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/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
index 80cedd5221d3c0dc475c631113e8782507067cb0..3a991a6ef6a8c3150bdc557219424cf13f1dc0cc 100644
--- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
@@ -2041,6 +2041,21 @@ public class ServerPlayer extends Player {
 
         this.camera = (Entity) (entity == null ? this : entity);
         if (entity1 != this.camera) {
+            // Paper start - Add PlayerStartSpectatingEntityEvent and PlayerStopSpectatingEntity
+            if (this.camera == this) {
+                com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent playerStopSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStopSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity());
+                if (!playerStopSpectatingEntityEvent.callEvent()) {
+                    this.camera = entity1; // rollback camera entity again
+                    return;
+                }
+            } else {
+                com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent playerStartSpectatingEntityEvent = new com.destroystokyo.paper.event.player.PlayerStartSpectatingEntityEvent(this.getBukkitEntity(), entity1.getBukkitEntity(), entity.getBukkitEntity());
+                if (!playerStartSpectatingEntityEvent.callEvent()) {
+                    this.camera = entity1; // rollback camera entity again
+                    return;
+                }
+            }
+            // Paper end - Add PlayerStartSpectatingEntityEvent and PlayerStopSpectatingEntity
             Level world = this.camera.level();
 
             if (world instanceof ServerLevel) {