Padrões de Ktor Server

Padrões de Servidor Ktor

Padrões abrangentes de Ktor para construir servidores HTTP robustos e de fácil manutenção com corrotinas Kotlin.

Quando Ativar

• Construindo servidores HTTP Ktor
• Configurando plugins Ktor (Auth, CORS, ContentNegotiation, StatusPages)
• Implementando APIs REST com Ktor
• Configurando injeção de dependência com Koin
• Escrevendo testes de integração Ktor com testApplication
• Trabalhando com WebSockets no Ktor

Estrutura da Aplicação

Layout Padrão do Projeto Ktor

src/main/kotlin/
├── com/exemplo/
│   ├── Application.kt           # Ponto de entrada, configuração do módulo
│   ├── plugins/
│   │   ├── Routing.kt           # Definições de rotas
│   │   ├── Serialization.kt     # Configuração de negociação de conteúdo
│   │   ├── Authentication.kt    # Configuração de autenticação
│   │   ├── StatusPages.kt       # Tratamento de erros
│   │   └── CORS.kt              # Configuração de CORS
│   ├── routes/
│   │   ├── UserRoutes.kt        # Endpoints /users
│   │   ├── AuthRoutes.kt        # Endpoints /auth
│   │   └── HealthRoutes.kt      # Endpoints /health
│   ├── models/
│   │   ├── User.kt              # Modelos de domínio
│   │   └── ApiResponse.kt       # Envelopes de resposta
│   ├── services/
│   │   ├── UserService.kt       # Lógica de negócios
│   │   └── AuthService.kt       # Lógica de autenticação
│   ├── repositories/
│   │   ├── UserRepository.kt    # Interface de acesso a dados
│   │   └── ExposedUserRepository.kt
│   └── di/
│       └── AppModule.kt         # Módulos Koin
src/test/kotlin/
├── com/exemplo/
│   ├── routes/
│   │   └── UserRoutesTest.kt
│   └── services/
│       └── UserServiceTest.kt

Ponto de Entrada da Aplicação

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

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

DSL de Roteamento

Rotas Básicas

// 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)
        }
    }
}

Organização de Rotas com Rotas Autenticadas

fun Route.userRoutes() {
    route("/users") {
        // Rotas públicas
        get { /* listar usuários */ }
        get("/{id}") { /* obter usuário */ }

        // Rotas protegidas
        authenticate("jwt") {
            post { /* criar usuário - requer autenticação */ }
            put("/{id}") { /* atualizar usuário - requer autenticação */ }
            delete("/{id}") { /* excluir usuário - requer autenticação */ }
        }
    }
}

Negociação de Conteúdo e Serialização

Configuração do kotlinx.serialization

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

Modelos Serializáveis

@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,
)

Serializadores Personalizados

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())
}

Autenticação

Autenticação JWT

// 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>("Token inválido ou expirado"))
            }
        }
    }
}

// Extraindo usuário do JWT
fun ApplicationCall.userId(): String =
    principal<JWTPrincipal>()
        ?.payload
        ?.getClaim("userId")
        ?.asString()
        ?: throw AuthenticationException("Nenhum userId no token")

Rotas de Autenticação

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>("Credenciais inválidas"),
                )
            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))
            }
        }
    }
}

Páginas de Status (Tratamento de Erros)

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

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

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

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

        exception<NotFoundException> { call, cause ->
            call.respond(
                HttpStatusCode.NotFound,
                ApiResponse.error<Unit>(cause.message ?: "Recurso não encontrado"),
            )
        }

        exception<Throwable> { call, cause ->
            call.application.log.error("Exceção não tratada", cause)
            call.respond(
                HttpStatusCode.InternalServerError,
                ApiResponse.error<Unit>("Erro interno do servidor"),
            )
        }

        status(HttpStatusCode.NotFound) { call, status ->
            call.respond(status, ApiResponse.error<Unit>("Rota não encontrada"))
        }
    }
}

Configuração de CORS

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

Injeção de Dependência com Koin

Definição do Módulo

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

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

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

// Configuração da aplicação
fun Application.configureDI() {
    install(Koin) {
        modules(appModule)
    }
}

Usando Koin em Rotas

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

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

Koin para Testes

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 retorna usuário") {
            coEvery { repository.findById("1") } returns testUser
            service.getById("1") shouldBe testUser
        }
    }
}

Validação de Requisições

// Validar dados da requisição nas rotas
fun Route.userRoutes() {
    val userService by inject<UserService>()

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

        // Validar
        require(request.name.isNotBlank()) { "Nome é obrigatório" }
        require(request.name.length <= 100) { "Nome deve ter no máximo 100 caracteres" }
        require(request.email.matches(Regex(".+@.+\\.+"))) { "Formato de email inválido" }

