How to setup protobuf in Android/IOS Kotlin Multiplatform project

Issue

First time using protobu and could not find an example of how to connect it to Kotlin Multiplatform. I created Multiplatform project Android/IOS with "shared" module where I need to use protobuf. Project structure:

Code in build.gradle shared.module lvl build.gradle shared.module lvl

plugins {
    kotlin("multiplatform")
    id("com.android.library")
    id("com.google.protobuf")
}

kotlin {
    android()
    listOf(
        iosX64(),
        iosArm64(),
        iosSimulatorArm64()
    ).forEach {
        it.binaries.framework {
            baseName = "shared"
        }
    }

    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4")
            }

        }
        val commonTest by getting {
            dependencies {
                implementation(kotlin("test"))
            }
        }
        val androidMain by getting
        val androidTest by getting
        val iosX64Main by getting
        val iosArm64Main by getting
        val iosSimulatorArm64Main by getting
        val iosMain by creating {
            dependsOn(commonMain)
            iosX64Main.dependsOn(this)
            iosArm64Main.dependsOn(this)
            iosSimulatorArm64Main.dependsOn(this)
        }
        val iosX64Test by getting
        val iosArm64Test by getting
        val iosSimulatorArm64Test by getting
        val iosTest by creating {
            dependsOn(commonTest)
            iosX64Test.dependsOn(this)
            iosArm64Test.dependsOn(this)
            iosSimulatorArm64Test.dependsOn(this)
        }
    }
}


android {
    namespace = "com.example.someproject"
    compileSdk = 33
    defaultConfig {
        minSdk = 21
        targetSdk = 33
    }

    protobuf {
        protoc {
            artifact = ("com.google.protobuf:protoc:3.21.9")
        }
        generateProtoTasks {
            all().forEach { task ->
                task.builtins {
                    java {
 //                   option 'lite' //Error - Unresolved reference: option
                    }
                    kotlin {
//                    option 'lite' //Error - Unresolved reference: option
                    }
                }
            }
        }
    }
    dependencies {
        implementation("com.google.protobuf:protobuf-javalite:3.21.9")
    }
}

My build.gradle project lvl: build gradle project lvl

buildscript {
    dependencies {
        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.9.1'
    }
}
plugins {
    id 'com.android.application' version '7.3.1' apply false
    id 'com.android.library' version '7.3.1' apply false
    id 'org.jetbrains.kotlin.android' version '1.7.20' apply false
    id 'com.google.protobuf' version '0.9.1' apply false
}

I tried to add path to my .proto files with sourceSets, but I got errors:

android {
    namespace = "com.example.someproject"
    compileSdk = 33
    defaultConfig {
        minSdk = 21
        targetSdk = 33
    }
    sourceSets {
        main { //Error - Unresolved reference: main
            proto { //Error - Unresolved reference: proto
                srcDir 'src/main/protobuf' //Error - Unresolved reference: srcDir
            }
            java {
                srcDirs 'build/generated/source/proto/main/java' //Error - Unresolved reference: srcDirs
                srcDirs 'build/generated/source/proto/main/kotlin' //Error - Unresolved reference: srcDirs
            }
        }
    }

    protobuf {
        protoc {
            artifact = ("com.google.protobuf:protoc:3.21.9")
        }
        generateProtoTasks {
            all().forEach { task ->
                task.builtins {
                    java {
 //                   option 'lite' //Error - Unresolved reference: option
                    }
                    kotlin {
//                    option 'lite' //Error - Unresolved reference: option
                    }
                }
            }
        }
    }
    dependencies {
        implementation("com.google.protobuf:protobuf-javalite:3.21.9")
    }
}

When I try to build project without sourceSets, I didn't get generated java/kotlin files in build/generated/source - path

And my question is: "How setup protobuf in Android/IOS project Kotlin multiplatform?"

Solution

If you want to use ProtoBuf library in shared module in common code, then you have to use library that supports Kotlin Multiplatform. You can take a look at official kotlinx.serialization library, it supports ProtoBuf. And you can use it in commonMain module.

Also take a look at community library

Or learn more about platform-specific implementations and use expect/actual mechanism

Another option will be use your ProtoBuf library and plugin in androidApp only and for iOS part use another iOS specific ProtoBuf library.

Answered By - Evgeny K