kotlin-ktor-patterns

Ktor 服务端模式

全面的 Ktor 模式，用于使用 Kotlin 协程构建健壮且可维护的 HTTP 服务器。

何时激活

• 构建 Ktor HTTP 服务器
• 配置 Ktor 插件（Auth、CORS、ContentNegotiation、StatusPages）
• 使用 Ktor 实现 REST API
• 使用 Koin 设置依赖注入
• 使用 testApplication 编写 Ktor 集成测试
• 在 Ktor 中使用 WebSocket

应用结构

标准 Ktor 项目布局

src/main/kotlin/
├── com/example/
│   ├── Application.kt           # 入口点，模块配置
│   ├── plugins/
│   │   ├── Routing.kt           # 路由定义
│   │   ├── Serialization.kt     # 内容协商设置
│   │   ├── Authentication.kt    # 认证配置
│   │   ├── StatusPages.kt       # 错误处理
│   │   └── CORS.kt              # CORS 配置
│   ├── routes/
│   │   ├── UserRoutes.kt        # /users 端点
│   │   ├── AuthRoutes.kt        # /auth 端点
│   │   └── HealthRoutes.kt      # /health 端点
│   ├── models/
│   │   ├── User.kt              # 领域模型
│   │   └── ApiResponse.kt       # 响应封装
│   ├── services/
│   │   ├── UserService.kt       # 业务逻辑
│   │   └── AuthService.kt       # 认证逻辑
│   ├── repositories/
│   │   ├── UserRepository.kt    # 数据访问接口
│   │   └── ExposedUserRepository.kt
│   └── di/
│       └── AppModule.kt         # Koin 模块
src/test/kotlin/
├── com/example/
│   ├── routes/
│   │   └── UserRoutesTest.kt
│   └── services/
│       └── UserServiceTest.kt

应用入口点

// 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)
        }
    }
}

使用认证路由组织路由

fun Route.userRoutes() {
    route("/users") {
        // 公共路由
        get { /* 列出用户 */ }
        get("/{id}") { /* 获取用户 */ }

        // 受保护的路由
        authenticate("jwt") {
            post { /* 创建用户 - 需要认证 */ }
            put("/{id}") { /* 更新用户 - 需要认证 */ }
            delete("/{id}") { /* 删除用户 - 需要认证 */ }
        }
    }
}

内容协商与序列化

kotlinx.serialization 设置

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

可序列化的模型

@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,
)

自定义序列化器

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())
}

认证

JWT 认证

// 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>("令牌无效或已过期"))
            }
        }
    }
}

// 从 JWT 中提取用户 ID
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("令牌中没有 userId")

认证路由

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>("无效的凭据"),
                )
            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))
            }
        }
    }
}

StatusPages（错误处理）

// plugins/StatusPages.kt
fun Application.configureStatusPages() {
    install(StatusPages) {
        exception<ContentTransformationException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>("无效的请求体: ${cause.message}"),
            )
        }

        exception<IllegalArgumentException> { call, cause ->
            call.respond(
                HttpStatusCode.BadRequest,
                ApiResponse.error<Unit>(cause.message ?: "错误的请求"),
            )
        }

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

        exception<AuthorizationException> { call, _ ->
            call.respond(
                HttpStatusCode.Forbidden,
                ApiResponse.error<Unit>("访问被拒绝"),
            )
        }

        exception<NotFoundException> { call, cause ->
            call.respond(
                HttpStatusCode.NotFound,
                ApiResponse.error<Unit>(cause.message ?: "资源未找到"),
            )
        }

        exception<Throwable> { call, cause ->
            call.application.log.error("未处理的异常", cause)
            call.respond(
                HttpStatusCode.InternalServerError,
                ApiResponse.error<Unit>("服务器内部错误"),
            )
        }

        status(HttpStatusCode.NotFound) { call, status ->
            call.respond(status, ApiResponse.error<Unit>("路由未找到"))
        }
    }
}

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 依赖注入

模块定义

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

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

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

// Application 设置
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 用于测试

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 返回用户") {
            coEvery { repository.findById("1") } returns testUser
            service.getById("1") shouldBe testUser
        }
    }
}

请求验证

// 在路由中验证请求数据
fun Route.userRoutes() {
    val userService by inject<UserService>()

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

        // 验证
        require(request.name.isNotBlank()) { "名称是必需的" }
        require(request.name.length <= 100) { "名称长度不能超过 100 个字符" }
        require(request.email.matches(Regex(".+@.+\\..+"))) { "邮箱格式无效" }

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

// 或者使用验证扩展函数
fun CreateUserRequest.validate() {
    require(name.isNotBlank()) { "名称是必需的" }
    require(name.length <= 100) { "名称长度不能超过 100 个字符" }
    require(email.matches(Regex(".+@.+\\..+"))) { "邮箱格式无效" }
}

WebSocket

fun Application.configureWebSockets() {
    install(WebSockets) {
        pingPeriod = 15.seconds
        timeout = 15.seconds
        maxFrameSize = 64 * 1024 // 64 KiB — 仅在协议需要更大帧时增加
        masking = false // 根据 RFC 6455，服务端到客户端的帧未掩码；客户端到服务端的帧始终由 Ktor 掩码
    }
}

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

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

        try {
            send("已连接！在线用户数: ${connections.size}")

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

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

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



…

[翻译时截断了]

测试

使用 testApplication 进行集成测试

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

    @Test
    fun `get users returns 200`() = testApplication {
        application {
            configureSerialization()
            configureDI()
            configureRouting()
        }

        coEvery { userService.getAll() } returns listOf(testUser)

        val response = client.get("/users")
        assertEquals(HttpStatusCode.OK, response.status)
    }
}

使用 TestClient 进行测试

class HealthRoutesTest {
    @Test
    fun `health endpoint returns ok`() = testApplication {
        application {
            configureRouting()
        }

        val response = client.get("/health")
        assertEquals(HttpStatusCode.OK, response.status)
        assertEquals("""{"status":"UP"}""", response.bodyAsText())
    }
}

配置

HOCON 配置

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

jwt {
    secret = "my-secret-key"
    issuer = "my-app"
    audience = "my-audience"
    realm = "my-realm"
}

环境变量覆盖

// 在 configureAuthentication 中使用
val jwtSecret = environment.config.propertyOrNull("jwt.secret")?.getString()
    ?: System.getenv("JWT_SECRET") ?: error("JWT_SECRET 未设置")

最佳实践

1. 分层架构：将路由（routes）、服务（services）、仓库（repositories）和模型（models）分离，以保持关注点分离。
2. 使用 kotlinx.serialization：使用 @Serializable 注解数据类，并利用 ignoreUnknownKeys 实现弹性。
3. 集中式错误处理：使用 StatusPages 优雅地处理异常，而不是在每个路由中使用 try-catch 块。
4. Koin for DI：在构造函数中注入依赖项，使代码易于测试。使用 by inject() 进行惰性注入。
5. 认证：将路由组织为公共和受保护区域。使用 JWT 进行无状态认证。
6. 请求验证：在服务层验证，使用 Kotlin 的 require() 或验证扩展函数。
7. 测试：使用 testApplication 测试完整的 HTTP 请求/响应周期。对所有外部依赖使用 mock。
8. CORS：在生产环境应用中明确声明允许的主机。在生产环境中避免使用 allowHost("*")。
9. WebSocket：管理连接生命周期（连接、广播、断开连接）。使用同步的集合来避免并发修改。
10. 配置：使用 HOCON 进行默认设置，使用环境变量进行秘密管理和环境特定覆盖。

另请参阅：完整的 Ktor 文档请访问 ktor.io。