src/main/java/cc/fascinated/common/packet/MinecraftJavaPacket.java

@@ -0,0 +1,89 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2024 Braydon (Rainnny).
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package cc.fascinated.common.packet;
+
+import lombok.NonNull;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+
+/**
+ * Represents a packet in the
+ * Minecraft Java protocol.
+ *
+ * @author Braydon
+ * @see <a href="https://wiki.vg/Protocol">Protocol Docs</a>
+ */
+public abstract class MinecraftJavaPacket {
+    /**
+     * Process this packet.
+     *
+     * @param inputStream the input stream to read from
+     * @param outputStream the output stream to write to
+     * @throws IOException if an I/O error occurs
+     */
+    public abstract void process(@NonNull DataInputStream inputStream, @NonNull DataOutputStream outputStream) throws IOException;
+
+    /**
+     * Write a variable integer to the output stream.
+     *
+     * @param outputStream the output stream to write to
+     * @param paramInt the integer to write
+     * @throws IOException if an I/O error occurs
+     */
+    protected final void writeVarInt(DataOutputStream outputStream, int paramInt) throws IOException {
+        while (true) {
+            if ((paramInt & 0xFFFFFF80) == 0) {
+                outputStream.writeByte(paramInt);
+                return;
+            }
+            outputStream.writeByte(paramInt & 0x7F | 0x80);
+            paramInt >>>= 7;
+        }
+    }
+
+    /**
+     * Read a variable integer from the input stream.
+     *
+     * @param inputStream the input stream to read from
+     * @return the integer that was read
+     * @throws IOException if an I/O error occurs
+     */
+    protected final int readVarInt(@NonNull DataInputStream inputStream) throws IOException {
+        int i = 0;
+        int j = 0;
+        while (true) {
+            int k = inputStream.readByte();
+            i |= (k & 0x7F) << j++ * 7;
+            if (j > 5) {
+                throw new RuntimeException("VarInt too big");
+            }
+            if ((k & 0x80) != 128) {
+                break;
+            }
+        }
+        return i;
+    }
+}

src/main/java/cc/fascinated/common/packet/impl/java/JavaPacketHandshakingInSetProtocol.java

@@ -0,0 +1,64 @@
+package cc.fascinated.common.packet.impl.java;
+
+import cc.fascinated.common.packet.MinecraftJavaPacket;
+import lombok.AllArgsConstructor;
+import lombok.NonNull;
+import lombok.ToString;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+
+/**
+ * This packet is sent by the client to the server to set
+ * the hostname, port, and protocol version of the client.
+ *
+ * @author Braydon
+ * @see <a href="https://wiki.vg/Protocol#Handshake">Protocol Docs</a>
+ */
+@AllArgsConstructor @ToString
+public final class JavaPacketHandshakingInSetProtocol extends MinecraftJavaPacket {
+    private static final byte ID = 0x00; // The ID of the packet
+    private static final int STATUS_HANDSHAKE = 1; // The status handshake ID
+
+    /**
+     * The hostname of the server.
+     */
+    @NonNull private final String hostname;
+
+    /**
+     * The port of the server.
+     */
+    private final int port;
+
+    /**
+     * The protocol version of the server.
+     */
+    private final int protocolVersion;
+
+    /**
+     * Process this packet.
+     *
+     * @param inputStream  the input stream to read from
+     * @param outputStream the output stream to write to
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public void process(@NonNull DataInputStream inputStream, @NonNull DataOutputStream outputStream) throws IOException {
+        try (ByteArrayOutputStream handshakeBytes = new ByteArrayOutputStream();
+             DataOutputStream handshake = new DataOutputStream(handshakeBytes)
+        ) {
+            handshake.writeByte(ID); // Write the ID of the packet
+            writeVarInt(handshake, protocolVersion); // Write the protocol version
+            writeVarInt(handshake, hostname.length()); // Write the length of the hostname
+            handshake.writeBytes(hostname); // Write the hostname
+            handshake.writeShort(port); // Write the port
+            writeVarInt(handshake, STATUS_HANDSHAKE); // Write the status handshake ID
+
+            // Write the handshake bytes to the output stream
+            writeVarInt(outputStream, handshakeBytes.size());
+            outputStream.write(handshakeBytes.toByteArray());
+        }
+    }
+}

src/main/java/cc/fascinated/common/packet/impl/java/JavaPacketStatusInStart.java

@@ -0,0 +1,62 @@
+package cc.fascinated.common.packet.impl.java;
+
+import cc.fascinated.common.packet.MinecraftJavaPacket;
+import lombok.Getter;
+import lombok.NonNull;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+
+/**
+ * This packet is sent by the client to the server to request the
+ * status of the server. The server will respond with a json object
+ * containing the server's status.
+ *
+ * @author Braydon
+ * @see <a href="https://wiki.vg/Protocol#Status_Request">Protocol Docs</a>
+ */
+@Getter
+public final class JavaPacketStatusInStart extends MinecraftJavaPacket {
+    private static final byte ID = 0x00; // The ID of the packet
+
+    /**
+     * The response json from the server, null if none.
+     */
+    private String response;
+
+    /**
+     * Process this packet.
+     *
+     * @param inputStream  the input stream to read from
+     * @param outputStream the output stream to write to
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public void process(@NonNull DataInputStream inputStream, @NonNull DataOutputStream outputStream) throws IOException {
+        // Send the status request
+        outputStream.writeByte(0x01); // Size of packet
+        outputStream.writeByte(ID);
+
+        // Read the status response
+        readVarInt(inputStream); // Size of the response
+        int id = readVarInt(inputStream);
+        if (id == -1) { // The stream was prematurely ended
+            throw new IOException("Server prematurely ended stream.");
+        } else if (id != ID) { // Invalid packet ID
+            throw new IOException("Server returned invalid packet ID.");
+        }
+
+        int length = readVarInt(inputStream); // Length of the response
+        if (length == -1) { // The stream was prematurely ended
+            throw new IOException("Server prematurely ended stream.");
+        } else if (length == 0) {
+            throw new IOException("Server returned unexpected value.");
+        }
+
+        // Get the json response
+        byte[] data = new byte[length];
+        inputStream.readFully(data);
+        response = new String(data);
+    }
+}

