How to generate a C# and TypeScript client for an ASP.NET Core API with NSwag

June 10, 2020 2-minute read

.NET • Swagger

.NET • Swagger • NSwag

NSwag is an awesome library for generating C# and TypeScript clients for Swagger APIs.

A complete example of this code can be found on our Github

This is an example of how to add an endpoint to your API to generate an Angular TypeScript client and a C# client. It’s possible to use NSwag with Swashbuckle. These methods retrieve the swagger json from the API and then return a client. You can provide your own class for AuthorizedApiBase and ApiClientConfig and there are numerous configuration options.

Install-Package NSwag.CodeGeneration.TypeScript

[Route("api/client")]
[ApiController]
[AllowAnonymous]
public class ClientController : Controller
{
    [HttpGet]
    [Route("typescript/angular")]
    public async Task<string> Get()
    {
        string baseUrl = $"{this.Request.Scheme}://{this.Request.Host.Value.ToString()}{this.Request.PathBase.Value.ToString()}";
        OpenApiDocument document = await OpenApiDocument.FromUrlAsync($"{baseUrl}/swagger/v1/swagger.json");

        TypeScriptClientGeneratorSettings settings = new TypeScriptClientGeneratorSettings
        {
            ClientBaseClass = "AuthorizedApiBase",
            ClassName = "ClientName",
            Template = TypeScriptTemplate.Angular,
            PromiseType = PromiseType.Promise,
            HttpClass = HttpClass.HttpClient,
            InjectionTokenType = InjectionTokenType.InjectionToken,
            ConfigurationClass ="ApiClientConfig"
        };

        TypeScriptClientGenerator generator = new TypeScriptClientGenerator(document, settings);
        string generatedCode = generator.GenerateFile();
    }
}

These classes would reside in your TypeScript project and can be configured however you like. ApiClientConfig.getBearerToken could return a token from local storage or from wherever you have it stored.

export class ApiClientConfig {
  /**
   * Returns a valid value for the Authorization header.
   * Used to dynamically inject the current auth header.
   */
  getBearerToken: () => '';
}

export class AuthorizedApiBase {
  private readonly config: ApiClientConfig;

  protected constructor(config: ApiClientConfig) {
    this.config = config;
  }

  protected transformOptions = (options: RequestInit): Promise<RequestInit> => {
    options.headers = {
      ...options.headers,
      'Authorization': 'Bearer ' + this.config.getBearerToken(),
    };
    return Promise.resolve(options);
  };

For C#

Install-Package NSwag.CodeGeneration.CSharp

[AllowAnonymous]
[HttpGet]
[Route("csharp")]
public async Task<string> CSharp()
{
    string baseUrl = $"{this.Request.Scheme}://{this.Request.Host.Value.ToString()}{this.Request.PathBase.Value.ToString()}";
    OpenApiDocument document = await OpenApiDocument.FromUrlAsync($"{baseUrl}/swagger/v1/swagger.json");

    CSharpClientGeneratorSettings settings = new CSharpClientGeneratorSettings
    {
        ClassName = "MyAPIClient",
        CSharpGeneratorSettings =
        {
            Namespace = "MyNamespace",
        }
    };

    CSharpClientGenerator generator = new CSharpClientGenerator(document, settings);
    string generatedCode = generator.GenerateFile();
    return generatedCode;
}