feat: packetlistener for handling Client/Server- bound packets

idofront-nms/src/main/kotlin/com/mineinabyss/idofront/nms/Packets.kt

@@ -0,0 +1,106 @@
+package com.mineinabyss.idofront.nms
+
+import io.netty.channel.ChannelDuplexHandler
+import io.netty.channel.ChannelHandlerContext
+import io.netty.channel.ChannelPromise
+import io.papermc.paper.network.ChannelInitializeListenerHolder
+import net.kyori.adventure.key.Key
+import net.minecraft.network.Connection
+import net.minecraft.network.protocol.Packet
+import net.minecraft.network.protocol.game.ClientGamePacketListener
+import net.minecraft.server.network.ServerGamePacketListenerImpl
+import org.bukkit.entity.Player
+import org.bukkit.plugin.java.JavaPlugin
+
+/**
+ * Intercept a Clientbound packet to either alter it or prevent it from being sent to the player
+ * @param key Optional key to register the packet-listener with
+ * @param intercept A lambda function that takes two parameters:
+ *  * `packet` (Packet<*>): The intercepted packet.
+ *  * `player` (Player?): The player associated with the intercepted packet, or `null` if the player is not available.
+ *  * The lambda should return the modified packet or `null` to prevent it from being sent.
+ * @return The modified packet or null to prevent it from sending
+ */
+fun JavaPlugin.interceptClientbound(key: String = "write_packet_interceptor", intercept: (Packet<*>, Player?) -> Packet<*>?) {
+    PacketListener.interceptClientbound(Key.key(this.name.lowercase(), key.substringAfter(":")), intercept)
+}
+
+/**
+ * Intercept a Clientbound packet to either alter it or prevent it from being sent to the player
+ * @param key Optional key to register the packet-listener with
+ * @param intercept A lambda function that takes two parameters:
+ *  * `packet` (Packet<*>): The intercepted packet.
+ *  * `player` (Player?): The player associated with the intercepted packet, or `null` if the player is not available.
+ *  * The lambda should return the modified packet or `null` to prevent it from being sent.
+ * @return The modified packet or null to prevent it from sending
+ */
+fun JavaPlugin.interceptServerbound(key: String = "read_packet_interceptor", intercept: (Packet<*>, Player?) -> Packet<*>?) {
+    PacketListener.interceptServerbound(Key.key(this.name.lowercase(), key.substringAfter(":")), intercept)
+}
+
+object PacketListener {
+
+    /**
+     * Intercept a Clientbound packet to either alter it or prevent it from being sent to the player
+     * @param key Optional key to register the packet-listener with
+     * @param intercept A lambda function that takes two parameters:
+     *  * `packet` (Packet<*>): The intercepted packet.
+     *  * `player` (Player?): The player associated with the intercepted packet, or `null` if the player is not available.
+     *  * The lambda should return the modified packet or `null` to prevent it from being sent.
+     * @return The modified packet or null to prevent it from sending
+     */
+    fun interceptClientbound(plugin: JavaPlugin, key: String = "write_packet_interceptor", intercept: (Packet<*>, Player?) -> Packet<*>?) {
+        interceptClientbound(Key.key(plugin.name.lowercase(), key.substringAfter(":")), intercept)
+    }
+
+    /**
+     * Intercept a Clientbound packet to either alter it or prevent it from being sent to the player
+     * @param key Optional key to register the packet-listener with
+     * @param intercept A lambda function that takes two parameters:
+     *  * `packet` (Packet<*>): The intercepted packet.
+     *  * `player` (Player?): The player associated with the intercepted packet, or `null` if the player is not available.
+     *  * The lambda should return the modified packet or `null` to prevent it from being sent.
+     * @return The modified packet or null to prevent it from sending
+     */
+    fun interceptServerbound(plugin: JavaPlugin, key: String = "read_packet_interceptor", intercept: (Packet<*>, Player?) -> Packet<*>?) {
+        interceptServerbound(Key.key(plugin.name.lowercase(), key.substringAfter(":")), intercept)
+    }
+
+    fun unregisterListener(plugin: JavaPlugin) {
+        ChannelInitializeListenerHolder.getListeners().keys.filter { it.namespace() == plugin.name.lowercase() }.forEach(ChannelInitializeListenerHolder::removeListener)
+    }
+
+    fun unregisterListener(key: Key) {
+        ChannelInitializeListenerHolder.removeListener(key)
+    }
+
+    internal fun interceptClientbound(key: Key? = null, intercept: (Packet<*>, Player?) -> Packet<*>?) {
+        val key = key ?: Key.key("write_packet_interceptor${ChannelInitializeListenerHolder.getListeners().keys.indexOfLast { it.value().startsWith("write_packet_interceptor") }.plus(1)}")
+
+        ChannelInitializeListenerHolder.addListener(key) { channel ->
+            channel.pipeline().addBefore("packet_handler", key.asString(), object : ChannelDuplexHandler() {
+                val connection = channel.pipeline()["packet_handler"] as Connection
+                override fun write(ctx: ChannelHandlerContext, packet: Any, promise: ChannelPromise) {
+                    val player = if (connection.packetListener is ClientGamePacketListener) connection.player.bukkitEntity else null
+                    if (packet is Packet<*>) intercept(packet, player)?.let { ctx.write(it, promise) }
+                    else ctx.write(packet, promise)
+                }
+            })
+        }
+    }
+
+    internal fun interceptServerbound(key: Key? = null, intercept: (Packet<*>, Player?) -> Packet<*>?) {
+        val key = key ?: Key.key("write_packet_interceptor${ChannelInitializeListenerHolder.getListeners().keys.indexOfLast { it.value().startsWith("read_packet_interceptor") }.plus(1)}")
+
+        ChannelInitializeListenerHolder.addListener(key) { channel ->
+            channel.pipeline().addBefore("packet_handler", key.asString(), object : ChannelDuplexHandler() {
+                val connection = channel.pipeline()["packet_handler"] as Connection
+                override fun channelRead(ctx: ChannelHandlerContext, packet: Any) {
+                    val player = if (connection.packetListener is ServerGamePacketListenerImpl) connection.player.bukkitEntity else null
+                    if (packet is Packet<*>) intercept(packet, player)?.let { ctx.fireChannelRead(it) }
+                    else ctx.fireChannelRead(packet)
+                }
+            })
+        }
+    }
+}