cleanup, fix 1.7 kick

build.gradle.kts

@@ -56,6 +56,7 @@ repositories {
 
 dependencies {
     implementation(kotlin("stdlib-jdk8"))
+    implementation(kotlin("reflect"))
 
     implementation("com.viaversion:viaversion:4.0.0-21w19a-SNAPSHOT") { isTransitive = false }
     implementation("com.viaversion:viabackwards:4.0.0-21w19a-SNAPSHOT") { isTransitive = false }

src/main/kotlin/com/viaversion/aas/Util.kt

@@ -24,6 +24,7 @@ import java.security.PrivateKey
 import java.security.PublicKey
 import java.security.SecureRandom
 import java.util.*
+import java.util.concurrent.TimeUnit
 import javax.crypto.Cipher
 import javax.crypto.spec.IvParameterSpec
 import javax.crypto.spec.SecretKeySpec
@@ -150,11 +151,20 @@ fun send(ch: Channel, obj: Any, flush: Boolean = false) {
     }
 }
 
-fun writeFlushClose(ch: Channel, obj: Any) {
-    ch.writeAndFlush(obj).addListener(ChannelFutureListener.CLOSE)
+fun writeFlushClose(ch: Channel, obj: Any, delay: Boolean = false) {
+    // https://github.com/VelocityPowered/Velocity/blob/dev/1.1.0/proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java#L252
+    ch.setAutoRead(false)
+    val action = {
+        ch.writeAndFlush(obj).addListener(ChannelFutureListener.CLOSE)
+    }
+    if (delay) {
+        ch.eventLoop().schedule(action, 250, TimeUnit.MILLISECONDS)
+    } else {
+        action()
+    }
 }
 
-fun readRemainingBytes(byteBuf: ByteBuf) = Type.REMAINING_BYTES.read(byteBuf)
+fun readRemainingBytes(byteBuf: ByteBuf) = Type.REMAINING_BYTES.read(byteBuf)!!
 fun ByteBuf.readByteArray(length: Int) = ByteArray(length).also { readBytes(it) }
 
 suspend fun hasJoined(username: String, hash: String): JsonObject {
@@ -168,7 +178,7 @@ suspend fun hasJoined(username: String, hash: String): JsonObject {
 fun generate128Bits() = ByteArray(16).also { secureRandom.nextBytes(it) }
 fun generateServerId() = ByteArray(13).let {
     secureRandom.nextBytes(it)
-    Base64.getEncoder().withoutPadding().encodeToString(it)
+    Base64.getEncoder().withoutPadding().encodeToString(it)!!
     // https://developer.mozilla.org/en-US/docs/Glossary/Base64 133% of original
 }
 

src/main/kotlin/com/viaversion/aas/handler/BackEndInit.kt

@@ -2,7 +2,6 @@ package com.viaversion.aas.handler
 
 import com.viaversion.aas.codec.FrameCodec
 import com.viaversion.aas.codec.MinecraftCodec
-import com.viaversion.aas.handler.autoprotocol.ProtocolDetectorHandler
 import com.viaversion.viaversion.connection.UserConnectionImpl
 import com.viaversion.viaversion.protocol.ProtocolPipelineImpl
 import io.netty.channel.Channel
@@ -21,11 +20,6 @@ class BackEndInit(val connectionData: ConnectionData) : ChannelInitializer<Chann
             .addLast("via-codec", ViaCodec(user))
             .addLast("timeout", ReadTimeoutHandler(30, TimeUnit.SECONDS))
             .addLast("mc", MinecraftCodec())
-            .also {
-                if (connectionData.viaBackServerVer == null) {
-                    it.addLast("protocol-detector", ProtocolDetectorHandler(connectionData))
-                }
-            }
             .addLast("handler", MinecraftHandler(connectionData, frontEnd = false))
     }
 }

