Go-Swagger in production wins and pitfalls 

Ilya Kaznacheev Remote Backend SWE Founder of Golang Voronezh Host of Z-Namespace podcast Organizer of conference and meetups Coffee geek 

Golang Voronezh - ~30 active members - meetups - events for beginners - open & friendly 

what swagger is? 

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SOAP JSON-PRC GraphQL gRPC OData REST 

Representational state transfer (REST) is a software architectural style that defines a set of constraints to be used for creating Web services Wikipedia 

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swagger: "2.0" info: title: Pet API version: "1.0.0" basePath: /api schemes: - http paths: /pets: get: summary: List all pets parameters: - name: limit in: query description: "How many items to return at one time" required: true type: integer responses: 200: description: an paged array of pets 400: description: unexpected error 

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why do we use swagger? 

my team trying to sync API changes... 

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go-swagger 

code generation swagger generate server -t internal/api --exclude-main 

generated code structure internal/api ├ models │ └ ... └ restapi ├ operations │ └ ... ├ configure_.go ├ doc.go ├ embedded_spec.go └ server.go 

our code generation rm -rf internal/api && mkdir -p internal/api swagger generate server -t internal/api --exclude-main go mod tidy 

and we're all set ? 

NO 

there are some problems - go-swagger is a framework, not a library - plenty of generated types for everything - incompatible with popular http-libraries 

let’s fix ’em all! 

serving net/http handlers type CustomResponder func(http.ResponseWriter, runtime.Producer) func (c CustomResponder) WriteResponse(w http.ResponseWriter, p runtime.Producer) { c(w, p) } func MetricsHandler(p instruments.GetMetricsParams) middleware.Responder { return CustomResponder(func(w http.ResponseWriter, _ runtime.Producer) { promhttp.Handler().ServeHTTP(w, p.HTTPRequest) }) } 

simple middleware api := operations.NewSwaggerPetstoreAPI(swaggerSpec) api.InstrumentsGetMetricsHandler = instruments.GetMetricsHandlerFunc(MetricsHandler) api.AddMiddlewareFor("GET", "/metrics", SomeMiddleware) srv := restapi.NewServer(api) srv.Serve() 

middleware with custom handler h := api.Serve(nil) r := chi.NewRouter() r.Use( middleware.Recoverer, ) r.With(AuthMiddleware).Group(func(r chi.Router) { r.Handle("/user/*", h) }) r.Mount("/", h) srv.ConfigureAPI() srv.SetHandler(r) srv.Serve() 

setup outside of configure_.go api.Logger = log.Printf api.HTMLProducer = runtime.TextProducer() srv := restapi.NewServer(api) srv.EnabledListeners = []string{"http"} srv.Port = conf.HTTPPort srv.Host = conf.HTTPAddr 

custom method names /store/order/{orderId}/items: get: tags: - store summary: Find purchase order items parameters: - name: orderId in: path required: true type: integer func GetOrderItems( param store.GetStoreOrderOrderIDItemsParams, ) middleware.Responder { items, err := getOrderItems(param.OrderID) if err != nil { return store.NewGetStoreOrderOrderIDItemsNotFound() } res := &models.OrderItems{} // // fill resopnse // return store.NewGetStoreOrderOrderIDItemsOK(). WithPayload(res) } 

custom method names /store/order/{orderId}/items: get: tags: - store summary: Find purchase order items operationId: getOrderItems parameters: - name: orderId in: path required: true type: integer func GetOrderItems( param store.GetOrderItemsParams, ) middleware.Responder { items, err := getOrderItems(param.OrderID) if err != nil { return store.NewGetOrderItemsNotFound() } res := &models.OrderItems{} // // fill resopnse // return store.NewGetOrderItemsOK(). WithPayload(res) } 

validity checks OrderItems: type: object properties: message: type: string maximum: 3 # swg/internal/api/models internal/api/models/order_items.go:45:55: cannot convert m.Message (type string) to type float64 

validity check cheat sheet numbers and integers - multipleOf - maximum - minimum - exclusiveMaximum - exclusiveMinimum strings - maxLength - minLength - pattern arrays - maxItems - minItems - uniqueItems - maxContains - minContains objects - maxProperties - minProperties - required - dependentRequired any type - type - enum - const 

extensions (tricks) x-omitempty x-nullable x-isnullable x-order x-go-custom-tag x-schemes x-go-name x-go-type x-go-json-string x-go-enum-ci 

unit tests func GetOrderByID(param store.GetOrderByIDParams) middleware.Responder { order := models.Order{ ID: 123, PetID: 456, Quantity: 20, Status: "approved", } if param.OrderID != order.ID { return store.NewGetOrderByIDNotFound().WithPayload(&models.ErrorMessage{ Code: http.StatusNotFound, Message: http.StatusText(http.StatusNotFound), }) } return store.NewGetOrderByIDOK().WithPayload(&order) } 

unit tests tests := []struct { name string req store.GetOrderByIDParams code int want string }{ { name: "good test", req: store.GetOrderByIDParams{OrderID: 123}, code: 200, want: `{"id":123,"petId":456,"quantity":20,"status":"approved"}`, }, { name: "bad test", req: store.GetOrderByIDParams{OrderID: 456}, code: 404, want: `{"message":"Not Found", "code":404}`, }, } 

unit tests for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { rr := httptest.NewRecorder() GetOrderByID(tt.req).WriteResponse(rr, runtime.JSONProducer()) assert.JSONEq(t, tt.want, rr.Body.String(), "wrong response body") assert.Equal(t, tt.code, rr.Code, "wrong response code") }) } 

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helpful links json-schema.org/specification.html swagger.io/docs/specification/2-0 goswagger.io 

bonus A pluggable go-swagger (in development) github.com/ilyakaznacheev/go-plugger 

bonus 2 Insomnia Designer insomnia.rest/products/designer 

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