Fix KRPC-173 (#315)

Author: Mr3zee

krpc/krpc-server/src/commonMain/kotlin/kotlinx/rpc/krpc/server/internal/KrpcServerService.kt

@@ -21,6 +21,7 @@ import kotlinx.serialization.KSerializer
 import kotlinx.serialization.SerialFormat
 import kotlinx.serialization.StringFormat
 import kotlin.coroutines.CoroutineContext
+import kotlin.reflect.typeOf
 
 internal class KrpcServerService<@Rpc T : Any>(
     private val service: T,
@@ -178,6 +179,13 @@ internal class KrpcServerService<@Rpc T : Any>(
                     is RpcInvokator.Field -> {
                         invokator.call(service)
                     }
+                }.let { interceptedValue ->
+                    // KRPC-173
+                    if (callable.returnType.kType == typeOf<Unit>()) {
+                        Unit
+                    } else {
+                        interceptedValue
+                    }
                 }
 
                 val returnType = callable.returnType

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

@@ -108,6 +108,8 @@ interface KrpcTestService : RemoteService {
 
     suspend fun answerToAnything(arg: String): Int
 
+    suspend fun krpc173()
+
     val plainFlowOfInts : Flow<Int>
 
     val plainFlowOfFlowsOfInts : Flow<Flow<Int>>

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

@@ -265,6 +265,15 @@ class KrpcTestServiceBackend(override val coroutineContext: CoroutineContext) :
         return 42
     }
 
+    private suspend fun doWork(): String {
+        delay(1)
+        return "qwerty"
+    }
+
+    override suspend fun krpc173() {
+        doWork()
+    }
+
     override val plainFlowOfInts: Flow<Int> = plainFlow { it }
 
     override val plainFlowOfFlowsOfInts: Flow<Flow<Int>> = plainFlow { plainFlow { i -> i } }

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

@@ -548,6 +548,11 @@ abstract class KrpcTransportTestBase {
         awaitAll(c1, c2)
     }
 
+    @Test
+    fun testKrpc173() = runTest {
+        assertEquals(Unit, client.krpc173())
+    }
+
     @Test
     fun testPlainFlowOfInts() = runTest {
         val flow = client.plainFlowOfInts.toList()