src/main/kotlin/com/viaversion/aas/handler/MinecraftHandler.kt

@@ -17,7 +17,7 @@ class MinecraftHandler(
 ) : SimpleChannelInboundHandler<Packet>() {
     lateinit var endRemoteAddress: SocketAddress
     val other: Channel? get() = if (frontEnd) data.backChannel else data.frontChannel
-    var msgDisconnected = false
+    var loggedDc = false
 
     override fun channelRead0(ctx: ChannelHandlerContext, packet: Packet) {
         if (ctx.channel().isActive) {

src/main/kotlin/com/viaversion/aas/handler/Util.kt

@@ -2,8 +2,12 @@ package com.viaversion.aas.handler
 
 import com.viaversion.aas.config.VIAaaSConfig
 import com.viaversion.aas.codec.packet.Packet
+import com.viaversion.aas.readRemainingBytes
 import com.viaversion.aas.send
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion
+import com.viaversion.viaversion.api.type.Type
+import io.netty.buffer.ByteBufAllocator
+import io.netty.buffer.Unpooled
 import io.netty.channel.ChannelPipeline
 import io.netty.handler.proxy.Socks5ProxyHandler
 import java.net.InetSocketAddress
@@ -12,11 +16,33 @@ fun forward(handler: MinecraftHandler, packet: Packet, flush: Boolean = false) {
     send(handler.other!!, packet, flush)
 }
 
-fun is1_7(handler: MinecraftHandler) = handler.data.frontVer!! <= ProtocolVersion.v1_7_6.version
+fun is17(handler: MinecraftHandler) = handler.data.frontVer!! <= ProtocolVersion.v1_7_6.version
 
 fun addSocks5(pipe: ChannelPipeline) {
     val addr = VIAaaSConfig.backendSocks5ProxyAddress
     if (addr != null) {
         pipe.addFirst(Socks5ProxyHandler(InetSocketAddress(addr, VIAaaSConfig.backendSocks5ProxyPort)))
     }
+}
+
+fun decodeBrand(data: ByteArray, is17: Boolean): String {
+    return if (is17) {
+        String(data, Charsets.UTF_8)
+    } else {
+        Type.STRING.read(Unpooled.wrappedBuffer(data))
+    }
+}
+
+fun encodeBrand(string: String, is17: Boolean): ByteArray {
+    return if (is17) {
+        string.toByteArray(Charsets.UTF_8)
+    } else {
+        val buf = ByteBufAllocator.DEFAULT.buffer()
+        try {
+            Type.STRING.write(buf, string)
+            readRemainingBytes(buf)
+        } finally {
+            buf.release()
+        }
+    }
 }

src/main/kotlin/com/viaversion/aas/handler/autoprotocol/ProtocolDetectionState.kt

@@ -1,11 +1,11 @@
 package com.viaversion.aas.handler.autoprotocol
 
 import com.google.gson.JsonParser
+import com.viaversion.aas.codec.packet.Packet
+import com.viaversion.aas.codec.packet.status.StatusResponse
 import com.viaversion.aas.handler.MinecraftHandler
 import com.viaversion.aas.handler.state.MinecraftConnectionState
 import com.viaversion.aas.mcLogger
-import com.viaversion.aas.codec.packet.Packet
-import com.viaversion.aas.codec.packet.status.StatusResponse
 import com.viaversion.aas.parseProtocol
 import com.viaversion.aas.util.StacklessException
 import com.viaversion.viaversion.api.protocol.packet.State
@@ -19,9 +19,10 @@ class ProtocolDetectionState(val future: CompletableFuture<ProtocolVersion>) : M
 
     override fun handlePacket(handler: MinecraftHandler, ctx: ChannelHandlerContext, packet: Packet) {
         handler.data.frontChannel.close()
-        if (packet !is StatusResponse) throw StacklessException("unexpected packet")
+        if (packet !is StatusResponse) throw StacklessException("Unexpected packet")
         val ver = JsonParser.parseString(packet.json).asJsonObject
-            .getAsJsonObject("version").get("protocol").asInt.parseProtocol()
+            .getAsJsonObject("version")
+            .get("protocol").asInt.parseProtocol()
         future.complete(ver)
         mcLogger.info("A.D.: ${handler.endRemoteAddress} $ver")
     }

