NamesApi.kt

interface NamesApi {

    @GET("names")
    fun getNamesAfter(@Query("after") afterName : String, @Query("limit") limit: Int) : Call<Array<String>>
}

NamesDataSource.kt

class NamesDataSource constructor(private val namesApi: NamesApi) : ItemKeyedDataSource<String, String>() {

    override fun loadInitial(params: LoadInitialParams<String>, callback: LoadInitialCallback<String>) {
        val response = namesApi.getNamesAfter("", params.requestedLoadSize).execute()

        val responseData = response.body()?.toList() ?: listOf()
        callback.onResult(responseData)
    }

    override fun loadAfter(params: LoadParams<String>, callback: LoadCallback<String>) {
        val response = namesApi.getNamesAfter(params.key, params.requestedLoadSize).execute()

        val responseData = response.body()?.toList() ?: listOf()
        callback.onResult(responseData)
    }

    override fun loadBefore(params: LoadParams<String>, callback: LoadCallback<String>) {

    }

    override fun getKey(item: String) = item
}

NamesDataSourceFactory.kt

class NamesDataSourceFactory @Inject constructor(private val namesApi: NamesApi) : DataSource.Factory<String, String>() {

    override fun create(): DataSource<String, String> {
        return NamesDataSource(namesApi)
    }

}