Compromise on warning of excessive velocity sets

We have long been receiving feedback about our warning messages when
excessive velocities are set on entities. We have, for the most part,
ignored much of this feedback because these warnings can be vital in
identifying the cause of a watchdog crash. These crashes would otherwise
be more difficult to identify without this information.

However, in many cases these warnings are unnecessarily verbose as the
server handles these excessive sets itself without user intervention.

As a compromise, we will only warn the user as part of a watchdog crash
log, and we will only include the most recent occurrence. This commit
represents a first effort on this front. It may need to be tweaked later
to provide more relevant information, such as the time it occurred,
and/or not printing the warning at all if the occurrence was a certain
time period ago.

Spigot-Server-Patches/Add-velocity-warnings.patch

@@ -4,6 +4,18 @@ 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 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -0,0 +0,0 @@ public final class CraftServer implements Server {
+     private final UUID invalidUserUUID = UUID.nameUUIDFromBytes("InvalidUsername".getBytes(Charsets.UTF_8));
+     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 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
@@ -14,11 +26,35 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      public void setVelocity(Vector vel) {
 +        // Paper start - Warn server owners when plugins try to set super high velocities
 +        if (!(this instanceof org.bukkit.entity.Projectile) && (vel.getX() > 4 || vel.getX() < -4 || vel.getY() > 4 || vel.getY() < -4 || vel.getZ() > 4 || vel.getZ() < -4)) {
-+            getServer().getLogger().warning("Excessive velocity set detected: tried to set velocity of entity #" + getEntityId() + " to (" + vel.getX() + "," + vel.getY() + "," + vel.getZ() + ").");
-+            Thread.dumpStack();
++            CraftServer.excessiveVelEx = new Exception("Excessive velocity set detected: tried to set velocity of entity #" + getEntityId() + " to (" + vel.getX() + "," + vel.getY() + "," + vel.getZ() + ").");
 +        }
 +        // Paper end
          entity.motX = vel.getX();
          entity.motY = vel.getY();
          entity.motZ = vel.getZ();
+diff --git a/src/main/java/org/spigotmc/WatchdogThread.java b/src/main/java/org/spigotmc/WatchdogThread.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/spigotmc/WatchdogThread.java
++++ b/src/main/java/org/spigotmc/WatchdogThread.java
+@@ -0,0 +0,0 @@ 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.blockLocation);
+                 }
+-                //
++                // 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 );
 --