Support binding to IFormFile in minimal routing APIs

[davidfowl]

Is your feature request related to a problem? Please describe.

Today we don't have any native support for binding to IFormFiles as part of the incoming request. This is convenient for applications that want to do file uploads.

Describe the solution you'd like

app.MapGet("/upload", async (IFormFile file) =>
{
    var uploads = Path.Combine(uploadsPath, file.FileName);
    using var fileStream = File.OpenWrite(uploads);
    using var uploadStream = file.OpenReadStream();
    await uploadStream.CopyToAsync(fileStream);
});

Additional context

• Should we support IFormFileCollection?
• Would we do matching by name? (yes)

Without this, it will look like this:

app.MapGet("/upload", async (HttpRequest req) =>
{
    if (!req.HasFormContentType)
    {
        return Results.BadRequest();
    }

    var form = await req.ReadFormAsync();
    var file = form.Files["file"];

    if (file is null)
    {
        return Results.BadRequest();
    }

    var uploads = Path.Combine(uploadsPath, file.FileName);
    using var fileStream = File.OpenWrite(uploads);
    using var uploadStream = file.OpenReadStream();
    await uploadStream.CopyToAsync(fileStream);

    return Results.NoContent();
});

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[jchannon]

The below API would be good too, to handle more than one file at a time.

app.MapGet("/upload", async (IEnumerable<IFormFile> files) =>
{
    //process the files 
});

[bradygaster]

I worked this up today in my side-by-side comparison solution and was sad to come across this feature parity gap.

Whilst this works fine with Web API:

[HttpPost]
[Route("/upload")]
public async Task UploadFile(IFormFile file, CancellationToken token)
{
    using (var stream = System.IO.File.OpenWrite("upload.txt"))
    {
        await file.CopyToAsync(stream);
    }
}

A similar approach fails to work in minimal API:

app.MapPost("/upload", async(IFormFile file, CancellationToken token) =>
{
    using (var stream = System.IO.File.OpenWrite("upload.txt"))
    {
        await file.CopyToAsync(stream);
    }
});

I'd like to see how we get to party. Or maybe add an analyzer when folks do this to provide guidance to the alternative approach in this issue.

[davidfowl]

The below API would be good too, to handle more than one file at a time.

@jchannon We would support IFormFileCollection.

The other thing missing here is [FromFile("name")] for completeness we'd want to add metadata to let you specify the name of the file entry.

The other piece of work is updating the API explorer to set the right request content type if we support file upload.

[martincostello]

Would it also make sense to support IFormCollection here too (via ReadFormAsync() on the request), with IFormFile and IFormFileCollection being "specialisms" of that support?

[martincostello]

I've put up a draft to try and get this working in #35158.

[davidfowl]

We didn't do forms because we haven't thought the CSRF/Antiforgery features