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/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 3139c194f9b1bc3510d51a81f13ae43d00a3dc29..13edb435b3fa65b4980bd7472aa5a5196f4d5b2b 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -339,4 +339,11 @@ public class PaperConfig {
             velocitySecretKey = secret.getBytes(StandardCharsets.UTF_8);
         }
     }
+
+    public static int maxBookPageSize = 2560;
+    public static double maxBookTotalSizeMultiplier = 0.98D;
+    private static void maxBookSize() {
+        maxBookPageSize = getInt("settings.book-size.page-max", maxBookPageSize);
+        maxBookTotalSizeMultiplier = getDouble("settings.book-size.total-multiplier", maxBookTotalSizeMultiplier);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index a6ad7747396f94def688b4d2783137180dc2bb84..b1c505d3fdcc2fb3496f80bee85e4895b9069dcb 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -999,6 +999,52 @@ public class ServerGamePacketListenerImpl implements ServerGamePacketListener {
 
     @Override
     public void handleEditBook(ServerboundEditBookPacket packet) {
+        // Paper start
+        ItemStack testStack = packet.getBook();
+        if (!craftServer.isPrimaryThread() && !testStack.isEmpty() && testStack.getTag() != null) {
+            ListTag pageList = testStack.getTag().getList("pages", 8);
+            if (pageList.size() > 100) {
+                ServerGamePacketListenerImpl.LOGGER.warn(this.player.getScoreboardName() + " tried to send a book with too many pages");
+                server.scheduleOnMain(() -> this.disconnect("Book too large!"));
+                return;
+            }
+            long byteTotal = 0;
+            int maxBookPageSize = com.destroystokyo.paper.PaperConfig.maxBookPageSize;
+            double multiplier = Math.max(0.3D, Math.min(1D, com.destroystokyo.paper.PaperConfig.maxBookTotalSizeMultiplier));
+            long byteAllowed = maxBookPageSize;
+            for (int i = 0; i < pageList.size(); ++i) {
+                String testString = pageList.getString(i);
+                int byteLength = testString.getBytes(java.nio.charset.StandardCharsets.UTF_8).length;
+                if (byteLength > 256 * 4) {
+                    ServerGamePacketListenerImpl.LOGGER.warn(this.player.getScoreboardName() + " tried to send a book with with a page too large!");
+                    server.scheduleOnMain(() -> this.disconnect("Book too large!"));
+                    return;
+                }
+                byteTotal += byteLength;
+                int length = testString.length();
+                int multibytes = 0;
+                if (byteLength != length) {
+                    for (char c : testString.toCharArray()) {
+                        if (c > 127) {
+                            multibytes++;
+                        }
+                    }
+                }
+                byteAllowed += (maxBookPageSize * Math.min(1, Math.max(0.1D, (double) length / 255D))) * multiplier;
+
+                if (multibytes > 1) {
+                    // penalize MB
+                    byteAllowed -= multibytes;
+                }
+            }
+
+            if (byteTotal > byteAllowed) {
+                ServerGamePacketListenerImpl.LOGGER.warn(this.player.getScoreboardName() + " tried to send too large of a book. Book Size: " + byteTotal + " - Allowed:  "+ byteAllowed + " - Pages: " + pageList.size());
+                server.scheduleOnMain(() -> this.disconnect("Book too large!"));
+                return;
+            }
+        }
+        // Paper end
         // CraftBukkit start
         if (this.lastBookTick + 20 > MinecraftServer.currentTick) {
             this.disconnect("Book edited too quickly!");