Introduce MessageIdentifier and related tests

node/src/integration-test/kotlin/net/corda/node/services/messaging/ArtemisMessagingTest.kt

@@ -24,6 +24,8 @@ import net.corda.testing.internal.TestingNamedCacheFactory
 import net.corda.testing.internal.configureDatabase
 import net.corda.coretesting.internal.rigorousMock
 import net.corda.coretesting.internal.stubs.CertificateStoreStubs
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
 import net.corda.testing.node.MockServices.Companion.makeTestDataSourceProperties
 import net.corda.testing.node.internal.MOCK_VERSION_INFO
 import org.apache.activemq.artemis.api.core.ActiveMQConnectionTimedOutException
@@ -35,7 +37,9 @@ import org.junit.Rule
 import org.junit.Test
 import org.junit.rules.TemporaryFolder
 import rx.subjects.PublishSubject
+import java.math.BigInteger
 import java.net.ServerSocket
+import java.time.Clock
 import java.util.concurrent.BlockingQueue
 import java.util.concurrent.LinkedBlockingQueue
 import java.util.concurrent.TimeUnit.MILLISECONDS
@@ -47,6 +51,7 @@ import kotlin.test.assertTrue
 class ArtemisMessagingTest {
     companion object {
         const val TOPIC = "platform.self"
+        private val MESSAGE_IDENTIFIER = MessageIdentifier(MessageType.DATA_MESSAGE, "XXXXXXXX", SessionId(BigInteger.valueOf(14)), 0, Clock.systemUTC().instant())
     }
 
     @Rule
@@ -142,7 +147,7 @@ class ArtemisMessagingTest {
     @Test(timeout=300_000)
 	fun `client should be able to send message to itself`() {
         val (messagingClient, receivedMessages) = createAndStartClientAndServer()
-        val message = messagingClient.createMessage(TOPIC, data = "first msg".toByteArray())
+        val message = messagingClient.createMessage(TOPIC, "first msg".toByteArray(), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         messagingClient.send(message, messagingClient.myAddress)
 
         val actual: Message = receivedMessages.take()
@@ -153,14 +158,14 @@ class ArtemisMessagingTest {
     @Test(timeout=300_000)
 	fun `client should fail if message exceed maxMessageSize limit`() {
         val (messagingClient, receivedMessages) = createAndStartClientAndServer()
-        val message = messagingClient.createMessage(TOPIC, data = ByteArray(MAX_MESSAGE_SIZE))
+        val message = messagingClient.createMessage(TOPIC, ByteArray(MAX_MESSAGE_SIZE), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         messagingClient.send(message, messagingClient.myAddress)
 
         val actual: Message = receivedMessages.take()
         assertTrue(ByteArray(MAX_MESSAGE_SIZE).contentEquals(actual.data.bytes))
         assertNull(receivedMessages.poll(200, MILLISECONDS))
 
-        val tooLagerMessage = messagingClient.createMessage(TOPIC, data = ByteArray(MAX_MESSAGE_SIZE + 1))
+        val tooLagerMessage = messagingClient.createMessage(TOPIC, ByteArray(MAX_MESSAGE_SIZE + 1), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         assertThatThrownBy {
             messagingClient.send(tooLagerMessage, messagingClient.myAddress)
         }.isInstanceOf(IllegalArgumentException::class.java)
@@ -172,14 +177,14 @@ class ArtemisMessagingTest {
     @Test(timeout=300_000)
 	fun `server should not process if incoming message exceed maxMessageSize limit`() {
         val (messagingClient, receivedMessages) = createAndStartClientAndServer(clientMaxMessageSize = 100_000, serverMaxMessageSize = 50_000)
-        val message = messagingClient.createMessage(TOPIC, data = ByteArray(50_000))
+        val message = messagingClient.createMessage(TOPIC, ByteArray(50_000), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         messagingClient.send(message, messagingClient.myAddress)
 
         val actual: Message = receivedMessages.take()
         assertTrue(ByteArray(50_000).contentEquals(actual.data.bytes))
         assertNull(receivedMessages.poll(200, MILLISECONDS))
 
-        val tooLagerMessage = messagingClient.createMessage(TOPIC, data = ByteArray(100_000))
+        val tooLagerMessage = messagingClient.createMessage(TOPIC, ByteArray(100_000), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         assertThatThrownBy {
             messagingClient.send(tooLagerMessage, messagingClient.myAddress)
         }.isInstanceOf(ActiveMQConnectionTimedOutException::class.java)
@@ -189,7 +194,7 @@ class ArtemisMessagingTest {
     @Test(timeout=300_000)
 	fun `platform version is included in the message`() {
         val (messagingClient, receivedMessages) = createAndStartClientAndServer(platformVersion = 3)
-        val message = messagingClient.createMessage(TOPIC, data = "first msg".toByteArray())
+        val message = messagingClient.createMessage(TOPIC, "first msg".toByteArray(), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         messagingClient.send(message, messagingClient.myAddress)
 
         val received = receivedMessages.take()

node/src/integration-test/kotlin/net/corda/services/messaging/P2PMessagingTest.kt

@@ -10,9 +10,13 @@ import net.corda.core.serialization.deserialize
 import net.corda.core.serialization.serialize
 import net.corda.core.utilities.getOrThrow
 import net.corda.core.utilities.seconds
+import net.corda.node.services.messaging.MessageIdentifier
 import net.corda.node.services.messaging.MessagingService
 import net.corda.node.services.messaging.ReceivedMessage
+import net.corda.node.services.messaging.SenderDeduplicationInfo
 import net.corda.node.services.messaging.send
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
 import net.corda.testing.driver.DriverDSL
 import net.corda.testing.driver.DriverParameters
 import net.corda.testing.driver.InProcess
@@ -23,12 +27,15 @@ import net.corda.testing.node.NotarySpec
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.Ignore
 import org.junit.Test
+import java.math.BigInteger
+import java.time.Clock
 import java.util.*
 import java.util.concurrent.atomic.AtomicBoolean
 
 class P2PMessagingTest {
     private companion object {
         val DISTRIBUTED_SERVICE_NAME = CordaX500Name("DistributedService", "London", "GB")
+        private val MESSAGE_IDENTIFIER = MessageIdentifier(MessageType.DATA_MESSAGE, "XXXXXXXX", SessionId(BigInteger.valueOf(14)), 0, Clock.systemUTC().instant())
     }
 
     @Test(timeout=300_000)
@@ -72,7 +79,7 @@ class P2PMessagingTest {
     private fun InProcess.respondWith(message: Any) {
         internalServices.networkService.addMessageHandler("test.request") { netMessage, _, handler ->
             val request = netMessage.data.deserialize<TestRequest>()
-            val response = internalServices.networkService.createMessage("test.response", message.serialize().bytes)
+            val response = internalServices.networkService.createMessage("test.response", message.serialize().bytes, SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
             internalServices.networkService.send(response, request.replyTo)
             handler.afterDatabaseTransaction()
         }
@@ -83,7 +90,7 @@ class P2PMessagingTest {
         internalServices.networkService.runOnNextMessage("test.response") { netMessage ->
             response.set(netMessage.data.deserialize())
         }
-        internalServices.networkService.send("test.request", TestRequest(replyTo = internalServices.networkService.myAddress), target)
+        internalServices.networkService.send("test.request", TestRequest(replyTo = internalServices.networkService.myAddress), target, SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         return response
     }
 

node/src/main/kotlin/net/corda/node/services/messaging/MessageIdentifier.kt

@@ -0,0 +1,93 @@
+package net.corda.node.services.messaging
+
+import net.corda.core.crypto.SecureHash
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
+import java.lang.IllegalStateException
+import java.math.BigInteger
+import java.time.Instant
+
+/**
+ * This represents the unique identifier for every message.
+ * It's composed of multiple segments.
+ *
+ * @property messageType the type of the message.
+ * @property shardIdentifier an identifier that can be used to partition messages into groups for sharding purposes.
+ *  This is supposed to have the same value for messages that correspond to the same business-level flow. It is
+ * @property sessionIdentifier the identifier of the session this message belongs to. This corresponds to the identifier of the session on the receiving side.
+ * @property sessionSequenceNumber the sequence number of the message inside the session. This can be used to handle out-of-order delivery.
+ * @property timestamp the time when the message was requested to be sent.
+ *  This is expected to remain the same across replays of the same message and represent the moment in time when this message  was initially scheduled to be sent.
+ */
+data class MessageIdentifier(
+        val messageType: MessageType,
+        val shardIdentifier: String,
+        val sessionIdentifier: SessionId,
+        val sessionSequenceNumber: Int,
+        val timestamp: Instant
+) {
+    init {
+        require(shardIdentifier.length == 8) { "Shard identifier needs to be 8 characters long, but it was $shardIdentifier" }
+    }
+
+    companion object {
+        const val LONG_SIZE_IN_HEX = 16 // 64 / 4
+        const val SESSION_ID_SIZE_IN_HEX = SessionId.MAX_BIT_SIZE / 4
+
+        fun parse(id: String): MessageIdentifier {
+            val prefix = id.substring(0, 2)
+            val messageType = prefixToMessageType(prefix)
+            val timestamp = java.lang.Long.parseUnsignedLong(id.substring(3, 19), 16)
+            val shardIdentifier = id.substring(20, 28)
+            val sessionId = BigInteger(id.substring(29, 61), 16)
+            val sessionSequenceNumber = Integer.parseInt(id.substring(62), 16)
+            return MessageIdentifier(messageType, shardIdentifier, SessionId(sessionId), sessionSequenceNumber, Instant.ofEpochMilli(timestamp))
+        }
+
+        private fun messageTypeToPrefix(messageType: MessageType): String {
+            return when(messageType) {
+                MessageType.SESSION_INIT -> "XI"
+                MessageType.SESSION_CONFIRM -> "XC"
+                MessageType.SESSION_REJECT -> "XR"
+                MessageType.DATA_MESSAGE -> "XD"
+                MessageType.SESSION_END -> "XE"
+                MessageType.SESSION_ERROR -> "XX"
+            }
+        }
+
+        private fun prefixToMessageType(prefix: String): MessageType {
+            return when(prefix) {
+                "XI" -> MessageType.SESSION_INIT
+                "XC" -> MessageType.SESSION_CONFIRM
+                "XR" -> MessageType.SESSION_REJECT
+                "XD" -> MessageType.DATA_MESSAGE
+                "XE" -> MessageType.SESSION_END
+                "XX" -> MessageType.SESSION_ERROR
+                else -> throw IllegalStateException("Invalid prefix: $prefix")
+            }
+        }
+    }
+
+    override fun toString(): String {
+        val prefix = messageTypeToPrefix(messageType)
+        val encodedSessionIdentifier = String.format("%1$0${SESSION_ID_SIZE_IN_HEX}X", sessionIdentifier.value)
+        val encodedSequenceNumber = Integer.toHexString(sessionSequenceNumber).toUpperCase()
+        val encodedTimestamp = String.format("%1$0${LONG_SIZE_IN_HEX}X", timestamp.toEpochMilli())
+        return "$prefix-$encodedTimestamp-$shardIdentifier-$encodedSessionIdentifier-$encodedSequenceNumber"
+    }
+
+}
+
+fun generateShardId(flowIdentifier: String): String {
+    return SecureHash.sha256(flowIdentifier).prefixChars(8)
+}
+
+/**
+ * A unique identifier for a sender that might be different across restarts.
+ * It is used to help identify when messages are being sent continuously without errors or message are sent after the sender recovered from an error.
+ */
+typealias SenderUUID = String
+/**
+ * A global sequence number for all the messages sent by a sender.
+ */
+typealias SenderSequenceNumber = Long

node/src/main/kotlin/net/corda/node/services/messaging/Messaging.kt

@@ -1,7 +1,6 @@
 package net.corda.node.services.messaging
 
 import co.paralleluniverse.fibers.Suspendable
-import net.corda.core.crypto.newSecureRandom
 import net.corda.core.identity.CordaX500Name
 import net.corda.core.messaging.MessageRecipients
 import net.corda.core.messaging.SingleMessageRecipient
@@ -9,9 +8,8 @@ import net.corda.core.node.services.PartyInfo
 import net.corda.core.serialization.CordaSerializable
 import net.corda.core.serialization.serialize
 import net.corda.core.utilities.ByteSequence
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.ExternalEvent
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.statemachine.SessionId
 import net.corda.nodeapi.internal.lifecycle.ServiceLifecycleSupport
 import java.time.Instant
 import javax.annotation.concurrent.ThreadSafe
@@ -32,7 +30,7 @@ interface MessagingService : ServiceLifecycleSupport {
      * A unique identifier for this sender that changes whenever a node restarts.  This is used in conjunction with a sequence
      * number for message de-duplication at the recipient.
      */
-    val ourSenderUUID: String
+    val ourSenderUUID: SenderUUID
 
     /**
      * The provided function will be invoked for each received message whose topic and session matches.  The callback
@@ -92,15 +90,25 @@ interface MessagingService : ServiceLifecycleSupport {
     @Suspendable
     fun sendAll(addressedMessages: List<AddressedMessage>)
 
+    /**
+     * Signal that a session has ended to the messaging layer, so that any necessary cleanup is performed.
+     *
+     * @param sessionId the identifier of the session that ended.
+     * @param senderUUID the sender UUID of the last message seen in the session or null if there was no sender UUID in that message.
+     * @param senderSequenceNumber the sender sequence number of the last message seen in the session or null if there was no sender sequence number in that message.
+     */
+    @Suspendable
+    fun sessionEnded(sessionId: SessionId, senderUUID: SenderUUID?, senderSequenceNumber: SenderSequenceNumber?)
+
     /**
      * Returns an initialised [Message] with the current time, etc, already filled in.
      *
      * @param topic identifier for the topic the message is sent to.
      * @param data the payload for the message.
-     * @param deduplicationId optional message deduplication ID including sender identifier.
+     * @param deduplicationInfo optional message deduplication information.
      * @param additionalHeaders optional additional message headers.
      */
-    fun createMessage(topic: String, data: ByteArray, deduplicationId: SenderDeduplicationId = SenderDeduplicationId(DeduplicationId.createRandom(newSecureRandom()), ourSenderUUID), additionalHeaders: Map<String, String> = emptyMap()): Message
+    fun createMessage(topic: String, data: ByteArray, deduplicationInfo: SenderDeduplicationInfo, additionalHeaders: Map<String, String>): Message
 
     /** Given information about either a specific node or a service returns its corresponding address */
     fun getAddressOfParty(partyInfo: PartyInfo): MessageRecipients
@@ -109,7 +117,7 @@ interface MessagingService : ServiceLifecycleSupport {
     val myAddress: SingleMessageRecipient
 }
 
-fun MessagingService.send(topicSession: String, payload: Any, to: MessageRecipients, deduplicationId: SenderDeduplicationId = SenderDeduplicationId(DeduplicationId.createRandom(newSecureRandom()), ourSenderUUID), additionalHeaders: Map<String, String> = emptyMap()) = send(createMessage(topicSession, payload.serialize().bytes, deduplicationId, additionalHeaders), to)
+fun MessagingService.send(topicSession: String, payload: Any, to: MessageRecipients, deduplicationInfo: SenderDeduplicationInfo, additionalHeaders: Map<String, String>) = send(createMessage(topicSession, payload.serialize().bytes, deduplicationInfo, additionalHeaders), to)
 
 interface MessageHandlerRegistration
 
@@ -128,7 +136,7 @@ interface Message {
     val topic: String
     val data: ByteSequence
     val debugTimestamp: Instant
-    val uniqueMessageId: DeduplicationId
+    val uniqueMessageId: MessageIdentifier
     val senderUUID: String?
     val additionalHeaders: Map<String, String>
 }

node/src/main/kotlin/net/corda/node/services/messaging/MessagingExecutor.kt

@@ -75,7 +75,7 @@ class MessagingExecutor(
             putStringProperty(P2PMessagingHeaders.topicProperty, SimpleString(message.topic))
             writeBodyBufferBytes(message.data.bytes)
             // Use the magic deduplication property built into Artemis as our message identity too
-            putStringProperty(org.apache.activemq.artemis.api.core.Message.HDR_DUPLICATE_DETECTION_ID, SimpleString(message.uniqueMessageId.toString))
+            putStringProperty(org.apache.activemq.artemis.api.core.Message.HDR_DUPLICATE_DETECTION_ID, SimpleString(message.uniqueMessageId.toString()))
             // If we are the sender (ie. we are not going through recovery of some sort), use sequence number short cut.
             if (ourSenderUUID == message.senderUUID) {
                 putStringProperty(P2PMessagingHeaders.senderUUID, SimpleString(ourSenderUUID))

node/src/main/kotlin/net/corda/node/services/messaging/P2PMessageDeduplicator.kt

@@ -1,56 +1,79 @@
 package net.corda.node.services.messaging
 
+import co.paralleluniverse.fibers.Suspendable
 import net.corda.core.crypto.SecureHash
 import net.corda.core.identity.CordaX500Name
 import net.corda.core.internal.NamedCacheFactory
-import net.corda.node.services.statemachine.DeduplicationId
+import net.corda.core.utilities.contextLogger
+import net.corda.node.services.statemachine.SessionId
 import net.corda.node.utilities.AppendOnlyPersistentMap
 import net.corda.nodeapi.internal.persistence.CordaPersistence
 import net.corda.nodeapi.internal.persistence.NODE_DATABASE_PREFIX
+import net.corda.nodeapi.internal.persistence.currentDBSession
+import java.math.BigInteger
 import java.time.Instant
 import java.util.concurrent.ConcurrentHashMap
 import javax.persistence.Column
 import javax.persistence.Entity
 import javax.persistence.Id
+import javax.persistence.Table
 
 /**
- * Encapsulate the de-duplication logic.
+ * This component is responsible for determining whether session-init messages are duplicates and it also keeps track of information related to
+ * sessions that can be used for this purpose.
  */
 class P2PMessageDeduplicator(cacheFactory: NamedCacheFactory, private val database: CordaPersistence) {
+
+    companion object {
+        private val logger = contextLogger()
+    }
+
     // A temporary in-memory set of deduplication IDs and associated high water mark details.
     // When we receive a message we don't persist the ID immediately,
     // so we store the ID here in the meantime (until the persisting db tx has committed). This is because Artemis may
     // redeliver messages to the same consumer if they weren't ACKed.
-    private val beingProcessedMessages = ConcurrentHashMap<DeduplicationId, MessageMeta>()
+    private val beingProcessedMessages = ConcurrentHashMap<MessageIdentifier, MessageMeta>()
-    private val processedMessages = createProcessedMessages(cacheFactory)
 
