Initial commit

src/commonMain/kotlin/cn/rtast/mcping/mc_primitives.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+package cn.rtast.mcping
+
+import cn.rtast.mcping.platform.PlatformBuffer
+import cn.rtast.mcping.platform.PlatformReadChannel
+
+
+internal fun PlatformBuffer.writeVarInt(value: Int) {
+    var v = value
+    while (true) {
+        if ((v and 0x7F.inv()) == 0) {
+            this.writeByte(v.toByte())
+            return
+        }
+        this.writeByte(((v and 0x7F) or 0x80).toByte())
+        v = v ushr 7
+    }
+}
+
+internal fun PlatformReadChannel.readVarInt(): Int {
+    var value = 0
+    var position = 0
+    while (true) {
+        val currentByte = this.readByte().toInt() and 0xFF
+        value = value or ((currentByte and 0x7F) shl position)
+        if ((currentByte and 0x80) == 0) break
+        position += 7
+        if (position >= 35) throw IllegalArgumentException("VarInt too long")
+    }
+    return value
+}
+
+internal fun PlatformBuffer.writeMcString(value: String) {
+    val bytes = value.encodeToByteArray()
+    this.writeVarInt(bytes.size)
+    this.writeBytes(bytes)
+}
+
+internal fun PlatformReadChannel.readMcString(): String {
+    val length = this.readVarInt()
+    val bytes = this.readBytes(length)
+    return bytes.decodeToString()
+}

src/commonMain/kotlin/cn/rtast/mcping/mcping.kt

@@ -0,0 +1,35 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping
+
+import cn.rtast.mcping.platform.PlatformSocket
+
+
+public fun mcping(host: String, port: Int): String {
+    val socket = PlatformSocket(host, port)
+    val receiveChannel = socket.openReadChannel()
+    val sendChannel = socket.openWriteChannel()
+
+    return try {
+        val handshakePacket = HandshakePacket(
+            protocolVersion = -1,
+            serverAddress = host,
+            serverPort = port.toUShort(),
+            nextState = 1
+        )
+        sendChannel.sendPacket(handshakePacket)
+        sendChannel.sendPacket(StatusRequestPacket)
+
+        receiveChannel.readVarInt()  // consume a varint
+        val packetId = receiveChannel.readVarInt()
+        if (packetId == StatusRequestPacket.packetId) receiveChannel.readMcString()
+        else throw IllegalStateException("Server does not respond correct packet id, expected ${StatusRequestPacket.packetId} but got $packetId")
+    } finally {
+        socket.close()
+    }
+}

src/commonMain/kotlin/cn/rtast/mcping/packet.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping
+
+import cn.rtast.mcping.platform.PlatformBuffer
+
+internal interface MinecraftPacket {
+    val packetId: Int
+
+    fun writePayload(buffer: PlatformBuffer)
+}
+
+// ref https://minecraft.wiki/w/Java_Edition_protocol/Packets#Handshake
+internal data class HandshakePacket(
+    val protocolVersion: Int,
+    val serverAddress: String,
+    val serverPort: UShort,
+    // 1 -> Status
+    val nextState: Int,
+) : MinecraftPacket {
+    override val packetId: Int = 0x00
+
+    override fun writePayload(buffer: PlatformBuffer) {
+        buffer.writeVarInt(protocolVersion)
+        buffer.writeMcString(serverAddress)
+        // write UShort
+        // write 2 bytes big endian
+        buffer.writeByte((serverPort.toInt() shr 8).toByte())
+        buffer.writeByte(serverPort.toByte())
+        buffer.writeVarInt(nextState)
+    }
+}
+
+// ref https://minecraft.wiki/w/Java_Edition_protocol/Packets#Status
+internal data object StatusRequestPacket : MinecraftPacket {
+    override val packetId: Int = 0x00
+    override fun writePayload(buffer: PlatformBuffer) {}
+}

src/commonMain/kotlin/cn/rtast/mcping/packet_writer.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping
+
+import cn.rtast.mcping.platform.PlatformBuffer
+import cn.rtast.mcping.platform.PlatformWriteChannel
+
+internal fun PlatformWriteChannel.sendPacket(packet: MinecraftPacket) {
+    val bodyBuffer = PlatformBuffer()
+    bodyBuffer.writeVarInt(packet.packetId)
+    packet.writePayload(bodyBuffer)
+    val frameBuffer = PlatformBuffer()
+    frameBuffer.writeVarInt(bodyBuffer.size)
+    frameBuffer.writeBytes(bodyBuffer.toByteArray())
+    val bytes = frameBuffer.toByteArray()
+    this.writeFully(bytes, 0, bytes.size)
+    this.flush()
+}

src/commonMain/kotlin/cn/rtast/mcping/platform/buffer.kt

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+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping.platform
+
+internal expect class PlatformBuffer() {
+    fun writeByte(value: Byte)
+    fun writeBytes(bytes: ByteArray)
+    fun readByte(): Byte
+    fun readBytes(length: Int): ByteArray
+    fun toByteArray(): ByteArray
+    val size: Int
+}

src/commonMain/kotlin/cn/rtast/mcping/platform/channels.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping.platform
+
+internal expect class PlatformReadChannel {
+    fun readByte(): Byte
+    fun readBytes(length: Int): ByteArray
+    fun readFully(out: ByteArray, start: Int = 0, end: Int = out.size)
+}
+
+internal expect class PlatformWriteChannel {
+    fun writeFully(value: ByteArray, startIndex: Int = 0, endIndex: Int = value.size)
+    fun flush()
+}

src/commonMain/kotlin/cn/rtast/mcping/platform/socket.kt

@@ -0,0 +1,14 @@
+/*
+ * Copyright © 2026 RTAkland
+ * Author: RTAkland
+ * Date: 2026/9/3
+ */
+
+
+package cn.rtast.mcping.platform
+
+internal expect class PlatformSocket internal constructor(host: String, port: Int){
+    fun openReadChannel(): PlatformReadChannel
+    fun openWriteChannel(): PlatformWriteChannel
+    fun close()
+}