Removed DeserializeAsKotlinObjectDef interface as serialisation of Kotlin objects is now handled automatically

core/src/main/kotlin/net/corda/core/contracts/TransactionTypes.kt

@@ -2,7 +2,6 @@ package net.corda.core.contracts
 
 import net.corda.core.identity.Party
 import net.corda.core.serialization.CordaSerializable
-import net.corda.core.serialization.DeserializeAsKotlinObjectDef
 import net.corda.core.transactions.LedgerTransaction
 import net.corda.core.transactions.TransactionBuilder
 import java.security.PublicKey
@@ -61,7 +60,7 @@ sealed class TransactionType {
     abstract fun verifyTransaction(tx: LedgerTransaction)
 
     /** A general transaction type where transaction validity is determined by custom contract code */
-    object General : TransactionType(), DeserializeAsKotlinObjectDef {
+    object General : TransactionType() {
         /** Just uses the default [TransactionBuilder] with no special logic */
         class Builder(notary: Party?) : TransactionBuilder(General, notary)
 
@@ -141,7 +140,7 @@ sealed class TransactionType {
      * A special transaction type for reassigning a notary for a state. Validation does not involve running
      * any contract code, it just checks that the states are unmodified apart from the notary field.
      */
-    object NotaryChange : TransactionType(), DeserializeAsKotlinObjectDef {
+    object NotaryChange : TransactionType() {
         /**
          * A transaction builder that automatically sets the transaction type to [NotaryChange]
          * and adds the list of participants to the signers set for every input state.

core/src/main/kotlin/net/corda/core/serialization/DefaultKryoCustomizer.kt

@@ -86,9 +86,6 @@ object DefaultKryoCustomizer {
             // This ensures a NonEmptySetSerializer is constructed with an initial value.
             register(NonEmptySet::class.java, NonEmptySetSerializer)
 
-            /** This ensures any kotlin objects that implement [DeserializeAsKotlinObjectDef] are read back in as singletons. */
-            addDefaultSerializer(DeserializeAsKotlinObjectDef::class.java, KotlinObjectSerializer)
-
             addDefaultSerializer(SerializeAsToken::class.java, SerializeAsTokenSerializer<SerializeAsToken>())
 
             register(MetaData::class.java, MetaDataSerializer)

core/src/main/kotlin/net/corda/core/serialization/Kryo.kt

@@ -462,20 +462,6 @@ inline fun <reified T> readListOfLength(kryo: Kryo, input: Input, minLen: Int =
     return list
 }
 
-/** Marker interface for kotlin object definitions so that they are deserialized as the singleton instance. */
-// TODO This is not needed anymore
-interface DeserializeAsKotlinObjectDef
-
-/** Serializer to deserialize kotlin object definitions marked with [DeserializeAsKotlinObjectDef]. */
-object KotlinObjectSerializer : Serializer<DeserializeAsKotlinObjectDef>() {
-    override fun read(kryo: Kryo, input: Input, type: Class<DeserializeAsKotlinObjectDef>): DeserializeAsKotlinObjectDef {
-        // read the public static INSTANCE field that kotlin compiler generates.
-        return type.getField("INSTANCE").get(null) as DeserializeAsKotlinObjectDef
-    }
-
-    override fun write(kryo: Kryo, output: Output, obj: DeserializeAsKotlinObjectDef) {}
-}
-
 // No ClassResolver only constructor.  MapReferenceResolver is the default as used by Kryo in other constructors.
 private val internalKryoPool = KryoPool.Builder { DefaultKryoCustomizer.customize(CordaKryo(makeAllButBlacklistedClassResolver())) }.build()
 private val kryoPool = KryoPool.Builder { DefaultKryoCustomizer.customize(CordaKryo(makeStandardClassResolver())) }.build()
@@ -533,7 +519,7 @@ inline fun <T : Any> Kryo.register(
     return register(
             type.java,
             object : Serializer<T>() {
-                override fun read(kryo: Kryo, input: Input, type: Class<T>): T = read(kryo, input)
+                override fun read(kryo: Kryo, input: Input, clazz: Class<T>): T = read(kryo, input)
                 override fun write(kryo: Kryo, output: Output, obj: T) = write(kryo, output, obj)
             }
     )

core/src/test/kotlin/net/corda/core/serialization/KryoTests.kt

@@ -3,10 +3,9 @@ package net.corda.core.serialization
 import com.esotericsoftware.kryo.Kryo
 import com.google.common.primitives.Ints
 import net.corda.core.crypto.*
+import net.corda.node.services.persistence.NodeAttachmentService
 import net.corda.testing.ALICE
 import net.corda.testing.BOB
-import net.corda.node.services.messaging.Ack
-import net.corda.node.services.persistence.NodeAttachmentService
 import net.corda.testing.BOB_PUBKEY
 import org.assertj.core.api.Assertions.assertThat
 import org.assertj.core.api.Assertions.assertThatThrownBy
@@ -16,7 +15,8 @@ import org.junit.Test
 import org.slf4j.LoggerFactory
 import java.io.ByteArrayInputStream
 import java.io.InputStream
-import java.security.cert.*
+import java.security.cert.CertPath
+import java.security.cert.CertificateFactory
 import java.time.Instant
 import java.util.*
 import kotlin.test.assertEquals
@@ -92,11 +92,10 @@ class KryoTests {
     }
 
     @Test
-    fun `write and read Ack`() {
-        val tokenizableBefore = Ack
-        val serializedBytes = tokenizableBefore.serialize(kryo)
-        val tokenizableAfter = serializedBytes.deserialize(kryo)
-        assertThat(tokenizableAfter).isSameAs(tokenizableBefore)
+    fun `write and read Kotlin object singleton`() {
+        val serialised = TestSingleton.serialize(kryo)
+        val deserialised = serialised.deserialize(kryo)
+        assertThat(deserialised).isSameAs(TestSingleton)
     }
 
     @Test
@@ -173,4 +172,7 @@ class KryoTests {
         override fun toString(): String = "Cyclic($value)"
     }
 
+    @CordaSerializable
+    private object TestSingleton
+
 }

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

@@ -8,7 +8,6 @@ import net.corda.core.messaging.SingleMessageRecipient
 import net.corda.core.node.services.DEFAULT_SESSION_ID
 import net.corda.core.node.services.PartyInfo
 import net.corda.core.serialization.CordaSerializable
-import net.corda.core.serialization.DeserializeAsKotlinObjectDef
 import net.corda.core.serialization.deserialize
 import net.corda.core.serialization.serialize
 import org.bouncycastle.asn1.x500.X500Name
@@ -229,10 +228,3 @@ object TopicStringValidator {
     /** @throws IllegalArgumentException if the given topic contains invalid characters */
     fun check(tag: String) = require(regex.matcher(tag).matches())
 }
-
-/**
- * A general Ack message that conveys no content other than it's presence for use when you want an acknowledgement
- * from a recipient.  Using [Unit] can be ambiguous as it is similar to [Void] and so could mean no response.
- */
-@CordaSerializable
-object Ack : DeserializeAsKotlinObjectDef

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

@@ -89,6 +89,7 @@ class StateMachineManager(val serviceHub: ServiceHubInternal,
         }
     }.build()
 
+    // TODO Move this into the blacklist and upgrade the blacklist to allow custom messages
     private object AutoCloseableSerialisationDetector : Serializer<AutoCloseable>() {
         override fun write(kryo: Kryo, output: Output, closeable: AutoCloseable) {
             val message = if (closeable is CloseableIterator<*>) {