-    private fun createProcessedMessages(cacheFactory: NamedCacheFactory): AppendOnlyPersistentMap<DeduplicationId, MessageMeta, ProcessedMessage, String> {
+    /**
+     * This table holds data *only* for sessions that have been initiated from a counterparty (e.g. ones we have received session-init messages from).
+     * This is because any other messages apart from session-init messages are deduplicated by the state machine.
+     */
+    private val sessionData = createSessionDataMap(cacheFactory)
+
+    private fun createSessionDataMap(cacheFactory: NamedCacheFactory): AppendOnlyPersistentMap<SessionId, MessageMeta, SessionData, BigInteger> {
         return AppendOnlyPersistentMap(
                 cacheFactory = cacheFactory,
-                name = "P2PMessageDeduplicator_processedMessages",
+                name = "P2PMessageDeduplicator_sessionData",
-                toPersistentEntityKey = { it.toString },
+                toPersistentEntityKey = { it.value },
-                fromPersistentEntity = { Pair(DeduplicationId(it.id), MessageMeta(it.insertionTime, it.hash, it.seqNo)) },
+                fromPersistentEntity = { Pair(SessionId(it.sessionId), MessageMeta(it.generationTime, it.senderHash, it.firstSenderSeqNo, it.lastSenderSeqNo)) },
-                toPersistentEntity = { key: DeduplicationId, value: MessageMeta ->
+                toPersistentEntity = { key: SessionId, value: MessageMeta ->
-                    ProcessedMessage().apply {
+                    SessionData().apply {
-                        id = key.toString
+                        sessionId = key.value
-                        insertionTime = value.insertionTime
+                        generationTime = value.generationTime
-                        hash = value.senderHash
+                        senderHash = value.senderHash
-                        seqNo = value.senderSeqNo
+                        firstSenderSeqNo = value.firstSenderSeqNo
+                        lastSenderSeqNo = value.lastSenderSeqNo
                     }
                 },
-                persistentEntityClass = ProcessedMessage::class.java
+                persistentEntityClass = SessionData::class.java
         )
     }
 
-    private fun isDuplicateInDatabase(msg: ReceivedMessage): Boolean = database.transaction { msg.uniqueMessageId in processedMessages }
+    private fun isDuplicateInDatabase(msg: ReceivedMessage): Boolean = database.transaction { msg.uniqueMessageId.sessionIdentifier in sessionData }
 
     // We need to incorporate the sending party, and the sessionInit flag as per the in-memory cache.
     private fun senderHash(senderKey: SenderKey) = SecureHash.sha256(senderKey.peer.toString() + senderKey.isSessionInit.toString() + senderKey.senderUUID).toString()
 
     /**
+     * Determines whether a session-init message is a duplicate.
+     * This is achieved by checking whether this message is currently being processed or if the associated session has already been created in the past.
+     * This method should be invoked only with session-init messages, otherwise it will fail with an [IllegalArgumentException].
+     *
      * @return true if we have seen this message before.
      */
-    fun isDuplicate(msg: ReceivedMessage): Boolean {
+    fun isDuplicateSessionInit(msg: ReceivedMessage): Boolean {
+        require(msg.isSessionInit) { "Message ${msg.uniqueMessageId} was not a session-init message." }
+
         if (beingProcessedMessages.containsKey(msg.uniqueMessageId)) {
             return true
         }
@@ -65,44 +88,86 @@ class P2PMessageDeduplicator(cacheFactory: NamedCacheFactory, private val databa
         val receivedSenderSeqNo = msg.senderSeqNo
         // We don't want a mix of nulls and values so we ensure that here.
         val senderHash: String? = if (receivedSenderUUID != null && receivedSenderSeqNo != null) senderHash(SenderKey(receivedSenderUUID, msg.peer, msg.isSessionInit)) else null
-        val senderSeqNo: Long? = if (senderHash != null) msg.senderSeqNo else null
+        val firstSenderSeqNo: Long? = if (senderHash != null) msg.senderSeqNo else null
-        beingProcessedMessages[msg.uniqueMessageId] = MessageMeta(Instant.now(), senderHash, senderSeqNo)
+        beingProcessedMessages[msg.uniqueMessageId] = MessageMeta(msg.uniqueMessageId.timestamp, senderHash, firstSenderSeqNo, null)
     }
 
     /**
      * Called inside a DB transaction to persist [deduplicationId].
      */
-    fun persistDeduplicationId(deduplicationId: DeduplicationId) {
+    fun persistDeduplicationId(deduplicationId: MessageIdentifier) {
-        processedMessages[deduplicationId] = beingProcessedMessages[deduplicationId]!!
+        sessionData[deduplicationId.sessionIdentifier] = beingProcessedMessages[deduplicationId]!!
     }
 
     /**
      * Called after the DB transaction persisting [deduplicationId] committed.
      * Any subsequent redelivery will be deduplicated using the DB.
      */
-    fun signalMessageProcessFinish(deduplicationId: DeduplicationId) {
+    fun signalMessageProcessFinish(deduplicationId: MessageIdentifier) {
         beingProcessedMessages.remove(deduplicationId)
     }
 
+    /**
+     * Called inside a DB transaction to update entry for corresponding session.
+     * The parameters [senderUUID] and [senderSequenceNumber] correspond to the last message seen from this session before it ended.
+     * If [senderUUID] is not null, then [senderSequenceNumber] is also expected to not be null.
+     */
+    @Suspendable
+    fun signalSessionEnd(sessionId: SessionId, senderUUID: String?, senderSequenceNumber: Long?) {
+        if (senderSequenceNumber != null && senderUUID != null) {
+            val existingEntry = sessionData[sessionId]
+            if (existingEntry != null) {
+                val newEntry = existingEntry.copy(lastSenderSeqNo = senderSequenceNumber)
+                sessionData.addOrUpdate(sessionId, newEntry) { k, v ->
+                    update(k, v)
+                }
+            }
+        }
+    }
+
+    private fun update(key: SessionId, value: MessageMeta): Boolean {
+        val session = currentDBSession()
+        val criteriaBuilder = session.criteriaBuilder
+        val criteriaUpdate = criteriaBuilder.createCriteriaUpdate(SessionData::class.java)
+        val queryRoot = criteriaUpdate.from(SessionData::class.java)
+        criteriaUpdate.set(SessionData::lastSenderSeqNo.name, value.lastSenderSeqNo)
+        criteriaUpdate.where(criteriaBuilder.equal(queryRoot.get<BigInteger>(SessionData::sessionId.name), key.value))
+        val update = session.createQuery(criteriaUpdate)
+        val rowsUpdated = update.executeUpdate()
+        return rowsUpdated != 0
+    }
+
     @Entity
     @Suppress("MagicNumber") // database column width
-    @javax.persistence.Table(name = "${NODE_DATABASE_PREFIX}message_ids")
+    @Table(name = "${NODE_DATABASE_PREFIX}session_data")
-    class ProcessedMessage(
+    class SessionData (
             @Id
-            @Column(name = "message_id", length = 64, nullable = false)
+            @Column(name = "session_id", nullable = false)
-            var id: String = "",
+            var sessionId: BigInteger = BigInteger.ZERO,
 
-            @Column(name = "insertion_time", nullable = false)
+            /**
-            var insertionTime: Instant = Instant.now(),
+             * The time the corresponding session-init message was originally generated on the sender side.
+             */
+            @Column(name = "init_generation_time", nullable = false)
+            var generationTime: Instant = Instant.now(),
 
-            @Column(name = "sender", length = 64, nullable = true)
+            @Column(name = "sender_hash", length = 64, nullable = true)
-            var hash: String? = "",
+            var senderHash: String? = "",
 
-            @Column(name = "sequence_number", nullable = true)
+            /**
-            var seqNo: Long? = null
+             * The sender sequence number of the first message seen in a session.
+             */
+            @Column(name = "init_sequence_number", nullable = true)
+            var firstSenderSeqNo: Long? = null,
+
+            /**
+             * The sender sequence number of the last message seen in a session before it was closed/terminated.
+             */
+            @Column(name = "last_sequence_number", nullable = true)
+            var lastSenderSeqNo: Long? = null
     )
 
-    private data class MessageMeta(val insertionTime: Instant, val senderHash: String?, val senderSeqNo: Long?)
+    private data class MessageMeta(val generationTime: Instant, val senderHash: String?, val firstSenderSeqNo: SenderSequenceNumber?, val lastSenderSeqNo: SenderSequenceNumber?)
 
     private data class SenderKey(val senderUUID: String, val peer: CordaX500Name, val isSessionInit: Boolean)
 }

node/src/main/kotlin/net/corda/node/services/messaging/P2PMessagingClient.kt

@@ -25,9 +25,9 @@ import net.corda.node.internal.artemis.ReactiveArtemisConsumer
 import net.corda.node.internal.artemis.ReactiveArtemisConsumer.Companion.multiplex
 import net.corda.node.services.api.NetworkMapCacheInternal
 import net.corda.node.services.config.NodeConfiguration
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.ExternalEvent
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
 import net.corda.node.utilities.AffinityExecutor
 import net.corda.node.utilities.errorAndTerminate
 import net.corda.nodeapi.internal.ArtemisMessagingComponent
@@ -101,8 +101,8 @@ class P2PMessagingClient(val config: NodeConfiguration,
 
     private class NodeClientMessage(override val topic: String,
                                     override val data: ByteSequence,
-                                    override val uniqueMessageId: DeduplicationId,
+                                    override val uniqueMessageId: MessageIdentifier,
-                                    override val senderUUID: String?,
+                                    override val senderUUID: SenderUUID?,
                                     override val additionalHeaders: Map<String, String>) : Message {
         override val debugTimestamp: Instant = Instant.now()
         override fun toString() = "$topic#${String(data.bytes)}"
@@ -371,7 +371,7 @@ class P2PMessagingClient(val config: NodeConfiguration,
             val user = requireNotNull(message.getStringProperty(HDR_VALIDATED_USER)) { "Message is not authenticated" }
             val platformVersion = message.required(P2PMessagingHeaders.platformVersionProperty) { getIntProperty(it) }
             // Use the magic deduplication property built into Artemis as our message identity too
-            val uniqueMessageId = message.required(HDR_DUPLICATE_DETECTION_ID) { DeduplicationId(message.getStringProperty(it)) }
+            val uniqueMessageId = message.required(HDR_DUPLICATE_DETECTION_ID) { MessageIdentifier.parse(message.getStringProperty(it)) }
             val receivedSenderUUID = message.getStringProperty(P2PMessagingHeaders.senderUUID)
             val receivedSenderSeqNo = if (message.containsProperty(P2PMessagingHeaders.senderSeqNo)) message.getLongProperty(P2PMessagingHeaders.senderSeqNo) else null
             val isSessionInit = message.getStringProperty(P2PMessagingHeaders.Type.KEY) == P2PMessagingHeaders.Type.SESSION_INIT_VALUE
@@ -392,8 +392,8 @@ class P2PMessagingClient(val config: NodeConfiguration,
     private class ArtemisReceivedMessage(override val topic: String,
                                          override val peer: CordaX500Name,
                                          override val platformVersion: Int,
-                                         override val uniqueMessageId: DeduplicationId,
+                                         override val uniqueMessageId: MessageIdentifier,
-                                         override val senderUUID: String?,
+                                         override val senderUUID: SenderUUID?,
                                          override val senderSeqNo: Long?,
                                          override val isSessionInit: Boolean,
                                          private val message: ClientMessage) : ReceivedMessage {
@@ -405,13 +405,18 @@ class P2PMessagingClient(val config: NodeConfiguration,
 
     internal fun deliver(artemisMessage: ClientMessage) {
         artemisToCordaMessage(artemisMessage)?.let { cordaMessage ->
-            if (!deduplicator.isDuplicate(cordaMessage)) {
+            if (cordaMessage.uniqueMessageId.messageType == MessageType.SESSION_INIT) {
+                if (!deduplicator.isDuplicateSessionInit(cordaMessage)) {
                     deduplicator.signalMessageProcessStart(cordaMessage)
                     deliver(cordaMessage, artemisMessage)
                 } else {
-                log.trace { "Discard duplicate message ${cordaMessage.uniqueMessageId} for ${cordaMessage.topic}" }
+                    log.debug { "Discarding duplicate session-init message with identifier: ${cordaMessage.uniqueMessageId}, senderUUID: ${cordaMessage.senderUUID}, senderSeqNo: ${cordaMessage.senderSeqNo}" }
                     messagingExecutor!!.acknowledge(artemisMessage)
                 }
+            } else {
+                // non session-init messages are directly handed to the state machine, which is responsible for performing deduplication.
+                deliver(cordaMessage, artemisMessage)
+            }
         }
     }
 
@@ -420,7 +425,11 @@ class P2PMessagingClient(val config: NodeConfiguration,
         val deliverTo = handlers[msg.topic]
         if (deliverTo != null) {
             try {
-                deliverTo(msg, HandlerRegistration(msg.topic, deliverTo), MessageDeduplicationHandler(artemisMessage, msg))
+                if (msg.uniqueMessageId.messageType == MessageType.SESSION_INIT) {
+                    deliverTo(msg, HandlerRegistration(msg.topic, deliverTo), MessageDeduplicationHandlerForSessionInitMessages(artemisMessage, msg))
+                } else {
+                    deliverTo(msg, HandlerRegistration(msg.topic, deliverTo), MessageDeduplicationHandlerForRegularMessages(artemisMessage, msg))
+                }
             } catch (e: Exception) {
                 log.error("Caught exception whilst executing message handler for ${msg.topic}", e)
             }
@@ -429,11 +438,11 @@ class P2PMessagingClient(val config: NodeConfiguration,
         }
     }
 
-    private inner class MessageDeduplicationHandler(val artemisMessage: ClientMessage, override val receivedMessage: ReceivedMessage) : DeduplicationHandler, ExternalEvent.ExternalMessageEvent {
+    private inner class MessageDeduplicationHandlerForSessionInitMessages(val artemisMessage: ClientMessage, override val receivedMessage: ReceivedMessage) : DeduplicationHandler, ExternalEvent.ExternalMessageEvent {
         override val externalCause: ExternalEvent
             get() = this
         override val flowId: StateMachineRunId by lazy { StateMachineRunId.createRandom() }
-        override val deduplicationHandler: MessageDeduplicationHandler
+        override val deduplicationHandler: MessageDeduplicationHandlerForSessionInitMessages
             get() = this
 
         override fun insideDatabaseTransaction() {
@@ -450,6 +459,27 @@ class P2PMessagingClient(val config: NodeConfiguration,
         }
     }
 
+    private inner class MessageDeduplicationHandlerForRegularMessages(val artemisMessage: ClientMessage, override val receivedMessage: ReceivedMessage) : DeduplicationHandler, ExternalEvent.ExternalMessageEvent {
+        override val externalCause: ExternalEvent
+            get() = this
+        override val flowId: StateMachineRunId by lazy { StateMachineRunId.createRandom() }
+        override val deduplicationHandler: MessageDeduplicationHandlerForRegularMessages
+            get() = this
+
+        /**
+         * Nothing to do, since deduplication information is kept in the state machine.
+         */
+        override fun insideDatabaseTransaction() {}
+
+        override fun afterDatabaseTransaction() {
+            messagingExecutor!!.acknowledge(artemisMessage)
+        }
+
+        override fun toString(): String {
+            return "${javaClass.simpleName}(${receivedMessage.uniqueMessageId})"
+        }
+    }
+
     /**
      * Initiates shutdown: if called from a thread that isn't controlled by the executor passed to the constructor
      * then this will block until all in-flight messages have finished being handled and acknowledged. If called
@@ -520,6 +550,11 @@ class P2PMessagingClient(val config: NodeConfiguration,
         }
     }
 
+    @Suspendable
+    override fun sessionEnded(sessionId: SessionId, senderUUID: SenderUUID?, senderSequenceNumber: SenderSequenceNumber?) {
+        deduplicator.signalSessionEnd(sessionId, senderUUID, senderSequenceNumber)
+    }
+
     override fun resolveTargetToArtemisQueue(address: MessageRecipients): String {
         return if (address == myAddress) {
             // If we are sending to ourselves then route the message directly to our P2P queue.
@@ -586,8 +621,8 @@ class P2PMessagingClient(val config: NodeConfiguration,
         handlers.remove(registration.topic)
     }
 
-    override fun createMessage(topic: String, data: ByteArray, deduplicationId: SenderDeduplicationId, additionalHeaders: Map<String, String>): Message {
+    override fun createMessage(topic: String, data: ByteArray, deduplicationInfo: SenderDeduplicationInfo, additionalHeaders: Map<String, String>): Message {
-        return NodeClientMessage(topic, OpaqueBytes(data), deduplicationId.deduplicationId, deduplicationId.senderUUID, additionalHeaders)
+        return NodeClientMessage(topic, OpaqueBytes(data), deduplicationInfo.messageIdentifier, deduplicationInfo.senderUUID, additionalHeaders)
     }
 
     override fun getAddressOfParty(partyInfo: PartyInfo): MessageRecipients {

node/src/main/kotlin/net/corda/node/services/messaging/SenderDeduplicationInfo.kt

@@ -0,0 +1,11 @@
+package net.corda.node.services.messaging
+
+/**
+ * This is a combination of a message's unique identifier along with a unique identifier for the sender of the message.
+ * The former can be used independently for deduplication purposes when receiving a message, but enriching it with the latter helps us
+ * optimise some paths and perform smarter deduplication logic per sender.
+ *
+ * The [senderUUID] property might be null if the flow is trying to replay messages and doesn't want an optimisation to ignore the message identifier
+ * because it could lead to false negatives (messages that are deemed duplicates, but are not).
+ */
+data class SenderDeduplicationInfo(val messageIdentifier: MessageIdentifier, val senderUUID: String?)

node/src/main/kotlin/net/corda/node/services/rpc/CheckpointDumperImpl.kt

@@ -513,7 +513,7 @@ class CheckpointDumperImpl(private val checkpointStorage: CheckpointStorage, pri
 
     private fun SessionState.toActiveSession(sessionId: SessionId): ActiveSession? {
         return if (this is SessionState.Initiated) {
-            ActiveSession(peerParty, sessionId, receivedMessages, peerFlowInfo, peerSinkSessionId)
+            ActiveSession(peerParty, sessionId, receivedMessages.values.toList(), peerFlowInfo, peerSinkSessionId)
         } else {
             null
         }

node/src/main/kotlin/net/corda/node/services/schema/NodeSchemaService.kt

@@ -43,7 +43,7 @@ class NodeSchemaService(private val extraSchemas: Set<MappedSchema> = emptySet()
                     BasicHSMKeyManagementService.PersistentKey::class.java,
                     NodeSchedulerService.PersistentScheduledState::class.java,
                     NodeAttachmentService.DBAttachment::class.java,
-                    P2PMessageDeduplicator.ProcessedMessage::class.java,
+                    P2PMessageDeduplicator.SessionData::class.java,
                     PersistentIdentityService.PersistentPublicKeyHashToCertificate::class.java,
                     PersistentIdentityService.PersistentPublicKeyHashToParty::class.java,
                     PersistentIdentityService.PersistentHashToPublicKey::class.java,

node/src/main/kotlin/net/corda/node/services/statemachine/Action.kt

@@ -6,6 +6,10 @@ import net.corda.core.flows.StateMachineRunId
 import net.corda.core.identity.Party
 import net.corda.core.internal.FlowAsyncOperation
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.messaging.SenderSequenceNumber
+import net.corda.node.services.messaging.SenderUUID
 import java.time.Instant
 import java.util.*
 
