Posted on Nov 25, 2021 • Originally published at gsferreira.com on Nov 24, 2021

Uploading files with ASP.NET Minimal APIs

With the .net 6 release, I was extremely excited to play with Minimal APIs.

One of the first things that I've done was to move an existing project to .net 6 and convert my Controllers into a Minimal API.

I've found the process easy, but I was surprised when the tests for an Upload endpoint failed.

My implementation after converting into Minimal API Endpoint was this. 👇

app.MapPost("/upload", async Task<IResult>(IFormFile request) => { if (request.Length == 0) return Results.BadRequest(); await using var stream = request.OpenReadStream(); var reader = new StreamReader(stream); var text = await reader.ReadToEndAsync(); return Results.Ok(text); });

And the test this. 👇

await using var application = new Application(); using var client = application.CreateClient(); using var formData = new MultipartFormDataContent(); await using var file = File.OpenRead("text.txt"); var streamContent = new StreamContent(file); formData.Add(streamContent, "file", "text.txt"); var response = await client.PostAsync("/upload", formData); response.StatusCode.Should().Be(HttpStatusCode.OK); var data = await response.Content.ReadAsStringAsync(); data.Should().Be("\"Hello World!\"");

The expected 200 OK status code was now a 415 Unsupported Media Type 🤔

That was strange. My first thought was that I was missing to define the content type accepted by that endpoint.

.Accepts<IFormFile>("multipart/form-data");

I realized I was stupid by thinking that since the code above is just about adding OpenAPI Metadata. 😅

Then, finally, I got it. Minimal APIs will try to bind attributes with the assumption that content is JSON.

So, how do I handle it?

I had to receive the HttpRequest request as an argument.

Then, I was able to read the Form and look for files.

app.MapPost("/upload", async Task<IResult>(HttpRequest request) => { if (!request.HasFormContentType) return Results.BadRequest(); var form = await request.ReadFormAsync(); var formFile = form.Files["file"]; if (formFile is null || formFile.Length == 0) return Results.BadRequest(); await using var stream = formFile.OpenReadStream(); var reader = new StreamReader(stream); var text = await reader.ReadToEndAsync(); return Results.Ok(text); });