From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Caleb Bassham <caleb.bassham@gmail.com>
Date: Fri, 28 Sep 2018 02:32:19 -0500
Subject: [PATCH] Call player spectator target events and improve
 implementation

Use a proper teleport for teleporting to entities in different
worlds.

Implementation improvements authored by Spottedleaf <Spottedleaf@users.noreply.github.com>
Validate that the target entity is valid and deny spectate
requests from frozen players.

Also, make sure the entity is spawned to the client before
sending the camera packet. If the entity isn't spawned clientside
when it receives the camera packet, then the client will not
spectate the target entity.

Co-authored-by: Spottedleaf <Spottedleaf@users.noreply.github.com>

diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
index 08e2e911d726e9d306f5fcc7755ab89f94959aa3..0eb5d6a58a9794ed366d03b76f01abb673a6827c 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -1663,15 +1663,59 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
         return (Entity) (this.spectatedEntity == null ? this : this.spectatedEntity);
     }
 
-    public void setSpectatorTarget(Entity entity) {
+    public void setSpectatorTarget(Entity newSpectatorTarget) {
+        // Paper start - Add PlayerStartSpectatingEntityEvent and PlayerStopSpectatingEntity Event and improve implementation
         Entity entity1 = this.getSpecatorTarget();
 
-        this.spectatedEntity = (Entity) (entity == null ? this : entity);
-        if (entity1 != this.spectatedEntity) {
-            this.playerConnection.sendPacket(new PacketPlayOutCamera(this.spectatedEntity));
-            this.playerConnection.a(this.spectatedEntity.locX(), this.spectatedEntity.locY(), this.spectatedEntity.locZ(), this.yaw, this.pitch, TeleportCause.SPECTATE); // CraftBukkit
+        if (newSpectatorTarget == null) {
+            newSpectatorTarget = this;
         }
 
+        if (entity1 == newSpectatorTarget) return; // new spec target is the current spec target
+
+        if (newSpectatorTarget == this) {
+            com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent playerStopSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity());
+
+            if (!playerStopSpectatingEntityEvent.callEvent()) {
+                return;
+            }
+        } else {
+            com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent playerStartSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity(), newSpectatorTarget.getBukkitEntity());
+
+            if (!playerStartSpectatingEntityEvent.callEvent()) {
+                return;
+            }
+        }
+        // Validate
+        if (newSpectatorTarget != this) {
+            if (newSpectatorTarget.dead || newSpectatorTarget.shouldBeRemoved || !newSpectatorTarget.valid || newSpectatorTarget.world == null) {
+                MinecraftServer.LOGGER.info("Blocking player " + this.toString() + " from spectating invalid entity " + newSpectatorTarget.toString());
+                return;
+            }
+            if (this.isFrozen()) {
+                // use debug: clients might maliciously spam this
+                MinecraftServer.LOGGER.debug("Blocking frozen player " + this.toString() + " from spectating entity " + newSpectatorTarget.toString());
+                return;
+            }
+        }
+
+        this.spectatedEntity = newSpectatorTarget; // only set after validating state
+
+        if (newSpectatorTarget != this) {
+            // Make sure we're in the right place
+            this.ejectPassengers(); // teleport can fail if we have passengers...
+            this.getBukkitEntity().teleport(new Location(newSpectatorTarget.getWorld().getWorld(), newSpectatorTarget.locX(), newSpectatorTarget.locY(), newSpectatorTarget.locZ(), this.yaw, this.pitch), TeleportCause.SPECTATE); // Correctly handle cross-world entities from api calls by using CB teleport
+
+            // Make sure we're tracking the entity before sending
+            PlayerChunkMap.EntityTracker tracker = ((WorldServer)newSpectatorTarget.world).getChunkProvider().playerChunkMap.trackedEntities.get(newSpectatorTarget.getId());
+            if (tracker != null) { // dumb plugins...
+                tracker.updatePlayer(this);
+            }
+        } else {
+            this.playerConnection.teleport(this.spectatedEntity.locX(), this.spectatedEntity.locY(), this.spectatedEntity.locZ(), this.yaw, this.pitch, TeleportCause.SPECTATE); // CraftBukkit
+        }
+        this.playerConnection.sendPacket(new PacketPlayOutCamera(newSpectatorTarget));
+        // Paper end
     }
 
     @Override
diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
index 6e3d66ab776146e2204539319412ea8bde17d58a..bb46e757b560d1bfec5c84d59971b51d9aa90bd8 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
@@ -1204,6 +1204,7 @@ public class PlayerConnection implements PacketListenerPlayIn {
     }
 
     // CraftBukkit start - Delegate to teleport(Location)
+    public final void teleport(double d0, double d1, double d2, float f, float f1, PlayerTeleportEvent.TeleportCause cause) { this.a(d0, d1, d2, f, f1, cause); } // Paper - OBFHELPER
     public void a(double d0, double d1, double d2, float f, float f1, PlayerTeleportEvent.TeleportCause cause) {
         this.a(d0, d1, d2, f, f1, Collections.<PacketPlayOutPosition.EnumPlayerTeleportFlags>emptySet(), cause);
     }