PaperMC/patches/server/0270-Book-size-limits.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 16 Nov 2018 23:08:50 -0500
Subject: [PATCH] Book size limits

Puts some limits on the size of books.

diff --git a/src/main/java/net/minecraft/network/protocol/game/ServerboundEditBookPacket.java b/src/main/java/net/minecraft/network/protocol/game/ServerboundEditBookPacket.java
index ed61767a64cdce37dc7c226ebd0d693a60de24a9..f634a830a2b58a419e84f969bd53eeae4f4513bb 100644
--- a/src/main/java/net/minecraft/network/protocol/game/ServerboundEditBookPacket.java
+++ b/src/main/java/net/minecraft/network/protocol/game/ServerboundEditBookPacket.java
@@ -16,9 +16,9 @@ public record ServerboundEditBookPacket(int slot, List<String> pages, Optional<S
     public static final StreamCodec<FriendlyByteBuf, ServerboundEditBookPacket> STREAM_CODEC = StreamCodec.composite(
         ByteBufCodecs.VAR_INT,
         ServerboundEditBookPacket::slot,
-        ByteBufCodecs.stringUtf8(8192).apply(ByteBufCodecs.list(200)),
+        ByteBufCodecs.stringUtf8(net.minecraft.world.item.component.WritableBookContent.PAGE_EDIT_LENGTH).apply(ByteBufCodecs.list(net.minecraft.world.item.component.WritableBookContent.MAX_PAGES)), // Paper - limit books
         ServerboundEditBookPacket::pages,
-        ByteBufCodecs.stringUtf8(128).apply(ByteBufCodecs::optional),
+        ByteBufCodecs.stringUtf8(net.minecraft.world.item.component.WrittenBookContent.TITLE_MAX_LENGTH).apply(ByteBufCodecs::optional), // Paper - limit books
         ServerboundEditBookPacket::title,
         ServerboundEditBookPacket::new
     );
diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index ce06a41d98bafc878918507404bd5d6cabc45776..aff0f55623365130f079818af9d6a2e448cfe342 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -1043,6 +1043,43 @@ public class ServerGamePacketListenerImpl extends ServerCommonPacketListenerImpl
 
     @Override
     public void handleEditBook(ServerboundEditBookPacket packet) {
+        // Paper start - Book size limits
+        if (!this.cserver.isPrimaryThread()) {
+            final List<String> pageList = packet.pages();
+            long byteTotal = 0;
+            final int maxBookPageSize = io.papermc.paper.configuration.GlobalConfiguration.get().itemValidation.bookSize.pageMax;
+            final double multiplier = Math.clamp(io.papermc.paper.configuration.GlobalConfiguration.get().itemValidation.bookSize.totalMultiplier, 0.3D, 1D);
+            long byteAllowed = maxBookPageSize;
+            for (final String page : pageList) {
+                final int byteLength = page.getBytes(java.nio.charset.StandardCharsets.UTF_8).length;
+                byteTotal += byteLength;
+                final int length = page.length();
+                int multiByteCharacters = 0;
+                if (byteLength != length) {
+                    // Count the number of multi byte characters
+                    for (final char c : page.toCharArray()) {
+                        if (c > 127) {
+                            multiByteCharacters++;
+                        }
+                    }
+                }
+
+                // Allow pages with fewer characters to consume less of the allowed byte quota
+                byteAllowed += maxBookPageSize * Math.clamp((double) length / 255D, 0.1D, 1) * multiplier;
+
+                if (multiByteCharacters > 1) {
+                    // Penalize multibyte characters
+                    byteAllowed -= multiByteCharacters;
+                }
+            }
+
+            if (byteTotal > byteAllowed) {
+                ServerGamePacketListenerImpl.LOGGER.warn("{} tried to send a book too large. Book size: {} - Allowed: {} - Pages: {}", this.player.getScoreboardName(), byteTotal, byteAllowed, pageList.size());
+                this.disconnect(Component.literal("Book too large!"));
+                return;
+            }
+        }
+        // Paper end - Book size limits
         // CraftBukkit start
         if (this.lastBookTick + 20 > MinecraftServer.currentTick) {
             this.disconnect(Component.literal("Book edited too quickly!"));