From 85717e8f26f10adcd7edff6d7eb6af12f850e5ac Mon Sep 17 00:00:00 2001
From: Joseph Hirschfeld <joe@ibj.io>
Date: Thu, 3 Mar 2016 02:48:12 -0600
Subject: [PATCH] Add velocity warnings


diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 19fef2496e..54864fe761 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -201,6 +201,7 @@ public final class CraftServer implements Server {
     public boolean ignoreVanillaPermissions = false;
     private final List<CraftPlayer> playerView;
     public int reloadCount;
+    public static Exception excessiveVelEx; // Paper - Velocity warnings
 
     private final class BooleanWrapper {
         private boolean value = true;
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
index 660e59ba15..466750f779 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
@@ -266,12 +266,44 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
     public void setVelocity(Vector velocity) {
         Preconditions.checkArgument(velocity != null, "velocity");
         velocity.checkFinite();
+
+        // Paper start - Warn server owners when plugins try to set super high velocities
+        if (!(this instanceof org.bukkit.entity.Projectile) && isUnsafeVelocity(velocity)) {
+            CraftServer.excessiveVelEx = new Exception("Excessive velocity set detected: tried to set velocity of entity " + entity.getName() + " id #" + getEntityId() + " to (" + velocity.getX() + "," + velocity.getY() + "," + velocity.getZ() + ").");
+        }
+        // Paper end
+
         entity.motX = velocity.getX();
         entity.motY = velocity.getY();
         entity.motZ = velocity.getZ();
         entity.velocityChanged = true;
     }
 
+    // Paper start
+    /**
+     * Checks if the given velocity is not necessarily safe in all situations.
+     * This function returning true does not mean the velocity is dangerous or to be avoided, only that it may be
+     * a detriment to performance on the server.
+     *
+     * It is not to be used as a hard rule of any sort.
+     * Paper only uses it to warn server owners in watchdog crashes.
+     *
+     * @param vel incoming velocity to check
+     * @return if the velocity has the potential to be a performance detriment
+     */
+    private static boolean isUnsafeVelocity(Vector vel) {
+        final double x = vel.getX();
+        final double y = vel.getY();
+        final double z = vel.getZ();
+
+        if (x > 4 || x < -4 || y > 4 || y < -4 || z > 4 || z < -4) {
+            return true;
+        }
+
+        return false;
+    }
+    // Paper end
+
     @Override
     public double getHeight() {
         return getHandle().length;
diff --git a/src/main/java/org/spigotmc/WatchdogThread.java b/src/main/java/org/spigotmc/WatchdogThread.java
index 8e32c4e2cd..c080a61185 100644
--- a/src/main/java/org/spigotmc/WatchdogThread.java
+++ b/src/main/java/org/spigotmc/WatchdogThread.java
@@ -76,7 +76,19 @@ public class WatchdogThread extends Thread
                     log.log( Level.SEVERE, "During the run of the server, a physics stackoverflow was supressed" );
                     log.log( Level.SEVERE, "near " + net.minecraft.server.World.lastPhysicsProblem );
                 }
-                //
+                // Paper start - Warn in watchdog if an excessive velocity was ever set
+                if ( org.bukkit.craftbukkit.CraftServer.excessiveVelEx != null )
+                {
+                    log.log( Level.SEVERE, "------------------------------" );
+                    log.log( Level.SEVERE, "During the run of the server, a plugin set an excessive velocity on an entity" );
+                    log.log( Level.SEVERE, "This may be the cause of the issue, or it may be entirely unrelated" );
+                    log.log( Level.SEVERE, org.bukkit.craftbukkit.CraftServer.excessiveVelEx.getMessage());
+                    for ( StackTraceElement stack : org.bukkit.craftbukkit.CraftServer.excessiveVelEx.getStackTrace() )
+                    {
+                        log.log( Level.SEVERE, "\t\t" + stack );
+                    }
+                }
+                // Paper end
                 log.log( Level.SEVERE, "------------------------------" );
                 log.log( Level.SEVERE, "Server thread dump (Look for plugins here before reporting to Paper!):" );
                 dumpThread( ManagementFactory.getThreadMXBean().getThreadInfo( MinecraftServer.getServer().primaryThread.getId(), Integer.MAX_VALUE ), log );
-- 
2.21.0