src/main/kotlin/com/viaversion/aas/handler/autoprotocol/ProtocolDetector.kt

@@ -6,35 +6,32 @@ import com.viaversion.aas.channelSocketFactory
 import com.viaversion.aas.childLoop
 import com.viaversion.aas.codec.FrameCodec
 import com.viaversion.aas.codec.MinecraftCodec
+import com.viaversion.aas.codec.packet.handshake.Handshake
+import com.viaversion.aas.codec.packet.status.StatusRequest
 import com.viaversion.aas.handler.ConnectionData
 import com.viaversion.aas.handler.MinecraftHandler
 import com.viaversion.aas.handler.addSocks5
-import com.viaversion.aas.mcLogger
-import com.viaversion.aas.codec.packet.handshake.Handshake
-import com.viaversion.aas.codec.packet.status.StatusRequest
 import com.viaversion.aas.send
 import com.viaversion.viaversion.api.protocol.packet.State
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion
 import io.netty.bootstrap.Bootstrap
 import io.netty.channel.Channel
-import io.netty.channel.ChannelFuture
+import io.netty.channel.ChannelFutureListener
 import io.netty.channel.ChannelInitializer
 import io.netty.channel.ChannelOption
 import io.netty.handler.timeout.ReadTimeoutHandler
 import io.netty.resolver.NoopAddressResolverGroup
-import io.netty.util.concurrent.Future
 import java.net.InetSocketAddress
 import java.util.concurrent.CompletableFuture
-import java.util.concurrent.ExecutionException
 import java.util.concurrent.TimeUnit
 
 object ProtocolDetector {
     private val SERVER_VER = CacheBuilder.newBuilder()
         .expireAfterAccess(100, TimeUnit.SECONDS)
-        .build(CacheLoader.from { address: InetSocketAddress? ->
+        .build<InetSocketAddress, CompletableFuture<ProtocolVersion>>(CacheLoader.from { address ->
             val future = CompletableFuture<ProtocolVersion>()
             try {
-                val ch: ChannelFuture = Bootstrap()
+                val ch = Bootstrap()
                     .group(childLoop)
                     .resolver(NoopAddressResolverGroup.INSTANCE)
                     .channelFactory(channelSocketFactory(childLoop))
@@ -42,7 +39,11 @@ object ProtocolDetector {
                     .option(ChannelOption.IP_TOS, 0x18)
                     .handler(object : ChannelInitializer<Channel>() {
                         override fun initChannel(channel: Channel) {
-                            val data = ConnectionData(channel, state = ProtocolDetectionState(future), frontVer = -1)
+                            val data = ConnectionData(
+                                channel,
+                                state = ProtocolDetectionState(future),
+                                frontVer = -1
+                            )
                             channel.pipeline().also { addSocks5(it) }
                                 .addLast("timeout", ReadTimeoutHandler(30, TimeUnit.SECONDS))
                                 .addLast("frame", FrameCodec())
@@ -51,33 +52,24 @@ object ProtocolDetector {
                         }
                     })
                     .connect(address!!)
-                ch.addListener { future1: Future<in Void> ->
-                    if (!future1.isSuccess) {
-                        future.completeExceptionally(future1.cause())
+                ch.addListener(ChannelFutureListener {
+                    if (!it.isSuccess) {
+                        future.completeExceptionally(it.cause())
                     } else {
-                        ch.channel().eventLoop().execute {
-                            val handshake = Handshake()
-                            handshake.address = address.hostString
-                            handshake.port = address.port
-                            handshake.protocolId = -1
-                            handshake.nextState = State.STATUS
-                            send(ch.channel(), handshake)
-                            send(ch.channel(), StatusRequest(), flush = true)
-                        }
+                        val handshake = Handshake()
+                        handshake.address = address.hostString
+                        handshake.port = address.port
+                        handshake.protocolId = -1
+                        handshake.nextState = State.STATUS
+                        send(ch.channel(), handshake)
+                        send(ch.channel(), StatusRequest(), flush = true)
                     }
-                }
+                })
             } catch (throwable: Throwable) {
                 future.completeExceptionally(throwable)
             }
             future
         })
 
