basic udp: need a package defrag/bust layer, IP won't work well

.idea/GitLink.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="uk.co.ben_gibson.git.link.SettingsState">
+    <option name="host" value="e0f86390-1091-4871-8aeb-f534fbc99cf0" />
+  </component>
+</project>

.idea/gradle.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>

src/commonMain/kotlin/net/sergeych/kiloparsec/ProxyDevice.kt

@@ -0,0 +1,12 @@
+package net.sergeych.kiloparsec
+
+import kotlinx.coroutines.channels.Channel
+
+class ProxyDevice(capacity: Int=1024) : Transport.Device {
+    override val input = Channel<UByteArray?>(capacity)
+    override val output= Channel<UByteArray?>(capacity)
+    override suspend fun close() {
+        runCatching { input.close() }
+        runCatching { output.close() }
+    }
+}

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/ConnectionId.kt

@@ -0,0 +1,6 @@
+package net.sergeych.kiloparsec.adapter
+
+internal data class ConnectionId(
+    val address: NetworkAddress,
+    val id: UInt,
+)

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/DatagramClient.kt

@@ -0,0 +1,117 @@
+package net.sergeych.kiloparsec.adapter
+
+import kotlinx.coroutines.*
+import net.sergeych.crypto.Key
+import net.sergeych.kiloparsec.KiloClientConnection
+import net.sergeych.kiloparsec.KiloInterface
+import net.sergeych.kiloparsec.ProxyDevice
+import net.sergeych.mp_logger.*
+import net.sergeych.mp_tools.globalLaunch
+import net.sergeych.tools.AtomicCounter
+import net.sergeych.utools.pack
+import net.sergeych.utools.unpack
+
+private val instanceCounter = AtomicCounter()
+
+class DatagramClient<S>(
+    private val connector: DatagramConnector,
+    val serverAddress: NetworkAddress,
+    private val localInterface: KiloInterface<S>,
+    private val clientSigningKey: Key.Signing? = null,
+    private val createSession: () -> S,
+) : LogTag("DGC:${instanceCounter.next()}") {
+
+    private var sessionId = 0u
+    private var isClosed = false
+    val job = globalLaunch {
+        while (isActive && !isClosed) {
+            openSession()
+            pumpSession()
+            debug { "closing session $sessionId" }
+            sessionId = 0u
+        }
+    }
+
+    private suspend fun pumpSession() {
+        try {
+            val proxyDevice = ProxyDevice()
+            val client = KiloClientConnection<S>(localInterface, proxyDevice, createSession(), clientSigningKey)
+            coroutineScope {
+                fun stop() {
+                    cancel()
+                }
+                launch {
+                    while (isActive) {
+                        if (sessionId == 0u) {
+                            error { "invalid zero sessionId in pump" }
+                            stop()
+                        } else {
+                            val data = proxyDevice.output.receive()
+                            if (data == null) {
+                                warning { "kiloconnection send empty frame: closing" }
+                                stop()
+                            } else {
+                                send(OuterPacket(sessionId, data))
+                            }
+                        }
+                    }
+                }
+                while (isActive) {
+                    val packet: OuterPacket = unpack(connector.incoming.receive().message)
+                    if (packet.id == 0u) {
+                        val result: DatagramResult = unpack(packet.payload)
+                        if (result is DatagramResult.Error) {
+                            if (result.error == DatagramError.Closed) {
+                                info { "connection is closed on the remote part" }
+                            } else {
+                                warning { "unexpected error while pumping: ${result.error}" }
+                            }
+                        } else {
+                            warning { "unexpected result: $result" }
+                        }
+                        stop()
+                    } else {
+                        proxyDevice.input.send(packet.payload)
+                    }
+                }
+            }
+            proxyDevice.close()
+        } catch (x: CancellationException) {
+            throw x
+        } catch (x: Exception) {
+            x.printStackTrace()
+        }
+    }
+
+    private suspend fun openSession() {
+        while (!isClosed) {
+            send(OuterPacket(0u, ubyteArrayOf()))
+            val packet: OuterPacket = unpack(connector.incoming.receive().message)
+            if (packet.id == 0u) {
+                when (val result: DatagramResult = unpack(packet.payload)) {
+                    is DatagramResult.Error -> {
+                        warning { "error opening connection: ${result.error}" }
+                    }
+
+                    is DatagramResult.Ok -> {
+                        debug { "connection established, our id is ${result.id}" }
+                        sessionId = result.id
+                        break
+                    }
+                }
+            } else {
+                warning { "received unexpected openSession id: ${packet.id}" }
+            }
+            delay(500)
+        }
+    }
+
+
+    private suspend fun send(packet: OuterPacket) {
+        connector.send(pack(packet), serverAddress)
+    }
+
+    fun close() {
+        job.cancel()
+    }
+}

