kotlin-ktor-patterns

Ktor 伺服器模式

全面的 Ktor 模式，用 Kotlin 協程建構穩健且易於維護的 HTTP 伺服器。

何時啟用

• 建構 Ktor HTTP 伺服器
• 配置 Ktor 插件（Auth、CORS、ContentNegotiation、StatusPages）
• 使用 Ktor 實作 REST API
• 使用 Koin 設定依賴注入
• 使用 testApplication 編寫 Ktor 整合測試
• 在 Ktor 中使用 WebSocket

應用程式結構

標準 Ktor 專案佈局

src/main/kotlin/
├── com/example/
│   ├── Application.kt           # 進入點、模組配置
│   ├── plugins/
│   │   ├── Routing.kt           # 路由定義
│   │   ├── Serialization.kt     # 內容協商設定
│   │   ├── Authentication.kt    # 認證配置
│   │   ├── StatusPages.kt       # 錯誤處理
│   │   └── CORS.kt              # CORS 配置
│   ├── 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       # 認證邏輯
│   ├── 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

應用程式進入點

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

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

路由 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, "缺少 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, "缺少 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, "缺少 id")
            val deleted = userService.delete(id)
            if (deleted) call.respond(HttpStatusCode.NoContent)
            else call.respond(HttpStatusCode.NotFound)
        }
    }
}

含認證路由的路由組織

fun Route.userRoutes() {
    route("/users") {
        // 公開路由
        get { /* 列出使用者 */ }
        get("/{id}") { /* 取得使用者 */ }

        // 受保護路由
        authenticate("jwt") {
            post { /* 建立使用者 - 需要認證 */ }
            put("/{id}") { /* 更新使用者 - 需要認證 */ }
            delete("/{id}") { /* 刪除使用者 - 需要認證 */ }
        }
    }
}

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())
}

認證

JWT 認證

// 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>("無效或過期的權杖"))
            }
        }
    }
}

// 從 JWT 中提取使用者
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("權杖中沒有 userId")

認證路由

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>("認證憑證無效"),
                )
            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))
            }
        }
    }
}

狀態頁面（錯誤處理）

// plugins/StatusPages.kt
fun Application.configureStatusPages() {
    install(StatusPages) {
        exception<ContentTransformationException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>("無效的要求主體：${cause.message}"),
            )
        }

        exception<IllegalArgumentException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>(cause.message ?: "錯誤的要求"),
            )
        }

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

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

        exception<NotFoundException> { call, cause ->
            call.respond(
                HttpStatusCode.NotFound,
                ApiResponse.error<Unit>(cause.message ?: "找不到資源"),
            )
        }

        exception<Throwable> { call, cause ->
            call.application.log.error("未處理的例外", cause)
            call.respond(
                HttpStatusCode.InternalServerError,
                ApiResponse.error<Unit>("內部伺服器錯誤"),
            )
        }

        status(HttpStatusCode.NotFound) { call, status ->
            call.respond(status, ApiResponse.error<Unit>("找不到路由"))
        }
    }
}

CORS 配置

// 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()) }

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

    // 服務
    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))
        }
    }
}

Koin 用於測試

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 回傳使用者") {
            coEvery { repository.findById("1") } returns testUser
            service.getById("1") shouldBe testUser
        }
    }
}

要求驗證

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

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

        // 驗證
        require(request.name.isNotBlank()) { "名稱為必填" }
        require(request.name.length <= 100) { "名稱必須在 100 個字元以內" }
        require(request.email.matches(Regex(".+@.+\\..+"))) { "電子郵件格式無效" }

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

// 或使用驗證擴充功能
fun CreateUserRequest.validate() {
    require(name.isNotBlank()) { "名稱為必填" }
    require(name.length <= 100) { "名稱必須在 100 個字元以內" }
    require(email.matches(Regex(".+@.+\\..+"))) { "電子郵件格式無效" }
}

WebSocket

fun Application.configureWebSockets() {
    install(WebSockets) {
        pingPeriod = 15.seconds
        timeout = 15.seconds
        maxFrameSize = 64 * 1024 // 64 KiB — 僅在協定需要更大框架時才增加
        masking = false // 根據 RFC 6455，伺服器到用戶端的框架是未遮罩的；用戶端到伺服器始終由 Ktor 遮罩
    }
}

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

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

        try {
            send("已連線！線上使用者數：${connections.size}")

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

                // 在鎖定下快照以避免 ConcurrentModificationException
                val snapshot = synchronized(connections) { connections.toList() }
                snapshot.forEach { conn ->
                    conn.session.send(Json.encodeToString(message))
                }
            }
        } catch (e: Exception) {
            logger.error("WebSocket 錯誤", e)
        } finally {
            connections -= thisConnection
        }
    }
}

