Services

Services are the centerpieces of the library. A service is an interface annotated with the @Rpc annotation, and contains a set of methods that can be executed remotely.

A simple service can be declared as follows:

        @Rpc
        interface MyService {
            suspend fun hello(name: String): String
        }
    

Here we declare the method hello, that accepts one argument and returns a string. The method is marked with a suspend modifier, which means that we use coroutines to send RPC requests.

To be able to use a service both in client and server code, the interface should be placed in the common module — kudos to Kotlin Multiplatform.

Now we can implement the service, so the server knows how to process incoming requests.

        class MyServiceImpl : MyService {
            override suspend fun hello(name: String): String {
                return "Hello, $name! I'm server!"
            }
        }
    

The server will use that implementation to answer the client requests.

Streaming

The library supports streaming of data. To declare a streaming method, you need to use the Flow type. For example, to declare a method that returns a stream of integers:

            @Rpc
            interface MyService {
                fun stream(): Flow<Int>
            }
        

Note that the method is not marked with the suspend modifier.

You can also pass a Flow as a parameter to the method. For example, to declare a method that accepts a stream of integers:

            @Rpc
            interface MyService {
                suspend fun sendStream(stream: Flow<Int>)
            }
        

Or make streams bidirectional:

            @Rpc
            interface MyService {
                fun bidi(stream: Flow<Int>): Flow<Int>
            }
        

Last modified: 13 June 2025