kotlin-ktor-패턴

Ktor 서버 패턴

Kotlin 코루틴을 사용하여 견고하고 유지보수 가능한 HTTP 서버를 구축하기 위한 포괄적인 Ktor 패턴입니다.

활성화 시점

• Ktor HTTP 서버 구축
• Ktor 플러그인 구성 (Auth, CORS, ContentNegotiation, StatusPages)
• Ktor로 REST API 구현
• Koin으로 의존성 주입 설정
• testApplication으로 Ktor 통합 테스트 작성
• Ktor에서 WebSocket 작업

애플리케이션 구조

표준 Ktor 프로젝트 레이아웃

src/main/kotlin/
├── com/example/
│   ├── Application.kt           # 진입점, 모듈 구성
│   ├── plugins/
│   │   ├── Routing.kt           # 라우트 정의
│   │   ├── Serialization.kt     # 콘텐츠 협상 설정
│   │   ├── Authentication.kt    # 인증 구성
│   │   ├── StatusPages.kt       # 오류 처리
│   │   └── CORS.kt              # CORS 구성
│   ├── routes/
│   │   ├── UserRoutes.kt        # /users 엔드포인트
│   │   ├── AuthRoutes.kt        # /auth 엔드포인트
│   │   └── HealthRoutes.kt      # /health 엔드포인트
│   ├── models/
│   │   ├── User.kt              # 도메인 모델
│   │   └── ApiResponse.kt       # 응답 래퍼
│   ├── services/
│   │   ├── UserService.kt       # 비즈니스 로직
│   │   └── AuthService.kt       # 인증 로직
│   ├── repositories/
│   │   ├── UserRepository.kt    # 데이터 액세스 인터페이스
│   │   └── ExposedUserRepository.kt
│   └── di/
│       └── AppModule.kt         # Koin 모듈
src/test/kotlin/
├── com/example/
│   ├── routes/
│   │   └── UserRoutesTest.kt
│   └── services/
│       └── UserServiceTest.kt

애플리케이션 진입점

// Application.kt
fun main() {
    embeddedServer(Netty, port = 8080, module = Application::module).start(wait = true)
}

fun Application.module() {
    configureSerialization()
    configureAuthentication()
    configureStatusPages()
    configureCORS()
    configureDI()
    configureRouting()
}

라우팅 DSL

기본 라우트

// plugins/Routing.kt
fun Application.configureRouting() {
    routing {
        userRoutes()
        authRoutes()
        healthRoutes()
    }
}

// routes/UserRoutes.kt
fun Route.userRoutes() {
    val userService by inject<UserService>()

    route("/users") {
        get {
            val users = userService.getAll()
            call.respond(users)
        }

        get("/{id}") {
            val id = call.parameters["id"]
                ?: return@get call.respond(HttpStatusCode.BadRequest, "Missing id")
            val user = userService.getById(id)
                ?: return@get call.respond(HttpStatusCode.NotFound)
            call.respond(user)
        }

        post {
            val request = call.receive<CreateUserRequest>()
            val user = userService.create(request)
            call.respond(HttpStatusCode.Created, user)
        }

        put("/{id}") {
            val id = call.parameters["id"]
                ?: return@put call.respond(HttpStatusCode.BadRequest, "Missing id")
            val request = call.receive<UpdateUserRequest>()
            val user = userService.update(id, request)
                ?: return@put call.respond(HttpStatusCode.NotFound)
            call.respond(user)
        }

        delete("/{id}") {
            val id = call.parameters["id"]
                ?: return@delete call.respond(HttpStatusCode.BadRequest, "Missing id")
            val deleted = userService.delete(id)
            if (deleted) call.respond(HttpStatusCode.NoContent)
            else call.respond(HttpStatusCode.NotFound)
        }
    }
}

인증된 라우트를 사용한 라우트 구성

fun Route.userRoutes() {
    route("/users") {
        // 공개 라우트
        get { /* 사용자 목록 */ }
        get("/{id}") { /* 사용자 조회 */ }

        // 보호된 라우트
        authenticate("jwt") {
            post { /* 사용자 생성 - 인증 필요 */ }
            put("/{id}") { /* 사용자 업데이트 - 인증 필요 */ }
            delete("/{id}") { /* 사용자 삭제 - 인증 필요 */ }
        }
    }
}

콘텐츠 협상 및 직렬화

kotlinx.serialization 설정

// plugins/Serialization.kt
fun Application.configureSerialization() {
    install(ContentNegotiation) {
        json(Json {
            prettyPrint = true
            isLenient = false
            ignoreUnknownKeys = true
            encodeDefaults = true
            explicitNulls = false
        })
    }
}

직렬화 가능 모델

@Serializable
data class UserResponse(
    val id: String,
    val name: String,
    val email: String,
    val role: Role,
    @Serializable(with = InstantSerializer::class)
    val createdAt: Instant,
)

@Serializable
data class CreateUserRequest(
    val name: String,
    val email: String,
    val role: Role = Role.USER,
)