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/DatagramError.kt

@@ -0,0 +1,7 @@
+package net.sergeych.kiloparsec.adapter
+
+enum class DatagramError {
+    Closed,
+    NotExists,
+    Busy
+}

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/DatagramResult.kt

@@ -0,0 +1,15 @@
+package net.sergeych.kiloparsec.adapter
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+@Serializable
+sealed class DatagramResult {
+    @Serializable
+    @SerialName("ok")
+    data class Ok(val id: UInt) : DatagramResult()
+
+    @Serializable
+    @SerialName("err")
+    data class Error(val error: DatagramError) : DatagramResult()
+}

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/DatagramServer.kt

@@ -0,0 +1,136 @@
+package net.sergeych.kiloparsec.adapter
+
+import kotlinx.coroutines.channels.ClosedReceiveChannelException
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.datetime.Instant
+import net.sergeych.crypto.Key
+import net.sergeych.kiloparsec.KiloInterface
+import net.sergeych.kiloparsec.KiloServerConnection
+import net.sergeych.kiloparsec.ProxyDevice
+import net.sergeych.mp_logger.LogTag
+import net.sergeych.mp_logger.debug
+import net.sergeych.mp_tools.globalLaunch
+import net.sergeych.tools.AtomicCounter
+import net.sergeych.utools.now
+import net.sergeych.utools.pack
+import net.sergeych.utools.unpack
+
+private val instanceCounter = AtomicCounter()
+
+private class Connection<S>(
+    val server: DatagramServer<S>,
+    val connection: KiloServerConnection<S>,
+    val device: ProxyDevice,
+    val connectionId: ConnectionId,
+    var lastActiveAt: Instant = now(),
+) {
+
+    suspend fun proceedFrame(frame: OuterPacket) {
+        lastActiveAt = now()
+        if (frame.payload.isEmpty()) {
+            // ping
+            server.sendData(connectionId,ubyteArrayOf())
+        } else
+            device.input.send(frame.payload)
+    }
+
+    private val job = globalLaunch {
+        while (isActive) {
+            val x = device.output.receive() ?: break
+            server.sendData(connectionId, x)
+        }
+    }
+
+    suspend fun close() {
+        job.cancel()
+        server.remove(connectionId)
+    }
+}
+
+class DatagramServer<S>(
+    private val connector: DatagramConnector,
+    private val localInterface: KiloInterface<S>,
+    private val serverSigningKey: Key.Signing? = null,
+    private val createSession: () -> S,
+) : LogTag("DGS:${instanceCounter.next()}") {
+
+    private val job = globalLaunch {
+        while (isActive) {
+            try {
+                val datagram = connector.incoming.receive()
+                val outer = unpack<OuterPacket>(datagram.message)
+                if (outer.id == 0u)
+                    setupNewConnection(datagram.address, outer)
+                else
+                    proceedExistingConnection(datagram.address, outer)
+            } catch (_: ClosedReceiveChannelException) {
+
+            }
+        }
+    }
+
+    private val access = Mutex()
+    private val connections = mutableMapOf<ConnectionId, Connection<S>>()
+
+    private fun findFreeId(address: NetworkAddress): UInt {
+        val existingIds = connections.keys.filter { it.address == address }.map { it.id }.toSet()
+        debug { "existing connections from $address: $existingIds" }
+        var i = 0u
+        while (i in existingIds) i++
+        debug { "found the free id: $i" }
+        return i
+    }
+
+    private suspend fun setupNewConnection(address: NetworkAddress, packet: OuterPacket) {
+        val id = access.withLock {
+            val connectionId = ConnectionId(address, findFreeId(address))
+            val proxy = ProxyDevice()
+            connections[connectionId] = Connection(
+                this,
+                KiloServerConnection(localInterface, proxy, createSession(), serverSigningKey),
+                proxy,
+                connectionId,
+            )
+            connectionId
+        }
+        sendResult(id,DatagramResult.Ok(id.id))
+    }
+
+    private suspend fun proceedExistingConnection(address: NetworkAddress, outerPacket: OuterPacket) {
+        val connectionId = ConnectionId(address, outerPacket.id)
+        val c = access.withLock { connections[connectionId] }
+        if (c == null) {
+            sendResult(connectionId, DatagramResult.Error(DatagramError.NotExists))
+        } else {
+            c.proceedFrame(outerPacket)
+        }
+    }
+
+    /**
+     * Important. Closing the server also closes the connector which is supposed to be "owned"
+     * exclusively by `DatagramServer`
+     */
+    fun close() {
+        job.cancel()
+        runCatching {
+            connector.close()
+        }
+    }
+
+    internal suspend fun remove(connectionId: ConnectionId) {
+        access.withLock {
+            connections.remove(connectionId)
+        }
+
+    }
+
+    internal suspend fun sendData(connectionId: ConnectionId,data: UByteArray) {
+        connector.send(pack(OuterPacket(connectionId.id, data)), connectionId.address)
+    }
+
+    internal suspend fun sendResult(connectionId: ConnectionId, result: DatagramResult) {
+        connector.send(pack(OuterPacket(0u, pack(result))), connectionId.address)
+    }
+}