@@ -25,7 +29,7 @@ sealed class Action {
     data class SendInitial(
             val destination: Destination,
             val initialise: InitialSessionMessage,
-            val deduplicationId: SenderDeduplicationId
+            val deduplicationInfo: SenderDeduplicationInfo
     ) : Action()
 
     /**
@@ -34,7 +38,7 @@ sealed class Action {
     data class SendExisting(
             val peerParty: Party,
             val message: ExistingSessionMessage,
-            val deduplicationId: SenderDeduplicationId
+            val deduplicationInfo: SenderDeduplicationInfo
     ) : Action()
 
     /**
@@ -95,12 +99,11 @@ sealed class Action {
     data class AcknowledgeMessages(val deduplicationHandlers: List<DeduplicationHandler>) : Action()
 
     /**
-     * Propagate [errorMessages] to [sessions].
+     * Propagate the specified error messages to the specified sessions.
-     * @param sessions a map from source session IDs to initiated sessions.
+     * @param errorsPerSession a map containing the error messages to be sent per session along with their identifiers.
      */
     data class PropagateErrors(
-            val errorMessages: List<ErrorSessionMessage>,
+            val errorsPerSession: Map<SessionState.Initiated, List<Pair<MessageIdentifier, ErrorSessionMessage>>>,
-            val sessions: List<SessionState.Initiated>,
             val senderUUID: String?
     ) : Action()
 
@@ -114,6 +117,11 @@ sealed class Action {
      */
     data class RemoveSessionBindings(val sessionIds: Set<SessionId>) : Action()
 
+    /**
+     * Signal sessions ended at the messaging layer.
+     */
+    data class SignalSessionsHasEnded(val terminatedSessions: Map<SessionId, Pair<SenderUUID?, SenderSequenceNumber?>>): Action()
+
     /**
      * Signal that the flow corresponding to [flowId] is considered started.
      */

node/src/main/kotlin/net/corda/node/services/statemachine/ActionExecutorImpl.kt

@@ -10,6 +10,7 @@ import net.corda.core.utilities.contextLogger
 import net.corda.core.utilities.trace
 import net.corda.node.services.api.CheckpointStorage
 import net.corda.node.services.api.ServiceHubInternal
+import net.corda.node.services.messaging.SenderDeduplicationInfo
 import net.corda.nodeapi.internal.persistence.contextDatabase
 import net.corda.nodeapi.internal.persistence.contextTransaction
 import net.corda.nodeapi.internal.persistence.contextTransactionOrNull
@@ -58,6 +59,7 @@ internal class ActionExecutorImpl(
             is Action.AddSessionBinding -> executeAddSessionBinding(action)
             is Action.RemoveSessionBindings -> executeRemoveSessionBindings(action)
             is Action.SignalFlowHasStarted -> executeSignalFlowHasStarted(action)
+            is Action.SignalSessionsHasEnded -> executeSignalSessionsHasEnded(action)
             is Action.RemoveFlow -> executeRemoveFlow(action)
             is Action.CreateTransaction -> executeCreateTransaction()
             is Action.RollbackTransaction -> executeRollbackTransaction()
@@ -132,16 +134,17 @@ internal class ActionExecutorImpl(
 
     @Suspendable
     private fun executePropagateErrors(action: Action.PropagateErrors) {
-        action.errorMessages.forEach { (exception) ->
+        val errors = action.errorsPerSession.values.flatMap { it.map { it.second } }.distinct()
+        errors.forEach { errorSessionMessage ->
+            val exception = errorSessionMessage.flowException
             log.warn("Propagating error", exception)
         }
-        for (sessionState in action.sessions) {
+        action.errorsPerSession.forEach { (sessionState, sessionErrors) ->
             // Don't propagate errors to the originating session
-            for (errorMessage in action.errorMessages) {
+            for ((id, msg) in sessionErrors) {
                 val sinkSessionId = sessionState.peerSinkSessionId
-                val existingMessage = ExistingSessionMessage(sinkSessionId, errorMessage)
+                val errorMsg = ExistingSessionMessage(sinkSessionId, msg)
-                val deduplicationId = DeduplicationId.createForError(errorMessage.errorId, sinkSessionId)
+                flowMessaging.sendSessionMessage(sessionState.peerParty, errorMsg, SenderDeduplicationInfo(id, action.senderUUID))
-                flowMessaging.sendSessionMessage(sessionState.peerParty, existingMessage, SenderDeduplicationId(deduplicationId, action.senderUUID))
             }
         }
     }
@@ -162,18 +165,18 @@ internal class ActionExecutorImpl(
 
     @Suspendable
     private fun executeSendInitial(action: Action.SendInitial) {
-        flowMessaging.sendSessionMessage(action.destination, action.initialise, action.deduplicationId)
+        flowMessaging.sendSessionMessage(action.destination, action.initialise, action.deduplicationInfo)
     }
 
     @Suspendable
     private fun executeSendExisting(action: Action.SendExisting) {
-        flowMessaging.sendSessionMessage(action.peerParty, action.message, action.deduplicationId)
+        flowMessaging.sendSessionMessage(action.peerParty, action.message, action.deduplicationInfo)
     }
 
     @Suspendable
     private fun executeSendMultiple(action: Action.SendMultiple) {
-        val messages = action.sendInitial.map { Message(it.destination, it.initialise, it.deduplicationId) } +
+        val messages = action.sendInitial.map { Message(it.destination, it.initialise, it.deduplicationInfo) } +
-                action.sendExisting.map { Message(it.peerParty, it.message, it.deduplicationId) }
+                action.sendExisting.map { Message(it.peerParty, it.message, it.deduplicationInfo) }
         flowMessaging.sendSessionMessages(messages)
     }
 
@@ -192,6 +195,13 @@ internal class ActionExecutorImpl(
         stateMachineManager.signalFlowHasStarted(action.flowId)
     }
 
+    @Suspendable
+    private fun executeSignalSessionsHasEnded(action: Action.SignalSessionsHasEnded) {
+        action.terminatedSessions.forEach { (sessionId, senderData) ->
+            flowMessaging.sessionEnded(sessionId, senderData.first, senderData.second)
+        }
+    }
+
     @Suspendable
     private fun executeRemoveFlow(action: Action.RemoveFlow) {
         stateMachineManager.removeFlow(action.flowId, action.removalReason, action.lastState)

node/src/main/kotlin/net/corda/node/services/statemachine/DeduplicationId.kt

@@ -1,53 +0,0 @@
-package net.corda.node.services.statemachine
-
-import java.security.SecureRandom
-
-/**
- * A deduplication ID of a flow message.
- */
-data class DeduplicationId(val toString: String) {
-    companion object {
-        /**
-         * Create a random deduplication ID. Note that this isn't deterministic, which means we will never dedupe it,
-         * unless we persist the ID somehow.
-         */
-        fun createRandom(random: SecureRandom) = DeduplicationId("R-${random.nextLong()}")
-
-        /**
-         * Create a deduplication ID for a normal clean state message. This is used to have a deterministic way of
-         * creating IDs in case the message-generating flow logic is replayed on hard failure.
-         *
-         * A normal deduplication ID consists of:
-         * 1. A deduplication seed set per session. This is the initiator's session ID, with a prefix for initiator
-         *    or initiated.
-         * 2. The number of *clean* suspends since the start of the flow.
-         * 3. An optional additional index, for cases where several messages are sent as part of the state transition.
-         *   Note that care must be taken with this index, it must be a deterministic counter. For example a naive
-         *   iteration over a HashMap will produce a different list of indeces than a previous run, causing the
-         *   message-id map to change, which means deduplication will not happen correctly.
-         */
-        fun createForNormal(checkpoint: Checkpoint, index: Int, session: SessionState): DeduplicationId {
-            return DeduplicationId("N-${session.deduplicationSeed}-${checkpoint.checkpointState.numberOfSuspends}-$index")
-        }
-
-        /**
-         * Create a deduplication ID for an error message. Note that these IDs live in a different namespace than normal
-         * IDs, as we don't want error conditions to affect the determinism of clean deduplication IDs. This allows the
-         * dirtiness state to be thrown away for resumption.
-         *
-         * An error deduplication ID consists of:
-         * 1. The error's ID. This is a unique value per "source" of error and is propagated.
-         *   See [net.corda.core.flows.IdentifiableException].
-         * 2. The recipient's session ID.
-         */
-        fun createForError(errorId: Long, recipientSessionId: SessionId): DeduplicationId {
-            return DeduplicationId("E-$errorId-${recipientSessionId.toLong}")
-        }
-    }
-}
-
-/**
- * Represents the deduplication ID of a flow message, and the sender identifier for the flow doing the sending.  The identifier might be
- * null if the flow is trying to replay messages and doesn't want an optimisation to ignore the deduplication ID.
- */
-data class SenderDeduplicationId(val deduplicationId: DeduplicationId, val senderUUID: String?)

node/src/main/kotlin/net/corda/node/services/statemachine/Event.kt

@@ -8,6 +8,9 @@ import net.corda.core.serialization.SerializedBytes
 import net.corda.core.transactions.SignedTransaction
 import net.corda.core.utilities.ProgressTracker
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderSequenceNumber
+import net.corda.node.services.messaging.SenderUUID
 import java.util.UUID
 
 /**
@@ -34,7 +37,10 @@ sealed class Event {
     data class DeliverSessionMessage(
             val sessionMessage: ExistingSessionMessage,
             override val deduplicationHandler: DeduplicationHandler,
-            val sender: Party
+            val sender: Party,
+            val messageIdentifier: MessageIdentifier,
+            val senderUUID: SenderUUID?,
+            val senderSequenceNumber: SenderSequenceNumber?
     ) : Event(), GeneratedByExternalEvent
 
     /**

node/src/main/kotlin/net/corda/node/services/statemachine/FlowCreator.kt

@@ -155,7 +155,8 @@ class FlowCreator(
             frozenFlowLogic,
             ourIdentity,
             flowCorDappVersion,
-            flowLogic.isEnabledTimedFlow()
+            flowLogic.isEnabledTimedFlow(),
+            serviceHub.clock.instant()
         ).getOrThrow()
 
         val state = createStateMachineState(
@@ -253,6 +254,7 @@ class FlowCreator(
         return StateMachineState(
             checkpoint = checkpoint,
             pendingDeduplicationHandlers = deduplicationHandler?.let { listOf(it) } ?: emptyList(),
+            closedSessionsPendingToBeSignalled = emptyMap(),
             isFlowResumed = false,
             future = null,
             isWaitingForFuture = false,

node/src/main/kotlin/net/corda/node/services/statemachine/FlowMessaging.kt

@@ -15,6 +15,9 @@ import net.corda.node.services.api.ServiceHubInternal
 import net.corda.node.services.messaging.DeduplicationHandler
 import net.corda.node.services.messaging.MessagingService
 import net.corda.node.services.messaging.ReceivedMessage
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.messaging.SenderSequenceNumber
+import net.corda.node.services.messaging.SenderUUID
 import net.corda.nodeapi.internal.ArtemisMessagingComponent.Companion.P2PMessagingHeaders
 import java.io.NotSerializableException
 
@@ -23,21 +26,24 @@ import java.io.NotSerializableException
  */
 interface FlowMessaging {
     /**
-     * Send [message] to [destination] using [deduplicationId].
+     * Send [message] to [destination] using [deduplicationInfo].
      */
     @Suspendable
-    fun sendSessionMessage(destination: Destination, message: SessionMessage, deduplicationId: SenderDeduplicationId)
+    fun sendSessionMessage(destination: Destination, message: SessionMessage, deduplicationInfo: SenderDeduplicationInfo)
 
     @Suspendable
     fun sendSessionMessages(messageData: List<Message>)
 
+    @Suspendable
+    fun sessionEnded(sessionId: SessionId, senderUUID: SenderUUID?, senderSequenceNumber: SenderSequenceNumber?)
+
     /**
      * Start the messaging using the [onMessage] message handler.
      */
     fun start(onMessage: (ReceivedMessage, deduplicationHandler: DeduplicationHandler) -> Unit)
 }
 
-data class Message(val destination: Destination, val sessionMessage: SessionMessage, val dedupId: SenderDeduplicationId)
+data class Message(val destination: Destination, val sessionMessage: SessionMessage, val dedupInfo: SenderDeduplicationInfo)
 
 /**
  * Implementation of [FlowMessaging] using a [ServiceHubInternal] to do the messaging and routing.
@@ -56,18 +62,23 @@ class FlowMessagingImpl(val serviceHub: ServiceHubInternal): FlowMessaging {
     }
 
     @Suspendable
-    override fun sendSessionMessage(destination: Destination, message: SessionMessage, deduplicationId: SenderDeduplicationId) {
+    override fun sendSessionMessage(destination: Destination, message: SessionMessage, deduplicationInfo: SenderDeduplicationInfo) {
-        val addressedMessage = createMessage(destination, message, deduplicationId)
+        val addressedMessage = createMessage(destination, message, deduplicationInfo)
         serviceHub.networkService.send(addressedMessage.message, addressedMessage.target, addressedMessage.sequenceKey)
     }
 
     @Suspendable
     override fun sendSessionMessages(messageData: List<Message>) {
-        val addressedMessages = messageData.map { createMessage(it.destination, it.sessionMessage, it.dedupId) }
+        val addressedMessages = messageData.map { createMessage(it.destination, it.sessionMessage, it.dedupInfo) }
         serviceHub.networkService.sendAll(addressedMessages)
     }
 
-    private fun createMessage(destination: Destination, message: SessionMessage, deduplicationId: SenderDeduplicationId): MessagingService.AddressedMessage {
+    @Suspendable
+    override fun sessionEnded(sessionId: SessionId, senderUUID: SenderUUID?, senderSequenceNumber: SenderSequenceNumber?) {
+        serviceHub.networkService.sessionEnded(sessionId, senderUUID, senderSequenceNumber)
+    }
+
+    private fun createMessage(destination: Destination, message: SessionMessage, deduplicationId: SenderDeduplicationInfo): MessagingService.AddressedMessage {
         // We assume that the destination type has already been checked by initiateFlow.
         // Destination may point to a stale well-known identity due to key rotation, so always resolve actual identity via IdentityService.
         val party = requireNotNull(serviceHub.identityService.wellKnownPartyFromAnonymous(destination as AbstractParty)) {
@@ -80,6 +91,7 @@ class FlowMessagingImpl(val serviceHub: ServiceHubInternal): FlowMessaging {
         }
         val networkMessage = serviceHub.networkService.createMessage(sessionTopic, serializeSessionMessage(message).bytes, deduplicationId, message.additionalHeaders(party))
         val partyInfo = requireNotNull(serviceHub.networkMapCache.getPartyInfo(party)) { "Don't know about ${party.description()}" }
+
         val address = serviceHub.networkService.getAddressOfParty(partyInfo)
         val sequenceKey = when (message) {
             is InitialSessionMessage -> message.initiatorSessionId

node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt

@@ -179,7 +179,7 @@ class FlowStateMachineImpl<R>(override val id: StateMachineRunId,
             val stateMachine = transientValues.stateMachine
             val oldState = transientState
             val actionExecutor = transientValues.actionExecutor
-            val transition = stateMachine.transition(event, oldState)
+            val transition = stateMachine.transition(event, oldState, serviceHub.clock.instant())
             val (continuation, newState) = transitionExecutor.executeTransition(
                 this,
                 oldState,

node/src/main/kotlin/net/corda/node/services/statemachine/SessionMessage.kt

@@ -4,6 +4,7 @@ import net.corda.core.flows.FlowException
 import net.corda.core.flows.FlowInfo
 import net.corda.core.serialization.CordaSerializable
 import net.corda.core.serialization.SerializedBytes
+import java.math.BigInteger
 import java.security.SecureRandom
 
 /**
@@ -21,9 +22,28 @@ import java.security.SecureRandom
 sealed class SessionMessage
 
 @CordaSerializable
-data class SessionId(val toLong: Long) {
+data class SessionId(val value: BigInteger) {
+    init {
+        require(value.signum() >= 0) { "Session identifier cannot be a negative number, but it was $value" }
+        require(value.bitLength() <= MAX_BIT_SIZE) { "The size of a session identifier cannot exceed $MAX_BIT_SIZE bits, but it was $value" }
+    }
+
+    /**
+     * This calculates the initiated session ID assuming this is the initiating session ID.
+     * This is the next larger number in the range [0, 2^[MAX_BIT_SIZE]] with wrap around the largest number in the interval.
+     */
+    fun calculateInitiatedSessionId(): SessionId {
+        return if (this.value == LARGEST_SESSION_ID)
+            SessionId(BigInteger.ZERO)
+        else
+            SessionId(this.value.plus(BigInteger.ONE))
+    }
+
     companion object {
-        fun createRandom(secureRandom: SecureRandom) = SessionId(secureRandom.nextLong())
+        const val MAX_BIT_SIZE = 128
+        val LARGEST_SESSION_ID = BigInteger.valueOf(2).pow(MAX_BIT_SIZE).minus(BigInteger.ONE)
+
+        fun createRandom(secureRandom: SecureRandom) = SessionId(BigInteger(MAX_BIT_SIZE, secureRandom))
     }
 }
 
@@ -118,3 +138,29 @@ data class RejectSessionMessage(val message: String, val errorId: Long) : Existi
  * protocols don't match up, e.g. one is waiting for the other, but the other side has already finished.
  */
 object EndSessionMessage : ExistingSessionMessagePayload()
+
+enum class MessageType {
+    SESSION_INIT,
+    SESSION_CONFIRM,
+    SESSION_REJECT,
+    DATA_MESSAGE,
+    SESSION_END,
+    SESSION_ERROR;
+
+    companion object {
+        fun inferFromMessage(message: SessionMessage): MessageType {
+            return when (message) {
+                is InitialSessionMessage -> SESSION_INIT
+                is ExistingSessionMessage -> {
+                    when(message.payload) {
+                        is ConfirmSessionMessage -> SESSION_CONFIRM
+                        is RejectSessionMessage -> SESSION_REJECT
+                        is DataSessionMessage -> DATA_MESSAGE
+                        is EndSessionMessage -> SESSION_END
+                        is ErrorSessionMessage -> SESSION_ERROR
+                    }
+                }
+            }
+        }
+    }
+}

node/src/main/kotlin/net/corda/node/services/statemachine/SingleThreadedStateMachineManager.kt

