Introduction of Swift OpenAPI Generator

API development is crucial to creating robust iOS applications in today’s fast-paced digital environment. Swift OpenAPI generator is the most powerful tool designed for streamlining the procedure that produces the swift code from the OpenAPI specifications. However, it is necessary to hire skilled iOS programmers who can use the tools to make a project easy without compromising the quality of an app. In this blog, we will see how the Swift OpenAPI Generator simplifies API development; with this, developers can make an exceptional user experience.

Overview of OpenAPI

OpenAPI is the specification that needs to document HTTP services. The OpenAPI document is written in either YAML or JSON files, and it is ready only by tools that help you automate the workflow. It will generate the necessary coding to send and receive HTTP requests.

OpenAPI solves the issue of communicating with an API contract between the service and its clients. It erases the requirements that will read the most inaccurate, handwritten files or analyze the work traffic. It will figure out the best way to call a service. It also avoids the time-consuming, repetitive, and error-free work while adopting the service for the first time and helps them continue the services.

Let’s consider a simple service known as GreetingService that:

  • Listen to an HTTP GET request at the / greet endpoint.
  • Have an optional parameter known as a name.
  • Return the HTTP status code 200 ok, with the JSON body, which will look like:


  “message” : “Hey, Guys!”


Also, a service can be described by utilizing the OpenAPI document below:

openapi: ‘3.0.3’


  title: GreetingService

  version: 1.0.0


  – url: “http://localhost:8080”

    description: “Localhost”




      operationId: getGreeting


        – name: name

          in: query


            type: string



          description: A success response with a greeting.




                $ref: “#/components/schemas/Greeting”






          type: string


        – message

This is just a basic example of an OpenAPI document that defines the structure of an HTTP request and response that has an HTTP technique, URL path and query parameters, HTTP status coding, and type of content. Thus, it appropriately uses the JSON Schema to give an idea about the structure of the response body.

Swift OpenAPI Generator

It is a SwiftPM plugin with an OpenAPI document. It will either produce the client code for performing the HTTP calls or the server code for handling those calls. This generated code will translate between the type-safe representation of each task’s input and output and the HTTP request and response underlying them.

So, whether you are creating an app that serves as a client for GreetingService or integrating the GreetingService itself, then at this time, Swift OpenAPI Generator will produce the networking code for you, and it also permits you to concentrate on the core logic:

Adopting a Plugin

If you wish to make the proper use of the Swift OpenAPI Generator, then you need to integrate this:

1. Add Package Dependencies for:

  • A package plugin will generate the code at a build time.
  • The runtime library will consist of the protocol definition that a generated code and extension libraries are utilizing.
  • A transport integration will permit plugging in your selected HTTP client library or the server framework.

2. Activate the package plugin on your target and include the target dependencies for the runtime and transport libraries.

3. Also, add the two following files to your target project:

  • openapi.yaml, an OpenAPI document that will describe your API
  • opneapi-generator-config. yaml, a configuration file for a plugin, which will have control over whether to produce the client or server code.

How to Use Generator API Client?

When developing an iOS app for the client, you need to provide two generated types.

APIProtocol: A swift protocol consists of one method per OpenAPI task. A GreetingService has a single process, known as getGreeting.

Client: A swift struct that integrates an API protocol, which is being used to make API calls to a server.

Let’s see the below example code that will instantiate the client and fetch the greeting from the server side:

import OpenAPIRuntime

import OpenAPIURLSession

// Instantiate your chosen transport library.

let transport: ClientTransport = URLSessionTransport()

// Create a client to connect to a server URL documented in the OpenAPI document.

let client = Client(

    serverURL: try Servers.server1(),

    transport: transport


// Make the HTTP call using a type-safe method.

let response = try await client.getGreeting(.init(query: .init(name: “Jane”)))

// Switch over the HTTP response status code.

switch response {

case .ok(let okResponse):

    // Switch over the response content type.

    switch okResponse.body {

    case .json(let greeting):

        // Print the greeting message.

        print(“👋 \(greeting.message)”)


case .undocumented(statusCode: let statusCode, _):

    // Handle HTTP response status codes that are not documented in the OpenAPI document.

    print(“🥺 undocumented response: \(statusCode)”)


How to Use Generated API Server Stubs?

While creating a server, you will get the two generated types for use in your coding language.

APIProtocol: A protocol that consists of one method per OpenAPI operation.

APIProtocol.registerHandlers: This is the particular method on the APIProtocol that registers only one handler as per the OpenAPI operation. It is also called a greeting method, which you will integrate into your project.

Below, see an example of the code to integrate a simple and easy handler, which we will utilize to begin the server.

import OpenAPIRuntime

import OpenAPIVapor

import Vapor

// A server implementation of the GreetingService API.

struct Handler: APIProtocol {

    func getGreeting(

        _ input: Operations.getGreeting.Input

    ) async throws -> Operations.getGreeting.Output {

        let message = “Hello, \( ?? “Stranger”)!”

        let greeting = Components.Schemas.Greeting(message: message)

        return .ok(.init(body: .json(greeting)))



// Create the Vapor app.

let app = Vapor.Application()

// Create the transport.

let transport: ServerTransport = VaporTransport(routesBuilder: app)

// Create the request handler, which contains your server logic.

let handler = Handler()

// Register the generated routes on the transport.

try handler.registerHandlers(on: transport)

// Start the server.


Wrap Up

Swift OpenAPI Generator is considered a game-changer in iOS app development, offering programmers a streamlined approach through the Integration of API. The Swift code, from an OpenAPI specification, will empower the team to concentrate on creating an exceptional user experience that will sacrifice the quality of an iOS app. Swift OpenAPI Generator presents the most significant tool that will speed up a development cycle and boost app productivity. By adopting this advanced technology, many businesses are ready to integrate APIs, minimize bugs, and improve the collaboration between the coders and stakeholders. As the demand for creative and innovative iOS apps is constantly rising, you need to consult with the best iOS app development company that can deliver robust solutions that will meet the changing user needs with the help of agility and efficiency. Let’s get in touch with us now!

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