From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Wed, 27 Feb 2019 22:18:40 -0500
Subject: [PATCH] Limit Client Sign length more

modified clients can send more data from the client
to the server and it would get stored on the sign as sent.

Mojang has a limit of 384 which is much higher than reasonable.

the client can barely render around 16 characters as-is, but formatting
codes can get it to be more than 16 actual length.

Set a limit of 80 which should give an average of 16 characters 2
sets of legacy formatting codes which should be plenty for all uses.

This does not strip any existing data from the NBT as plugins
may use this for storing data out of the rendered area.

it only impacts data sent from the client.

Set -DPaper.maxSignLength=XX to change limit or -1 to disable

diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index 0103c76c183d0e866a98c26f2d1cf557ba4f67e8..d24d42ef0a00b9420700e58f555f8448f8d01747 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -254,6 +254,7 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Ser
     private int aboveGroundVehicleTickCount;
     private int receivedMovePacketCount;
     private int knownMovePacketCount;
+    private static final int MAX_SIGN_LINE_LENGTH = Integer.getInteger("Paper.maxSignLength", 80);
     private static final long KEEPALIVE_LIMIT = Long.getLong("paper.playerconnection.keepalive", 30) * 1000; // Paper - provide property to set keepalive limit
 
     public ServerGamePacketListenerImpl(MinecraftServer server, Connection connection, ServerPlayer player) {
@@ -2847,10 +2848,20 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Ser
             List<net.kyori.adventure.text.Component> lines = new java.util.ArrayList<>();
 
             for (int i = 0; i < list.size(); ++i) {
+                // Paper start - cap line length - modified clients can send longer data than normal
+                net.minecraft.server.network.TextFilter.FilteredText currentLine = list.get(i);
+                if (MAX_SIGN_LINE_LENGTH > 0 && currentLine.getRaw().length() > MAX_SIGN_LINE_LENGTH) {
+                    // This handles multibyte characters as 1
+                    int offset = currentLine.getRaw().codePoints().limit(MAX_SIGN_LINE_LENGTH).map(Character::charCount).sum();
+                    if (offset < currentLine.getRaw().length()) {
+                        list.set(i, currentLine = net.minecraft.server.network.TextFilter.FilteredText.passThrough(currentLine.getRaw().substring(0, offset))); // this will break any filtering, but filtering is NYI as of 1.17
+                    }
+                }
+                // Paper end
                 if (this.player.isTextFilteringEnabled()) {
-                    lines.add(net.kyori.adventure.text.Component.text(SharedConstants.filterText(list.get(i).getFiltered())));
+                    lines.add(net.kyori.adventure.text.Component.text(SharedConstants.filterText(currentLine.getFiltered())));
                 } else {
-                    lines.add(net.kyori.adventure.text.Component.text(SharedConstants.filterText(list.get(i).getRaw())));
+                    lines.add(net.kyori.adventure.text.Component.text(SharedConstants.filterText(currentLine.getRaw())));
                 }
             }
             SignChangeEvent event = new SignChangeEvent((org.bukkit.craftbukkit.block.CraftBlock) player.getWorld().getBlockAt(x, y, z), this.player.getBukkitEntity(), lines);