@Serializable
data class ApiResponse<T>(
    val success: Boolean,
    val data: T? = null,
    val error: String? = null,
) {
    companion object {
        fun <T> ok(data: T): ApiResponse<T> = ApiResponse(success = true, data = data)
        fun <T> error(message: String): ApiResponse<T> = ApiResponse(success = false, error = message)
    }
}

@Serializable
data class PaginatedResponse<T>(
    val data: List<T>,
    val total: Long,
    val page: Int,
    val limit: Int,
)

사용자 정의 직렬 변환기

object InstantSerializer : KSerializer<Instant> {
    override val descriptor = PrimitiveSerialDescriptor("Instant", PrimitiveKind.STRING)
    override fun serialize(encoder: Encoder, value: Instant) =
        encoder.encodeString(value.toString())
    override fun deserialize(decoder: Decoder): Instant =
        Instant.parse(decoder.decodeString())
}

인증

JWT 인증

// plugins/Authentication.kt
fun Application.configureAuthentication() {
    val jwtSecret = environment.config.property("jwt.secret").getString()
    val jwtIssuer = environment.config.property("jwt.issuer").getString()
    val jwtAudience = environment.config.property("jwt.audience").getString()
    val jwtRealm = environment.config.property("jwt.realm").getString()

    install(Authentication) {
        jwt("jwt") {
            realm = jwtRealm
            verifier(
                JWT.require(Algorithm.HMAC256(jwtSecret))
                    .withAudience(jwtAudience)
                    .withIssuer(jwtIssuer)
                    .build()
            )
            validate { credential ->
                if (credential.payload.audience.contains(jwtAudience)) {
                    JWTPrincipal(credential.payload)
                } else {
                    null
                }
            }
            challenge { _, _ ->
                call.respond(HttpStatusCode.Unauthorized, ApiResponse.error<Unit>("Invalid or expired token"))
            }
        }
    }
}

// JWT에서 사용자 추출
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("No userId in token")

인증 라우트

fun Route.authRoutes() {
    val authService by inject<AuthService>()

    route("/auth") {
        post("/login") {
            val request = call.receive<LoginRequest>()
            val token = authService.login(request.email, request.password)
                ?: return@post call.respond(
                    HttpStatusCode.Unauthorized,
                    ApiResponse.error<Unit>("Invalid credentials"),
                )
            call.respond(ApiResponse.ok(TokenResponse(token)))
        }

        post("/register") {
            val request = call.receive<RegisterRequest>()
            val user = authService.register(request)
            call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
        }

        authenticate("jwt") {
            get("/me") {
                val userId = call.userId()
                val user = authService.getProfile(userId)
                call.respond(ApiResponse.ok(user))
            }
        }
    }
}

상태 페이지 (오류 처리)

// plugins/StatusPages.kt
fun Application.configureStatusPages() {
    install(StatusPages) {
        exception<ContentTransformationException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>("Invalid request body: ${cause.message}"),
            )
        }

        exception<IllegalArgumentException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>(cause.message ?: "Bad request"),
            )
        }

        exception<AuthenticationException> { call, _ ->
            call.respond(
                HttpStatusCode.Unauthorized,
                ApiResponse.error<Unit>("Authentication required"),
            )
        }

        exception<AuthorizationException> { call, _ ->
            call.respond(
                HttpStatusCode.Forbidden,
                ApiResponse.error<Unit>("Access denied"),
            )
        }

        exception<NotFoundException> { call, cause ->
            call.respond(
                HttpStatusCode.NotFound,
                ApiResponse.error<Unit>(cause.message ?: "Resource not found"),
            )
        }

        exception<Throwable> { call, cause ->
            call.application.log.error("Unhandled exception", cause)
            call.respond(
                HttpStatusCode.InternalServerError,
                ApiResponse.error<Unit>("Internal server error"),
            )
        }

        status(HttpStatusCode.NotFound) { call, status ->
            call.respond(status, ApiResponse.error<Unit>("Route not found"))
        }
    }
}

CORS 구성

// plugins/CORS.kt
fun Application.configureCORS() {
    install(CORS) {
        allowHost("localhost:3000")
        allowHost("example.com", schemes = listOf("https"))
        allowHeader(HttpHeaders.ContentType)
        allowHeader(HttpHeaders.Authorization)
        allowMethod(HttpMethod.Put)
        allowMethod(HttpMethod.Delete)
        allowMethod(HttpMethod.Patch)
        allowCredentials = true
        maxAgeInSeconds = 3600
    }
}

Koin 의존성 주입

모듈 정의

// di/AppModule.kt
val appModule = module {
    // 데이터베이스
    single<Database> { DatabaseFactory.create(get()) }

    // 리포지토리
    single<UserRepository> { ExposedUserRepository(get()) }
    single<OrderRepository> { ExposedOrderRepository(get()) }

    // 서비스
    single { UserService(get()) }
    single { OrderService(get(), get()) }
    single { AuthService(get(), get()) }
}

