Shared Networking with Ktor

Why Share Networking?

HTTP calls, JSON parsing, and error handling are the same on every platform. Put them in commonMain. Each platform only provides the HTTP engine.

Versions: Ktor 3.x and kotlinx.serialization 1.8.x.

Step 1: Add Dependencies

In shared/build.gradle.kts, add Ktor, serialization, and the engine per platform.

// shared/build.gradle.kts (top plugins)
plugins {
    kotlin("multiplatform")
    kotlin("plugin.serialization") version "2.4.10"
}

kotlin {
    sourceSets {
        commonMain.dependencies {
            implementation("io.ktor:ktor-client-core:3.2.0")
            implementation("io.ktor:ktor-client-content-negotiation:3.2.0")
            implementation("io.ktor:ktor-serialization-kotlinx-json:3.2.0")
            implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.1")
            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
        }
        androidMain.dependencies {
            implementation("io.ktor:ktor-client-okhttp:3.2.0")
        }
        iosMain.dependencies {
            implementation("io.ktor:ktor-client-darwin:3.2.0")
        }
    }
}

Ktor auto-detects the engine (OkHttp on Android, Darwin on iOS) from these dependencies.

Step 2: Define the Data Model

Mark classes with @Serializable so they can be converted to and from JSON.

// commonMain
import kotlinx.serialization.Serializable

@Serializable
data class Post(
    val id: Int,
    val title: String,
    val body: String,
)

Step 3: Create the Client

// commonMain
import io.ktor.client.HttpClient
import io.ktor.client.call.body
import io.ktor.client.plugins.contentnegotiation.ContentNegotiation
import io.ktor.client.request.get
import io.ktor.client.request.post
import io.ktor.client.request.setBody
import io.ktor.http.ContentType
import io.ktor.http.contentType
import io.ktor.serialization.kotlinx.json.json
import kotlinx.serialization.json.Json

class PostApi {
    private val client = HttpClient {
        install(ContentNegotiation) {
            json(Json { ignoreUnknownKeys = true })
        }
    }

    suspend fun getPost(id: Int): Post {
        return client.get("https://jsonplaceholder.typicode.com/posts/$id").body()
    }

    suspend fun createPost(post: Post): Post {
        return client.post("https://jsonplaceholder.typicode.com/posts") {
            contentType(ContentType.Application.Json)
            setBody(post)
        }.body()
    }
}

Step 4: Use It

// commonMain (suspend fun)
suspend fun demo() {
    val api = PostApi()
    val post = api.getPost(1)
    println(post.title)
}

Diagram: commonMain holds the API and model. Each platform supplies only the HTTP engine.

Loading diagram...

Expected Output

sunt aut facere repellat provident occaecati

Error Handling

Wrap calls in runCatching to handle network errors in common code:

suspend fun safeGet(id: Int): Result<Post> = runCatching { api.getPost(id) }

Practice Exercise

1. Add a User data class (id, name, email) with @Serializable.
2. Add a getUser(id: Int) GET request to https://jsonplaceholder.typicode.com/users/1.
3. Write a safeGet wrapper using runCatching.
4. Call it from both Android and iOS and print the user's name.