--- a/net/minecraft/stats/ServerRecipeBook.java
+++ b/net/minecraft/stats/ServerRecipeBook.java
@@ -4,6 +4,7 @@
 import com.mojang.logging.LogUtils;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
 import java.util.function.Consumer;
@@ -19,27 +20,35 @@
 import net.minecraft.world.item.crafting.RecipeManager;
 import org.slf4j.Logger;
 
+import org.bukkit.craftbukkit.event.CraftEventFactory; // CraftBukkit
+
 public class ServerRecipeBook extends RecipeBook {
+
     public static final String RECIPE_BOOK_TAG = "recipeBook";
     private static final Logger LOGGER = LogUtils.getLogger();
 
+    public ServerRecipeBook() {}
+
     public int addRecipes(Collection<RecipeHolder<?>> recipes, ServerPlayer player) {
         List<ResourceLocation> list = Lists.newArrayList();
         int i = 0;
+        Iterator iterator = recipes.iterator();
 
-        for (RecipeHolder<?> recipeHolder : recipes) {
-            ResourceLocation resourceLocation = recipeHolder.id();
-            if (!this.known.contains(resourceLocation) && !recipeHolder.value().isSpecial()) {
-                this.add(resourceLocation);
-                this.addHighlight(resourceLocation);
-                list.add(resourceLocation);
-                CriteriaTriggers.RECIPE_UNLOCKED.trigger(player, recipeHolder);
-                i++;
+        while (iterator.hasNext()) {
+            RecipeHolder<?> recipeholder = (RecipeHolder) iterator.next();
+            ResourceLocation minecraftkey = recipeholder.id();
+
+            if (!this.known.contains(minecraftkey) && !recipeholder.value().isSpecial() && CraftEventFactory.handlePlayerRecipeListUpdateEvent(player, minecraftkey)) { // CraftBukkit
+                this.add(minecraftkey);
+                this.addHighlight(minecraftkey);
+                list.add(minecraftkey);
+                CriteriaTriggers.RECIPE_UNLOCKED.trigger(player, recipeholder);
+                ++i;
             }
         }
 
         if (list.size() > 0) {
-            this.sendRecipes(ClientboundRecipePacket.State.ADD, player, list);
+            this.sendRecipes(ClientboundRecipePacket.Action.ADD, player, list);
         }
 
         return i;
@@ -48,71 +57,86 @@
     public int removeRecipes(Collection<RecipeHolder<?>> recipes, ServerPlayer player) {
         List<ResourceLocation> list = Lists.newArrayList();
         int i = 0;
+        Iterator iterator = recipes.iterator();
 
-        for (RecipeHolder<?> recipeHolder : recipes) {
-            ResourceLocation resourceLocation = recipeHolder.id();
-            if (this.known.contains(resourceLocation)) {
-                this.remove(resourceLocation);
-                list.add(resourceLocation);
-                i++;
+        while (iterator.hasNext()) {
+            RecipeHolder<?> recipeholder = (RecipeHolder) iterator.next();
+            ResourceLocation minecraftkey = recipeholder.id();
+
+            if (this.known.contains(minecraftkey)) {
+                this.remove(minecraftkey);
+                list.add(minecraftkey);
+                ++i;
             }
         }
 
-        this.sendRecipes(ClientboundRecipePacket.State.REMOVE, player, list);
+        this.sendRecipes(ClientboundRecipePacket.Action.REMOVE, player, list);
         return i;
     }
 
-    private void sendRecipes(ClientboundRecipePacket.State state, ServerPlayer player, List<ResourceLocation> recipes) {
+    private void sendRecipes(ClientboundRecipePacket.Action state, ServerPlayer player, List<ResourceLocation> recipes) {
+        if (player.connection == null) return; // SPIGOT-4478 during PlayerLoginEvent
         player.connection.send(new ClientboundRecipePacket(state, recipes, Collections.emptyList(), this.getBookSettings()));
     }
 
     public CompoundTag toNbt() {
-        CompoundTag compoundTag = new CompoundTag();
-        this.getBookSettings().write(compoundTag);
-        ListTag list = new ListTag();
+        CompoundTag nbttagcompound = new CompoundTag();
 
