minecraft server pinger

ServerStatus.java

package pulutalauncher.util.server;

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import javax.imageio.ImageIO;

public class ServerStatus implements Serializable {

	private static final long serialVersionUID = 1L;

	public static class Player implements Serializable {

		private static final long serialVersionUID = 1L;

		private String name;
		private String id;

		public Player(String name, String id) {
			this.name = name;
			this.id = id;
		}

		public String getName() {
			return name;
		}

		public String getId() {
			return id;
		}

		@Override
		public String toString() {
			return "[name=" + name + ", id=" + id + "]";
		}

	}

	private String description;
	private int maxPlayers;
	private int onlinePlayers;
	private String version;
	private String protocol;
	private int ping;
	private transient BufferedImage favicon;

	public ServerStatus(String description, int maxPlayers, int onlinePlayers, String version, String protocol, BufferedImage favicon, int ping) {
		this.description = description;
		this.maxPlayers = maxPlayers;
		this.onlinePlayers = onlinePlayers;
		this.version = version;
		this.protocol = protocol;
		this.favicon = favicon;
		this.ping = ping;
	}

	public String getDescription() {
		return description;
	}

	public int getMaxPlayers() {
		return maxPlayers;
	}

	public int getOnlinePlayers() {
		return onlinePlayers;
	}

	public String getVersion() {
		return version;
	}

	public String getProtocol() {
		return protocol;
	}

	public BufferedImage getFavicon() {
		return favicon;
	}

	public int getPing() {
		return ping;
	}

	@Override
	public String toString() {
		return "ServerStatus [description=" + description + ", maxPlayers=" + maxPlayers + ", onlinePlayers=" + onlinePlayers + ", version=" + version + ", protocol=" + protocol + ", favicon=" + favicon + ", ping=" + ping + "]";
	}

	private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
		in.defaultReadObject();
		favicon = ImageIO.read(in);
	}

	private void writeObject(ObjectOutputStream out) throws IOException {
		out.defaultWriteObject();
		ImageIO.write(favicon, "PNG", out);
	}

}

ServerStatusFetcher.java

package pulutalauncher.util.server;

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.Objects;
import javax.imageio.ImageIO;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.json.JSONException;
import org.json.JSONObject;
import com.github.to2mbn.jyal.util.Base64;

public class ServerStatusFetcher {

	private static final Logger LOGGER = LogManager.getFormatterLogger();
	private static final String FAVICON_HEADER = "data:image/png;base64,";

	private String hostName;
	private int port;
	private int timeout;

	public ServerStatusFetcher(String hostName) {
		this(hostName, 25565, 8000);
	}

	public ServerStatusFetcher(String hostName, int port) {
		this(hostName, port, 8000);
	}

	public ServerStatusFetcher(String hostName, int port, int timeout) {
		Objects.requireNonNull(hostName);
		if (port < 0) {
			throw new IllegalArgumentException("port<0");
		}
		this.hostName = hostName;
		this.port = port;
		this.timeout = timeout;
	}

	public ServerStatus fetch() throws IOException {
		LOGGER.debug("resolving host %s, port %d", hostName, port);
		InetSocketAddress host = new InetSocketAddress(hostName, port);

		LOGGER.debug("fetching server status: %s", host);
		byte[] handshake = generateHandshakePackage(host);
		byte[] responseData;
		long t0 = System.currentTimeMillis();
		try (Socket socket = new Socket()) {
			socket.setSoTimeout(timeout);
			socket.connect(host, timeout);

			try (DataOutputStream out = new DataOutputStream(socket.getOutputStream()); DataInputStream in = new DataInputStream(socket.getInputStream())) {
				LOGGER.debug("send handshake packet, length %d", handshake.length);
				writeVarInt(out, handshake.length); // prepend size
				out.write(handshake); // write handshake packet
				out.writeByte(0x01); // size is only 1
				out.writeByte(0x00); // packet id for ping

				int size = readVarInt(in); // size of packet
				LOGGER.debug("packet size: %d", size);
				int id = readVarInt(in); // packet id
				if (id == -1)
					throw new IOException("Premature end of stream.");
				if (id != 0x00)
					throw new IOException("Invalid packet id:" + id); // we want a status response

				int length = readVarInt(in); // length of json string
				LOGGER.debug("data length: %d", length);
				if (length == -1)
					throw new IOException("Premature end of stream.");
				if (length == 0)
					throw new IOException("Invalid string length.");

				responseData = new byte[length];
				in.readFully(responseData); // read json string
			}
		}
		long t1 = System.currentTimeMillis();
		String response = new String(responseData, "UTF-8");
		LOGGER.debug("server status response from %s: %s", host, response);

		try {
			return handle(new JSONObject(response), t1 - t0);
		} catch (JSONException | IOException e) {
			throw new IOException("failed to handle response", e);
		}
	}

	private ServerStatus handle(JSONObject response, long ping) throws JSONException, IOException {
		String description = response.optString("description", null);

		int maxPlayers = 0;
		int onlinePlayers = 0;
		if (response.has("players")) {
			JSONObject players = response.getJSONObject("players");
			maxPlayers = players.optInt("max");
			onlinePlayers = players.optInt("online");
		}

		String protocol = null;
		String name = null;
		if (response.has("version")) {
			JSONObject version = response.getJSONObject("version");
			protocol = version.optString("protocol", null);
			name = version.optString("name", null);
		}

		BufferedImage favicon = null;
		if (response.has("favicon")) {
			favicon = getFavicon(response.getString("favicon"));
		}

		return new ServerStatus(description, maxPlayers, onlinePlayers, name, protocol, favicon, (int) ping);
	}

	private BufferedImage getFavicon(String favicon) throws IOException {
		if (!favicon.startsWith(FAVICON_HEADER)) {
			LOGGER.warn("bad favicon header: %s", favicon);
			throw new IOException("bad favicon header");
		}
		String base64encoded = favicon.substring(FAVICON_HEADER.length());
		byte[] decoded = Base64.decode(base64encoded.toCharArray());
		return ImageIO.read(new ByteArrayInputStream(decoded));
	}

	private byte[] generateHandshakePackage(InetSocketAddress host) throws IOException {
		ByteArrayOutputStream bout = new ByteArrayOutputStream();
		DataOutputStream out = new DataOutputStream(bout);
		out.writeByte(0x00); // packet id for handshake
		writeVarInt(out, 4); // protocol version
		writeVarInt(out, host.getHostString().length()); // host length
		out.writeBytes(host.getHostString()); // host string
		out.writeShort(host.getPort()); // port
		writeVarInt(out, 1); // state (1 for handshake)
		return bout.toByteArray();
	}

	private int readVarInt(DataInputStream in) throws IOException {
		int i = 0;
		int j = 0;
		for (;;) {
			int k = in.readByte();
			i |= (k & 0x7F) << j++ * 7;
			if (j > 5) {
				throw new IOException("VarInt too big: " + j);
			}
			if ((k & 0x80) != 128) {
				break;
			}
		}
		return i;
	}

	private void writeVarInt(DataOutputStream out, int paramInt) throws IOException {
		for (;;) {
			if ((paramInt & 0xFFFFFF80) == 0) {
				out.writeByte(paramInt);
				return;
			}

			out.writeByte(paramInt & 0x7F | 0x80);
			paramInt >>>= 7;
		}
	}

}