Code/net/minecraft/server/network/LegacyQueryHandler.java

package net.minecraft.server.network;

import com.mojang.logging.LogUtils;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.net.SocketAddress;
import java.util.Locale;
import net.minecraft.server.ServerInfo;
import org.slf4j.Logger;

public class LegacyQueryHandler extends ChannelInboundHandlerAdapter {
    private static final Logger LOGGER = LogUtils.getLogger();
    private final ServerInfo server;

    public LegacyQueryHandler(ServerInfo p_298392_) {
        this.server = p_298392_;
    }

    @Override
    public void channelRead(ChannelHandlerContext p_9686_, Object p_9687_) {
        ByteBuf bytebuf = (ByteBuf)p_9687_;
        bytebuf.markReaderIndex();
        boolean flag = true;

        try {
            try {
                if (bytebuf.readUnsignedByte() != 254) {
                    return;
                }

                SocketAddress socketaddress = p_9686_.channel().remoteAddress();
                int i = bytebuf.readableBytes();
                if (i == 0) {
                    LOGGER.debug("Ping: (<1.3.x) from {}", socketaddress);
                    String s = createVersion0Response(this.server);
                    sendFlushAndClose(p_9686_, createLegacyDisconnectPacket(p_9686_.alloc(), s));
                } else {
                    if (bytebuf.readUnsignedByte() != 1) {
                        return;
                    }

                    if (bytebuf.isReadable()) {
                        if (!readCustomPayloadPacket(bytebuf)) {
                            return;
                        }

                        LOGGER.debug("Ping: (1.6) from {}", socketaddress);
                    } else {
                        LOGGER.debug("Ping: (1.4-1.5.x) from {}", socketaddress);
                    }

                    String s1 = createVersion1Response(this.server);
                    sendFlushAndClose(p_9686_, createLegacyDisconnectPacket(p_9686_.alloc(), s1));
                }

                bytebuf.release();
                flag = false;
            } catch (RuntimeException runtimeexception) {
            }
        } finally {
            if (flag) {
                bytebuf.resetReaderIndex();
                p_9686_.channel().pipeline().remove(this);
                p_9686_.fireChannelRead(p_9687_);
            }
        }
    }

    private static boolean readCustomPayloadPacket(ByteBuf p_297429_) {
        short short1 = p_297429_.readUnsignedByte();
        if (short1 != 250) {
            return false;
        } else {
            String s = LegacyProtocolUtils.readLegacyString(p_297429_);
            if (!"MC|PingHost".equals(s)) {
                return false;
            } else {
                int i = p_297429_.readUnsignedShort();
                if (p_297429_.readableBytes() != i) {
                    return false;
                } else {
                    short short2 = p_297429_.readUnsignedByte();
                    if (short2 < 73) {
                        return false;
                    } else {
                        String s1 = LegacyProtocolUtils.readLegacyString(p_297429_);
                        int j = p_297429_.readInt();
                        return j <= 65535;
                    }
                }
            }
        }
    }

    private static String createVersion0Response(ServerInfo p_300881_) {
        return String.format(Locale.ROOT, "%s\u00a7%d\u00a7%d", p_300881_.getMotd(), p_300881_.getPlayerCount(), p_300881_.getMaxPlayers());
    }

    private static String createVersion1Response(ServerInfo p_297753_) {
        return String.format(
            Locale.ROOT,
            "\u00a71\u0000%d\u0000%s\u0000%s\u0000%d\u0000%d",
            127,
            p_297753_.getServerVersion(),
            p_297753_.getMotd(),
            p_297753_.getPlayerCount(),
            p_297753_.getMaxPlayers()
        );
    }

    private static void sendFlushAndClose(ChannelHandlerContext p_9681_, ByteBuf p_9682_) {
        p_9681_.pipeline().firstContext().writeAndFlush(p_9682_).addListener(ChannelFutureListener.CLOSE);
    }

    private static ByteBuf createLegacyDisconnectPacket(ByteBufAllocator p_298175_, String p_298389_) {
        ByteBuf bytebuf = p_298175_.buffer();
        bytebuf.writeByte(255);
        LegacyProtocolUtils.writeLegacyString(bytebuf, p_298389_);
        return bytebuf;
    }
}