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 8719381d942789bf80f4b0394cec12e7394ce871..f64a83a6a9f8aaa0c1bbd6c2e3d0af28c06cbbd6 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -1696,15 +1696,59 @@ 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 17247eb9c08de10da50b94d65ac3f05453805137..f0d8388d6ac0ed5546d34f628a6b2ba6c56b1c61 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
@@ -1133,6 +1133,7 @@ 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);
     }