-    fun detectVersion(address: InetSocketAddress): CompletableFuture<ProtocolVersion> {
-        return try {
-            SERVER_VER[address]
-        } catch (e: ExecutionException) {
-            mcLogger.warn("Protocol auto detector error: ", e)
-            CompletableFuture.completedFuture(null)
-        }
-    }
+    fun detectVersion(address: InetSocketAddress): CompletableFuture<ProtocolVersion> = SERVER_VER[address]
 }

src/main/kotlin/com/viaversion/aas/handler/autoprotocol/ProtocolDetectorHandler.kt

@@ -1,86 +0,0 @@
-package com.viaversion.aas.handler.autoprotocol
-
-import com.viaversion.aas.handler.ConnectionData
-import com.viaversion.aas.handler.MinecraftHandler
-import com.viaversion.aas.mcLogger
-import io.netty.channel.ChannelDuplexHandler
-import io.netty.channel.ChannelHandlerContext
-import io.netty.channel.ChannelPromise
-import java.net.InetSocketAddress
-import java.util.concurrent.TimeUnit
-import java.util.function.Consumer
-
-// https://github.com/ViaVersion/ViaFabric/blob/mc-1.16/src/main/java/com/github/creeper123123321/viafabric/handler/clientside/ProtocolDetectionHandler.java
-class ProtocolDetectorHandler(val connectionData: ConnectionData) : ChannelDuplexHandler() {
-    private val queuedMessages = ArrayDeque<Pair<Any, ChannelPromise>>()
-    private var hold = true
-    private var pendentFlush = false
-
-    @Throws(Exception::class)
-    override fun channelActive(ctx: ChannelHandlerContext) {
-        super.channelActive(ctx)
-        val handler = ctx.channel().pipeline().get(MinecraftHandler::class.java)
-        val address = handler.endRemoteAddress
-        if (address is InetSocketAddress) {
-            val timeoutRun = ctx.executor().schedule({
-                mcLogger.warn("Timeout protocol A.D. $address")
-                ctx.pipeline().remove(this)
-            }, 10, TimeUnit.SECONDS)
-            ProtocolDetector.detectVersion(address).whenComplete { protocol, _ ->
-                if (protocol != null && protocol.version != -1) {
-                    connectionData.viaBackServerVer = protocol.version
-                } else {
-                    connectionData.viaBackServerVer = -1 // fallback
-                }
-
-                ctx.pipeline().remove(this)
-                timeoutRun.cancel(false)
-            }
-            // Let's cache it before we need it
-        }
-    }
-
-    @Throws(Exception::class)
-    override fun write(ctx: ChannelHandlerContext, msg: Any, promise: ChannelPromise) {
-        if (!hold) {
-            drainQueue(ctx)
-            super.write(ctx, msg, promise)
-        } else {
-            queuedMessages.add(Pair(msg, promise))
-        }
-    }
-
-    @Throws(Exception::class)
-    override fun flush(ctx: ChannelHandlerContext) {
-        if (!hold) {
-            drainQueue(ctx)
-            super.flush(ctx)
-        } else {
-            pendentFlush = true
-        }
-    }
-
-    @Throws(Exception::class)
-    override fun channelInactive(ctx: ChannelHandlerContext) {
-        drainQueue(ctx)
-        super.channelInactive(ctx)
-    }
-
-    private fun drainQueue(ctx: ChannelHandlerContext) {
-        queuedMessages.forEach(Consumer {
-            ctx.write(
-                it.first,
-                it.second
-            )
-        })
-        queuedMessages.clear()
-        if (pendentFlush) ctx.flush()
-        pendentFlush = false
-    }
-
-    @Throws(Exception::class)
-    override fun handlerRemoved(ctx: ChannelHandlerContext) {
-        drainQueue(ctx)
-        super.handlerRemoved(ctx)
-    }
-}