@@ -37,6 +37,10 @@ import net.corda.node.internal.InitiatedFlowFactory
 import net.corda.node.services.api.CheckpointStorage
 import net.corda.node.services.api.ServiceHubInternal
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.messaging.SenderSequenceNumber
+import net.corda.node.services.messaging.SenderUUID
 import net.corda.node.services.statemachine.FlowStateMachineImpl.Companion.currentStateMachine
 import net.corda.node.services.statemachine.interceptors.DumpHistoryOnErrorInterceptor
 import net.corda.node.services.statemachine.interceptors.HospitalisingInterceptor
@@ -703,7 +707,7 @@ internal class SingleThreadedStateMachineManager(
         val sender = serviceHub.networkMapCache.getPeerByLegalName(peer)
         if (sender != null) {
             when (sessionMessage) {
-                is ExistingSessionMessage -> onExistingSessionMessage(sessionMessage, sender, event)
+                is ExistingSessionMessage -> onExistingSessionMessage(sessionMessage, sender, event, event.receivedMessage.uniqueMessageId, event.receivedMessage.senderUUID, event.receivedMessage.senderSeqNo)
                 is InitialSessionMessage -> onSessionInit(sessionMessage, sender, event)
             }
         } else {
@@ -716,7 +720,10 @@ internal class SingleThreadedStateMachineManager(
     private fun onExistingSessionMessage(
         sessionMessage: ExistingSessionMessage,
         sender: Party,
-        externalEvent: ExternalEvent.ExternalMessageEvent
+        externalEvent: ExternalEvent.ExternalMessageEvent,
+        messageIdentifier: MessageIdentifier,
+        senderUUID: SenderUUID?,
+        senderSequenceNumber: SenderSequenceNumber?
     ) {
         try {
             val deduplicationHandler = externalEvent.deduplicationHandler
@@ -734,7 +741,7 @@ internal class SingleThreadedStateMachineManager(
                     logger.info("Cannot find flow corresponding to session ID - $recipientId.")
                 }
             } else {
-                val event = Event.DeliverSessionMessage(sessionMessage, deduplicationHandler, sender)
+                val event = Event.DeliverSessionMessage(sessionMessage, deduplicationHandler, sender, messageIdentifier, senderUUID, senderSequenceNumber)
                 innerState.withLock {
                     flows[flowId]?.run { fiber.scheduleEvent(event) }
                         // If flow is not running add it to the list of external events to be processed if/when the flow resumes.
@@ -751,7 +758,7 @@ internal class SingleThreadedStateMachineManager(
     private fun onSessionInit(sessionMessage: InitialSessionMessage, sender: Party, event: ExternalEvent.ExternalMessageEvent) {
         try {
             val initiatedFlowFactory = getInitiatedFlowFactory(sessionMessage)
-            val initiatedSessionId = SessionId.createRandom(secureRandom)
+            val initiatedSessionId = event.receivedMessage.uniqueMessageId.sessionIdentifier
             val senderSession = FlowSessionImpl(sender, sender, initiatedSessionId)
             val flowLogic = initiatedFlowFactory.createFlow(senderSession)
             val initiatedFlowInfo = when (initiatedFlowFactory) {
@@ -763,9 +770,8 @@ internal class SingleThreadedStateMachineManager(
                 is InitiatedFlowFactory.CorDapp -> null
             }
             startInitiatedFlow(
-                    event.flowId,
+                    event,
                     flowLogic,
-                    event.deduplicationHandler,
                     senderSession,
                     initiatedSessionId,
                     sessionMessage,
@@ -800,24 +806,24 @@ internal class SingleThreadedStateMachineManager(
 
     @Suppress("LongParameterList")
     private fun <A> startInitiatedFlow(
-            flowId: StateMachineRunId,
+            event: ExternalEvent.ExternalMessageEvent,
             flowLogic: FlowLogic<A>,
-            initiatingMessageDeduplicationHandler: DeduplicationHandler,
             peerSession: FlowSessionImpl,
             initiatedSessionId: SessionId,
             initiatingMessage: InitialSessionMessage,
             senderCoreFlowVersion: Int?,
             initiatedFlowInfo: FlowInfo
     ) {
-        val flowStart = FlowStart.Initiated(peerSession, initiatedSessionId, initiatingMessage, senderCoreFlowVersion, initiatedFlowInfo)
+        val flowStart = FlowStart.Initiated(peerSession, initiatedSessionId, initiatingMessage, senderCoreFlowVersion, initiatedFlowInfo,
+                event.receivedMessage.uniqueMessageId.shardIdentifier, event.receivedMessage.senderUUID, event.receivedMessage.senderSeqNo)
         val ourIdentity = ourFirstIdentity
         startFlowInternal(
-                flowId,
+                event.flowId,
                 InvocationContext.peer(peerSession.counterparty.name),
                 flowLogic,
                 flowStart,
                 ourIdentity,
-                initiatingMessageDeduplicationHandler
+                event.deduplicationHandler
         )
     }
 

node/src/main/kotlin/net/corda/node/services/statemachine/StaffedFlowHospital.kt

@@ -21,6 +21,8 @@ import net.corda.core.utilities.debug
 import net.corda.core.utilities.minutes
 import net.corda.core.utilities.seconds
 import net.corda.node.services.FinalityHandler
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
 import org.hibernate.exception.ConstraintViolationException
 import rx.subjects.PublishSubject
 import java.io.Closeable
@@ -169,7 +171,9 @@ class StaffedFlowHospital(private val flowMessaging: FlowMessaging,
 
         log.info("Sending session initiation error back to $sender", error)
 
-        flowMessaging.sendSessionMessage(sender, replyError, SenderDeduplicationId(DeduplicationId.createRandom(secureRandom), ourSenderUUID))
+        val messageType = MessageType.inferFromMessage(replyError)
+        val messageIdentifier = MessageIdentifier(messageType, event.receivedMessage.uniqueMessageId.shardIdentifier, sessionMessage.initiatorSessionId, 0, event.receivedMessage.uniqueMessageId.timestamp)
+        flowMessaging.sendSessionMessage(sender, replyError, SenderDeduplicationInfo(messageIdentifier, ourSenderUUID))
         event.deduplicationHandler.afterDatabaseTransaction()
     }
 

node/src/main/kotlin/net/corda/node/services/statemachine/StateMachineState.kt

@@ -22,11 +22,16 @@ import net.corda.core.serialization.internal.CheckpointSerializationContext
 import net.corda.core.serialization.internal.checkpointDeserialize
 import net.corda.core.utilities.Try
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderSequenceNumber
+import net.corda.node.services.messaging.SenderUUID
+import java.lang.IllegalArgumentException
 import java.lang.IllegalStateException
 import java.security.Principal
 import java.time.Instant
 import java.util.concurrent.Future
 import java.util.concurrent.Semaphore
+import kotlin.math.max
 
 /**
  * The state of the state machine, capturing the state of a flow. It consists of two parts, an *immutable* part that is
@@ -35,6 +40,7 @@ import java.util.concurrent.Semaphore
  * @param checkpoint the persisted part of the state.
  * @param flowLogic the [FlowLogic] associated with the flow. Note that this is mutable by the user.
  * @param pendingDeduplicationHandlers the list of incomplete deduplication handlers.
+ * @param closedSessionsPendingToBeSignalled the sessions that have been closed and need to be signalled to the messaging layer on the next checkpoint (along with some metadata).
  * @param isFlowResumed true if the control is returned (or being returned) to "user-space" flow code. This is used
  *   to make [Event.DoRemainingWork] idempotent.
  * @param isWaitingForFuture true if the flow is waiting for the completion of a future triggered by one of the statemachine's actions
@@ -61,6 +67,7 @@ data class StateMachineState(
     val checkpoint: Checkpoint,
     val flowLogic: FlowLogic<*>,
     val pendingDeduplicationHandlers: List<DeduplicationHandler>,
+    val closedSessionsPendingToBeSignalled: Map<SessionId, Pair<SenderUUID?, SenderSequenceNumber?>>,
     val isFlowResumed: Boolean,
     val isWaitingForFuture: Boolean,
     var future: Future<*>?,
@@ -123,7 +130,8 @@ data class Checkpoint(
                 frozenFlowLogic: SerializedBytes<FlowLogic<*>>,
                 ourIdentity: Party,
                 subFlowVersion: SubFlowVersion,
-                isEnabledTimedFlow: Boolean
+                isEnabledTimedFlow: Boolean,
+                timestamp: Instant
         ): Try<Checkpoint> {
             return SubFlow.create(flowLogicClass, subFlowVersion, isEnabledTimedFlow).map { topLevelSubFlow ->
                 Checkpoint(
@@ -135,7 +143,8 @@ data class Checkpoint(
                         listOf(topLevelSubFlow),
                         numberOfSuspends = 0,
                         // We set this to 1 here to avoid an extra copy and increment in UnstartedFlowTransition.createInitialCheckpoint
-                        numberOfCommits = 1
+                        numberOfCommits = 1,
+                        suspensionTime = timestamp
                     ),
                     flowState = FlowState.Unstarted(flowStart, frozenFlowLogic),
                     errorState = ErrorState.Clean
@@ -235,6 +244,7 @@ data class Checkpoint(
 }
 
 /**
+<<<<<<< HEAD
  * @param invocationContext The initiator of the flow.
  * @param ourIdentity The identity the flow is run as.
  * @param sessions Map of source session ID to session state.
@@ -242,6 +252,7 @@ data class Checkpoint(
  * @param subFlowStack The stack of currently executing subflows.
  * @param numberOfSuspends The number of flow suspends due to IO API calls.
  * @param numberOfCommits The number of times this checkpoint has been persisted.
+ * @param suspensionTime the time of the last suspension. This is supposed to be used as a stable timestamp in case of replays.
  */
 @CordaSerializable
 data class CheckpointState(
@@ -251,7 +262,8 @@ data class CheckpointState(
     val sessionsToBeClosed: Set<SessionId>,
     val subFlowStack: List<SubFlow>,
     val numberOfSuspends: Int,
-    val numberOfCommits: Int
+    val numberOfCommits: Int,
+    val suspensionTime: Instant
 )
 
 /**
@@ -262,44 +274,162 @@ sealed class SessionState {
     abstract val deduplicationSeed: String
 
     /**
-     * We haven't yet sent the initialisation message
+     * the sender UUID last seen in this session, if there was one.
+     */
+    abstract val lastSenderUUID: SenderUUID?
+
+    /**
+     * the sender sequence number last seen in this session, if there was one.
+     */
+    abstract val lastSenderSeqNo: SenderSequenceNumber?
+
+    /**
+     * the messages that have been received and are pending processing indexed by their sequence number.
+     * this could be any [ExistingSessionMessagePayload] type in theory, but it in practice it can only be one of the following types now:
+     *   * [DataSessionMessage]
+     *   * [ErrorSessionMessage]
+     *   * [EndSessionMessage]
+     */
+    abstract val receivedMessages: Map<Int, ExistingSessionMessagePayload>
+
+    /**
+     * Returns a new session state with the specified messages added to the list of received messages.
+     */
+    fun addReceivedMessages(message: ExistingSessionMessagePayload, messageIdentifier: MessageIdentifier, senderUUID: String?, senderSequenceNumber: Long?): SessionState {
+        val newReceivedMessages = receivedMessages.plus(messageIdentifier.sessionSequenceNumber to message)
+        val (newLastSenderUUID, newLastSenderSeqNo) = calculateSenderInfo(lastSenderUUID, lastSenderSeqNo, senderUUID, senderSequenceNumber)
+        return when(this) {
+            is Uninitiated -> { copy(receivedMessages = newReceivedMessages, lastSenderUUID = newLastSenderUUID, lastSenderSeqNo = newLastSenderSeqNo) }
+            is Initiating -> { copy(receivedMessages = newReceivedMessages, lastSenderUUID = newLastSenderUUID, lastSenderSeqNo = newLastSenderSeqNo) }
+            is Initiated -> { copy(receivedMessages = newReceivedMessages, lastSenderUUID = newLastSenderUUID, lastSenderSeqNo = newLastSenderSeqNo) }
+        }
+    }
+
+    private fun calculateSenderInfo(currentSender: String?, currentSenderSeqNo: Long?, msgSender: String?, msgSenderSeqNo: Long?): Pair<String?, Long?> {
+        return if (msgSender != null && msgSenderSeqNo != null) {
+            if (currentSenderSeqNo != null)
+                Pair(msgSender, max(msgSenderSeqNo, currentSenderSeqNo))
+            else
+                Pair(msgSender, msgSenderSeqNo)
+        } else {
+            Pair(currentSender, currentSenderSeqNo)
+        }
+    }
+
+    /**
+     * We haven't yet sent the initialisation message.
+     * This really means that the flow is in a state before sending the initialisation message,
+     * but in reality it could have sent it before and fail before reaching the next checkpoint, thus ending up replaying from the last checkpoint.
+     *
+     * @param hasBeenAcknowledged whether a positive response to a session initiation has already been received and the associated confirmation message, if so.
+     * @param hasBeenRejected whether a negative response to a session initiation has already been received and the associated rejection message, if so.
      */
     data class Uninitiated(
             val destination: Destination,
             val initiatingSubFlow: SubFlow.Initiating,
             val sourceSessionId: SessionId,
-            val additionalEntropy: Long
+            val additionalEntropy: Long,
+            val hasBeenAcknowledged: Pair<Party, ConfirmSessionMessage>?,
+            val hasBeenRejected: RejectSessionMessage?,
+            override val receivedMessages: Map<Int, ExistingSessionMessagePayload>,
+            override val lastSenderUUID: String?,
+            override val lastSenderSeqNo: Long?
     ) : SessionState() {
-        override val deduplicationSeed: String get() = "R-${sourceSessionId.toLong}-$additionalEntropy"
+        override val deduplicationSeed: String get() = "R-${sourceSessionId.value}-$additionalEntropy"
     }
 
     /**
      * We have sent the initialisation message but have not yet received a confirmation.
+     * @property bufferedMessages the messages that have been buffered to be sent after the session is confirmed from the other side.
      * @property rejectionError if non-null the initiation failed.
+     * @property nextSendingSeqNumber the sequence number of the next message to be sent.
+     * @property shardId the shard ID of the associated flow to be embedded on all the messages sent from this session.
      */
     data class Initiating(
-            val bufferedMessages: List<Pair<DeduplicationId, ExistingSessionMessagePayload>>,
+            val bufferedMessages: List<Pair<MessageIdentifier, ExistingSessionMessagePayload>>,
             val rejectionError: FlowError?,
-            override val deduplicationSeed: String
+            override val deduplicationSeed: String,
-    ) : SessionState()
+            val nextSendingSeqNumber: Int,
+            val shardId: String,
+            override val receivedMessages: Map<Int, ExistingSessionMessagePayload>,
+            override val lastSenderUUID: String?,
+            override val lastSenderSeqNo: Long?
+    ) : SessionState() {
+
+        /**
+         * Buffers an outgoing message to be sent when ready.
+         * Returns the new form of the state
+         */
+        fun bufferMessage(messageIdentifier: MessageIdentifier, messagePayload: ExistingSessionMessagePayload): SessionState {
+            return this.copy(bufferedMessages = bufferedMessages + Pair(messageIdentifier, messagePayload), nextSendingSeqNumber = nextSendingSeqNumber + 1)
+        }
+
+        /**
+         * A batched form of [bufferMessage].
+         */
+        fun bufferMessages(messages: List<Pair<MessageIdentifier, ExistingSessionMessagePayload>>): SessionState {
+            return this.copy(bufferedMessages = bufferedMessages + messages, nextSendingSeqNumber = nextSendingSeqNumber + messages.size)
+        }
+    }
 
     /**
      * We have received a confirmation, the peer party and session id is resolved.
-     * @property receivedMessages the messages that have been received and are pending processing.
-     *   this could be any [ExistingSessionMessagePayload] type in theory, but it in practice it can only be one of the following types now:
-     *   * [DataSessionMessage]
-     *   * [ErrorSessionMessage]
-     *   * [EndSessionMessage]
      * @property otherSideErrored whether the session has received an error from the other side.
+     * @property nextSendingSeqNumber the sequence number that corresponds to the next message to be sent.
+     * @property lastProcessedSeqNumber the sequence number of the last message that has been processed.
+     * @property shardId the shard ID of the associated flow to be embedded on all the messages sent from this session.
      */
     data class Initiated(
             val peerParty: Party,
             val peerFlowInfo: FlowInfo,
-            val receivedMessages: List<ExistingSessionMessagePayload>,
             val otherSideErrored: Boolean,
             val peerSinkSessionId: SessionId,
-            override val deduplicationSeed: String
+            override val deduplicationSeed: String,
-    ) : SessionState()
+            val nextSendingSeqNumber: Int,
+            val lastProcessedSeqNumber: Int,
+            val shardId: String,
+            override val receivedMessages: Map<Int, ExistingSessionMessagePayload>,
+            override val lastSenderUUID: String?,
+            override val lastSenderSeqNo: Long?
+    ) : SessionState() {
+
+        /**
+         * Indicates whether this message has already been processed.
+         */
+        fun isDuplicate(messageIdentifier: MessageIdentifier): Boolean {
+            return messageIdentifier.sessionSequenceNumber <= lastProcessedSeqNumber
+        }
+
+        /**
+         * Indicates whether the session has an error message pending from the other side.
+         */
+        fun hasErrored(): Boolean {
+            return hasNextMessageArrived() && receivedMessages[lastProcessedSeqNumber + 1] is ErrorSessionMessage
+        }
+
+        /**
+         * Indicates whether the next expected message has arrived.
+         */
+        fun hasNextMessageArrived(): Boolean {
+            return receivedMessages.containsKey(lastProcessedSeqNumber + 1)
+        }
+
+        /**
+         * Returns the next message to be processed and the new session state.
+         * If you want to check first whether the next message has arrived, call [hasNextMessageArrived]
+         *
+         * @throws [IllegalArgumentException] if the next hasn't arrived.
+         */
+        fun extractMessage(): Pair<ExistingSessionMessagePayload, Initiated> {
+            if (!hasNextMessageArrived()) {
+                throw IllegalArgumentException("Tried to extract a message that hasn't arrived yet.")
+            }
+
+            val message = receivedMessages[lastProcessedSeqNumber + 1]!!
+            val newState = this.copy(receivedMessages = receivedMessages.minus(lastProcessedSeqNumber + 1), lastProcessedSeqNumber = lastProcessedSeqNumber + 1)
+            return Pair(message, newState)
+        }
+    }
 }
 
 typealias SessionMap = Map<SessionId, SessionState>
@@ -321,7 +451,10 @@ sealed class FlowStart {
             val initiatedSessionId: SessionId,
             val initiatingMessage: InitialSessionMessage,
             val senderCoreFlowVersion: Int?,
-            val initiatedFlowInfo: FlowInfo
+            val initiatedFlowInfo: FlowInfo,
+            val shardIdentifier: String,
+            val senderUUID: String?,
+            val senderSequenceNumber: Long?
     ) : FlowStart() { override fun toString() = "Initiated" }
 }
 

