Add a way to enforce DTLS session expiration (#60)

* Add a way to enforce DTLS session expiration

* Fix linting

* Address comments

* Apply suggestion

Author: akolosov-n

kotlin-mbedtls-netty/src/main/kotlin/org/opencoap/ssl/netty/DatagramPacketWithContext.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,7 @@ import java.net.InetSocketAddress
 class DatagramPacketWithContext(
     data: ByteBuf,
     recipient: InetSocketAddress?,
-    sender: InetSocketAddress,
+    sender: InetSocketAddress?,
     val sessionContext: DtlsSessionContext
 ) : DatagramPacket(data, recipient, sender) {
 

kotlin-mbedtls-netty/src/main/kotlin/org/opencoap/ssl/netty/DtlsChannelHandler.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -90,6 +90,14 @@ class DtlsChannelHandler @JvmOverloads constructor(
 
     override fun write(ctx: ChannelHandlerContext, msg: Any, promise: ChannelPromise) {
         when (msg) {
+            is DatagramPacketWithContext -> {
+                write(msg, promise, ctx)
+                if (msg.sessionContext.sessionExpirationHint) {
+                    promise.toCompletableFuture().thenAccept {
+                        dtlsServer.closeSession(msg.recipient())
+                    }
+                }
+            }
             is DatagramPacket -> write(msg, promise, ctx)
             is SessionAuthenticationContext -> {
                 msg.map.forEach { (key, value) ->

kotlin-mbedtls-netty/src/test/kotlin/org/opencoap/ssl/netty/EchoHandler.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,14 +30,21 @@ class EchoHandler : ChannelInboundHandlerAdapter() {
 
         val sessionContext = DatagramPacketWithContext.contextFrom(msg)
         val authContext = (sessionContext.authenticationContext["AUTH"] ?: "")
+        val dgramContent = dgram.content().toByteArray()
+        val goToSleep = dgramContent.toString(Charset.defaultCharset()).endsWith(":sleep")
 
-        val reply = ctx.alloc().buffer(dgram.content().readableBytes() + 20)
+        val reply = ctx.alloc().buffer(dgramContent.size + 20)
         reply.writeBytes(echoPrefix)
         reply.writeCharSequence(authContext, Charset.defaultCharset())
-        reply.writeBytes(dgram.content())
+        reply.writeBytes(dgramContent)
 
-        dgram.release()
-
-        ctx.writeAndFlush(DatagramPacket(reply, dgram.sender()))
+        ctx.writeAndFlush(
+            DatagramPacketWithContext(
+                reply,
+                dgram.sender(),
+                null,
+                sessionContext.copy(sessionExpirationHint = goToSleep)
+            )
+        )
     }
 }

kotlin-mbedtls-netty/src/test/kotlin/org/opencoap/ssl/netty/NettyTest.kt

@@ -23,6 +23,7 @@ import io.netty.channel.socket.DatagramChannel
 import io.netty.channel.socket.DatagramPacket
 import io.netty.util.concurrent.DefaultThreadFactory
 import org.assertj.core.api.Assertions.assertThatThrownBy
+import org.awaitility.kotlin.await
 import org.junit.jupiter.api.AfterAll
 import org.junit.jupiter.api.AfterEach
 import org.junit.jupiter.api.Assertions.assertEquals
@@ -224,4 +225,29 @@ class NettyTest {
         assertEquals(0, dtlsServer.numberOfSessions)
         client.close()
     }
+
+    @Test
+    fun `server should store session if hinted to do so`() {
+        val client = NettyTransportAdapter.connect(clientConf, srvAddress).mapToString()
+
+        // when normal packet is sent
+        assertTrue(client.send("hi").await())
+        assertEquals("ECHO:hi", client.receive(5.seconds).await())
+
+        // then session should not be stored
+        assertEquals(1, dtlsServer.numberOfSessions)
+        assertEquals(0, sessionStore.size())
+
+        // when a packet with session expiration hint is sent
+        assertTrue(client.send("hi:sleep").await())
+        assertEquals("ECHO:hi:sleep", client.receive(5.seconds).await())
+
+        // then session must be stored
+        await.atMost(5.seconds).untilAsserted {
+            assertEquals(0, dtlsServer.numberOfSessions)
+            assertEquals(1, sessionStore.size())
+        }
+
+        client.close()
+    }
 }

kotlin-mbedtls/src/main/kotlin/org/opencoap/ssl/transport/DtlsServer.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -118,6 +118,10 @@ class DtlsServer(
         }
     }
 
