PaperMC/nms-patches/HandshakeListener.patch

--- a/net/minecraft/server/HandshakeListener.java
+++ b/net/minecraft/server/HandshakeListener.java
@@ -1,7 +1,17 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import java.net.InetAddress;
+import java.util.HashMap;
+// CraftBukkit end
+
 public class HandshakeListener implements PacketHandshakingInListener {
 
+    // CraftBukkit start - add fields
+    private static final HashMap<InetAddress, Long> throttleTracker = new HashMap<InetAddress, Long>();
+    private static int throttleCounter = 0;
+    // CraftBukkit end
+
     private final MinecraftServer a;
     private final NetworkManager b;
 
@@ -16,6 +26,41 @@
             this.b.setProtocol(EnumProtocol.LOGIN);
             ChatMessage chatmessage;
 
+            // CraftBukkit start - Connection throttle
+            try {
+                long currentTime = System.currentTimeMillis();
+                long connectionThrottle = MinecraftServer.getServer().server.getConnectionThrottle();
+                InetAddress address = ((java.net.InetSocketAddress) this.b.getSocketAddress()).getAddress();
+
+                synchronized (throttleTracker) {
+                    if (throttleTracker.containsKey(address) && !"127.0.0.1".equals(address.getHostAddress()) && currentTime - throttleTracker.get(address) < connectionThrottle) {
+                        throttleTracker.put(address, currentTime);
+                        chatmessage = new ChatMessage("Connection throttled! Please wait before reconnecting.");
+                        this.b.sendPacket(new PacketLoginOutDisconnect(chatmessage));
+                        this.b.close(chatmessage);
+                        return;
+                    }
+
+                    throttleTracker.put(address, currentTime);
+                    throttleCounter++;
+                    if (throttleCounter > 200) {
+                        throttleCounter = 0;
+
+                        // Cleanup stale entries
+                        java.util.Iterator iter = throttleTracker.entrySet().iterator();
+                        while (iter.hasNext()) {
+                            java.util.Map.Entry<InetAddress, Long> entry = (java.util.Map.Entry) iter.next();
+                            if (entry.getValue() > connectionThrottle) {
+                                iter.remove();
+                            }
+                        }
+                    }
+                }
+            } catch (Throwable t) {
+                org.apache.logging.log4j.LogManager.getLogger().debug("Failed to check connection throttle", t);
+            }
+            // CraftBukkit end
+
             if (packethandshakinginsetprotocol.c() > 393) {
                 chatmessage = new ChatMessage("multiplayer.disconnect.outdated_server", new Object[] { "1.13"});
                 this.b.sendPacket(new PacketLoginOutDisconnect(chatmessage));
@@ -26,6 +71,7 @@
                 this.b.close(chatmessage);
             } else {
                 this.b.setPacketListener(new LoginListener(this.a, this.b));
+                ((LoginListener) this.b.i()).hostname = packethandshakinginsetprotocol.hostname + ":" + packethandshakinginsetprotocol.port; // CraftBukkit - set hostname
             }
             break;