src/main/java/cc/fascinated/controller/ServerController.java

@@ -0,0 +1,18 @@
+package cc.fascinated.controller;
+
+import cc.fascinated.model.server.MinecraftServer;
+import cc.fascinated.service.pinger.impl.JavaMinecraftServerPinger;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping(value = "/server/")
+public class ServerController {
+
+    @ResponseBody
+    @GetMapping(value = "/{hostname}", produces = MediaType.APPLICATION_JSON_VALUE)
+    public ResponseEntity<MinecraftServer> getServer(@PathVariable String hostname) {
+        return ResponseEntity.ok(JavaMinecraftServerPinger.INSTANCE.ping(hostname, 25565));
+    }
+}

src/main/java/cc/fascinated/model/mojang/JavaServerStatusToken.java

@@ -0,0 +1,13 @@
+package cc.fascinated.model.mojang;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.ToString;
+
+/**
+ * @author Braydon
+ */
+@AllArgsConstructor @Getter @ToString
+public final class JavaServerStatusToken {
+    private final String description;
+}

src/main/java/cc/fascinated/model/server/JavaMinecraftServer.java

@@ -0,0 +1,10 @@
+package cc.fascinated.model.server;
+
+/**
+ * @author Braydon
+ */
+public final class JavaMinecraftServer extends MinecraftServer {
+    public JavaMinecraftServer(String hostname, int port, String motd) {
+        super(hostname, port, motd);
+    }
+}

src/main/java/cc/fascinated/model/server/MinecraftServer.java

@@ -0,0 +1,15 @@
+package cc.fascinated.model.server;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.ToString;
+
+/**
+ * @author Braydon
+ */
+@AllArgsConstructor @Getter @ToString
+public class MinecraftServer {
+    private final String hostname;
+    private final int port;
+    private final String motd;
+}

src/main/java/cc/fascinated/service/pinger/MinecraftServerPinger.java

@@ -0,0 +1,9 @@
+package cc.fascinated.service.pinger;
+
+/**
+ * @author Braydon
+ * @param <T> the type of server to ping
+ */
+public interface MinecraftServerPinger<T> {
+    T ping(String hostname, int port);
+}

src/main/java/cc/fascinated/service/pinger/impl/JavaMinecraftServerPinger.java

@@ -0,0 +1,53 @@
+package cc.fascinated.service.pinger.impl;
+
+import cc.fascinated.Main;
+import cc.fascinated.common.packet.impl.java.JavaPacketHandshakingInSetProtocol;
+import cc.fascinated.common.packet.impl.java.JavaPacketStatusInStart;
+import cc.fascinated.model.mojang.JavaServerStatusToken;
+import cc.fascinated.model.server.JavaMinecraftServer;
+import cc.fascinated.service.pinger.MinecraftServerPinger;
+import lombok.extern.log4j.Log4j2;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+
+/**
+ * @author Braydon
+ */
+@Log4j2(topic = "Java Pinger")
+public final class JavaMinecraftServerPinger implements MinecraftServerPinger<JavaMinecraftServer> {
+    public static final JavaMinecraftServerPinger INSTANCE = new JavaMinecraftServerPinger();
+
+    private static final int TIMEOUT = 3000; // The timeout for the socket
+
+    @Override
+    public JavaMinecraftServer ping(String hostname, int port) {
+        log.info("Pinging {}:{}...", hostname, port);
+
+        // Open a socket connection to the server
+        try (Socket socket = new Socket()) {
+            socket.setTcpNoDelay(true);
+            socket.connect(new InetSocketAddress(hostname, port), TIMEOUT);
+
+            // Open data streams to begin packet transaction
+            try (DataInputStream inputStream = new DataInputStream(socket.getInputStream());
+                 DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream())) {
+                // Begin handshaking with the server
+                new JavaPacketHandshakingInSetProtocol(hostname, port, 47).process(inputStream, outputStream);
+
+                // Send the status request to the server, and await back the response
+                JavaPacketStatusInStart packetStatusInStart = new JavaPacketStatusInStart();
+                packetStatusInStart.process(inputStream, outputStream);
+                System.out.println("packetStatusInStart.getResponse() = " + packetStatusInStart.getResponse());
+                JavaServerStatusToken token = Main.GSON.fromJson(packetStatusInStart.getResponse(), JavaServerStatusToken.class);
+                return new JavaMinecraftServer(hostname, port, token.getDescription());
+            }
+        } catch (IOException ex) {
+            ex.printStackTrace();
+        }
+        return null;
+    }
+}