How to create Auto-generated clients (client SDKs) for OpenAPI specification API

Autogenerated clients, also known as client SDKs (Software Development Kits), are libraries generated from an API specification, such as an OpenAPI specification, that help developers interact with an API more easily. These clients abstract the complexities of making HTTP requests and handling responses, allowing developers to focus on business logic rather than the intricacies of API communication.

Why Use Autogenerated Clients?

1. Consistency: Ensures consistent implementation of API interactions across different languages and projects.
2. Productivity: Saves development time by providing ready-to-use functions and classes that encapsulate API calls.
3. Error Reduction: Minimizes the chances of making mistakes in request formatting and error handling.
4. Documentation: Often includes inline documentation generated from the API specification, helping developers understand how to use the API effectively.

How to Generate Clients

The process typically involves the following steps:

1. Define the API Specification: Create an OpenAPI (or other format) specification that describes your API.
2. Use a Code Generation Tool: Use tools like Swagger Codegen, OpenAPI Generator, or Postman to generate client code.
3. Integrate the Generated Code: Include the generated client library in your project.

Example

Step 1: Define the API Specification (OpenAPI)

Here’s an example OpenAPI specification for a simple "Pet Store" API:

openapi: 3.0.0
info:
  title: Pet Store API
  description: API for managing a pet store
  version: 1.0.0
servers:
  - url: https://api.petstore.com/v1
paths:
  /pets:
    get:
      summary: List all pets
      responses:
        '200':
          description: A list of pets.
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Pet'
    post:
      summary: Create a pet
      requestBody:
        description: Pet to add to the store
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/NewPet'
      responses:
        '201':
          description: Pet created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'
components:
  schemas:
    Pet:
      type: object
      properties:
        id:
          type: string
        name:
          type: string
        tag:
          type: string
    NewPet:
      type: object
      required:
        - name
      properties:
        name:
          type: string
        tag:
          type: string

Step 2: Use a Code Generation Tool

Using OpenAPI Generator, you can generate a client library in various programming languages. Here’s an example command to generate a Python client:

openapi-generator-cli generate -i openapi.yaml -g python -o ./python-client

Step 3: Integrate the Generated Code

Assuming you generated a Python client, you can integrate and use it in your project as follows:

1. Install the Client Library: Navigate to the generated directory and install the package using pip.

pip install ./python-client

2. Use the Client in Your Code:

from petstore_client import ApiClient, Configuration
from petstore_client.api.pets_api import PetsApi
from petstore_client.model.new_pet import NewPet

# Configure the client
configuration = Configuration()
configuration.host = "https://api.petstore.com/v1"
api_client = ApiClient(configuration)

# Create an instance of the API class
api_instance = PetsApi(api_client)

# List all pets
pets = api_instance.list_pets()
print(pets)

# Add a new pet
new_pet = NewPet(name="Fluffy", tag="dog")
created_pet = api_instance.create_pet(new_pet)
print(created_pet)

Tools for Generating Clients

1. OpenAPI Generator:

   • Supports a wide range of programming languages.
   • Command-line tool, Maven plugin, Gradle plugin, and more.
   • OpenAPI Generator Documentation

2. Swagger Codegen:

   • Similar to OpenAPI Generator, but with fewer updates.
   • Supports multiple languages and frameworks.
   • Swagger Codegen Documentation

3. Postman:

   • Allows you to import OpenAPI specifications and generate collections that can be used to create client code.
   • Postman Documentation

4. NSwag:

   • A .NET-specific toolchain for generating C# client code and server stubs from OpenAPI specifications.
   • NSwag Documentation