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/DeliverSessionMessageTransition.kt

@@ -3,6 +3,7 @@ package net.corda.node.services.statemachine.transitions
 import net.corda.core.flows.UnexpectedFlowEndException
 import net.corda.core.utilities.contextLogger
 import net.corda.core.utilities.debug
+import net.corda.core.utilities.trace
 import net.corda.node.services.statemachine.Action
 import net.corda.node.services.statemachine.ConfirmSessionMessage
 import net.corda.node.services.statemachine.DataSessionMessage
@@ -13,7 +14,7 @@ import net.corda.node.services.statemachine.ExistingSessionMessage
 import net.corda.node.services.statemachine.FlowError
 import net.corda.node.services.statemachine.FlowState
 import net.corda.node.services.statemachine.RejectSessionMessage
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.messaging.SenderDeduplicationInfo
 import net.corda.node.services.statemachine.SessionState
 import net.corda.node.services.statemachine.StateMachineState
 
@@ -87,56 +88,78 @@ class DeliverSessionMessageTransition(
                 val initiatedSession = SessionState.Initiated(
                         peerParty = event.sender,
                         peerFlowInfo = message.initiatedFlowInfo,
-                        receivedMessages = emptyList(),
+                        receivedMessages = emptyMap(),
                         peerSinkSessionId = message.initiatedSessionId,
                         deduplicationSeed = sessionState.deduplicationSeed,
-                        otherSideErrored = false
+                        otherSideErrored = false,
+                        nextSendingSeqNumber = sessionState.nextSendingSeqNumber,
+                        lastProcessedSeqNumber = 0,
+                        shardId = sessionState.shardId,
+                        lastSenderUUID = event.senderUUID,
+                        lastSenderSeqNo = event.senderSequenceNumber
                 )
                 val newCheckpoint = currentState.checkpoint.addSession(
                         event.sessionMessage.recipientSessionId to initiatedSession
                 )
                 // Send messages that were buffered pending confirmation of session.
-                val sendActions = sessionState.bufferedMessages.map { (deduplicationId, bufferedMessage) ->
+                val sendActions = sessionState.bufferedMessages.map { (messageId, bufferedMessage) ->
                     val existingMessage = ExistingSessionMessage(message.initiatedSessionId, bufferedMessage)
-                    Action.SendExisting(initiatedSession.peerParty, existingMessage, SenderDeduplicationId(deduplicationId, startingState.senderUUID))
+                    Action.SendExisting(initiatedSession.peerParty, existingMessage, SenderDeduplicationInfo(messageId, startingState.senderUUID))
                 }
                 actions.addAll(sendActions)
                 currentState = currentState.copy(checkpoint = newCheckpoint)
             }
-            else -> freshErrorTransition(UnexpectedEventInState())
+            is SessionState.Initiated -> {
+                log.trace { "Discarding duplicate confirmation for session ${event.sessionMessage.recipientSessionId} with ${sessionState.peerParty}" }
+            }
+            is SessionState.Uninitiated -> {
+                val newSessionState = sessionState.copy(hasBeenAcknowledged = Pair(event.sender, message))
+                val newCheckpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
+                currentState = currentState.copy(checkpoint = newCheckpoint)
+            }
         }
     }
 
     private fun TransitionBuilder.dataMessageTransition(sessionState: SessionState, message: DataSessionMessage) {
-        // We received a data message. The corresponding session must be Initiated.
         return when (sessionState) {
             is SessionState.Initiated -> {
-                // Buffer the message in the session's receivedMessages buffer.
+                if (!sessionState.isDuplicate(event.messageIdentifier)) {
-                val newSessionState = sessionState.copy(
+                    val newSessionState = sessionState.addReceivedMessages(message, event.messageIdentifier, event.senderUUID, event.senderSequenceNumber)
-                        receivedMessages = sessionState.receivedMessages + message
-                )
-
                     currentState = currentState.copy(
-                        checkpoint = currentState.checkpoint.addSession(
+                            checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
-                                event.sessionMessage.recipientSessionId to newSessionState
                     )
+                } else {
+                    log.trace { "Discarding duplicate data message for session ${event.sessionMessage.recipientSessionId} with ${sessionState.peerParty}" }
+                }
+            }
+            is SessionState.Initiating, is SessionState.Uninitiated -> {
+                val newSessionState = sessionState.addReceivedMessages(message, event.messageIdentifier, event.senderUUID, event.senderSequenceNumber)
+                currentState = currentState.copy(
+                        checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
                 )
             }
-            else -> freshErrorTransition(UnexpectedEventInState())
         }
     }
 
     private fun TransitionBuilder.errorMessageTransition(sessionState: SessionState, payload: ErrorSessionMessage) {
+        val sequenceNumber = event.messageIdentifier.sessionSequenceNumber
         return when (sessionState) {
             is SessionState.Initiated -> {
-                val checkpoint = currentState.checkpoint
+                if (sequenceNumber > sessionState.lastProcessedSeqNumber) {
-                val sessionId = event.sessionMessage.recipientSessionId
+                    val newSessionState = sessionState.addReceivedMessages(payload, event.messageIdentifier, event.senderUUID, event.senderSequenceNumber)
-                val newSessionState = sessionState.copy(receivedMessages = sessionState.receivedMessages + payload)
                     currentState = currentState.copy(
-                        checkpoint = checkpoint.addSession(sessionId to newSessionState)
+                            checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
+                    )
+                } else {
+                    log.trace { "Discarding duplicate error message for session ${event.sessionMessage.recipientSessionId} with ${sessionState.peerParty}" }
+                }
+            }
+            is SessionState.Initiating, is SessionState.Uninitiated -> {
+                val newSessionState = sessionState.addReceivedMessages(payload, event.messageIdentifier, event.senderUUID, event.senderSequenceNumber)
+                currentState = currentState.copy(
+                        checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
                 )
             }
-            else -> freshErrorTransition(UnexpectedEventInState())
         }
     }
 
@@ -145,42 +168,42 @@ class DeliverSessionMessageTransition(
         return when (sessionState) {
             is SessionState.Initiating -> {
                 if (sessionState.rejectionError != null) {
-                    // Double reject
+                    log.trace { "Discarding duplicate session rejection message for session ${event.sessionMessage.recipientSessionId}" }
-                    freshErrorTransition(UnexpectedEventInState())
                 } else {
-                    val checkpoint = currentState.checkpoint
-                    val sessionId = event.sessionMessage.recipientSessionId
                     val flowError = FlowError(payload.errorId, exception)
                     currentState = currentState.copy(
-                            checkpoint = checkpoint.addSession(sessionId to sessionState.copy(rejectionError = flowError))
+                            checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to sessionState.copy(rejectionError = flowError))
                     )
                 }
             }
-            else -> freshErrorTransition(UnexpectedEventInState())
+            is SessionState.Uninitiated -> {
+                currentState = currentState.copy(
+                        checkpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to sessionState.copy(hasBeenRejected = payload))
+                )
+            }
+            is SessionState.Initiated -> {
+                freshErrorTransition(UnexpectedEventInState("A session rejection message was received for an already established session ${event.messageIdentifier.sessionIdentifier}."))
+            }
         }
     }
 
     private fun TransitionBuilder.endMessageTransition(payload: EndSessionMessage) {
+        val flowState = currentState.checkpoint.flowState
+        // flow must have already been started when session end messages are being delivered.
+        if (flowState !is FlowState.Started)
+            return freshErrorTransition(UnexpectedEventInState())
 
         val sessionId = event.sessionMessage.recipientSessionId
         val sessions = currentState.checkpoint.checkpointState.sessions
         // a check has already been performed to confirm the session exists for this message before this method is invoked.
         val sessionState = sessions[sessionId]!!
         when (sessionState) {
-            is SessionState.Initiated -> {
+            is SessionState.Initiated, is SessionState.Initiating, is SessionState.Uninitiated -> {
-                val flowState = currentState.checkpoint.flowState
+                val newSessionState = sessionState.addReceivedMessages(payload, event.messageIdentifier, event.senderUUID, event.senderSequenceNumber)
-                // flow must have already been started when session end messages are being delivered.
-                if (flowState !is FlowState.Started)
-                    return freshErrorTransition(UnexpectedEventInState())
-
-                val newSessionState = sessionState.copy(receivedMessages = sessionState.receivedMessages + payload)
                 val newCheckpoint = currentState.checkpoint.addSession(event.sessionMessage.recipientSessionId to newSessionState)
                                                            .addSessionsToBeClosed(setOf(event.sessionMessage.recipientSessionId))
                 currentState = currentState.copy(checkpoint = newCheckpoint)
             }
-            else -> {
-                freshErrorTransition(PrematureSessionEndException(event.sessionMessage.recipientSessionId))
-            }
         }
     }
 

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/ErrorFlowTransition.kt

@@ -1,6 +1,7 @@
 package net.corda.node.services.statemachine.transitions
 
 import net.corda.core.flows.FlowException
+import net.corda.node.services.messaging.MessageIdentifier
 import net.corda.node.services.statemachine.*
 
 /**
@@ -40,16 +41,28 @@ class ErrorFlowTransition(
         return builder {
             // If we're errored and propagating do the actual propagation and update the index.
             if (remainingErrorsToPropagate.isNotEmpty() && errorState.propagating) {
-                val (initiatedSessions, newSessions) = bufferErrorMessagesInInitiatingSessions(
+                val (initiatedSessions, newSessionStates) = bufferErrorMessagesInInitiatingSessions(
                         startingState.checkpoint.checkpointState.sessions,
                         errorMessages
                 )
+                val sessionsWithAdvancedSeqNumbers = mutableMapOf<SessionId, SessionState>()
+                val errorsPerSession = initiatedSessions.map { (sessionId, sessionState) ->
+                    var currentSeqNumber = sessionState.nextSendingSeqNumber
+                    val errorsWithId = errorMessages.map { errorMsg ->
+                        val messageIdentifier = MessageIdentifier(MessageType.SESSION_ERROR, sessionState.shardId, sessionState.peerSinkSessionId, currentSeqNumber, startingState.checkpoint.checkpointState.suspensionTime)
+                        currentSeqNumber++
+                        Pair(messageIdentifier, errorMsg)
+                    }.toList()
+                    sessionsWithAdvancedSeqNumbers[sessionId] = sessionState.copy(nextSendingSeqNumber = currentSeqNumber)
+                    Pair(sessionState, errorsWithId)
+                }.toMap()
+
                 val newCheckpoint = startingState.checkpoint.copy(
                         errorState = errorState.copy(propagatedIndex = allErrors.size),
-                        checkpointState = startingState.checkpoint.checkpointState.copy(sessions = newSessions)
+                        checkpointState = startingState.checkpoint.checkpointState.copy(sessions = newSessionStates + sessionsWithAdvancedSeqNumbers)
                 )
                 currentState = currentState.copy(checkpoint = newCheckpoint)
-                actions += Action.PropagateErrors(errorMessages, initiatedSessions, startingState.senderUUID)
+                actions += Action.PropagateErrors(errorsPerSession, startingState.senderUUID)
             }
 
             // If we're errored but not propagating keep processing events.
@@ -81,16 +94,27 @@ class ErrorFlowTransition(
                         isCheckpointUpdate = currentState.isAnyCheckpointPersisted
                     )
                 }
+                val signalSessionsEndMap = currentState.checkpoint.checkpointState.sessions.map { (sessionId, sessionState) ->
+                    sessionId to Pair(sessionState.lastSenderUUID, sessionState.lastSenderSeqNo)
+                }.toMap()
 
                 actions += Action.CreateTransaction
                 actions += removeOrPersistCheckpoint
                 actions += Action.PersistDeduplicationFacts(startingState.pendingDeduplicationHandlers)
+                actions += Action.SignalSessionsHasEnded(signalSessionsEndMap)
                 actions += Action.ReleaseSoftLocks(context.id.uuid)
                 actions += Action.CommitTransaction(currentState)
                 actions += Action.AcknowledgeMessages(startingState.pendingDeduplicationHandlers)
                 actions += Action.RemoveSessionBindings(startingState.checkpoint.checkpointState.sessions.keys)
                 actions += Action.RemoveFlow(context.id, FlowRemovalReason.ErrorFinish(allErrors), currentState)
 
+                currentState = currentState.copy(
+                        checkpoint = newCheckpoint,
+                        pendingDeduplicationHandlers = emptyList(),
+                        closedSessionsPendingToBeSignalled = emptyMap(),
+                        isRemoved = true
+                )
+
                 FlowContinuation.Abort
             } else {
                 // Otherwise keep processing events. This branch happens when there are some outstanding initiating
@@ -112,31 +136,37 @@ class ErrorFlowTransition(
         }
     }
 
-    // Buffer error messages in Initiating sessions, return the initialised ones.
+    /**
+     * Buffers errors message for initiating states and filters the initiated states.
+     * Returns a pair that consists of:
+     * - a map containing the initiated states as filtered from the ones provided as input.
+     * - a map containing the new state of all the sessions.
+     */
     private fun bufferErrorMessagesInInitiatingSessions(
             sessions: Map<SessionId, SessionState>,
             errorMessages: List<ErrorSessionMessage>
-    ): Pair<List<SessionState.Initiated>, Map<SessionId, SessionState>> {
+    ): Pair<Map<SessionId, SessionState.Initiated>, Map<SessionId, SessionState>> {
-        val newSessions = sessions.mapValues { (sourceSessionId, sessionState) ->
+        val newSessionStates = sessions.mapValues { (sourceSessionId, sessionState) ->
             if (sessionState is SessionState.Initiating && sessionState.rejectionError == null) {
-                // *prepend* the error messages in order to error the other sessions ASAP. The other messages will
+                var currentSequenceNumber = sessionState.nextSendingSeqNumber
-                // be delivered all the same, they just won't trigger flow resumption because of dirtiness.
+                val errorMessagesWithDeduplication = errorMessages.map { errorMessage ->
-                val errorMessagesWithDeduplication = errorMessages.map {
+                    val messageIdentifier = MessageIdentifier(MessageType.SESSION_ERROR, sessionState.shardId, sourceSessionId.calculateInitiatedSessionId(), currentSequenceNumber, startingState.checkpoint.checkpointState.suspensionTime)
-                    DeduplicationId.createForError(it.errorId, sourceSessionId) to it
+                    currentSequenceNumber++
+                    messageIdentifier to errorMessage
                 }
-                sessionState.copy(bufferedMessages = errorMessagesWithDeduplication + sessionState.bufferedMessages)
+                sessionState.bufferMessages(errorMessagesWithDeduplication)
             } else {
                 sessionState
             }
         }
         // if we have already received error message from the other side, we don't include that session in the list to avoid propagating errors.
-        val initiatedSessions = sessions.values.mapNotNull { session ->
+        val initiatedSessions = sessions.mapNotNull { (sessionId, sessionState) ->
-            if (session is SessionState.Initiated && !session.otherSideErrored) {
+            if (sessionState is SessionState.Initiated && !sessionState.otherSideErrored) {
-                session
+                sessionId to sessionState
             } else {
                 null
             }
-        }
+        }.toMap()
-        return Pair(initiatedSessions, newSessions)
+        return Pair(initiatedSessions, newSessionStates)
     }
 }

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/KilledFlowTransition.kt

@@ -2,14 +2,15 @@ package net.corda.node.services.statemachine.transitions
 
 import net.corda.core.flows.FlowException
 import net.corda.core.flows.KilledFlowException
+import net.corda.node.services.messaging.MessageIdentifier
 import net.corda.node.services.statemachine.Action
 import net.corda.node.services.statemachine.Checkpoint
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.ErrorSessionMessage
 import net.corda.node.services.statemachine.Event
 import net.corda.node.services.statemachine.FlowError
 import net.corda.node.services.statemachine.FlowRemovalReason
 import net.corda.node.services.statemachine.FlowState
+import net.corda.node.services.statemachine.MessageType
 import net.corda.node.services.statemachine.SessionId
 import net.corda.node.services.statemachine.SessionState
 import net.corda.node.services.statemachine.StateMachineState
@@ -27,24 +28,37 @@ class KilledFlowTransition(
             val killedFlowErrorMessage = createErrorMessageFromError(killedFlowError)
             val errorMessages = listOf(killedFlowErrorMessage)
 
-            val (initiatedSessions, newSessions) = bufferErrorMessagesInInitiatingSessions(
+            val (initiatedSessions, newSessionStates) = bufferErrorMessagesInInitiatingSessions(
                 startingState.checkpoint.checkpointState.sessions,
                 errorMessages
             )
 
+            val sessionsWithAdvancedSeqNumbers = mutableMapOf<SessionId, SessionState>()
+            val errorsPerSession = initiatedSessions.map { (sessionId, sessionState) ->
+                var currentSeqNumber = sessionState.nextSendingSeqNumber
+                val errorsWithId = errorMessages.map { errorMsg ->
+                    val messageIdentifier = MessageIdentifier(MessageType.SESSION_ERROR, sessionState.shardId, sessionState.peerSinkSessionId, currentSeqNumber, startingState.checkpoint.checkpointState.suspensionTime)
+                    currentSeqNumber++
+                    Pair(messageIdentifier, errorMsg)
+                }.toList()
+                sessionsWithAdvancedSeqNumbers[sessionId] = sessionState.copy(nextSendingSeqNumber = currentSeqNumber)
+                Pair(sessionState, errorsWithId)
+            }.toMap()
+
             val newCheckpoint = startingState.checkpoint.copy(
                     status = Checkpoint.FlowStatus.KILLED,
                     flowState = FlowState.Finished,
-                checkpointState = startingState.checkpoint.checkpointState.copy(sessions = newSessions)
+                    checkpointState = startingState.checkpoint.checkpointState.copy(sessions = newSessionStates + sessionsWithAdvancedSeqNumbers)
             )
 
             currentState = currentState.copy(
                     checkpoint = newCheckpoint,
                     pendingDeduplicationHandlers = emptyList(),
+                    closedSessionsPendingToBeSignalled = emptyMap(),
                     isRemoved = true
             )
 
