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Marco Gomiero
FOSDEM
From Mobile to
Backend with
Kotlin and Ktor
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FOSDEM - @marcoGomier
Marco Gomiero
👨💻 Android Engineer @ TIER 🛴 🇩🇪 🇮🇹
Google Developer Expert for Kotlin
> Twitter: @marcoGomier
> Github: prof18
> Website: marcogomiero.com
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FOSDEM - @marcoGomier
🤔 Why?
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FOSDEM - @marcoGomier
• Side project
• Understand how things works “on the other side”
• Help you teammates
🤔 Why?
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FOSDEM - @marcoGomier
* based on a true story
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FOSDEM - @marcoGomier
Ktor
https://ktor.io/
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FOSDEM - @marcoGomier
Ktor
• Kotlin
• Lightweight and flexible
• Asynchronous with Coroutines
• Unopinionated
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FOSDEM - @marcoGomier
Unopinionated
• Whatever architecture
• Whatever pattern
Knowledge Transfer
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FOSDEM
@marcoGomier
Architecture
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FOSDEM - @marcoGomier
Android
Activity/Fragment
ViewModel
Repository
Local Data Source Remote Data Source
Application
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FOSDEM - @marcoGomier
Resource*
Repository
Local Data Source Remote Data Source
Application
* or Controller
Ktor
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FOSDEM - @marcoGomier
Resource
Repository
Local Data Source Remote Data Source
Application
Activity/Fragment
ViewModel
Repository
Local Data Source Remote Data Source
Application
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FOSDEM - @marcoGomier
Domain
Data
Resource
Repository
Local Data Source Remote Data Source
Application
Activity/Fragment
ViewModel
Repository
Local Data Source Remote Data Source
Application
Presentation
Application
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FOSDEM - @marcoGomier
Application
class MyApp : Application() {
override fun onCreate() {
super.onCreate()
if (BuildConfig.DEBUG) {
Timber.plant(Timber.DebugTree())
}
initAnalytics()
initCrashReporting()
initRandomLib()
}
}
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FOSDEM - @marcoGomier
fun Application.module() {
install(Koin) {
slf4jLogger()
modules(koinModules)
}
setupConfig()
setupDatabase()
install(ContentNegotiation) {
json()
}
install(CallLogging) {
level = Level.INFO
}
install(Locations)
routing {
setupEndpoint()
}
}
Application
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FOSDEM - @marcoGomier
Plugin
https://ktor.io/docs/plugins.html
• Add a specific feature to your backend
• Highly customisable
• No plugin activated by default
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FOSDEM - @marcoGomier
Plugin
https://ktor.io/docs/
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FOSDEM - @marcoGomier
Domain
Data
Presentation
Application
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FOSDEM - @marcoGomier
Presentation
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
...
}
}
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FOSDEM - @marcoGomier
fun Route.jokeEndpoint() {
val jokeRepository by inject()
get {
call.respond(jokeRepository.getRandomJoke())
}
post { apiCallParams
->
val name = apiCallParams.name
jokeRepository.watch(name)
call.respond("Ok")
}
}
Presentation
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FOSDEM - @marcoGomier
Domain
Data
Presentation
Application
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FOSDEM - @marcoGomier
Domain
class JokeRepositoryImpl(
private val jokeLocalDataSource: JokeLocalDataSource
) : JokeRepository {
override suspend fun getRandomJoke(): JokeDTO {
// ...
