Add API for client-side signs (#11903)

paper-api/src/main/java/io/papermc/paper/event/packet/UncheckedSignChangeEvent.java

@@ -0,0 +1,94 @@
+package io.papermc.paper.event.packet;
+
+import io.papermc.paper.math.BlockPosition;
+import io.papermc.paper.math.Position;
+import java.util.Collections;
+import java.util.List;
+import net.kyori.adventure.text.Component;
+import org.bukkit.block.sign.Side;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.player.PlayerEvent;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Unmodifiable;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * Called when a client attempts to modify a sign, but the location at which the sign should be edited
+ * has not yet been checked for the existence of a real sign.
+ * <p>
+ * Cancelling this event will prevent further processing of the sign change, but needs further handling
+ * by the plugin as the client's local world might be in an inconsistent state.
+ *
+ * @see Player#openVirtualSign(Position, Side)
+ */
+@NullMarked
+@ApiStatus.Experimental
+public class UncheckedSignChangeEvent extends PlayerEvent implements Cancellable {
+
+    private static final HandlerList HANDLER_LIST = new HandlerList();
+    private boolean cancel = false;
+    private final BlockPosition editedBlockPosition;
+    private final Side side;
+    private final List<Component> lines;
+
+    @ApiStatus.Internal
+    public UncheckedSignChangeEvent(
+        final Player editor,
+        final BlockPosition editedBlockPosition,
+        final Side side,
+        final List<Component> lines
+    ) {
+        super(editor);
+        this.editedBlockPosition = editedBlockPosition;
+        this.side = side;
+        this.lines = lines;
+    }
+
+    /**
+     * Gets the location at which a potential sign was edited.
+     *
+     * @return location where the change happened
+     */
+    public BlockPosition getEditedBlockPosition() {
+        return editedBlockPosition;
+    }
+
+    /**
+     * Gets which side of the sign was edited.
+     *
+     * @return {@link Side} that was edited
+     */
+    public Side getSide() {
+        return side;
+    }
+
+    /**
+     * Gets the lines that the player has entered.
+     *
+     * @return the lines
+     */
+    public @Unmodifiable List<Component> lines() {
+        return Collections.unmodifiableList(lines);
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancel;
+    }
+
+    @Override
+    public void setCancelled(final boolean cancel) {
+        this.cancel = cancel;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return HANDLER_LIST;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLER_LIST;
+    }
+}

paper-api/src/main/java/org/bukkit/entity/Player.java

@@ -12,6 +12,7 @@ import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
 import io.papermc.paper.entity.LookAnchor;
 import io.papermc.paper.entity.PlayerGiveResult;
+import io.papermc.paper.math.Position;
 import org.bukkit.BanEntry;
 import org.bukkit.DyeColor;
 import org.bukkit.Effect;
@@ -52,7 +53,6 @@ import org.bukkit.plugin.Plugin;
 import org.bukkit.plugin.messaging.PluginMessageRecipient;
 import org.bukkit.potion.PotionEffect;
 import org.bukkit.potion.PotionEffectType;
-import org.bukkit.profile.PlayerProfile;
 import org.bukkit.scoreboard.Scoreboard;
 import org.jetbrains.annotations.ApiStatus;
 import org.jspecify.annotations.NullMarked;
@@ -3449,6 +3449,21 @@ public interface Player extends HumanEntity, Conversable, OfflinePlayer, PluginM
      */
     public void openSign(Sign sign, Side side);
 
+    /**
+     * Open a sign for editing by the player.
+     * <p>
+     * The sign must only be placed locally for the player, which can be done with {@link #sendBlockChange(Location, BlockData)} and {@link #sendBlockUpdate(Location, TileState)}.
+     * A side-effect of this is that normal events, like {@link org.bukkit.event.block.SignChangeEvent} will not be called (unless there is an actual sign in the world).
+     * Additionally, the client may enforce distance limits to the opened position.
+     * </p>
+     *
+     * @param block The block where the client has a sign placed
+     * @param side The side to edit
+     * @see io.papermc.paper.event.packet.UncheckedSignChangeEvent
+     */
+    @ApiStatus.Experimental
+    void openVirtualSign(Position block, Side side);
+
     /**
      * Shows the demo screen to the player, this screen is normally only seen in
      * the demo version of the game.

paper-server/patches/sources/net/minecraft/server/network/ServerGamePacketListenerImpl.java.patch

@@ -2486,7 +2486,7 @@
              } else if (flag && flag2) {
                  if (this.dropSpamThrottler.isUnderThreshold()) {
                      this.dropSpamThrottler.increment();
-@@ -1895,11 +_,24 @@
+@@ -1895,15 +_,38 @@
  
      @Override
      public void handleSignUpdate(ServerboundSignUpdatePacket packet) {
@@ -2512,6 +2512,20 @@
          this.player.resetLastActionTime();
          ServerLevel serverLevel = this.player.serverLevel();
          BlockPos pos = packet.getPos();
+         if (serverLevel.hasChunkAt(pos)) {
++            // Paper start - Add API for client-side signs
++            if (!new io.papermc.paper.event.packet.UncheckedSignChangeEvent(
++                this.player.getBukkitEntity(),
++                io.papermc.paper.util.MCUtil.toPosition(pos),
++                packet.isFrontText() ? org.bukkit.block.sign.Side.FRONT : org.bukkit.block.sign.Side.BACK,
++                filteredText.stream().<net.kyori.adventure.text.Component>map(line -> net.kyori.adventure.text.Component.text(line.raw())).toList())
++                .callEvent()) {
++                return;
++            }
++            // Paper end - Add API for client-side signs
+             if (!(serverLevel.getBlockEntity(pos) instanceof SignBlockEntity signBlockEntity)) {
+                 return;
+             }
 @@ -1915,14 +_,32 @@
      @Override
      public void handlePlayerAbilities(ServerboundPlayerAbilitiesPacket packet) {

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -12,6 +12,8 @@ import io.papermc.paper.configuration.GlobalConfiguration;
 import io.papermc.paper.entity.LookAnchor;
 import io.papermc.paper.entity.PaperPlayerGiveResult;
 import io.papermc.paper.entity.PlayerGiveResult;
+import io.papermc.paper.math.Position;
+import io.papermc.paper.util.MCUtil;
 import it.unimi.dsi.fastutil.shorts.ShortArraySet;
 import it.unimi.dsi.fastutil.shorts.ShortSet;
 import java.io.ByteArrayOutputStream;
@@ -73,6 +75,7 @@ import net.minecraft.network.protocol.game.ClientboundHurtAnimationPacket;
 import net.minecraft.network.protocol.game.ClientboundLevelEventPacket;
 import net.minecraft.network.protocol.game.ClientboundLevelParticlesPacket;
 import net.minecraft.network.protocol.game.ClientboundMapItemDataPacket;
+import net.minecraft.network.protocol.game.ClientboundOpenSignEditorPacket;
 import net.minecraft.network.protocol.game.ClientboundPlayerInfoRemovePacket;
 import net.minecraft.network.protocol.game.ClientboundPlayerInfoUpdatePacket;
 import net.minecraft.network.protocol.game.ClientboundRemoveMobEffectPacket;
@@ -3037,6 +3040,13 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
         CraftSign.openSign(sign, this, side);
     }
 
+    @Override
+    public void openVirtualSign(Position block, Side side) {
+        if (this.getHandle().connection == null) return;
+
+        this.getHandle().connection.send(new ClientboundOpenSignEditorPacket(MCUtil.toBlockPos(block), side == Side.FRONT));
+    }
+
     @Override
     public void showDemoScreen() {
         if (this.getHandle().connection == null) return;