fix wrong unchecked null cast (potential NPE) (#445)

Co-authored-by: Alexander Sysoev <a.sysoev2308@gmail.com>

Author: y9maly

krpc/krpc-client/src/commonMain/kotlin/kotlinx/rpc/krpc/client/KrpcClient.kt

@@ -172,7 +172,7 @@ public abstract class KrpcClient : RpcClient, KrpcEndpoint {
 
     private val serverSupportedPlugins: CompletableDeferred<Set<KrpcPlugin>> = CompletableDeferred()
 
-    private val requestChannels = RpcInternalConcurrentHashMap<String, Channel<Any?>>()
+    private val requestChannels = RpcInternalConcurrentHashMap<String, Channel<Result<Any?>>>()
 
     @InternalRpcApi
     final override val supportedPlugins: Set<KrpcPlugin>
@@ -247,11 +247,11 @@ public abstract class KrpcClient : RpcClient, KrpcEndpoint {
 
             val callId = "$connectionId:${callable.name}:$id"
 
-            val channel = Channel<T>()
+            val channel = Channel<Result<T>>()
 
             try {
                 @Suppress("UNCHECKED_CAST")
-                requestChannels[callId] = channel as Channel<Any?>
+                requestChannels[callId] = channel as Channel<Result<Any?>>
 
                 val request = serializeRequest(
                     callId = callId,
@@ -308,7 +308,7 @@ public abstract class KrpcClient : RpcClient, KrpcEndpoint {
         }
     }
 
-    private suspend fun <T> FlowCollector<T>.consumeAndEmitServerMessages(channel: Channel<T>) {
+    private suspend fun <T> FlowCollector<T>.consumeAndEmitServerMessages(channel: Channel<Result<T>>) {
         while (true) {
             val element = channel.receiveCatching()
             if (element.isClosed) {
@@ -317,14 +317,22 @@ public abstract class KrpcClient : RpcClient, KrpcEndpoint {
             }
 
             if (!element.isFailure) {
-                emit(element.getOrThrow())
+                val result = element.getOrThrow()
+                result.fold(
+                    onSuccess = { value ->
+                        emit(value)
+                    },
+                    onFailure = { throwable ->
+                        throw throwable
+                    }
+                )
             }
         }
     }
 
     private suspend fun <T, @Rpc R : Any> handleServerStreamingMessage(
         message: KrpcCallMessage,
-        channel: Channel<T>,
+        channel: Channel<Result<T>>,
         callable: RpcCallable<R>,
     ) {
         when (message) {
@@ -355,7 +363,7 @@ public abstract class KrpcClient : RpcClient, KrpcEndpoint {
                 }
 
                 @Suppress("UNCHECKED_CAST")
-                channel.send(value.getOrNull() as T)
+                channel.send(value as Result<T>)
             }
 
             is KrpcCallMessage.StreamFinished -> {

krpc/krpc-test/src/commonMain/kotlin/kotlinx/rpc/krpc/test/KrpcTestService.kt

@@ -64,6 +64,7 @@ interface KrpcTestService {
     suspend fun nullableReturn(returnNull: Boolean): TestClass?
     suspend fun variance(arg2: TestList<in TestClass>, arg3: TestList2<TestClass>): TestList<out TestClass>?
     suspend fun collectOnce(flow: Flow<String>)
+    suspend fun returnTestClassThatThrowsWhileDeserialization(value: Int): TestClassThatThrowsWhileDeserialization
 
     suspend fun nonSerializableClass(localDate: LocalDate): LocalDate
     suspend fun nonSerializableClassWithSerializer(

krpc/krpc-test/src/commonMain/kotlin/kotlinx/rpc/krpc/test/KrpcTestServiceBackend.kt

@@ -98,6 +98,10 @@ class KrpcTestServiceBackend : KrpcTestService {
         return arg1
     }
 
+    override suspend fun returnTestClassThatThrowsWhileDeserialization(value: Int): TestClassThatThrowsWhileDeserialization {
+        return TestClassThatThrowsWhileDeserialization(value)
+    }
+
     override suspend fun nullableParam(arg1: String?): String {
         return arg1 ?: "null"
     }

krpc/krpc-test/src/commonMain/kotlin/kotlinx/rpc/krpc/test/KrpcTransportTestBase.kt

@@ -20,6 +20,7 @@ import kotlinx.rpc.krpc.server.KrpcServer
 import kotlinx.rpc.registerService
 import kotlinx.rpc.withService
 import kotlinx.serialization.KSerializer
+import kotlinx.serialization.SerializationException
 import kotlinx.serialization.descriptors.PrimitiveKind
 import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
 import kotlinx.serialization.descriptors.SerialDescriptor
@@ -460,6 +461,17 @@ abstract class KrpcTransportTestBase {
     fun testUnitFlow() = runTest {
         assertEquals(Unit, client.unitFlow().toList().single())
     }
+
+    @Test
+    fun testPR445() = runTest {
+        assertFailsWith<SerializationException> {
+            val result = client.returnTestClassThatThrowsWhileDeserialization(42)
+            @Suppress("SENSELESS_COMPARISON")
+            if (result == null) {
+                assertNotNull(result, "result must not be null")
+            }
+        }
+    }
 }
 
 private val JS_EXTENDED_TIMEOUT = if (isJs) 300.seconds else 60.seconds

krpc/krpc-test/src/commonMain/kotlin/kotlinx/rpc/krpc/test/TestClass.kt

@@ -4,7 +4,12 @@
 
 package kotlinx.rpc.krpc.test
 
+import kotlinx.serialization.KSerializer
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.builtins.serializer
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
 
 @Suppress("EqualsOrHashCode", "detekt.EqualsWithHashCodeExist")
 @Serializable
@@ -15,6 +20,27 @@ open class TestClass(val value: Int = 0) {
     }
 }
 
+@Suppress("EqualsOrHashCode", "detekt.EqualsWithHashCodeExist")
+@Serializable(with = TestClassThatThrowsWhileDeserialization.Serializer::class)
+class TestClassThatThrowsWhileDeserialization(val value: Int = 0) {
+    object Serializer : KSerializer<TestClassThatThrowsWhileDeserialization> {
+        override val descriptor = Int.serializer().descriptor
+
+        override fun serialize(encoder: Encoder, value: TestClassThatThrowsWhileDeserialization) {
+            encoder.encodeInt(value.value)
+        }
+
+        override fun deserialize(decoder: Decoder): TestClassThatThrowsWhileDeserialization {
+            throw SerializationException("Its TestClassThatThrowsWhileDeserialization")
+        }
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (other !is TestClassThatThrowsWhileDeserialization) return false
+        return value == other.value
+    }
+}
+
 @Serializable
 data class TestList<@Suppress("unused") T : TestClass>(val value: Int = 42)