src/main/kotlin/com/viaversion/aas/handler/state/HandshakeState.kt

@@ -84,6 +84,7 @@ class HandshakeState : MinecraftConnectionState {
     }
 
     override fun disconnect(handler: MinecraftHandler, msg: String) {
+        super.disconnect(handler, msg)
         handler.data.frontChannel.close() // Not worth logging
     }
 

src/main/kotlin/com/viaversion/aas/handler/state/LoginState.kt

@@ -5,10 +5,10 @@ import com.google.gson.Gson
 import com.viaversion.aas.*
 import com.viaversion.aas.codec.CompressionCodec
 import com.viaversion.aas.codec.CryptoCodec
-import com.viaversion.aas.handler.MinecraftHandler
-import com.viaversion.aas.handler.forward
 import com.viaversion.aas.codec.packet.Packet
 import com.viaversion.aas.codec.packet.login.*
+import com.viaversion.aas.handler.MinecraftHandler
+import com.viaversion.aas.handler.forward
 import com.viaversion.aas.util.StacklessException
 import com.viaversion.viaversion.api.protocol.packet.State
 import io.netty.channel.Channel
@@ -32,6 +32,8 @@ class LoginState : MinecraftConnectionState {
     var started = false
     override val state: State
         get() = State.LOGIN
+    override val logDc: Boolean
+        get() = true
 
     override fun handlePacket(handler: MinecraftHandler, ctx: ChannelHandlerContext, packet: Packet) {
         when (packet) {

src/main/kotlin/com/viaversion/aas/handler/state/MinecraftConnectionState.kt

@@ -12,10 +12,11 @@ interface MinecraftConnectionState {
         handler: MinecraftHandler, ctx: ChannelHandlerContext,
         packet: Packet
     )
+    val logDc: Boolean get() = false
 
     fun disconnect(handler: MinecraftHandler, msg: String) {
-        if (!handler.msgDisconnected) {
-            handler.msgDisconnected = true
+        if (logDc && !handler.loggedDc) {
+            handler.loggedDc = true
             mcLogger.info("DC ${handler.endRemoteAddress}: $msg")
         }
     }

src/main/kotlin/com/viaversion/aas/handler/state/PlayState.kt

@@ -1,27 +1,23 @@
 package com.viaversion.aas.handler.state
 
 import com.google.gson.JsonPrimitive
-import com.viaversion.aas.config.VIAaaSConfig
-import com.viaversion.aas.handler.MinecraftHandler
-import com.viaversion.aas.handler.forward
-import com.viaversion.aas.handler.is1_7
 import com.viaversion.aas.codec.packet.Packet
 import com.viaversion.aas.codec.packet.UnknownPacket
 import com.viaversion.aas.codec.packet.play.Kick
 import com.viaversion.aas.codec.packet.play.PluginMessage
+import com.viaversion.aas.config.VIAaaSConfig
+import com.viaversion.aas.handler.*
 import com.viaversion.aas.parseProtocol
-import com.viaversion.aas.readRemainingBytes
 import com.viaversion.aas.util.StacklessException
 import com.viaversion.aas.writeFlushClose
 import com.viaversion.viaversion.api.protocol.packet.State
-import com.viaversion.viaversion.api.type.Type
-import io.netty.buffer.ByteBufAllocator
-import io.netty.buffer.Unpooled
 import io.netty.channel.ChannelHandlerContext
 
 object PlayState : MinecraftConnectionState {
     override val state: State
         get() = State.PLAY
+    override val logDc: Boolean
+        get() = true
 
     override fun handlePacket(handler: MinecraftHandler, ctx: ChannelHandlerContext, packet: Packet) {
         when {
@@ -35,32 +31,25 @@ object PlayState : MinecraftConnectionState {
         when (pluginMessage.channel) {
             "MC|Brand", "brand", "minecraft:brand" -> {
                 if (!VIAaaSConfig.showBrandInfo) return
-                val brand = if (is1_7(handler)) {
-                    String(pluginMessage.data, Charsets.UTF_8)
-                } else {
-                    Type.STRING.read(Unpooled.wrappedBuffer(pluginMessage.data))
-                } + " (VIAaaS C: ${handler.data.frontVer!!.parseProtocol()} S: ${
-                    handler.data.viaBackServerVer!!.parseProtocol()
-                })"
 