-            actions += Action.PropagateErrors(errorMessages, initiatedSessions, startingState.senderUUID)
+            actions += Action.PropagateErrors(errorsPerSession, startingState.senderUUID)
 
             if (!startingState.isFlowResumed) {
                 actions += Action.CreateTransaction
@@ -59,7 +73,12 @@ class KilledFlowTransition(
                 actions += Action.AddFlowException(context.id, killedFlowError.exception)
             }
 
+            val signalSessionsEndMap = currentState.checkpoint.checkpointState.sessions.map { (sessionId, sessionState) ->
+                sessionId to Pair(sessionState.lastSenderUUID, sessionState.lastSenderSeqNo)
+            }.toMap()
+
             actions += Action.PersistDeduplicationFacts(startingState.pendingDeduplicationHandlers)
+            actions += Action.SignalSessionsHasEnded(signalSessionsEndMap)
             actions += Action.ReleaseSoftLocks(context.id.uuid)
             actions += Action.CommitTransaction(currentState)
             actions += Action.AcknowledgeMessages(startingState.pendingDeduplicationHandlers)
@@ -91,32 +110,37 @@ class KilledFlowTransition(
         }
     }
 
-    // Purposely left the same as [bufferErrorMessagesInInitiatingSessions] in [ErrorFlowTransition] so that it can be refactored
+    /**
-    // Buffer error messages in Initiating sessions, return the initialised ones.
+     * Buffers errors message for initiating states and filters the initiated states.
+     * Returns a pair that consists of:
+     * - a map containing the initiated states as filtered from the ones provided as input.
+     * - a map containing the new state of all the sessions.
+     */
     private fun bufferErrorMessagesInInitiatingSessions(
         sessions: Map<SessionId, SessionState>,
         errorMessages: List<ErrorSessionMessage>
-    ): Pair<List<SessionState.Initiated>, Map<SessionId, SessionState>> {
+    ): Pair<Map<SessionId, SessionState.Initiated>, Map<SessionId, SessionState>> {
         val newSessions = sessions.mapValues { (sourceSessionId, sessionState) ->
             if (sessionState is SessionState.Initiating && sessionState.rejectionError == null) {
-                // *prepend* the error messages in order to error the other sessions ASAP. The other messages will
+                var currentSequenceNumber = sessionState.nextSendingSeqNumber
-                // be delivered all the same, they just won't trigger flow resumption because of dirtiness.
+                val errorMessagesWithDeduplication = errorMessages.map { errorMessage ->
-                val errorMessagesWithDeduplication = errorMessages.map {
+                    val messageIdentifier = MessageIdentifier(MessageType.SESSION_ERROR, sessionState.shardId, sourceSessionId.calculateInitiatedSessionId(), currentSequenceNumber, startingState.checkpoint.checkpointState.suspensionTime)
-                    DeduplicationId.createForError(it.errorId, sourceSessionId) to it
+                    currentSequenceNumber++
+                    messageIdentifier to errorMessage
                 }
-                sessionState.copy(bufferedMessages = errorMessagesWithDeduplication + sessionState.bufferedMessages)
+                sessionState.bufferMessages(errorMessagesWithDeduplication)
             } else {
                 sessionState
             }
         }
         // if we have already received error message from the other side, we don't include that session in the list to avoid propagating errors.
-        val initiatedSessions = sessions.values.mapNotNull { session ->
+        val initiatedSessions = sessions.mapNotNull { (sessionId, sessionState) ->
-            if (session is SessionState.Initiated && !session.otherSideErrored) {
+            if (sessionState is SessionState.Initiated && !sessionState.otherSideErrored) {
-                session
+                sessionId to sessionState
             } else {
                 null
             }
-        }
+        }.toMap()
         return Pair(initiatedSessions, newSessions)
     }
 

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/StartedFlowTransition.kt

@@ -10,6 +10,9 @@ import net.corda.core.internal.FlowIORequest
 import net.corda.core.serialization.SerializedBytes
 import net.corda.core.utilities.contextLogger
 import net.corda.core.utilities.toNonEmptySet
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.messaging.generateShardId
 import net.corda.node.services.statemachine.*
 import org.slf4j.Logger
 import kotlin.collections.LinkedHashMap
@@ -177,14 +180,19 @@ class StartedFlowTransition(
             }
 
             if (existingSessionsToRemove.isNotEmpty()) {
-                val sendEndMessageActions = existingSessionsToRemove.values.mapIndexed { index, state ->
+                val sendEndMessageActions = existingSessionsToRemove.map { (_, sessionState) ->
-                    val sinkSessionId = (state as SessionState.Initiated).peerSinkSessionId
+                    val sinkSessionId = (sessionState as SessionState.Initiated).peerSinkSessionId
                     val message = ExistingSessionMessage(sinkSessionId, EndSessionMessage)
-                    val deduplicationId = DeduplicationId.createForNormal(currentState.checkpoint, index, state)
+                    val messageType = MessageType.inferFromMessage(message)
-                    Action.SendExisting(state.peerParty, message, SenderDeduplicationId(deduplicationId, currentState.senderUUID))
+                    val messageIdentifier = MessageIdentifier(messageType, generateShardId(context.id.toString()), sinkSessionId, sessionState.nextSendingSeqNumber, currentState.checkpoint.checkpointState.suspensionTime)
+                    Action.SendExisting(sessionState.peerParty, message, SenderDeduplicationInfo(messageIdentifier, currentState.senderUUID))
                 }
+                val signalSessionsEndMap = existingSessionsToRemove.map { (sessionId, _) ->
+                    val sessionState = currentState.checkpoint.checkpointState.sessions[sessionId]!!
+                    sessionId to Pair(sessionState.lastSenderUUID, sessionState.lastSenderSeqNo)
+                }.toMap()
 
-                currentState = currentState.copy(checkpoint = currentState.checkpoint.removeSessions(existingSessionsToRemove.keys))
+                currentState = currentState.copy(checkpoint = currentState.checkpoint.removeSessions(existingSessionsToRemove.keys), closedSessionsPendingToBeSignalled = currentState.closedSessionsPendingToBeSignalled + signalSessionsEndMap)
                 actions.add(Action.RemoveSessionBindings(sessionIdsToRemove))
                 actions.add(Action.SendMultiple(emptyList(), sendEndMessageActions))
             }
@@ -239,23 +247,23 @@ class StartedFlowTransition(
 
     @Suppress("ComplexMethod", "NestedBlockDepth")
     private fun pollSessionMessages(sessions: SessionMap, sessionIds: Set<SessionId>): PollResult? {
-        val newSessionMessages = LinkedHashMap(sessions)
+        val newSessionStates = LinkedHashMap(sessions)
         val resultMessages = LinkedHashMap<SessionId, SerializedBytes<Any>>()
         var someNotFound = false
         for (sessionId in sessionIds) {
             val sessionState = sessions[sessionId]
             when (sessionState) {
                 is SessionState.Initiated -> {
-                    val messages = sessionState.receivedMessages
+                    if (!sessionState.hasNextMessageArrived()) {
-                    if (messages.isEmpty()) {
                         someNotFound = true
                     } else {
-                        newSessionMessages[sessionId] = sessionState.copy(receivedMessages = messages.subList(1, messages.size).toList())
+                        val (message, newState) = sessionState.extractMessage()
+                        newSessionStates[sessionId] = newState
                         // at this point, we've already checked for errors and session ends, so it's guaranteed that the first message will be a data message.
-                        resultMessages[sessionId] = if (messages[0] is EndSessionMessage) {
+                        resultMessages[sessionId] = if (message is EndSessionMessage) {
                             throw UnexpectedFlowEndException("Received session end message instead of a data session message. Mismatched send and receive?")
                         } else {
-                            (messages[0] as DataSessionMessage).payload
+                            (message as DataSessionMessage).payload
                         }
                     }
                 }
@@ -267,14 +275,13 @@ class StartedFlowTransition(
         return if (someNotFound) {
             return null
         } else {
-            PollResult(resultMessages, newSessionMessages)
+            PollResult(resultMessages, newSessionStates)
         }
     }
 
     private fun TransitionBuilder.sendInitialSessionMessagesIfNeeded(sourceSessions: Set<SessionId>) {
         val checkpoint = startingState.checkpoint
         val newSessions = LinkedHashMap<SessionId, SessionState>(checkpoint.checkpointState.sessions)
-        var index = 0
         for (sourceSessionId in sourceSessions) {
             val sessionState = checkpoint.checkpointState.sessions[sourceSessionId]
             if (sessionState == null) {
@@ -283,14 +290,22 @@ class StartedFlowTransition(
             if (sessionState !is SessionState.Uninitiated) {
                 continue
             }
+            val shardId = generateShardId(context.id.toString())
+            val counterpartySessionId = sourceSessionId.calculateInitiatedSessionId()
             val initialMessage = createInitialSessionMessage(sessionState.initiatingSubFlow, sourceSessionId, sessionState.additionalEntropy, null)
             val newSessionState = SessionState.Initiating(
                     bufferedMessages = emptyList(),
                     rejectionError = null,
-                    deduplicationSeed = sessionState.deduplicationSeed
+                    deduplicationSeed = sessionState.deduplicationSeed,
+                    nextSendingSeqNumber = 1,
+                    shardId = shardId,
+                    receivedMessages = emptyMap(),
+                    lastSenderUUID = null,
+                    lastSenderSeqNo = null
             )
-            val deduplicationId = DeduplicationId.createForNormal(checkpoint, index++, newSessionState)
+            val messageType = MessageType.inferFromMessage(initialMessage)
-            actions.add(Action.SendInitial(sessionState.destination, initialMessage, SenderDeduplicationId(deduplicationId, startingState.senderUUID)))
+            val messageIdentifier = MessageIdentifier(messageType, shardId, counterpartySessionId, 0, checkpoint.checkpointState.suspensionTime)
+            actions.add(Action.SendInitial(sessionState.destination, initialMessage, SenderDeduplicationInfo(messageIdentifier, startingState.senderUUID)))
             newSessions[sourceSessionId] = newSessionState
         }
         currentState = currentState.copy(checkpoint = checkpoint.setSessions(sessions = newSessions))
@@ -313,37 +328,60 @@ class StartedFlowTransition(
     private fun TransitionBuilder.sendToSessionsTransition(sourceSessionIdToMessage: Map<SessionId, SerializedBytes<Any>>) {
         val checkpoint = startingState.checkpoint
         val newSessions = LinkedHashMap(checkpoint.checkpointState.sessions)
-        var index = 0
-
         val messagesByType = sourceSessionIdToMessage.toList()
                 .map { (sourceSessionId, message) -> Triple(sourceSessionId, checkpoint.checkpointState.sessions[sourceSessionId]!!, message) }
                 .groupBy { it.second::class }
 
-        val sendInitialActions = messagesByType[SessionState.Uninitiated::class]?.map { (sourceSessionId, sessionState, message) ->
+        val sendInitialActions = messagesByType[SessionState.Uninitiated::class]?.mapNotNull { (sourceSessionId, sessionState, message) ->
             val uninitiatedSessionState = sessionState as SessionState.Uninitiated
-            val deduplicationId = DeduplicationId.createForNormal(checkpoint, index++, sessionState)
+            val shardId = generateShardId(context.id.toString())
-            val initialMessage = createInitialSessionMessage(uninitiatedSessionState.initiatingSubFlow, sourceSessionId, uninitiatedSessionState.additionalEntropy, message)
+            if (sessionState.hasBeenAcknowledged != null) {
+                newSessions[sourceSessionId] = SessionState.Initiated(
+                        peerParty = sessionState.hasBeenAcknowledged.first,
+                        peerFlowInfo = sessionState.hasBeenAcknowledged.second.initiatedFlowInfo,
+                        receivedMessages = emptyMap(),
+                        otherSideErrored = false,
+                        peerSinkSessionId = sessionState.hasBeenAcknowledged.second.initiatedSessionId,
+                        deduplicationSeed = sessionState.deduplicationSeed,
+                        nextSendingSeqNumber = 1,
+                        lastProcessedSeqNumber = 0,
+                        shardId = shardId,
+                        lastSenderUUID = null,
+                        lastSenderSeqNo = null
+                )
+                null
+            } else {
                 newSessions[sourceSessionId] = SessionState.Initiating(
                         bufferedMessages = emptyList(),
                         rejectionError = null,
-                    deduplicationSeed = uninitiatedSessionState.deduplicationSeed
+                        deduplicationSeed = sessionState.deduplicationSeed,
+                        nextSendingSeqNumber = 1,
+                        shardId = shardId,
+                        receivedMessages = emptyMap(),
+                        lastSenderUUID = null,
+                        lastSenderSeqNo = null
                 )
-            Action.SendInitial(uninitiatedSessionState.destination, initialMessage, SenderDeduplicationId(deduplicationId, startingState.senderUUID))
+                val initialMessage = createInitialSessionMessage(uninitiatedSessionState.initiatingSubFlow, sourceSessionId, uninitiatedSessionState.additionalEntropy, message)
+                val messageType = MessageType.inferFromMessage(initialMessage)
+                val messageIdentifier = MessageIdentifier(messageType, shardId, sourceSessionId.calculateInitiatedSessionId(), 0, checkpoint.checkpointState.suspensionTime)
+                Action.SendInitial(uninitiatedSessionState.destination, initialMessage, SenderDeduplicationInfo(messageIdentifier, startingState.senderUUID))
+            }
         } ?: emptyList()
         messagesByType[SessionState.Initiating::class]?.forEach { (sourceSessionId, sessionState, message) ->
             val initiatingSessionState = sessionState as SessionState.Initiating
             val sessionMessage = DataSessionMessage(message)
-            val deduplicationId = DeduplicationId.createForNormal(checkpoint, index++, initiatingSessionState)
+            val messageIdentifier = MessageIdentifier(MessageType.DATA_MESSAGE, sessionState.shardId, sourceSessionId.calculateInitiatedSessionId(), sessionState.nextSendingSeqNumber, checkpoint.checkpointState.suspensionTime)
-            val newBufferedMessages = initiatingSessionState.bufferedMessages + Pair(deduplicationId, sessionMessage)
+            newSessions[sourceSessionId] = initiatingSessionState.bufferMessage(messageIdentifier, sessionMessage)
-            newSessions[sourceSessionId] = initiatingSessionState.copy(bufferedMessages = newBufferedMessages)
         }
-        val sendExistingActions = messagesByType[SessionState.Initiated::class]?.map {(_, sessionState, message) ->
+        val sendExistingActions = messagesByType[SessionState.Initiated::class]?.map {(sourceSessionId, sessionState, message) ->
             val initiatedSessionState = sessionState as SessionState.Initiated
             val sessionMessage = DataSessionMessage(message)
-            val deduplicationId = DeduplicationId.createForNormal(checkpoint, index++, initiatedSessionState)
             val sinkSessionId = initiatedSessionState.peerSinkSessionId
             val existingMessage = ExistingSessionMessage(sinkSessionId, sessionMessage)
-            Action.SendExisting(initiatedSessionState.peerParty, existingMessage, SenderDeduplicationId(deduplicationId, startingState.senderUUID))
+            val messageType = MessageType.inferFromMessage(existingMessage)
+            val messageIdentifier = MessageIdentifier(messageType, sessionState.shardId, sessionState.peerSinkSessionId, sessionState.nextSendingSeqNumber, checkpoint.checkpointState.suspensionTime)
+            newSessions[sourceSessionId] = initiatedSessionState.copy(nextSendingSeqNumber = initiatedSessionState.nextSendingSeqNumber + 1)
+            Action.SendExisting(initiatedSessionState.peerParty, existingMessage, SenderDeduplicationInfo(messageIdentifier, startingState.senderUUID))
         } ?: emptyList()
 
         if (sendInitialActions.isNotEmpty() || sendExistingActions.isNotEmpty()) {
@@ -372,11 +410,10 @@ class StartedFlowTransition(
                             }
                         }
                         is SessionState.Initiated -> {
-                            if (sessionState.receivedMessages.isNotEmpty() && sessionState.receivedMessages.first() is ErrorSessionMessage) {
+                            if (sessionState.hasErrored()) {
-                                val errorMessage = sessionState.receivedMessages.first() as ErrorSessionMessage
+                                val (message, newSessionState) = sessionState.extractMessage()
-                                val exception = convertErrorMessageToException(errorMessage, sessionState.peerParty)
+                                val exception = convertErrorMessageToException(message as ErrorSessionMessage, sessionState.peerParty)
-                                val newSessionState = sessionState.copy(receivedMessages = sessionState.receivedMessages.subList(1, sessionState.receivedMessages.size), otherSideErrored = true)
+                                val newCheckpoint = startingState.checkpoint.addSession(sessionId to newSessionState.copy(otherSideErrored = true))
-                                val newCheckpoint = startingState.checkpoint.addSession(sessionId to newSessionState)
                                 newState = startingState.copy(checkpoint = newCheckpoint)
                                 listOf(exception)
                             } else {
@@ -541,8 +578,8 @@ class StartedFlowTransition(
 
     private fun findSessionsToBeTerminated(startingState: StateMachineState): SessionMap {
         return startingState.checkpoint.checkpointState.sessionsToBeClosed.mapNotNull { sessionId ->
-            val sessionState = startingState.checkpoint.checkpointState.sessions[sessionId]!! as SessionState.Initiated
+            val sessionState = startingState.checkpoint.checkpointState.sessions[sessionId]!!
-            if (sessionState.receivedMessages.isNotEmpty() && sessionState.receivedMessages.first() is EndSessionMessage) {
+            if (sessionState is SessionState.Initiated && sessionState.receivedMessages.containsKey(sessionState.lastProcessedSeqNumber + 1) && sessionState.receivedMessages[sessionState.lastProcessedSeqNumber + 1] is EndSessionMessage) {
                 sessionId to sessionState
             } else {
                 null

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/StateMachine.kt

@@ -4,12 +4,13 @@ import net.corda.core.flows.StateMachineRunId
 import net.corda.node.services.statemachine.Event
 import net.corda.node.services.statemachine.StateMachineState
 import java.security.SecureRandom
+import java.time.Instant
 
 class StateMachine(
         val id: StateMachineRunId,
         val secureRandom: SecureRandom
 ) {
-    fun transition(event: Event, state: StateMachineState): TransitionResult {
+    fun transition(event: Event, state: StateMachineState, time: Instant): TransitionResult {
-        return TopLevelTransition(TransitionContext(id, secureRandom), state, event).transition()
+        return TopLevelTransition(TransitionContext(id, secureRandom, time), state, event).transition()
     }
 }