// 애플리케이션 설정
fun Application.configureDI() {
    install(Koin) {
        modules(appModule)
    }
}

라우트에서 Koin 사용

fun Route.userRoutes() {
    val userService by inject<UserService>()

    route("/users") {
        get {
            val users = userService.getAll()
            call.respond(ApiResponse.ok(users))
        }
    }
}

테스트를 위한 Koin

class UserServiceTest : FunSpec(), KoinTest {
    override fun extensions() = listOf(KoinExtension(testModule))

    private val testModule = module {
        single<UserRepository> { mockk() }
        single { UserService(get()) }
    }

    private val repository by inject<UserRepository>()
    private val service by inject<UserService>()

    init {
        test("getUser returns user") {
            coEvery { repository.findById("1") } returns testUser
            service.getById("1") shouldBe testUser
        }
    }
}

요청 유효성 검사

// 라우트에서 요청 데이터 검증
fun Route.userRoutes() {
    val userService by inject<UserService>()

    post("/users") {
        val request = call.receive<CreateUserRequest>()

        // Validate
        require(request.name.isNotBlank()) { "Name is required" }
        require(request.name.length <= 100) { "Name must be 100 characters or less" }
        require(request.email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }

        val user = userService.create(request)
        call.respond(HttpStatusCode.Created, ApiResponse.ok(user))
    }
}

// 또는 유효성 검사 확장 함수 사용
fun CreateUserRequest.validate() {
    require(name.isNotBlank()) { "Name is required" }
    require(name.length <= 100) { "Name must be 100 characters or less" }
    require(email.matches(Regex(".+@.+\\..+"))) { "Invalid email format" }
}

웹소켓

fun Application.configureWebSockets() {
    install(WebSockets) {
        pingPeriod = 15.seconds
        timeout = 15.seconds
        maxFrameSize = 64 * 1024 // 64 KiB — Increase only if your protocol requires larger frames
        masking = false // Server-to-client frames are unmasked per RFC 6455; client-to-server are always masked by Ktor
    }
}

fun Route.chatRoutes() {
    val connections = Collections.synchronizedSet<Connection>(LinkedHashSet())

    webSocket("/chat") {
        val thisConnection = Connection(this)
        connections += thisConnection

        try {
            send("Connected! Users online: ${connections.size}")

            for (frame in incoming) {
                frame as? Frame.Text ?: continue
                val text = frame.readText()
                val message = ChatMessage(thisConnection.name, text)

                // Snapshot under lock to avoid ConcurrentModificationException
                val snapshot = synchronized(connections) { connections.toList() }
                snapshot.forEach { conn ->
                    conn.session.send(Json.encodeToString(message))
                }
            }
        } catch (e: Exception) {
            logger.error("WebSocket error", e)
        } finally {
            connections -= thisConnection
        }
    }
}

data class Connection(val session: DefaultWebSocketSession) {
    val name: String = "User-${counter.getAndIncrement()}"

    companion object {
        private val counter = AtomicInteger(1)
    }
}

@Serializable
data class ChatMessage(
    val user: String,
    val text: String,
    val timestamp: Long = Clock.System.now().toEpochMilliseconds(),
)

테스트

testApplication을 사용한 통합 테스트

// build.gradle.kts
/*
dependencies {
    testImplementation("io.ktor:ktor-server-test-host-jvm")
    testImplementation("io.ktor:ktor-client-content-negotiation-jvm")
    testImplementation("io.kotest:kotest-runner-junit5:5.9.1")
    testImplementation("io.mockk:mockk:1.13.12")
}
*/

class UserRoutesTest : FunSpec({
    val userRepository = mockk<UserRepository>()

    val testModule = module {
        single<UserRepository> { userRepository }
        single { UserService(get()) }
    }

    testApplication {
        application {
            configureSerialization()
            configureStatusPages()
            configureDI(listOf(testModule))
            configureRouting()
        }

        val client = createClient {
            install(ContentNegotiation) {
                json(Json {
                    ignoreUnknownKeys = true
                })
            }
        }

        test("GET /users returns list of users") {
            coEvery { userRepository.findAll() } returns listOf(testUser)

            val response = client.get("/users")
            response.status shouldBe HttpStatusCode.OK
            response.body<UserRoutesTest>() shouldBe listOf(testUser)
        }

        test("GET /users/{id} returns 404 for non-existent user") {
            coEvery { userRepository.findById("999") } returns null

            val response = client.get("/users/999")
            response.status shouldBe HttpStatusCode.NotFound
        }
    }
})

서비스 단위 테스트

class UserServiceTest : FunSpec({
    val userRepository = mockk<UserRepository>()
    val userService = UserService(userRepository)

    test("createUser should save user and return result") {
        val request = CreateUserRequest("John", "[email protected]")
        val savedUser = User(id = "1", name = "John", email = "[email protected]")

        coEvery { userRepository.save(any()) } returns savedUser

        val result = userService.create(request)

        result shouldBe savedUser
        coVerify { userRepository.save(any()) }
    }
})