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/NetworkProvider.kt

@@ -15,11 +15,25 @@ interface NetworkAddress {
  * Multiplatform datagram abstraction
  */
 interface Datagram {
+    /**
+     * Received message
+     */
     val message: UByteArray
+
+    /**
+     * Address from where the message was sent
+     */
     val address: NetworkAddress
+
+    /**
+     * Send a datagram in response, e.g., to the [address].
+     * This method is optimized per single per-datagram use. If you need to send many datagram, use [DatagramConnector].
+     */
     suspend fun respondWith(message: UByteArray)
 }
-interface DatagramReceiver {
+
+@OptIn(ExperimentalStdlibApi::class)
+interface DatagramConnector: AutoCloseable {
 
     val incoming: ReceiveChannel<Datagram>
     suspend fun send(message: UByteArray, networkAddress: NetworkAddress)
@@ -30,7 +44,7 @@ interface DatagramReceiver {
 
     suspend fun send(message: UByteArray,host: String,port: Int) =
         send(message, NetworkAddress(host,port))
-    fun close()
+    override fun close()
 }
 
 expect fun networkAddressOf(address: String): NetworkAddress

src/commonMain/kotlin/net/sergeych/kiloparsec/adapter/OuterPacket.kt

@@ -0,0 +1,9 @@
+package net.sergeych.kiloparsec.adapter
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+internal data class OuterPacket(
+    val id: UInt,
+    val payload: UByteArray,
+)

src/commonMain/kotlin/net/sergeych/tools/AtomicCounter.kt

@@ -0,0 +1,8 @@
+package net.sergeych.tools
+
+class AtomicCounter(startWith: Long=0) {
+    private var op = ProtectedOp()
+    private var  counter = startWith
+
+    fun next(): Long = op { counter++ }
+}

src/jvmMain/kotlin/net/sergeych/kiloparsec/adapter/UdpServer.kt

@@ -3,8 +3,6 @@ package net.sergeych.kiloparsec.adapter
 import kotlinx.coroutines.*
 import kotlinx.coroutines.channels.BufferOverflow
 import kotlinx.coroutines.channels.Channel
-import kotlinx.coroutines.sync.Mutex
-import kotlinx.coroutines.sync.withLock
 import net.sergeych.mp_logger.LogTag
 import net.sergeych.mp_logger.exception
 import net.sergeych.mp_logger.info
@@ -42,28 +40,28 @@ class UdpDatagram(override val message: UByteArray, val inetAddress: InetAddress
         JvmNetworkAddress(inetAddress, port)
     }
 
-    private val access = Mutex()
-
-    private var socket: DatagramSocket? = null
     override suspend fun respondWith(message: UByteArray) {
         withContext(Dispatchers.IO) {
-            access.withLock {
-                if (socket == null) socket = DatagramSocket()
+            // We expect datagram is most often respond once or not responded at all, and
+            // we create and close a socket to send
+            DatagramSocket().use { socket ->
                 val packet = DatagramPacket(
                     message.toByteArray(),
                     message.size,
                     inetAddress,
                     port
                 )
-                socket!!.send(packet)
+                socket.send(packet)
             }
         }
     }
+
 }
 
+
 @OptIn(DelicateCoroutinesApi::class)
 class UdpServer(val port: Int) :
-    DatagramReceiver, LogTag("UDPS:${counter.incrementAndGet()}") {
+    DatagramConnector, LogTag("UDPS:${counter.incrementAndGet()}") {
     private var isClosed = false