+    fun closeSession(addr: InetSocketAddress) {
+        sessions.remove(addr)?.storeAndClose()
+    }
+
     fun loadSession(sessBuf: SessionWithContext?, adr: InetSocketAddress, cid: ByteArray): Boolean {
         return try {
             if (sessBuf == null) {

kotlin-mbedtls/src/main/kotlin/org/opencoap/ssl/transport/DtlsServerTransport.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -95,8 +95,16 @@ class DtlsServerTransport private constructor(
     override fun send(packet: Packet<ByteBuffer>): CompletableFuture<Boolean> = executor.supply {
         val encPacket = dtlsServer.encrypt(packet.buffer, packet.peerAddress)?.let(packet::map)
 
-        when (encPacket) {
-            null -> completedFuture(false)
+        when {
+            encPacket == null -> completedFuture(false)
+            packet.sessionContext.sessionExpirationHint -> {
+                transport.send(encPacket).thenApply { isSuccess ->
+                    if (isSuccess) {
+                        dtlsServer.closeSession(packet.peerAddress)
+                    }
+                    isSuccess
+                }
+            }
             else -> transport.send(encPacket)
         }
     }.thenCompose(Function.identity())

kotlin-mbedtls/src/main/kotlin/org/opencoap/ssl/transport/DtlsSessionContext.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
+ * Copyright (c) 2022-2024 kotlin-mbedtls contributors (https://github.com/open-coap/kotlin-mbedtls)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,7 +24,8 @@ data class DtlsSessionContext @JvmOverloads constructor(
     val authenticationContext: AuthenticationContext = emptyMap(),
     val peerCertificateSubject: String? = null,
     val cid: ByteArray? = null,
-    val sessionStartTimestamp: Instant? = null
+    val sessionStartTimestamp: Instant? = null,
+    val sessionExpirationHint: Boolean = false
 ) {
     companion object {
         @JvmField
@@ -44,6 +45,7 @@ data class DtlsSessionContext @JvmOverloads constructor(
             if (!cid.contentEquals(other.cid)) return false
         } else if (other.cid != null) return false
         if (sessionStartTimestamp != other.sessionStartTimestamp) return false
+        if (sessionExpirationHint != other.sessionExpirationHint) return false
 
         return true
     }
@@ -53,6 +55,7 @@ data class DtlsSessionContext @JvmOverloads constructor(
         result = 31 * result + (peerCertificateSubject?.hashCode() ?: 0)
         result = 31 * result + (cid?.contentHashCode() ?: 0)
         result = 31 * result + (sessionStartTimestamp?.hashCode() ?: 0)
+        result = 31 * result + (sessionExpirationHint.hashCode())
         return result
     }
 }

kotlin-mbedtls/src/test/kotlin/org/opencoap/ssl/transport/DtlsServerTransportTest.kt

@@ -476,6 +476,29 @@ class DtlsServerTransportTest {
         client.close()
     }
 
+    @Test
+    fun `server should store session if hinted to do so`() {
+        // given
+        server = DtlsServerTransport.create(conf, sessionStore = sessionStore)
+        val serverReceived = server.receive(1.seconds)
+        val client = DtlsTransmitter.connect(server, clientConfig).await().mapToString()
+
+        client.send("dupa")
+        server.send(Packet("dupa".toByteBuffer(), serverReceived.await().peerAddress))
+        assertEquals("dupa", client.receive(1.seconds).await())
+
+        client.send("sleep")
+        server.send(Packet("sleep".toByteBuffer(), serverReceived.await().peerAddress, sessionContext = DtlsSessionContext(sessionExpirationHint = true)))
+        assertEquals("sleep", client.receive(1.seconds).await())
+
+        await.atMost(5.seconds).untilAsserted {
+            assertEquals(1, sessionStore.size())
+            assertEquals(0, server.numberOfSessions())
+        }
+
+        client.close()
+    }
+
     private fun <T> Transport<T>.dropReceive(drop: (Int) -> Boolean): Transport<T> {
         val underlying = this
         var i = 0