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 c45910b192bcc6171a2ae98a525fdc7008c2185f..74d77d3dd5a7f05242d2105c8cfbe10b1a054a1f 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -296,6 +296,7 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
     private final LastSeenMessagesValidator lastSeenMessagesValidator;
     private final FutureChain chatMessageChain;
     private static final long KEEPALIVE_LIMIT = Long.getLong("paper.playerconnection.keepalive", 30) * 1000; // Paper - provide property to set keepalive limit
+    private static final int MAX_SIGN_LINE_LENGTH = Integer.getInteger("Paper.maxSignLength", 80); // Paper
 
     public ServerGamePacketListenerImpl(MinecraftServer server, Connection connection, ServerPlayer player) {
         this.lastChatTimeStamp = new AtomicReference(Instant.EPOCH);
@@ -3288,7 +3289,19 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
 
     @Override
     public void handleSignUpdate(ServerboundSignUpdatePacket packet) {
-        List<String> list = (List) Stream.of(packet.getLines()).map(ChatFormatting::stripFormatting).collect(Collectors.toList());
+        // Paper start - cap line length - modified clients can send longer data than normal
+        String[] lines = packet.getLines();
+        for (int i = 0; i < lines.length; ++i) {
+            if (MAX_SIGN_LINE_LENGTH > 0 && lines[i].length() > MAX_SIGN_LINE_LENGTH) {
+                // This handles multibyte characters as 1
+                int offset = lines[i].codePoints().limit(MAX_SIGN_LINE_LENGTH).map(Character::charCount).sum();
+                if (offset < lines[i].length()) {
+                    lines[i] = lines[i].substring(0, offset); // this will break any filtering, but filtering is NYI as of 1.17
+                }
+            }
+        }
+        List<String> list = (List) Stream.of(lines).map(ChatFormatting::stripFormatting).collect(Collectors.toList());
+        // Paper end
 
         this.filterTextPacket(list).thenAcceptAsync((list1) -> {
             this.updateSignText(packet, list1);