-                if (is1_7(handler)) {
-                    pluginMessage.data = brand.toByteArray(Charsets.UTF_8)
-                } else {
-                    val buf = ByteBufAllocator.DEFAULT.buffer()
-                    try {
-                        Type.STRING.write(buf, brand)
-                        pluginMessage.data = readRemainingBytes(buf)
-                    } finally {
-                        buf.release()
-                    }
-                }
+                val brand = "${
+                    decodeBrand(
+                        pluginMessage.data,
+                        is17(handler)
+                    )
+                }${" (VIAaaS C: ${handler.data.frontVer?.parseProtocol()} S: ${handler.data.viaBackServerVer?.parseProtocol()})"}"
+
+                pluginMessage.data = encodeBrand(brand, is17(handler))
             }
         }
     }
 
     override fun disconnect(handler: MinecraftHandler, msg: String) {
         super.disconnect(handler, msg)
-        writeFlushClose(handler.data.frontChannel,
-            Kick().also { it.msg = JsonPrimitive("[VIAaaS] §c$msg").toString() })
+        writeFlushClose(
+            handler.data.frontChannel,
+            Kick().also { it.msg = JsonPrimitive("[VIAaaS] §c$msg").toString() },
+            delay = is17(handler)
+        )
     }
 }

src/main/kotlin/com/viaversion/aas/handler/state/StatusState.kt

@@ -3,12 +3,12 @@ package com.viaversion.aas.handler.state
 import com.google.gson.JsonArray
 import com.google.gson.JsonObject
 import com.google.gson.JsonParser
-import com.viaversion.aas.config.VIAaaSConfig
-import com.viaversion.aas.handler.MinecraftHandler
-import com.viaversion.aas.handler.forward
 import com.viaversion.aas.codec.packet.Packet
 import com.viaversion.aas.codec.packet.UnknownPacket
 import com.viaversion.aas.codec.packet.status.StatusResponse
+import com.viaversion.aas.config.VIAaaSConfig
+import com.viaversion.aas.handler.MinecraftHandler
+import com.viaversion.aas.handler.forward
 import com.viaversion.aas.parseProtocol
 import com.viaversion.aas.util.StacklessException
 import com.viaversion.aas.writeFlushClose
@@ -20,6 +20,8 @@ import java.util.*
 object StatusState : MinecraftConnectionState {
     override val state: State
         get() = State.STATUS
+    override val logDc: Boolean
+        get() = true
 
     override fun handlePacket(handler: MinecraftHandler, ctx: ChannelHandlerContext, packet: Packet) {
         if (packet is UnknownPacket) throw StacklessException("Invalid packet")
@@ -38,8 +40,8 @@ object StatusState : MinecraftConnectionState {
                 it.addProperty("id", UUID.nameUUIDFromBytes("VIAaaS".toByteArray(Charsets.UTF_8)).toString())
                 it.addProperty(
                     "name",
-                    "§9VIAaaS§r C: §7${handler.data.frontVer!!.parseProtocol()}§r S: §7${
-                        handler.data.viaBackServerVer!!.parseProtocol()
+                    "§9VIAaaS§r C: §7${handler.data.frontVer?.parseProtocol()}§r S: §7${
+                        handler.data.viaBackServerVer?.parseProtocol()
                     }"
                 )
             })

