How to download file on browser from Dotnet core endpoint

Question

I have a react front-end and the dotnet core web API project on the back-end. I have an endpoint on which a client can request a file using fileId from my react application. My back-end application will get the file path using a database. After that I am converting that file into a FileStream and returning a file Object from the end-point.

I am able to get a file path and converting into a stream but when I am returning a file from the endpoint but I am not getting any file download on the browser. The file extension can be any so I am using application/octet-stream as a content type.

Here is my code:

[HttpGet]
public async Task<ActionResult> GET([FromRoute] string fileId)
{
   try
   {
       string filePath = repo.getFilePath(fileId);
       FileStream fileStream = new FileStream(filePath, FileMode.Open);
       return File(fileStream, "application/octet-stream");

   }
   catch(Exception ex)
   {
       return Content(ex.Message);
   }
}

Answer 1

I have faced this issue few time ago.

I developed an endpoint on the API that takes a file from the physical directory and makes it downloadable via virtual path.

Frontend side I call a controller that does a simple redirect to the url of the virtual directory, which starts the download.

Here is my solution for .net core 5

appsettings.json

into appsetting.json define

• Download Url

• Virtual Directory Path

• Physical Storage Path

  "PhysicalPath": "C:\\PhysicalPath\\",
  "VirtualPath": "/VirtualPath",
  "DownloadUrl": "https://localhost:1234",
  

Strartup.cs

Inside the Startup.cs into ConfigureServices method allow the cors:

public void ConfigureServices(IServiceCollection services)
   {
      ...
   
                services.AddCors(options =>
                {
                    options.AddPolicy(
                        name: "AllowOrigin",
                        builder => {
                            builder.AllowAnyOrigin()
                                    .AllowAnyMethod()
                                    .AllowAnyHeader();
                        });
                });
       ...
    }

at the end of Configure method define PysicalFileProvider.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
 ...
 app.UseFileServer(new FileServerOptions
 {
   FileProvider = newPhysicalFileProvider(Configuration.GetSection("PhysicalPath").Value),
                        RequestPath = new PathString(Configuration.GetSection("VirtualPath").Value),
                        EnableDirectoryBrowsing = false
  });
}

Controller

[ApiController]
public class FileController : ControllerBase
{ 
    private readonly IConfiguration _configuration;
   
    public FileController(IConfiguration configuration)
    {
        _configuration = configuration;
    }
    /// <summary>
    /// Get Phisical File .
    /// </summary>
    /// <returns></returns>
    [HttpGet]
    [Route("{id}/{filename}")]
    public async Task<IActionResult> Get(long id, string filename)
    {
        string url = "{0}{1}/{2}";
        url = string.Format(url, _configuration.GetSection("AppUrl").Value, _configuration.GetSection("VirtualPath").Value, filename);

        return Redirect(url);
    }
}

if you try to call that method on swagger you recive this answer

but if you call the method by the frontend you could downlod the file.