Port Sponge's heap dump command feature to Paper

To dump the server heap, run the following command:
`/paper heap`

This is added with the intent that it is useful for administrators and
developers to more easily identify and resolve memory leaks. Both by examining
these dumps themselves and by more easily allowing them to send them to
knowledgable parties.

This is a nearly line-for-line port of the same Sponge feature. So all
credit for the idea and implementation belongs to the that team.

Specifically the following commits:
be08be04b0
5e10a1b795

Spigot-Server-Patches/Paper-config-files.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Paper config files
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperCommand.java b/src/main/java/com/destroystokyo/paper/PaperCommand.java
 new file mode 100644
-index 000000000..2096d3f97
+index 000000000..cd67ab2bb
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/PaperCommand.java
 @@ -0,0 +0,0 @@
@@ -17,15 +17,18 @@ index 000000000..2096d3f97
 +import org.bukkit.ChatColor;
 +import org.bukkit.command.Command;
 +import org.bukkit.command.CommandSender;
++import org.bukkit.craftbukkit.CraftServer;
 +
 +import java.io.File;
++import java.time.LocalDateTime;
++import java.time.format.DateTimeFormatter;
 +
 +public class PaperCommand extends Command {
 +
 +    public PaperCommand(String name) {
 +        super(name);
 +        this.description = "Paper related commands";
-+        this.usageMessage = "/paper [reload | version]";
++        this.usageMessage = "/paper [heap | reload | version]";
 +        this.setPermission("bukkit.command.paper");
 +    }
 +
@@ -38,26 +41,46 @@ index 000000000..2096d3f97
 +            return false;
 +        }
 +
-+        if (args[0].equals("reload")) {
-+            Command.broadcastCommandMessage(sender, ChatColor.RED + "Please note that this command is not supported and may cause issues.");
-+            Command.broadcastCommandMessage(sender, ChatColor.RED + "If you encounter any issues please use the /stop command to restart your server.");
-+
-+            MinecraftServer console = MinecraftServer.getServer();
-+            com.destroystokyo.paper.PaperConfig.init((File) console.options.valueOf("paper-settings"));
-+            for (WorldServer world : console.worlds) {
-+                world.paperConfig.init();
-+            }
-+            console.server.reloadCount++;
-+
-+            Command.broadcastCommandMessage(sender, ChatColor.GREEN + "Paper config reload complete.");
-+        }
-+
-+        if (args[0].equals("version")) {
-+            org.bukkit.Bukkit.getServer().getCommandMap().getCommand("version").execute(sender, commandLabel, new String[0]);
++        switch (args[0])  {
++            case "heap":
++                dumpHeap(sender);
++                break;
++            case "reload":
++                doReload(sender);
++                break;
++            case "ver":
++            case "version":
++                org.bukkit.Bukkit.getServer().getCommandMap().getCommand("version").execute(sender, commandLabel, new String[0]);
++                break;
++            default:
++                sender.sendMessage(ChatColor.RED + "Usage: " + usageMessage);
++                return false;
 +        }
 +
 +        return true;
 +    }
++
++    private void dumpHeap(CommandSender sender) {
++        File file = new File(new File(new File("."), "dumps"),
++                "heap-dump-" + DateTimeFormatter.ofPattern("yyyy-MM-dd_HH.mm.ss").format(LocalDateTime.now()) + "-server.bin");
++        Command.broadcastCommandMessage(sender, ChatColor.YELLOW + "Writing JVM heap data to " + file);
++        CraftServer.dumpHeap(file);
++        Command.broadcastCommandMessage(sender, ChatColor.GREEN + "Heap dump complete");
++    }
++
++    private void doReload(CommandSender sender) {
++        Command.broadcastCommandMessage(sender, ChatColor.RED + "Please note that this command is not supported and may cause issues.");
++        Command.broadcastCommandMessage(sender, ChatColor.RED + "If you encounter any issues please use the /stop command to restart your server.");
++
++        MinecraftServer console = MinecraftServer.getServer();
++        com.destroystokyo.paper.PaperConfig.init((File) console.options.valueOf("paper-settings"));
++        for (WorldServer world : console.worlds) {
++            world.paperConfig.init();
++        }
++        console.server.reloadCount++;
++
++        Command.broadcastCommandMessage(sender, ChatColor.GREEN + "Paper config reload complete.");
++    }
 +}
 diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 new file mode 100644
@@ -347,7 +370,7 @@ index f5d387511..fd204ad7a 100644
          this.world = new CraftWorld((WorldServer) this, gen, env);
          this.ticksPerAnimalSpawns = this.getServer().getTicksPerAnimalSpawns(); // CraftBukkit
 diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
-index 67ee8c55e..51981c386 100644
+index 67ee8c55e..ad075615a 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 {
@@ -374,6 +397,30 @@ index 67ee8c55e..51981c386 100644
          overrideAllCommandBlockCommands = commandsConfiguration.getStringList("command-block-overrides").contains("*");
  
          int pollCount = 0;
+@@ -0,0 +0,0 @@ public final class CraftServer implements Server {
+     {
+         return spigot;
+     }
++
++    // Paper start
++    @SuppressWarnings({"rawtypes", "unchecked"})
++    public static void dumpHeap(File file) {
++        try {
++            if (file.getParentFile() != null) {
++                file.getParentFile().mkdirs();
++            }
++
++            Class clazz = Class.forName("com.sun.management.HotSpotDiagnosticMXBean");
++            javax.management.MBeanServer server = java.lang.management.ManagementFactory.getPlatformMBeanServer();
++            Object hotspotMBean = java.lang.management.ManagementFactory.newPlatformMXBeanProxy(server, "com.sun.management:type=HotSpotDiagnostic", clazz);
++            java.lang.reflect.Method m = clazz.getMethod("dumpHeap", String.class, boolean.class);
++            m.invoke(hotspotMBean, file.getPath(), true);
++        } catch (Throwable t) {
++            Bukkit.getLogger().severe("Could not write heap to " + file);
++        }
++    }
++    // Paper end
+ }
 diff --git a/src/main/java/org/bukkit/craftbukkit/Main.java b/src/main/java/org/bukkit/craftbukkit/Main.java
 index a151451d5..0c5862a3f 100644
 --- a/src/main/java/org/bukkit/craftbukkit/Main.java