src/main/kotlin/com/viaversion/aas/handler/state/Util.kt

@@ -2,29 +2,38 @@ package com.viaversion.aas.handler.state
 
 import com.google.common.net.HostAndPort
 import com.viaversion.aas.*
+import com.viaversion.aas.codec.packet.handshake.Handshake
 import com.viaversion.aas.config.VIAaaSConfig
 import com.viaversion.aas.handler.BackEndInit
 import com.viaversion.aas.handler.MinecraftHandler
+import com.viaversion.aas.handler.autoprotocol.ProtocolDetector
 import com.viaversion.aas.handler.forward
-import com.viaversion.aas.codec.packet.handshake.Handshake
 import com.viaversion.aas.util.StacklessException
 import com.viaversion.viaversion.api.protocol.packet.State
 import io.netty.bootstrap.Bootstrap
-import io.netty.channel.ChannelFuture
+import io.netty.channel.Channel
 import io.netty.channel.ChannelFutureListener
 import io.netty.channel.ChannelOption
 import io.netty.channel.socket.SocketChannel
 import io.netty.resolver.NoopAddressResolverGroup
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.future.await
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withTimeoutOrNull
 import java.net.Inet4Address
 import java.net.InetAddress
 import java.net.InetSocketAddress
+import java.util.concurrent.CompletableFuture
 
-private fun createBackChannel(handler: MinecraftHandler, socketAddr: InetSocketAddress, state: State): ChannelFuture {
+private fun createBackChannel(
+    handler: MinecraftHandler,
+    socketAddr: InetSocketAddress,
+    state: State
+): CompletableFuture<Channel> {
+    val future = CompletableFuture<Channel>()
     val loop = handler.data.frontChannel.eventLoop()
-    return Bootstrap()
+    Bootstrap()
         .handler(BackEndInit(handler.data))
         .channelFactory(channelSocketFactory(loop.parent()))
         .group(loop)
@@ -35,58 +44,85 @@ private fun createBackChannel(handler: MinecraftHandler, socketAddr: InetSocketA
         .resolver(NoopAddressResolverGroup.INSTANCE)
         .connect(socketAddr)
         .addListener(ChannelFutureListener {
-            if (it.isSuccess) {
+            try {
+                if (!it.isSuccess) throw it.cause()
+
                 mcLogger.info("+ ${handler.endRemoteAddress} -> $socketAddr")
                 handler.data.backChannel = it.channel() as SocketChannel
 
-                val packet = Handshake()
-                packet.nextState = state
-                packet.protocolId = handler.data.frontVer!!
-                packet.address = socketAddr.hostString
-                packet.port = socketAddr.port
+                GlobalScope.launch {
+                    if (handler.data.viaBackServerVer == null) {
+                        try {
+                            val detectedProtocol = withTimeoutOrNull(10_000) {
+                                ProtocolDetector.detectVersion(socketAddr).await()
+                            }
 
-                forward(handler, packet, true)
+                            if (detectedProtocol != null && detectedProtocol.version != -1) {
+                                handler.data.viaBackServerVer = detectedProtocol.version
+                            } else {
+                                handler.data.viaBackServerVer = -1 // fallback
+                            }
+                        } catch (e: Exception) {
+                            mcLogger.warn("Failed to auto-detect version for $socketAddr: $e")
+                            mcLogger.debug("Stacktrace: ", e)
+                        }
+                    }
 
-                handler.data.frontChannel.setAutoRead(true)
+                    val packet = Handshake()
+                    packet.nextState = state
+                    packet.protocolId = handler.data.frontVer!!
+                    packet.address = socketAddr.hostString
+                    packet.port = socketAddr.port
+
+                    forward(handler, packet, true)
+
+                    handler.data.frontChannel.setAutoRead(true)
+                    future.complete(it.channel())
+                }
+            } catch (e: Exception) {
+                future.completeExceptionally(it.cause())
             }
         })
+    return future
 }
 