-        for (ResourceLocation resourceLocation : this.known) {
-            list.add(StringTag.valueOf(resourceLocation.toString()));
+        this.getBookSettings().write(nbttagcompound);
+        ListTag nbttaglist = new ListTag();
+        Iterator iterator = this.known.iterator();
+
+        while (iterator.hasNext()) {
+            ResourceLocation minecraftkey = (ResourceLocation) iterator.next();
+
+            nbttaglist.add(StringTag.valueOf(minecraftkey.toString()));
         }
 
-        compoundTag.put("recipes", list);
-        ListTag list1 = new ListTag();
+        nbttagcompound.put("recipes", nbttaglist);
+        ListTag nbttaglist1 = new ListTag();
+        Iterator iterator1 = this.highlight.iterator();
 
-        for (ResourceLocation resourceLocation1 : this.highlight) {
-            list1.add(StringTag.valueOf(resourceLocation1.toString()));
+        while (iterator1.hasNext()) {
+            ResourceLocation minecraftkey1 = (ResourceLocation) iterator1.next();
+
+            nbttaglist1.add(StringTag.valueOf(minecraftkey1.toString()));
         }
 
-        compoundTag.put("toBeDisplayed", list1);
-        return compoundTag;
+        nbttagcompound.put("toBeDisplayed", nbttaglist1);
+        return nbttagcompound;
     }
 
     public void fromNbt(CompoundTag tag, RecipeManager recipeManager) {
         this.setBookSettings(RecipeBookSettings.read(tag));
-        ListTag list = tag.getList("recipes", 8);
-        this.loadRecipes(list, this::add, recipeManager);
-        ListTag list1 = tag.getList("toBeDisplayed", 8);
-        this.loadRecipes(list1, this::addHighlight, recipeManager);
+        ListTag nbttaglist = tag.getList("recipes", 8);
+
+        this.loadRecipes(nbttaglist, this::add, recipeManager);
+        ListTag nbttaglist1 = tag.getList("toBeDisplayed", 8);
+
+        this.loadRecipes(nbttaglist1, this::addHighlight, recipeManager);
     }
 
     private void loadRecipes(ListTag tags, Consumer<RecipeHolder<?>> recipeConsumer, RecipeManager recipeManager) {
-        for (int i = 0; i < tags.size(); i++) {
-            String string = tags.getString(i);
+        for (int i = 0; i < tags.size(); ++i) {
+            String s = tags.getString(i);
 
             try {
-                ResourceLocation resourceLocation = new ResourceLocation(string);
-                Optional<RecipeHolder<?>> optional = recipeManager.byKey(resourceLocation);
+                ResourceLocation minecraftkey = new ResourceLocation(s);
+                Optional<RecipeHolder<?>> optional = recipeManager.byKey(minecraftkey);
+
                 if (optional.isEmpty()) {
-                    LOGGER.error("Tried to load unrecognized recipe: {} removed now.", resourceLocation);
+                    ServerRecipeBook.LOGGER.error("Tried to load unrecognized recipe: {} removed now.", minecraftkey);
                 } else {
-                    recipeConsumer.accept(optional.get());
+                    recipeConsumer.accept((RecipeHolder) optional.get());
                 }
-            } catch (ResourceLocationException var8) {
-                LOGGER.error("Tried to load improperly formatted recipe: {} removed now.", string);
+            } catch (ResourceLocationException resourcekeyinvalidexception) {
+                ServerRecipeBook.LOGGER.error("Tried to load improperly formatted recipe: {} removed now.", s);
             }
         }
+
     }
 
     public void sendInitialRecipeBook(ServerPlayer player) {
-        player.connection.send(new ClientboundRecipePacket(ClientboundRecipePacket.State.INIT, this.known, this.highlight, this.getBookSettings()));
+        player.connection.send(new ClientboundRecipePacket(ClientboundRecipePacket.Action.INIT, this.known, this.highlight, this.getBookSettings()));
     }
 }