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/TopLevelTransition.kt

@@ -7,9 +7,9 @@ import net.corda.core.serialization.deserialize
 import net.corda.core.utilities.Try
 import net.corda.core.utilities.contextLogger
 import net.corda.node.services.messaging.DeduplicationHandler
+import net.corda.node.services.messaging.MessageIdentifier
 import net.corda.node.services.statemachine.Action
 import net.corda.node.services.statemachine.Checkpoint
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.EndSessionMessage
 import net.corda.node.services.statemachine.ErrorState
 import net.corda.node.services.statemachine.Event
@@ -19,7 +19,8 @@ import net.corda.node.services.statemachine.FlowRemovalReason
 import net.corda.node.services.statemachine.FlowSessionImpl
 import net.corda.node.services.statemachine.FlowState
 import net.corda.node.services.statemachine.InitialSessionMessage
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.statemachine.MessageType
 import net.corda.node.services.statemachine.SessionId
 import net.corda.node.services.statemachine.SessionMessage
 import net.corda.node.services.statemachine.SessionState
@@ -197,7 +198,8 @@ class TopLevelTransition(
                        checkpointState.invocationContext
                    },
                    numberOfSuspends = checkpointState.numberOfSuspends + 1,
-                   numberOfCommits = checkpointState.numberOfCommits + 1
+                   numberOfCommits = checkpointState.numberOfCommits + 1,
+                   suspensionTime = context.time
                 )
                 copy(
                     flowState = FlowState.Started(event.ioRequest, event.fiber),
@@ -217,11 +219,13 @@ class TopLevelTransition(
                 currentState = startingState.copy(
                     checkpoint = newCheckpoint,
                     pendingDeduplicationHandlers = emptyList(),
+                    closedSessionsPendingToBeSignalled = emptyMap(),
                     isFlowResumed = false,
                     isAnyCheckpointPersisted = true
                 )
                 actions += Action.PersistCheckpoint(context.id, newCheckpoint, isCheckpointUpdate = startingState.isAnyCheckpointPersisted)
                 actions += Action.PersistDeduplicationFacts(startingState.pendingDeduplicationHandlers)
+                actions += Action.SignalSessionsHasEnded(startingState.closedSessionsPendingToBeSignalled)
                 actions += Action.CommitTransaction(currentState)
                 actions += Action.AcknowledgeMessages(startingState.pendingDeduplicationHandlers)
                 actions += Action.ScheduleEvent(Event.DoRemainingWork)
@@ -240,12 +244,14 @@ class TopLevelTransition(
                         checkpoint = checkpoint.copy(
                             checkpointState = checkpoint.checkpointState.copy(
                                 numberOfSuspends = checkpoint.checkpointState.numberOfSuspends + 1,
-                                numberOfCommits = checkpoint.checkpointState.numberOfCommits + 1
+                                numberOfCommits = checkpoint.checkpointState.numberOfCommits + 1,
+                                    suspensionTime = context.time
                             ),
                             flowState = FlowState.Finished,
                             result = event.returnValue,
                             status = Checkpoint.FlowStatus.COMPLETED
-                        ),
+                        ).removeSessions(checkpoint.checkpointState.sessions.keys),
+                        closedSessionsPendingToBeSignalled = emptyMap(),
                         pendingDeduplicationHandlers = emptyList(),
                         isFlowResumed = false,
                         isRemoved = true
@@ -263,7 +269,12 @@ class TopLevelTransition(
                         )
                     }
 
+                    val signalSessionsEndMap = startingState.checkpoint.checkpointState.sessions.map { (sessionId, sessionState) ->
+                        sessionId to Pair(sessionState.lastSenderUUID, sessionState.lastSenderSeqNo)
+                    }.toMap()
+
                     actions += Action.PersistDeduplicationFacts(startingState.pendingDeduplicationHandlers)
+                    actions += Action.SignalSessionsHasEnded(signalSessionsEndMap)
                     actions += Action.ReleaseSoftLocks(event.softLocksId)
                     actions += Action.CommitTransaction(currentState)
                     actions += Action.AcknowledgeMessages(startingState.pendingDeduplicationHandlers)
@@ -284,11 +295,12 @@ class TopLevelTransition(
     }
 
     private fun TransitionBuilder.sendEndMessages() {
-        val sendEndMessageActions = currentState.checkpoint.checkpointState.sessions.values.mapIndexed { index, state ->
+        val sendEndMessageActions = startingState.checkpoint.checkpointState.sessions.map { (sessionId, state) ->
             if (state is SessionState.Initiated) {
                 val message = ExistingSessionMessage(state.peerSinkSessionId, EndSessionMessage)
-                val deduplicationId = DeduplicationId.createForNormal(currentState.checkpoint, index, state)
+                val messageType = MessageType.inferFromMessage(message)
-                Action.SendExisting(state.peerParty, message, SenderDeduplicationId(deduplicationId, currentState.senderUUID))
+                val messageIdentifier = MessageIdentifier(messageType, state.shardId, state.peerSinkSessionId, state.nextSendingSeqNumber, startingState.checkpoint.checkpointState.suspensionTime)
+                Action.SendExisting(state.peerParty, message, SenderDeduplicationInfo(messageIdentifier, startingState.senderUUID))
             } else {
                 null
             }
@@ -306,7 +318,7 @@ class TopLevelTransition(
             }
             val sourceSessionId = SessionId.createRandom(context.secureRandom)
             val sessionImpl = FlowSessionImpl(event.destination, event.wellKnownParty, sourceSessionId)
-            val newSessions = checkpoint.checkpointState.sessions + (sourceSessionId to SessionState.Uninitiated(event.destination, initiatingSubFlow, sourceSessionId, context.secureRandom.nextLong()))
+            val newSessions = checkpoint.checkpointState.sessions + (sourceSessionId to SessionState.Uninitiated(event.destination, initiatingSubFlow, sourceSessionId, context.secureRandom.nextLong(), null, null, emptyMap(), null, null))
             currentState = currentState.copy(checkpoint = checkpoint.setSessions(newSessions))
             actions.add(Action.AddSessionBinding(context.id, sourceSessionId))
             FlowContinuation.Resume(sessionImpl)
@@ -361,10 +373,12 @@ class TopLevelTransition(
                         numberOfCommits = startingState.checkpoint.checkpointState.numberOfCommits + 1
                     )
                 ),
-                pendingDeduplicationHandlers = startingState.pendingDeduplicationHandlers - flowStartEvents
+                pendingDeduplicationHandlers = startingState.pendingDeduplicationHandlers - flowStartEvents,
+                closedSessionsPendingToBeSignalled = emptyMap()
             )
             actions += Action.CreateTransaction
             actions += Action.PersistDeduplicationFacts(flowStartEvents)
+            actions += Action.SignalSessionsHasEnded(startingState.closedSessionsPendingToBeSignalled)
             actions += Action.PersistCheckpoint(context.id, newCheckpoint, isCheckpointUpdate = startingState.isAnyCheckpointPersisted)
             actions += Action.CommitTransaction(currentState)
             actions += Action.AcknowledgeMessages(flowStartEvents)
@@ -401,4 +415,5 @@ class TopLevelTransition(
             FlowContinuation.Abort
         }
     }
+
 }

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/Transition.kt

@@ -3,6 +3,7 @@ package net.corda.node.services.statemachine.transitions
 import net.corda.core.flows.StateMachineRunId
 import net.corda.node.services.statemachine.StateMachineState
 import java.security.SecureRandom
+import java.time.Instant
 
 /**
  * An interface used to separate out different parts of the state machine transition function.
@@ -28,5 +29,6 @@ interface Transition {
 
 class TransitionContext(
         val id: StateMachineRunId,
-        val secureRandom: SecureRandom
+        val secureRandom: SecureRandom,
+        val time: Instant
 )

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/TransitionBuilder.kt

@@ -80,6 +80,6 @@ class TransitionBuilder(val context: TransitionContext, initialState: StateMachi
 }
 
 class CannotFindSessionException(sessionId: SessionId) : IllegalStateException("Couldn't find session with id $sessionId")
-class UnexpectedEventInState : IllegalStateException("Unexpected event")
+class UnexpectedEventInState(message: String = "") : IllegalStateException("An unexpected event happened. $message")
 class PrematureSessionCloseException(sessionId: SessionId): IllegalStateException("The following session was closed before it was initialised: $sessionId")
 class PrematureSessionEndException(sessionId: SessionId): IllegalStateException("A premature session end message was received before the session was initialised: $sessionId")

node/src/main/kotlin/net/corda/node/services/statemachine/transitions/UnstartedFlowTransition.kt

@@ -1,14 +1,15 @@
 package net.corda.node.services.statemachine.transitions
 
 import net.corda.core.flows.FlowInfo
+import net.corda.node.services.messaging.MessageIdentifier
 import net.corda.node.services.statemachine.Action
 import net.corda.node.services.statemachine.ConfirmSessionMessage
 import net.corda.node.services.statemachine.DataSessionMessage
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.ExistingSessionMessage
 import net.corda.node.services.statemachine.FlowStart
 import net.corda.node.services.statemachine.FlowState
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.statemachine.MessageType
 import net.corda.node.services.statemachine.SessionState
 import net.corda.node.services.statemachine.StateMachineState
 
@@ -50,25 +51,28 @@ class UnstartedFlowTransition(
                         appName = initiatingMessage.appName
                 ),
                 receivedMessages = if (initiatingMessage.firstPayload == null) {
-                    emptyList()
+                    emptyMap()
                 } else {
-                    listOf(DataSessionMessage(initiatingMessage.firstPayload))
+                    mapOf(0 to DataSessionMessage(initiatingMessage.firstPayload))
                 },
-                deduplicationSeed = "D-${initiatingMessage.initiatorSessionId.toLong}-${initiatingMessage.initiationEntropy}",
+                deduplicationSeed = "D-${initiatingMessage.initiatorSessionId.value}-${initiatingMessage.initiationEntropy}",
-                otherSideErrored = false
+                otherSideErrored = false,
+                nextSendingSeqNumber = 1,
+                lastProcessedSeqNumber = if (initiatingMessage.firstPayload == null) {
+                    0
+                } else {
+                    -1
+                },
+                shardId = flowStart.shardIdentifier,
+                lastSenderUUID = flowStart.senderUUID,
+                lastSenderSeqNo = flowStart.senderSequenceNumber
         )
         val confirmationMessage = ConfirmSessionMessage(flowStart.initiatedSessionId, flowStart.initiatedFlowInfo)
         val sessionMessage = ExistingSessionMessage(initiatingMessage.initiatorSessionId, confirmationMessage)
-        currentState = currentState.copy(
+        val messageType = MessageType.inferFromMessage(sessionMessage)
-                checkpoint = currentState.checkpoint.setSessions(mapOf(flowStart.initiatedSessionId to initiatedState))
+        val messageIdentifier = MessageIdentifier(messageType, flowStart.shardIdentifier, initiatingMessage.initiatorSessionId, 0, currentState.checkpoint.checkpointState.suspensionTime)
-        )
+        currentState = currentState.copy(checkpoint = currentState.checkpoint.setSessions(mapOf(flowStart.initiatedSessionId to initiatedState)))
-        actions.add(
+        actions.add(Action.SendExisting(flowStart.peerSession.counterparty, sessionMessage, SenderDeduplicationInfo(messageIdentifier, currentState.senderUUID)))
-                Action.SendExisting(
-                        flowStart.peerSession.counterparty,
-                        sessionMessage,
-                        SenderDeduplicationId(DeduplicationId.createForNormal(currentState.checkpoint, 0, initiatedState), currentState.senderUUID)
-                )
-        )
     }
 
     // Create initial checkpoint and acknowledge triggering messages.

node/src/main/kotlin/net/corda/node/utilities/NodeNamedCache.kt

@@ -55,7 +55,7 @@ open class DefaultNamedCacheFactory protected constructor(private val metricRegi
                 name == "FlowDrainingMode_nodeProperties" -> caffeine.maximumSize(defaultCacheSize)
                 name == "ContractUpgradeService_upgrades" -> caffeine.maximumSize(defaultCacheSize)
                 name == "PersistentUniquenessProvider_transactions" -> caffeine.maximumSize(defaultCacheSize)
-                name == "P2PMessageDeduplicator_processedMessages" -> caffeine.maximumSize(defaultCacheSize)
+                name == "P2PMessageDeduplicator_sessionData" -> caffeine.maximumSize(defaultCacheSize)
                 name == "DeduplicationChecker_watermark" -> caffeine
                 name == "BFTNonValidatingNotaryService_transactions" -> caffeine.maximumSize(defaultCacheSize)
                 name == "RaftUniquenessProvider_transactions" -> caffeine.maximumSize(defaultCacheSize)

node/src/main/resources/migration/node-core.changelog-master.xml

@@ -34,5 +34,7 @@
     <include file="migration/node-core.changelog-v19.xml"/>
     <include file="migration/node-core.changelog-v19-postgres.xml"/>
     <include file="migration/node-core.changelog-v19-keys.xml"/>
+    <include file="migration/node-core.changelog-v20.xml"/>
+    <include file="migration/node-core.changelog-v21.xml"/>
 
 </databaseChangeLog>

node/src/main/resources/migration/node-core.changelog-v21.xml

@@ -0,0 +1,28 @@
+<?xml version="1.1" encoding="UTF-8" standalone="no"?>
+<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                   xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.5.xsd"
+                   logicalFilePath="migration/node-services.changelog-init.xml">
+
+    <changeSet author="R3.Corda" id="add_session_data_table">
+        <createTable tableName="node_session_data">
+            <column name="session_id" type="NUMBER(128)">
+                <constraints nullable="false"/>
+            </column>
+            <column name="init_generation_time" type="timestamp">
+                <constraints nullable="false"/>
+            </column>
+            <column name="sender_hash" type="NVARCHAR(64)">
+                <constraints nullable="true"/>
+            </column>
+            <column name="init_sequence_number" type="BIGINT">
+                <constraints nullable="true"/>
+            </column>
+            <column name="last_sequence_number" type="BIGINT">
+                <constraints nullable="true"/>
+            </column>
+        </createTable>
+        <addPrimaryKey columnNames="session_id" constraintName="node_session_data_pk" tableName="node_session_data"/>
+    </changeSet>
+
+</databaseChangeLog>

node/src/test/kotlin/net/corda/node/services/messaging/MessageIdentifierTest.kt

@@ -0,0 +1,47 @@
+package net.corda.node.services.messaging
+
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
+import org.assertj.core.api.Assertions
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+import java.lang.IllegalArgumentException
+import java.math.BigInteger
+import java.time.Instant
+
+class MessageIdentifierTest {
+
+    private val shardIdentifier = "XXXXXXXX"
+    private val sessionIdentifier = SessionId(BigInteger.valueOf(14))
+    private val sessionSequenceNumber = 1
+    private val timestamp = Instant.ofEpochMilli(100)
+
+    private val messageIdString = "XI-0000000000000064-XXXXXXXX-0000000000000000000000000000000E-1"
+
+    @Test(timeout=300_000)
+    fun `can parse message identifier from string value`() {
+        val messageIdentifier = MessageIdentifier(MessageType.SESSION_INIT, shardIdentifier, sessionIdentifier, sessionSequenceNumber, timestamp)
+
+        assertThat(messageIdentifier.toString()).isEqualTo(messageIdString)
+    }
+
+    @Test(timeout=300_000)
+    fun `can convert message identifier object to string value`() {
+        val messageIdentifierString = messageIdString
+
+        val messageIdentifier = MessageIdentifier.parse(messageIdentifierString)
+        assertThat(messageIdentifier.messageType).isInstanceOf(MessageType.SESSION_INIT::class.java)
+        assertThat(messageIdentifier.shardIdentifier).isEqualTo(shardIdentifier)
+        assertThat(messageIdentifier.sessionIdentifier).isEqualTo(sessionIdentifier)
+        assertThat(messageIdentifier.sessionSequenceNumber).isEqualTo(1)
+        assertThat(messageIdentifier.timestamp).isEqualTo(timestamp)
+    }
+
+    @Test(timeout=300_000)
+    fun `shard identifier needs to be 8 characters long`() {
+        Assertions.assertThatThrownBy { MessageIdentifier(MessageType.SESSION_INIT, "XX", sessionIdentifier, 1, timestamp) }
+                .isInstanceOf(IllegalArgumentException::class.java)
+                .hasMessage("Shard identifier needs to be 8 characters long, but it was XX")
+    }
+
+}

node/src/test/kotlin/net/corda/node/services/messaging/SessionIdTest.kt

@@ -0,0 +1,28 @@
+package net.corda.node.services.messaging
+
+import net.corda.node.services.statemachine.SessionId
+import org.assertj.core.api.Assertions.assertThatThrownBy
+import org.junit.Test
+import java.lang.IllegalArgumentException
+import java.math.BigInteger
+
+class SessionIdTest {
+
+    @Test(timeout=300_000)
+    fun `session identifier cannot be negative`() {
+        assertThatThrownBy { SessionId(BigInteger.valueOf(-1)) }
+                .isInstanceOf(IllegalArgumentException::class.java)
+                .hasMessage("Session identifier cannot be a negative number, but it was -1")
+    }
+
+    @Test(timeout=300_000)
+    fun `session identifier needs to be a number that can be represented in maximum 128 bits`() {
+        val largestSessionIdentifierValue = BigInteger.valueOf(2).pow(128).minus(BigInteger.ONE)
+        val largestValidSessionId = SessionId(largestSessionIdentifierValue)
+
+        assertThatThrownBy { SessionId(largestSessionIdentifierValue.plus(BigInteger.ONE)) }
+                .isInstanceOf(IllegalArgumentException::class.java)
+                .hasMessage("The size of a session identifier cannot exceed 128 bits, but it was 340282366920938463463374607431768211456")
+    }
+
+}

node/src/test/kotlin/net/corda/node/services/persistence/DBCheckpointStorageTests.kt

