Services

To define a service, create a new .proto file in the proto folder next to your source sets:

        ├── build.gradle.kts
        ├── settings.gradle.kts
        └── src
            ├── main
            │   ├── kotlin
            │   │   ├── Client.kt
            │   │   ├── ImageRecognizer.kt
            │   │   └── Server.kt
            │   └── resources
            │       └── logback.xml
            └── proto
                └── image-recognizer.proto
    

Inside the .proto file define your service:

        syntax = "proto3";

        message Image {
          bytes data = 1;
        }

        message RecogniseResult {
          int32 category = 1;
        }

        service ImageRecognizer {
          rpc recognize(Image) returns (RecogniseResult);
        }
    

This will generate the necessary code, including the most important interfaces: ImageRecognizer, Image, RecogniseResult:

        @Grpc
        interface ImageRecognizer {
            suspend fun recognize(image: Image): RecogniseResult
        }

        interface RecogniseResult {
            val category: Int

            companion object
        }

        interface Image {
            val data: ByteArray

            companion object
        }
    

You can implement the ImageRecognizer:

        class ImageRecognizerImpl : ImageRecognizer {
            override suspend fun recognize(image: Image): RecogniseResult {
                val byte = image.data[0].toInt()
                delay(100) // heavy processing
                val result = RecogniseResult {
                    category = if (byte == 0) 0 else 1
                }
                return result
            }
        }
    

Here you can also see the usage of the RecogniseResult interface. To create an instance, use its .invoke() extension function:

        RecogniseResult {
            category = 0
        }
    

Limitations

Current known limitations:

Mandatory java and kotlin protoc generation in addition to our codegen
Kotlin/JVM project only

If you encounter other unexpected limitations or bugs, please report them

Last modified: 14 July 2025