kotlin-ktor-patterns

Ktor 伺服器開發模式

運用 Kotlin 協程（Coroutines）建構強健且易於維護的 HTTP 伺服器，提供完整的 Ktor 開發模式與實務指南。

何時啟用

• 建置 Ktor HTTP 伺服器
• 設定 Ktor 外掛（Auth、CORS、ContentNegotiation、StatusPages）
• 透過 Ktor 實作 REST API
• 使用 Koin 設定依賴注入（Dependency Injection）
• 運用 testApplication 撰寫 Ktor 整合測試
• 在 Ktor 中使用 WebSockets

應用程式架構

標準 Ktor 專案目錄結構

src/main/kotlin/
├── com/example/
│   ├── Application.kt           # 入口點與模組設定
│   ├── plugins/
│   │   ├── Routing.kt           # 路由定義
│   │   ├── Serialization.kt     # 內容協商設定
│   │   ├── Authentication.kt    # 身份驗證設定
│   │   ├── StatusPages.kt       # 錯誤處理
│   │   └── CORS.kt              # CORS 設定
│   ├── routes/
│   │   ├── UserRoutes.kt        # /users 端點
│   │   ├── AuthRoutes.kt        # /auth 端點
│   │   └── HealthRoutes.kt      # /health 端點
│   ├── models/
│   │   ├── User.kt              # 領域模型
│   │   └── ApiResponse.kt       # 回應封裝
│   ├── services/
│   │   ├── UserService.kt       # 商業邏輯
│   │   └── AuthService.kt       # 驗證邏輯
│   ├── repositories/
│   │   ├── UserRepository.kt    # 資料存取介面
│   │   └── ExposedUserRepository.kt
│   └── di/
│       └── AppModule.kt         # Koin 模組
src/test/kotlin/
├── com/example/
│   ├── routes/
│   │   └── UserRoutesTest.kt
│   └── services/
│       └── UserServiceTest.kt

應用程式入口點

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

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

Routing DSL

基本路由

// 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)
        }
    }
}

結合身份驗證的路由組織

fun Route.userRoutes() {
    route("/users") {
        // 公開路由
        get { /* 取得使用者清單 */ }
        get("/{id}") { /* 取得指定使用者 */ }

        // 受保護路由
        authenticate("jwt") {
            post { /* 新增使用者 - 需驗證 */ }
            put("/{id}") { /* 更新使用者 - 需驗證 */ }
            delete("/{id}") { /* 刪除使用者 - 需驗證 */ }
        }
    }
}

內容協商與序列化

kotlinx.serialization 設定

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

可序列化模型

@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,
)

自訂序列化器

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())
}

身份驗證

JWT 身份驗證

// 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"))
            }
        }
    }
}

// 從 JWT 提取使用者 ID
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("No userId in token")

驗證路由

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))
            }
        }
    }
}

Status Pages (全局例外控制與錯誤處理)

// 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 設定

// 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 依賴注入

模組定義

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

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

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

// 應用程式設定
fun Application.configureDI() {
    install(Koin) {
        modules(appModule)
    }
}

在路由中使用 Koin

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

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

測試時使用 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
        }
    }
}

請求驗證

// 在路由中驗證請求資料
fun Route.userRoutes() {
    val userService by inject<UserService>()

    post("/users") {