvider.java

@@ -0,0 +1,24 @@
+package net.ess3.provider.providers;
+
+import net.ess3.provider.TickCountProvider;
+import net.essentialsx.providers.ProviderData;
+import net.essentialsx.providers.ProviderTest;
+import org.bukkit.Bukkit;
+
+@ProviderData(description = "Paper Tick Count Provider")
+public class PaperTickCountProvider implements TickCountProvider {
+    @Override
+    public int getTickCount() {
+        return Bukkit.getCurrentTick();
+    }
+
+    @ProviderTest
+    public static boolean test() {
+        try {
+            Bukkit.class.getDeclaredMethod("getCurrentTick");
+            return true;
+        } catch (final NoSuchMethodException ignored) {
+            return false;
+        }
+    }
+}