-private fun tryBackAddress(
+private suspend fun tryBackAddresses(
     handler: MinecraftHandler,
-    iterator: Iterator<InetSocketAddress>,
+    addresses: Iterable<InetSocketAddress>,
     state: State,
-    success: () -> Unit,
 ) {
-    val fail = { e: Throwable ->
-        if (!iterator.hasNext()) {
-            // We're in the event loop
-            handler.disconnect("Couldn't connect: $e")
-        } else if (handler.data.frontChannel.isActive) {
-            tryBackAddress(handler, iterator, state, success)
+    var latestException: Exception? = null
+    for (socketAddr in addresses) {
+        try {
+            if ((socketAddr.address != null && checkLocalAddress(socketAddr.address))
+                || matchesAddress(socketAddr, VIAaaSConfig.blockedBackAddresses)
+                || !matchesAddress(socketAddr, VIAaaSConfig.allowedBackAddresses)
+            ) {
+                throw StacklessException("Not allowed")
+            }
+
+            createBackChannel(handler, socketAddr, state).await()
+            return // Finally it worked!
+        } catch (e: Exception) {
+            latestException = e
         }
     }
-    try {
-        val socketAddr = iterator.next()
 
-        if ((socketAddr.address != null && checkLocalAddress(socketAddr.address))
-            || matchesAddress(socketAddr, VIAaaSConfig.blockedBackAddresses)
-            || !matchesAddress(socketAddr, VIAaaSConfig.allowedBackAddresses)
-        ) {
-            throw StacklessException("Not allowed")
-        }
+    throw StacklessException("Latest attempt failed", latestException)
+}
 
-        createBackChannel(handler, socketAddr, state).addListener {
-            if (it.isSuccess) {
-                success()
-            } else {
-                fail(it.cause())
-            }
-        }
-    } catch (e: Exception) {
-        handler.data.frontChannel.eventLoop().submit {
-            fail(e)
-        }
+private fun resolveBackendAddresses(hostAndPort: HostAndPort): List<InetSocketAddress> {
+    val srvResolved = resolveSrv(hostAndPort)
+
+    val removedEndDot = srvResolved.host.replace(Regex("\\.$"), "")
+
+    return when {
+        removedEndDot.endsWith(".onion", ignoreCase = true) ->
+            listOf(InetSocketAddress.createUnresolved(removedEndDot, srvResolved.port))
+        else -> InetAddress.getAllByName(srvResolved.host)
+            .groupBy { it is Inet4Address }
+            .toSortedMap() // I'm sorry, IPv4, but my true love is IPv6... We can still be friends though...
+            .map { InetSocketAddress(it.value.random(), srvResolved.port) }
     }
 }
 
@@ -94,23 +130,12 @@ fun connectBack(handler: MinecraftHandler, address: String, port: Int, state: St
     handler.data.frontChannel.setAutoRead(false)
     GlobalScope.launch(Dispatchers.IO) {
         try {
-            val srvResolved = resolveSrv(HostAndPort.fromParts(address, port))
+            val addresses = resolveBackendAddresses(HostAndPort.fromParts(address, port))
 
-            val removedEndDot = srvResolved.host.replace(Regex("\\.$"), "")
+            if (addresses.isEmpty()) throw StacklessException("Hostname has no IP address")
 
-            val iterator = when {
-                removedEndDot.endsWith(".onion", ignoreCase = true) ->
-                    listOf(InetSocketAddress.createUnresolved(removedEndDot, srvResolved.port))
-                        .iterator()
-                else -> InetAddress.getAllByName(srvResolved.host)
-                    .groupBy { it is Inet4Address }
-                    .toSortedMap() // I'm sorry, IPv4, but my true love is IPv6... We can still be friends though...
-                    .map { InetSocketAddress(it.value.random(), srvResolved.port) }
-                    .iterator()
-            }
-
-            if (!iterator.hasNext()) throw StacklessException("Hostname has no IP address")
-            tryBackAddress(handler, iterator, state, success)
+            tryBackAddresses(handler, addresses, state)
+            success()
         } catch (e: Exception) {
             handler.data.frontChannel.eventLoop().submit {
                 handler.disconnect("Couldn't connect: $e")