}
}
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FOSDEM - @marcoGomier
Domain
Data
Presentation
Application
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FOSDEM - @marcoGomier
Room
class LocalDatasource(
private val db: RoomDatabase
) {
suspend fun getAllowedApps(): List {
return db.allowedAppDAO().getAllAllowedApps()
}
}
@Entity(tableName = "allowed_app")
data class AllowedApp(
@PrimaryKey val packageName: String,
@ColumnInfo val appName: String
)
@Dao
interface AllowedAppDAO {
@Query("SELECT * FROM allowed_app")
suspend fun getAllAllowedApps(): List
}
Data
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FOSDEM - @marcoGomier
Exposed
https://github.com/JetBrains/Exposed
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FOSDEM - @marcoGomier
Exposed
class JokeLocalDataSourceImpl : JokeLocalDataSource {
override suspend fun getAllJokes(): List {
val joke = newSuspendedTransaction {
val query = JokeTable.selectAll()
Joke.wrapRows(query).toList()
}
}
}
object JokeTable: IdTable(name = "joke") {
val createdAt = datetime("created_at")
val updatedAt = datetime("updated_at")
val value = text("value")
override val id: Column>
= varchar("joke_id", 255).entityId()
override val primaryKey: PrimaryKey = PrimaryKey(id)
}
class Joke(id: EntityID): Entity(id) {
companion object: EntityClass(JokeTable)
var createdAt by JokeTable.createdAt
var updatedAt by JokeTable.updatedAt
var value by JokeTable.value
}
Data
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FOSDEM - @marcoGomier
EmailThreadTable.join(EmailFolderTable, JoinType.INNER, additionalConstraint = {
(EmailThreadTable.id eq EmailFolderTable.threadId).and(
EmailThreadTable.account eq EmailFolderTable.accountId
)
})
.select { EmailThreadTable.account eq account.id.value and (EmailFolderTable.folderId eq folderId) }
.orderBy(EmailThreadTable.lastEmailDate, SortOrder.DESC)
.limit(n = pageSize)
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FOSDEM
@marcoGomier
Dependency Injection
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FOSDEM - @marcoGomier https://insert-koin.io/docs/quickstart/ktor
Koin
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FOSDEM - @marcoGomier
val appModule = module {
single { HelloRepositoryImpl() }
factory { MySimplePresenter(get()) }
}
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FOSDEM - @marcoGomier
class MyApplication : Application() {
override fun onCreate() {
super.onCreate()
startKoin {
androidLogger()
androidContext(this@MyApplication)
modules(appModule)
}
}
}
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FOSDEM - @marcoGomier
class MainActivity : AppCompatActivity() {
val firstPresenter: MySimplePresenter by inject()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
...
}
}
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FOSDEM - @marcoGomier
val appModule = module {
single { JokeLocalDataSourceImpl() }
single { JokeRepositoryImpl(get()) }
}
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FOSDEM - @marcoGomier
fun Application.module() {
install(Koin) {
slf4jLogger()
modules(koinModules)
}
...
}
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FOSDEM - @marcoGomier
fun Route.jokeEndpoint() {
val jokeRepository by inject()
get {
call.respond(jokeRepository.getRandomJoke())
}
post { apiCallParams
->
val name = apiCallParams.name
jokeRepository.watch(name)
call.respond("Ok")
}
}
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FOSDEM
@marcoGomier
Logging
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FOSDEM - @marcoGomier
Timber
class MyApplication : Application() {
override fun onCreate() {
super.onCreate()
if (BuildConfig.DEBUG) {
Timber.plant(Timber.DebugTree())
} else {
//
Log to somewhere else
}
}
}
https://github.com/JakeWharton/timber
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FOSDEM - @marcoGomier https://github.com/JakeWharton/timber
Timber.d(“Message")
Timber.v("Message")
Timber.i("Message")
Timber.w("Message")
Timber.wtf("Message")
Timber.e(exception)
Timber
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FOSDEM - @marcoGomier
SLF4J
http://www.slf4j.org/index.html
routing {
get("/api/v1") {
call.application.environment.log.info("Hello from /api/v1!")
}
}
fun Application.module(testing: Boolean = false) {
log.info("Hello from module!")
}
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FOSDEM - @marcoGomier
val logger = LoggerFactory.getLogger(MyClass
::
class.java)
inline fun T.getLogger(): Logger {
return LoggerFactory.getLogger(T
::
class.java)
}
class MyClass {
private val logger = getLogger()
fun main() {
logger.info("Hello World")
}
}
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FOSDEM - @marcoGomier
logger.trace("Message")
logger.debug("Message")
logger.info("Message")
logger.warn("Message")
logger.error("Message")
SLF4J
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FOSDEM - @marcoGomier
logback.xml
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FOSDEM - @marcoGomier
logback.xml
%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
${LOG_DEST}/ktor-chuck-norris-sample.log
${LOG_DEST}/ktor-chuck-norris-sample.%d{yyyy-MM-dd}.log
${LOG_MAX_HISTORY}
3GB
%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
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FOSDEM
@marcoGomier
Secrets
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FOSDEM - @marcoGomier
local.properties
tmdbKey="private_key"
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FOSDEM - @marcoGomier
val String.byProperty: String?
