add packet limiter for incoming packets

proxy/src/main/java/net/md_5/bungee/conf/Configuration.java

@@ -69,6 +69,7 @@ public class Configuration implements ProxyConfig
     private boolean preventProxyConnections;
     private boolean forgeSupport;
     private boolean rejectTransfers;
+    private int maxPacketsPerSecond = 2000;
 
     public void load()
     {
@@ -105,6 +106,7 @@ public void load()
         preventProxyConnections = adapter.getBoolean( "prevent_proxy_connections", preventProxyConnections );
         forgeSupport = adapter.getBoolean( "forge_support", forgeSupport );
         rejectTransfers = adapter.getBoolean( "reject_transfers", rejectTransfers );
+        maxPacketsPerSecond = adapter.getInt( "max_packets_per_second", maxPacketsPerSecond );
 
         disabledCommands = new CaseInsensitiveSet( (Collection<String>) adapter.getList( "disabled_commands", Arrays.asList( "disabledcommandhere" ) ) );
 

proxy/src/main/java/net/md_5/bungee/netty/HandlerBoss.java

@@ -10,6 +10,7 @@
 import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.util.logging.Level;
+import lombok.Setter;
 import net.md_5.bungee.api.ProxyServer;
 import net.md_5.bungee.connection.CancelSendSignal;
 import net.md_5.bungee.connection.InitialHandler;
@@ -18,6 +19,7 @@
 import net.md_5.bungee.protocol.OverflowPacketException;
 import net.md_5.bungee.protocol.PacketWrapper;
 import net.md_5.bungee.protocol.Protocol;
+import net.md_5.bungee.util.PacketLimiter;
 import net.md_5.bungee.util.QuietException;
 
 /**
@@ -28,6 +30,8 @@
 public class HandlerBoss extends ChannelInboundHandlerAdapter
 {
 
+    @Setter
+    private PacketLimiter limiter;
     private ChannelWrapper channel;
     private PacketHandler handler;
     private boolean healthCheck;
@@ -80,6 +84,11 @@ public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exceptio
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
     {
+        if ( limiter != null )
+        {
+            limiter.received();
+        }
+
         if ( msg instanceof HAProxyMessage )
         {
             HAProxyMessage proxy = (HAProxyMessage) msg;

proxy/src/main/java/net/md_5/bungee/netty/PipelineUtils.java

@@ -51,6 +51,7 @@
 import net.md_5.bungee.protocol.Varint21FrameDecoder;
 import net.md_5.bungee.protocol.Varint21LengthFieldExtraBufPrepender;
 import net.md_5.bungee.protocol.Varint21LengthFieldPrepender;
+import net.md_5.bungee.util.PacketLimiter;
 
 public class PipelineUtils
 {
@@ -82,7 +83,14 @@ protected void initChannel(Channel ch) throws Exception
             ch.pipeline().addAfter( FRAME_DECODER, PACKET_DECODER, new MinecraftDecoder( Protocol.HANDSHAKE, true, ProxyServer.getInstance().getProtocolVersion() ) );
             ch.pipeline().addAfter( FRAME_PREPENDER, PACKET_ENCODER, new MinecraftEncoder( Protocol.HANDSHAKE, true, ProxyServer.getInstance().getProtocolVersion() ) );
             ch.pipeline().addBefore( FRAME_PREPENDER, LEGACY_KICKER, legacyKicker );
-            ch.pipeline().get( HandlerBoss.class ).setHandler( new InitialHandler( BungeeCord.getInstance(), listener ) );
+
+            HandlerBoss handlerBoss = ch.pipeline().get( HandlerBoss.class );
+            handlerBoss.setHandler( new InitialHandler( BungeeCord.getInstance(), listener ) );
+            int packetLimit = BungeeCord.getInstance().getConfig().getMaxPacketsPerSecond();
+            if ( packetLimit > 0 )
+            {
+                handlerBoss.setLimiter( new PacketLimiter( packetLimit ) );
+            }
 
             if ( listener.isProxyProtocol() )
             {

proxy/src/main/java/net/md_5/bungee/util/PacketLimiter.java

@@ -0,0 +1,26 @@
+package net.md_5.bungee.util;
+
+import lombok.RequiredArgsConstructor;
+
+@RequiredArgsConstructor
+public class PacketLimiter
+{
+    // max amount of packets allowed per second
+    private final int limit;
+    private int counter;
+    private long nextSecond;
+
+    public void received()
+    {
+        if ( ++counter == limit )
+        {
+            long now = System.currentTimeMillis();
+            if ( nextSecond > now )
+            {
+                throw new QuietException( "exceeded packet limit" );
+            }
+            nextSecond = now + 1000;
+            counter = 0;
+        }
+    }
+}