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

private val counter = java.util.concurrent.atomic.AtomicInteger()

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

整合測試

testApplication 設定

class UserRoutesTest {
    @Test
    fun `test GET users returns 200`() = testApplication {
        application {
            module()
        }

        client.get("/users").apply {
            assertEquals(HttpStatusCode.OK, status)
        }
    }

    @Test
    fun `test GET user by id returns 404 for unknown`() = testApplication {
        application {
            module()
        }

        client.get("/users/unknown-id").apply {
            assertEquals(HttpStatusCode.NotFound, status)
        }
    }

    @Test
    fun `test POST user creates user`() = testApplication {
        application {
            configureSerialization()
            configureRouting()
        }

        val request = CreateUserRequest(name = "Test", email = "[email protected]")

        client.post("/users") {
            contentType(ContentType.Application.Json)
            setBody(request)
        }.apply {
            assertEquals(HttpStatusCode.Created, status)
        }
    }
}

測試 Koin 模組

class AuthRoutesTest {
    @Test
    fun `test authentication flow`() = testApplication {
        environment {
            config = MapApplicationConfig(
                "jwt.secret" to "test-secret",
                "jwt.issuer" to "test-issuer",
                "jwt.audience" to "test-audience",
                "jwt.realm" to "test-realm",
            )
        }

        application {
            configureSerialization()
            configureAuthentication()
            configureDI()
            configureRouting()
        }

        // 註冊
        val registerRequest = RegisterRequest(
            name = "Test",
            email = "[email protected]",
            password = "password123",
        )

        client.post("/auth/register") {
            contentType(ContentType.Application.Json)
            setBody(registerRequest)
        }.apply {
            assertEquals(HttpStatusCode.Created, status)
        }

        // 登入並取得權杖
        val loginRequest = LoginRequest(
            email = "[email protected]",
            password = "password123",
        )

        val loginResponse = client.post("/auth/login") {
            contentType(ContentType.Application.Json)
            setBody(loginRequest)
        }.body<ApiResponse<TokenResponse>>()

        val token = loginResponse.data!!.token

        // 使用權杖存取受保護端點
        client.get("/auth/me") {
            bearerAuth(token)
        }.apply {
            assertEquals(HttpStatusCode.OK, status)
        }

        // 無權杖時應被拒絕
        client.get("/auth/me").apply {
            assertEquals(HttpStatusCode.Unauthorized, status)
        }
    }
}

配置參考

application.conf

ktor {
    deployment {
        port = 8080
        host = 0.0.0.0
    }
    application {
        modules = [com.example.ApplicationKt.module]
    }
}

jwt {
    secret = "your-256-bit-secret"
    issuer = "http://localhost:8080"
    audience = "http://localhost:3000"
    realm = "example-realm"
}

build.gradle.kts 依賴

dependencies {
    // 伺服器
    implementation("io.ktor:ktor-server-core:2.3.x")
    implementation("io.ktor:ktor-server-netty:2.3.x")
    implementation("io.ktor:ktor-server-content-negotiation:2.3.x")
    implementation("io.ktor:ktor-server-auth:2.3.x")
    implementation("io.ktor:ktor-server-auth-jwt:2.3.x")
    implementation("io.ktor:ktor-server-cors:2.3.x")
    implementation("io.ktor:ktor-server-status-pages:2.3.x")
    implementation("io.ktor:ktor-server-websockets:2.3.x")

    // 序列化
    implementation("io.ktor:ktor-serialization-kotlinx-json:2.3.x")
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.x")

    // DI
    implementation("io.insert-koin:koin-core:3.5.x")
    implementation("io.insert-koin:koin-ktor:3.5.x")

    // 測試
    testImplementation("io.ktor:ktor-server-test-host:2.3.x")
    testImplementation("io.ktor:ktor-client-content-negotiation:2.3.x")
    testImplementation("org.jetbrains.kotlin:kotlin-test:1.9.x")
    testImplementation("io.insert-koin:koin-test:3.5.x")
    testImplementation("io.mockk:mockk:1.13.x")
}

注意事項

• 始終使用 testApplication 進行整合測試，以避免真實伺服器需求
• 在 StatusPages 中處理例外狀況，以確保 API 回應保持一致
• 使用 Koin 模組進行依賴注入，以保持測試的簡潔性
• 在需要時分離公開和受保護路由，以明確辨識認證需求
• 設定 kotlinx.serialization 的 ignoreUnknownKeys = true，以在 JSON 回應中具有彈性
• WebSocket 連接應該使用同步集合進行管理，以避免並發修改問題