get() {
val local = java.util.Properties()
val localProperties: File = rootProject.file("local.properties")
if (localProperties.exists()) {
localProperties.inputStream().use { local.load(it) }
return local.getProperty(this)
}
return null
}
tmdbKey="private_key"
buildConfigField("String", "TMDB_KEY", "\"${"tmdbKey".byProperty
?:
"")}\"")
build.gradle.kts
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FOSDEM - @marcoGomier
tmdbKey="private_key"
buildConfigField("String", "TMDB_KEY", "\"${"tmdbKey".byProperty
?:
"")}\"")
val myKey: String = BuildConfig.TMDB_KEY
NetworkApiInterceptor.kt
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FOSDEM - @marcoGomier
application.conf
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FOSDEM - @marcoGomier
application.conf
ktor {
deployment {
port = 8080
port = ${?PORT}
}
application {
modules = [com.prof18.ktor.chucknorris.sample.ApplicationKt.module]
}
server {
isProd = false
}
database {
driverClass = "com.mysql.cj.jdbc.Driver"
url = "jdbc:mysql:
/
/
localhost:3308/chucknorris?useUnicode=true&characterEncoding=UTF-8"
user = "root"
password = "password"
maxPoolSize = 3
}
}
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FOSDEM - @marcoGomier
fun Application.setupConfig() {
val appConfig by inject()
//
Server
val serverObject = environment.config.config("ktor.server")
val isProd = serverObject.property("isProd").getString().toBoolean()
appConfig.serverConfig = ServerConfig(isProd)
}
data class ServerConfig(
val isProd: Boolean
)
class AppConfig {
lateinit var serverConfig: ServerConfig
//
Place here other configurations
}
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FOSDEM - @marcoGomier
fun Application.module() {
...
setupConfig()
val appConfig by inject()
...
}
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FOSDEM - @marcoGomier
java -jar ktor-backend.jar -config=/config-folder/application.conf
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FOSDEM
@marcoGomier
Testing
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FOSDEM - @marcoGomier
• Unit Test
->
Just regular Kotlin Unit tests
• androidTest
->
TestEngine
Testing
https://ktor.io/docs/testing.html
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FOSDEM - @marcoGomier
@Test
fun testRequests() = withTestApplication(module(testing = true)) {
with(handleRequest(HttpMethod.Get, "/")) {
assertEquals(HttpStatusCode.OK, response.status())
assertEquals("Hello from Ktor Testable sample application", response.content)
}
https://ktor.io/docs/testing.html
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FOSDEM
@marcoGomier
Deploy
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FOSDEM - @marcoGomier
Deploy
• aar
• apk
• aab
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FOSDEM - @marcoGomier https://github.com/johnrengelman/shadow
./gradlew assembleRelease
./gradlew bundleRelease
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FOSDEM - @marcoGomier
Deploy
• Fat JAR
• Executable JVM application
• WAR
• GraalVM
https://ktor.io/docs/deploy.html
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FOSDEM - @marcoGomier
• Fat JAR
• Executable JVM application
• WAR
• GraalVM
https://ktor.io/docs/deploy.html
Deploy
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FOSDEM - @marcoGomier
build.gradle.kts
https://github.com/johnrengelman/shadow
plugins {
...
id("com.github.johnrengelman.shadow") version "7.0.0"
}
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FOSDEM - @marcoGomier https://github.com/johnrengelman/shadow
tasks {
shadowJar {
manifest {
attributes(Pair("Main-Class", "io.ktor.server.netty.EngineMain"))
}
}
}
build.gradle.kts
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FOSDEM - @marcoGomier https://github.com/johnrengelman/shadow
tasks {
shadowJar {
manifest {
attributes(Pair("Main-Class", "io.ktor.server.netty.EngineMain"))
}
}
}
application {
mainClass.set("io.ktor.server.netty.EngineMain")
}
build.gradle.kts
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FOSDEM - @marcoGomier https://github.com/johnrengelman/shadow
./gradlew shadowJar
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FOSDEM - @marcoGomier
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FOSDEM
@marcoGomier
Conclusions
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FOSDEM - @marcoGomier
• Ktor is flexible and unopinionated
->
Knowledge Transfer
• Mobile knowledge can be adapted
• Effective scaling and deploying can be hard
• “Going to the other side” enrich your dev vision
Conclusions
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FOSDEM - @marcoGomier https://github.com/prof18/ktor-chuck-norris-sample
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Bibliography / Useful Links
• https:
//
ktor.io/
• https:
//
ktor.io/learn/
• https:
//
ktor.io/docs/welcome.html
• https:
//
github.com/JetBrains/Exposed/wiki
• https:
//
www.marcogomiero.com/posts/2021/ktor-project-structure/
• https:
//
www.marcogomiero.com/posts/2021/ktor-logging-on-disk/
• https:
//
www.marcogomiero.com/posts/2021/ktor-in-memory-db-testing/
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Marco Gomiero
FOSDEM
Thank you!
> Twitter: @marcoGomier
> Github: prof18
> Website: marcogomiero.com