@@ -873,7 +873,8 @@ class DBCheckpointStorageTests {
             frozenLogic,
             ALICE,
             SubFlowVersion.CoreFlow(version),
-            false
+            false,
+            Clock.systemUTC().instant()
         )
             .getOrThrow()
         return id to checkpoint

node/src/test/kotlin/net/corda/node/services/rpc/CheckpointDumperImplTest.kt

@@ -194,7 +194,7 @@ class CheckpointDumperImplTest {
             override fun call() {}
         }
         val frozenLogic = logic.checkpointSerialize(context = CheckpointSerializationDefaults.CHECKPOINT_CONTEXT)
-        val checkpoint = Checkpoint.create(InvocationContext.shell(), FlowStart.Explicit, logic.javaClass, frozenLogic, myself.identity.party, SubFlowVersion.CoreFlow(version), false)
+        val checkpoint = Checkpoint.create(InvocationContext.shell(), FlowStart.Explicit, logic.javaClass, frozenLogic, myself.identity.party, SubFlowVersion.CoreFlow(version), false, Clock.systemUTC().instant())
                 .getOrThrow()
         return id to checkpoint
     }

node/src/test/kotlin/net/corda/node/services/statemachine/FlowFrameworkTests.kt

@@ -8,7 +8,6 @@ import net.corda.client.rpc.notUsed
 import net.corda.core.concurrent.CordaFuture
 import net.corda.core.contracts.ContractState
 import net.corda.core.crypto.SecureHash
-import net.corda.core.crypto.random63BitValue
 import net.corda.core.flows.Destination
 import net.corda.core.flows.FinalityFlow
 import net.corda.core.flows.FlowException
@@ -42,6 +41,8 @@ import net.corda.core.utilities.ProgressTracker.Change
 import net.corda.core.utilities.getOrThrow
 import net.corda.core.utilities.seconds
 import net.corda.core.utilities.unwrap
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
 import net.corda.node.services.persistence.CheckpointPerformanceRecorder
 import net.corda.node.services.persistence.DBCheckpointStorage
 import net.corda.node.services.persistence.checkpoints
@@ -80,6 +81,8 @@ import org.junit.Before
 import org.junit.Test
 import rx.Notification
 import rx.Observable
+import java.math.BigInteger
+import java.security.SecureRandom
 import java.sql.SQLTransientConnectionException
 import java.time.Clock
 import java.time.Duration
@@ -571,7 +574,7 @@ class FlowFrameworkTests {
 
     @Test(timeout=300_000)
 	fun `session init with unknown class is sent to the flow hospital, from where we then drop it`() {
-        aliceNode.sendSessionMessage(InitialSessionMessage(SessionId(random63BitValue()), 0, "not.a.real.Class", 1, "", null), bob)
+        aliceNode.sendSessionMessage(InitialSessionMessage(SessionId.createRandom(SecureRandom()), 0, "not.a.real.Class", 1, "", null), bob)
         mockNet.runNetwork()
         assertThat(receivedSessionMessages).hasSize(1) // Only the session-init is expected as the session-reject is blocked by the flow hospital
         val medicalRecords = bobNode.smm.flowHospital.track().apply { updates.notUsed() }.snapshot
@@ -587,7 +590,7 @@ class FlowFrameworkTests {
 
     @Test(timeout=300_000)
 	fun `non-flow class in session init`() {
-        aliceNode.sendSessionMessage(InitialSessionMessage(SessionId(random63BitValue()), 0, String::class.java.name, 1, "", null), bob)
+        aliceNode.sendSessionMessage(InitialSessionMessage(SessionId.createRandom(SecureRandom()), 0, String::class.java.name, 1, "", null), bob)
         mockNet.runNetwork()
         assertThat(receivedSessionMessages).hasSize(2) // Only the session-init and session-reject are expected
         val lastMessage = receivedSessionMessages.last().message as ExistingSessionMessage
@@ -897,7 +900,7 @@ class FlowFrameworkTests {
     }
         //region Helpers
 
-    private val normalEnd = ExistingSessionMessage(SessionId(0), EndSessionMessage) // NormalSessionEnd(0)
+    private val normalEnd = ExistingSessionMessage(SessionId(BigInteger.valueOf(0)), EndSessionMessage) // NormalSessionEnd(0)
 
     private fun assertSessionTransfers(vararg expected: SessionTransfer) {
         assertThat(receivedSessionMessages).containsExactly(*expected)
@@ -1039,21 +1042,21 @@ class FlowFrameworkTests {
 }
 
 internal fun sessionConfirm(flowVersion: Int = 1) =
-    ExistingSessionMessage(SessionId(0), ConfirmSessionMessage(SessionId(0), FlowInfo(flowVersion, "")))
+    ExistingSessionMessage(SessionId(BigInteger.valueOf(0)), ConfirmSessionMessage(SessionId(BigInteger.valueOf(0)), FlowInfo(flowVersion, "")))
 
 internal inline fun <reified P : FlowLogic<*>> TestStartedNode.getSingleFlow(): Pair<P, CordaFuture<*>> {
     return smm.findStateMachines(P::class.java).single()
 }
 
 private fun sanitise(message: SessionMessage) = when (message) {
-    is InitialSessionMessage -> message.copy(initiatorSessionId = SessionId(0), initiationEntropy = 0, appName = "")
+    is InitialSessionMessage -> message.copy(initiatorSessionId = SessionId(BigInteger.valueOf(0)), initiationEntropy = 0, appName = "")
     is ExistingSessionMessage -> {
         val payload = message.payload
         message.copy(
-            recipientSessionId = SessionId(0),
+            recipientSessionId = SessionId(BigInteger.valueOf(0)),
             payload = when (payload) {
                 is ConfirmSessionMessage -> payload.copy(
-                    initiatedSessionId = SessionId(0),
+                    initiatedSessionId = SessionId(BigInteger.valueOf(0)),
                     initiatedFlowInfo = payload.initiatedFlowInfo.copy(appName = "")
                 )
                 is ErrorSessionMessage -> payload.copy(
@@ -1076,7 +1079,8 @@ internal fun Observable<MessageTransfer>.toSessionTransfers(): Observable<Sessio
 internal fun TestStartedNode.sendSessionMessage(message: SessionMessage, destination: Party) {
     services.networkService.apply {
         val address = getAddressOfParty(PartyInfo.SingleNode(destination, emptyList()))
-        send(createMessage(FlowMessagingImpl.sessionTopic, message.serialize().bytes), address)
+        val messageIdentifier = MessageIdentifier(MessageType.DATA_MESSAGE, "XXXXXXXX", SessionId(BigInteger.valueOf(14)), 0, Clock.systemUTC().instant())
+        send(createMessage(FlowMessagingImpl.sessionTopic, message.serialize().bytes, SenderDeduplicationInfo(messageIdentifier, null), emptyMap()), address)
     }
 }
 
@@ -1087,7 +1091,7 @@ inline fun <reified T> DatabaseTransaction.findRecordsFromDatabase(): List<T> {
 }
 
 internal fun errorMessage(errorResponse: FlowException? = null) =
-    ExistingSessionMessage(SessionId(0), ErrorSessionMessage(errorResponse, 0))
+    ExistingSessionMessage(SessionId(BigInteger.valueOf(0)), ErrorSessionMessage(errorResponse, 0))
 
 internal infix fun TestStartedNode.sent(message: SessionMessage): Pair<Int, SessionMessage> = Pair(internals.id, message)
 internal infix fun Pair<Int, SessionMessage>.to(node: TestStartedNode): SessionTransfer =
@@ -1103,10 +1107,10 @@ internal data class SessionTransfer(val from: Int, val message: SessionMessage,
 }
 
 internal fun sessionInit(clientFlowClass: KClass<out FlowLogic<*>>, flowVersion: Int = 1, payload: Any? = null): InitialSessionMessage {
-    return InitialSessionMessage(SessionId(0), 0, clientFlowClass.java.name, flowVersion, "", payload?.serialize())
+    return InitialSessionMessage(SessionId(BigInteger.valueOf(0)), 0, clientFlowClass.java.name, flowVersion, "", payload?.serialize())
 }
 
-internal fun sessionData(payload: Any) = ExistingSessionMessage(SessionId(0), DataSessionMessage(payload.serialize()))
+internal fun sessionData(payload: Any) = ExistingSessionMessage(SessionId(BigInteger.valueOf(0)), DataSessionMessage(payload.serialize()))
 
 @InitiatingFlow
 internal open class SendFlow(private val payload: Any, private vararg val otherParties: Party) : FlowLogic<FlowInfo>() {

node/src/test/kotlin/net/corda/node/services/statemachine/FlowFrameworkTripartyTests.kt

@@ -18,6 +18,7 @@ import org.junit.After
 import org.junit.Before
 import org.junit.Test
 import rx.Observable
+import java.math.BigInteger
 import java.util.*
 
 class FlowFrameworkTripartyTests {
@@ -168,7 +169,7 @@ class FlowFrameworkTripartyTests {
         )
     }
 
-    private val normalEnd = ExistingSessionMessage(SessionId(0), EndSessionMessage) // NormalSessionEnd(0)
+    private val normalEnd = ExistingSessionMessage(SessionId(BigInteger.valueOf(0)), EndSessionMessage) // NormalSessionEnd(0)
 
     private fun assertSessionTransfers(node: TestStartedNode, vararg expected: SessionTransfer): List<SessionTransfer> {
         val actualForNode = receivedSessionMessages.filter { it.from == node.internals.id || it.to == node.network.myAddress }

node/src/test/kotlin/net/corda/node/services/statemachine/SessionIdTest.kt

@@ -0,0 +1,42 @@
+package net.corda.node.services.statemachine
+
+import org.assertj.core.api.Assertions.*
+import org.junit.Test
+import java.lang.IllegalArgumentException
+import java.math.BigInteger
+
+class SessionIdTest {
+
+    companion object {
+        private val LARGEST_SESSION_ID_VALUE = BigInteger.valueOf(2).pow(128).minus(BigInteger.ONE)
+    }
+
+    @Test(timeout=300_000)
+    fun `session id must be positive and representable in 128 bits`() {
+        assertThatThrownBy { SessionId(BigInteger.ZERO.minus(BigInteger.ONE)) }
+                .isInstanceOf(IllegalArgumentException::class.java)
+                .hasMessage("Session identifier cannot be a negative number, but it was -1")
+
+        assertThatThrownBy { SessionId(LARGEST_SESSION_ID_VALUE.plus(BigInteger.ONE)) }
+                .isInstanceOf(IllegalArgumentException::class.java)
+                .hasMessageContaining("The size of a session identifier cannot exceed 128 bits, but it was")
+
+        val correctSessionId = SessionId(LARGEST_SESSION_ID_VALUE)
+    }
+
+    @Test(timeout=300_000)
+    fun `initiated session id is calculated properly`() {
+        val sessionId = SessionId(BigInteger.ONE)
+        val initiatedSessionId = sessionId.calculateInitiatedSessionId()
+        assertThat(initiatedSessionId.value.toLong()).isEqualTo(2)
+
+    }
+
+    @Test(timeout=300_000)
+    fun `calculation of initiated session id wraps around`() {
+        val sessionId = SessionId(LARGEST_SESSION_ID_VALUE)
+        val initiatedSessionId = sessionId.calculateInitiatedSessionId()
+        assertThat(initiatedSessionId.value.toLong()).isEqualTo(0)
+    }
+
+}

testing/node-driver/src/main/kotlin/net/corda/testing/node/internal/InMemoryMessage.kt

@@ -2,7 +2,7 @@ package net.corda.testing.node.internal
 
 import net.corda.core.utilities.ByteSequence
 import net.corda.node.services.messaging.Message
-import net.corda.node.services.statemachine.DeduplicationId
+import net.corda.node.services.messaging.MessageIdentifier
 import java.time.Instant
 
 /**
@@ -10,7 +10,7 @@ import java.time.Instant
  */
 data class InMemoryMessage(override val topic: String,
                            override val data: ByteSequence,
-                           override val uniqueMessageId: DeduplicationId,
+                           override val uniqueMessageId: MessageIdentifier,
                            override val debugTimestamp: Instant = Instant.now(),
                            override val senderUUID: String? = null) : Message {
 

testing/node-driver/src/main/kotlin/net/corda/testing/node/internal/MockNodeMessagingService.kt

@@ -1,5 +1,6 @@
 package net.corda.testing.node.internal
 
+import co.paralleluniverse.fibers.Suspendable
 import net.corda.core.flows.StateMachineRunId
 import net.corda.core.identity.CordaX500Name
 import net.corda.core.identity.PartyAndCertificate
@@ -13,9 +14,9 @@ import net.corda.core.utilities.OpaqueBytes
 import net.corda.core.utilities.contextLogger
 import net.corda.node.services.config.NodeConfiguration
 import net.corda.node.services.messaging.*
-import net.corda.node.services.statemachine.DeduplicationId
 import net.corda.node.services.statemachine.ExternalEvent
-import net.corda.node.services.statemachine.SenderDeduplicationId
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.statemachine.SessionId
 import net.corda.node.utilities.AffinityExecutor
 import net.corda.nodeapi.internal.lifecycle.ServiceStateHelper
 import net.corda.nodeapi.internal.lifecycle.ServiceStateSupport
@@ -46,9 +47,9 @@ class MockNodeMessagingService(private val configuration: NodeConfiguration,
     }
 
     private val state = ThreadBox(InnerState())
-    private val processedMessages: MutableSet<DeduplicationId> = Collections.synchronizedSet(HashSet<DeduplicationId>())
+    private val processedMessages: MutableSet<MessageIdentifier> = Collections.synchronizedSet(HashSet())
 
-    override val ourSenderUUID: String = UUID.randomUUID().toString()
+    override val ourSenderUUID: SenderUUID = UUID.randomUUID().toString()
 
     private var _myAddress: InMemoryMessagingNetwork.PeerHandle? = null
     override val myAddress: InMemoryMessagingNetwork.PeerHandle get() = checkNotNull(_myAddress) { "Not started" }
@@ -167,6 +168,11 @@ class MockNodeMessagingService(private val configuration: NodeConfiguration,
         }
     }
 
+    @Suspendable
+    override fun sessionEnded(sessionId: SessionId, senderUUID: SenderUUID?, senderSequenceNumber: SenderSequenceNumber?) {
+        // nothing to do here.
+    }
+
     override fun close() {
         backgroundThread?.let {
             it.interrupt()
@@ -178,8 +184,8 @@ class MockNodeMessagingService(private val configuration: NodeConfiguration,
     }
 
     /** Returns the given (topic & session, data) pair as a newly created message object. */
-    override fun createMessage(topic: String, data: ByteArray, deduplicationId: SenderDeduplicationId, additionalHeaders: Map<String, String>): Message {
+    override fun createMessage(topic: String, data: ByteArray, deduplicationInfo: SenderDeduplicationInfo, additionalHeaders: Map<String, String>): Message {
-        return InMemoryMessage(topic, OpaqueBytes(data), deduplicationId.deduplicationId, senderUUID = deduplicationId.senderUUID)
+        return InMemoryMessage(topic, OpaqueBytes(data), deduplicationInfo.messageIdentifier, senderUUID = deduplicationInfo.senderUUID)
     }
 
     /**
@@ -269,7 +275,7 @@ class MockNodeMessagingService(private val configuration: NodeConfiguration,
     private data class InMemoryReceivedMessage(override val topic: String,
                                                override val data: ByteSequence,
                                                override val platformVersion: Int,
-                                               override val uniqueMessageId: DeduplicationId,
+                                               override val uniqueMessageId: MessageIdentifier,
                                                override val debugTimestamp: Instant,
                                                override val peer: CordaX500Name,
                                                override val senderUUID: String? = null,

testing/node-driver/src/test/kotlin/net/corda/testing/node/internal/InternalMockNetworkTests.kt

@@ -4,14 +4,24 @@ import net.corda.core.messaging.AllPossibleRecipients
 import net.corda.core.serialization.internal.effectiveSerializationEnv
 import net.corda.node.services.messaging.Message
 import net.corda.coretesting.internal.rigorousMock
+import net.corda.node.services.messaging.MessageIdentifier
+import net.corda.node.services.messaging.SenderDeduplicationInfo
+import net.corda.node.services.statemachine.MessageType
+import net.corda.node.services.statemachine.SessionId
 import org.assertj.core.api.Assertions.assertThatThrownBy
 import org.junit.After
 import org.junit.Test
+import java.math.BigInteger
+import java.time.Clock
 import java.util.*
 import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class InternalMockNetworkTests {
+    companion object {
+        private val MESSAGE_IDENTIFIER = MessageIdentifier(MessageType.DATA_MESSAGE, "XXXXXXXX", SessionId(BigInteger.valueOf(14)), 0, Clock.systemUTC().instant())
+    }
+
     lateinit var mockNet: InternalMockNetwork
 
     @After
@@ -39,7 +49,7 @@ class InternalMockNetworkTests {
         }
 
         // Node 1 sends a message and it should end up in finalDelivery, after we run the network
-        node1.network.send(node1.network.createMessage("test.topic", data = bits), node2.network.myAddress)
+        node1.network.send(node1.network.createMessage("test.topic", bits, SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap()), node2.network.myAddress)
 
         mockNet.runNetwork(rounds = 1)
 
@@ -58,7 +68,7 @@ class InternalMockNetworkTests {
 
         var counter = 0
         listOf(node1, node2, node3).forEach { it.network.addMessageHandler("test.topic") { _, _, _ -> counter++ } }
-        node1.network.send(node2.network.createMessage("test.topic", data = bits), rigorousMock<AllPossibleRecipients>())
+        node1.network.send(node2.network.createMessage("test.topic", bits, SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap()), rigorousMock<AllPossibleRecipients>())
         mockNet.runNetwork(rounds = 1)
         assertEquals(3, counter)
     }
@@ -79,8 +89,8 @@ class InternalMockNetworkTests {
             received++
         }
 
-        val invalidMessage = node2.network.createMessage("invalid_message", data = ByteArray(1))
+        val invalidMessage = node2.network.createMessage("invalid_message", ByteArray(1), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
-        val validMessage = node2.network.createMessage("valid_message", data = ByteArray(1))
+        val validMessage = node2.network.createMessage("valid_message", ByteArray(1), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         node2.network.send(invalidMessage, node1.network.myAddress)
         mockNet.runNetwork()
         assertEquals(0, received)
@@ -91,8 +101,8 @@ class InternalMockNetworkTests {
 
         // Here's the core of the test; previously the unhandled message would cause runNetwork() to abort early, so
         // this would fail. Make fresh messages to stop duplicate uniqueMessageId causing drops
-        val invalidMessage2 = node2.network.createMessage("invalid_message", data = ByteArray(1))
+        val invalidMessage2 = node2.network.createMessage("invalid_message", ByteArray(1), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
-        val validMessage2 = node2.network.createMessage("valid_message", data = ByteArray(1))
+        val validMessage2 = node2.network.createMessage("valid_message", ByteArray(1), SenderDeduplicationInfo(MESSAGE_IDENTIFIER, null), emptyMap())
         node2.network.send(invalidMessage2, node1.network.myAddress)
         node2.network.send(validMessage2, node1.network.myAddress)
         mockNet.runNetwork()