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

// Ou usar uma extensão de validação
fun CreateUserRequest.validate() {
    require(name.isNotBlank()) { "Nome é obrigatório" }
    require(name.length <= 100) { "Nome deve ter no máximo 100 caracteres" }
    require(email.matches(Regex(".+@.+\\.+"))) { "Formato de email inválido" }
}

WebSockets

fun Application.configureWebSockets() {
    install(WebSockets) {
        pingPeriod = 15.seconds
        timeout = 15.seconds
        maxFrameSize = 64 * 1024 // 64 KiB — aumente apenas se seu protocolo exigir quadros maiores
        masking = false // Quadros servidor-para-cliente não são mascarados conforme RFC 6455; cliente-para-servidor são sempre mascarados pelo Ktor
    }
}

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

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

        try {
            send("Conectado! Usuários online: ${connections.size}")

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

                // Instantâneo sob bloqueio para evitar ConcurrentModificationException
                val snapshot = synchronized(connections) { connections.toList() }
                snapshot.forEach { conn ->
                    conn.session.send(Json.encodeToString(message))
                }
            }
        } catch (e: Exception) {
            logger.error("Erro no WebSocket", e)
        } finally {
            connections -= thisConnection
        }
    }
}

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

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

Testes com testApplication

Configuração Básica de Teste

// build.gradle.kts
dependencies {
    testImplementation("io.ktor:ktor-server-test-host:")
    testImplementation("io.ktor:ktor-client-content-negotiation:")
    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5:")
}

// routes/UserRoutesTest.kt
class UserRoutesTest {

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

    @Test
    fun `should return list of users`() = testApplication {
        application {
            configureSerialization()
            configureDI()
            configureRouting()
        }

        client.get("/users").apply {
            assertEquals(HttpStatusCode.OK, status)
            val response = body<ApiResponse<List<UserResponse>>>()
            assertTrue(response.success)
            assertNotNull(response.data)
        }
    }

    @Test
    fun `should return 404 for non-existent user`() = testApplication {
        application {
            configureSerialization()
            configureDI()
            configureRouting()
        }

        client.get("/users/999").apply {
            assertEquals(HttpStatusCode.NotFound, status)
        }
    }

    @Test
    fun `should create user and return 201`() = testApplication {
        application {
            configureSerialization()
            configureDI()
            configureRouting()
        }

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

        client.post("/users") {
            contentType(ContentType.Application.Json)
            setBody(request)
        }.apply {
            assertEquals(HttpStatusCode.Created, status)
            val response = body<ApiResponse<UserResponse>>()
            assertTrue(response.success)
            assertEquals("João", response.data?.name)
        }
    }

    @Test
    fun `should return 401 for protected route without token`() = testApplication {
        application {
            configureSerialization()
            configureAuthentication()
            configureDI()
            configureRouting()
        }

        client.post("/users") {
            contentType(ContentType.Application.Json)
            setBody(CreateUserRequest("Admin", "[email protected]"))
        }.apply {
            assertEquals(HttpStatusCode.Unauthorized, status)
        }
    }
}

Teste de Autenticação com Token

@Test
fun `should return 200 for authenticated request`() = testApplication {
    application {
        configureSerialization()
        configureAuthentication()
        configureDI()
        configureRouting()
    }

    val token = generateTestToken()

    client.get("/auth/me") {
        bearerAuth(token)
    }.apply {
        assertEquals(HttpStatusCode.OK, status)
    }
}

private fun generateTestToken(): String {
    return JWT.create()
        .withAudience("test-audience")
        .withIssuer("test-issuer")
        .withClaim("userId", "123")
        .sign(Algorithm.HMAC256("test-secret"))
}

Variáveis de Ambiente e Configuração

application.conf

ktor {
    deployment {
        port = 8080
    }
    application {
        modules = [
            "com.exemplo.ApplicationKt.module",
            "com.exemplo.PluginsKt.configureSerialization",
            "com.exemplo.PluginsKt.configureAuthentication",
            "com.exemplo.PluginsKt.configureStatusPages",
            "com.exemplo.PluginsKt.configureCORS",
            "com.exemplo.PluginsKt.configureWebSockets",
            "com.exemplo.DIModuleKt.configureDI",
            "com.exemplo.PluginsKt.configureRouting"
        ]
    }
    jwt {
        secret = ${?JWT_SECRET}
        issuer = ${?JWT_ISSUER}
        audience = ${?JWT_AUDIENCE}
        realm = ${?JWT_REALM}
    }
}

Variáveis de Ambiente

export JWT_SECRET=seu-super-segredo-aqui
export JWT_ISSUER=https://exemplo.com
export JWT_AUDIENCE=https://api.exemplo.com
export JWT_REALM=Exemplo Realm
export DATABASE_URL=jdbc:postgresql://localhost:5432/minhabase
export DATABASE_USER=usuario
export DATABASE_PASSWORD=senha

Referências

• Documentação do Ktor
• Injeção de Dependência com Koin
• Documentação do kotlinx.serialization
• Framework de Testes Ktor