What is the correct way to download a file via the NSwag Code Generator (angular 2 typescript)

Question

I try to download a file via an angular 2 typescript client. The link generated in Swagger UI works fine, but the generated typescript client does not.

The controller looks like this:

    [HttpGet("export")]
    [SwaggerResponse((int) HttpStatusCode.OK, Type = typeof(FileContentResult))]
    [ProducesResponseType(typeof(FileResult), (int) HttpStatusCode.OK)]
    [Produces("text/csv")]
    public virtual FileResult Export(int Id, string fileType, CsvFormat format, bool includeHeader)
    {
        .
        .
        .
        FileStreamResult file = new FileStreamResult(s, "text/csv");
        file.FileDownloadName = ts.Name + "." + fileType;

        return file;
    }

Swagger UI:

The generated typescript client looks like this. As you can see the responseText is set but never returned. What am I missing?

protected processRestTimeSeriesExportGet(response: Response): Observable<void> {
    const status = response.status; 

    if (status === 200) {
        const responseText = response.text();
        return Observable.of<void>(<any>null);
    } else if (status !== 200 && status !== 204) {
        const responseText = response.text();
        return throwException("An unexpected server error occurred.", status, responseText);
    }
    return Observable.of<void>(<any>null);
}

Best regards

Answer 1

Eric Gontier's solution works great for Swashbuckle 4 and NSwag 12. If you've upgraded to swashbuckle 5 and thus OpenApi 3 and NSwag 13, then the solution is different. Instead you'll need a custom operation filter, and an reusable attribute to indicate the content-type result:

Custom attribute

/// <summary>
/// Indicates swashbuckle should expose the result of the method as a file in open api (see https://swagger.io/docs/specification/describing-responses/)
/// </summary>
[AttributeUsage(AttributeTargets.Method)]
public class FileResultContentTypeAttribute : Attribute
{
    public FileResultContentTypeAttribute(string contentType)
    {
        ContentType = contentType;
    }

    /// <summary>
    /// Content type of the file e.g. image/png
    /// </summary>
    public string ContentType { get; }
}

Operation filter

public class FileResultContentTypeOperationFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        var requestAttribute = context.MethodInfo.GetCustomAttributes(typeof(FileResultContentTypeAttribute), false)
            .Cast<FileResultContentTypeAttribute>()
            .FirstOrDefault();

        if (requestAttribute == null) return;

        operation.Responses.Clear();
        operation.Responses.Add("200", new OpenApiResponse
        {
            Content = new Dictionary<string, OpenApiMediaType>
            {
                {
                    requestAttribute.ContentType, new OpenApiMediaType
                    {
                        Schema = new OpenApiSchema
                        {
                            Type = "string",
                            Format = "binary"
                        }
                    }
                }
            }
        });
    }
}

Startup.cs

services.AddSwaggerGen(options =>
{
    ...
    options.OperationFilter<FileResultContentTypeOperationFilter>();
}

Sample Controller

Then annotate your controller with the attribute.

[HttpPost]
[Route("{fileName}.csv")]
[FileResultContentType("text/csv")]
public async Task<ActionResult> Generate(string fileName, [FromBody]MyDto myDto)
{
    var fileMemoryStream = GetCsvAsBytes(myDto);
    return File(fileMemoryStream,
        "text/csv", fileName + ".csv");
}

Answer 2

Found the response of this problem :

In startup add :

services.AddSwaggerGen(options =>
{   
options.MapType<FileContentResult>(() => new Schema
       {
                Type = "file",
            });
}

And for your controller :

[HttpPost()]
    [SwaggerResponse(200, typeof(FileContentResult))]
    [ProducesResponseType(typeof(FileContentResult), 200)]
    public async Task<FileResult> MyMethod(Viewmodel vm)
    {

A late response but for people who has the same problem ...

Answer 3

In the API, Required Nuget packages:

1. Microsoft.AspNetCore.StaticFiles // To determine MimeType
2. NSwag.Annotations // To map the return type of API with Angular Service Generated by NSwag

Search for the pacakges in Nuget and install them.

Then In Startup.cs,

services.AddSwaggerGen(options =>
{
    // Swagger Configurations
    options.MapType<FileContentResult>(() => new Schema
    {
        Type = "file"
    });
});

Now add a method to get the MimeType of file

private string GetMimeType(string fileName)
{
    var provider = new FileExtensionContentTypeProvider();
    string contentType;
    if (!provider.TryGetContentType(fileName, out contentType))
    {
        contentType = "application/octet-stream";
    }
    return contentType;
} 

Now Add a method to download file

[SwaggerResponse(200, typeof(FileContentResult))]
[ProducesResponseType(typeof(FileContentResult), 200)]
public FileContentResult DownloadDocument(string fileName)
{ 
    // _environment => IHostingEnvironment Instance
    var filepath = Path.Combine($"{this._environment.WebRootPath}\\path-to\\filename}");

    var mimeType = this.GetMimeType(filename);

    // Checks if file exists 
    var fileBytes = File.ReadAllBytes(filepath);
    return new FileContentResult(fileBytes, mimeType)
    {
        FileDownloadName = filename
    };
}

Now the downloadFile method in angular service generated by NSwag will return Observable. To Consume the service, first install file-saver using npm i file-saver. Then import it in component
import { saveAs } from 'file-saver';

downloadDocument = (filename: string): void => {
    this._service.downloadDocument(filename).subscribe((res) => {
      saveAs(res.data, 'filename');
    });
  };

This will download file.