Question 87281 in ASP.NET Question posted in
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How do I do file upload using ASP.NET Core 6 minimal api?

I want to create a simple file upload endpoint in ASP.NET Core 6 and thought it would be as easy as described here https://dotnetthoughts.net/handling-file-uploads-in-openapi-with-aspnet-core/.

When I have an endpoint defined like:

app.MapPost("/upload", (IFormFile file) =>
{
    //Do something with the file
    return Results.Ok();
}).Accepts<IFormFile>("multipart/form-data").Produces(200);

I get a 415 back when I call the endpoint. The message I get back is something like:

Expected a supported JSON media type but got "multipart/form-data; …

Not sure why it expected a supported json when I say that the endpoint should accept multipart/form-data.

Any ideas or thoughts on what to do here?

Tags:

4

Answers


  1. 0

    Currently out of the box support for binding in Minimal APIs is quite limited. Supported binding sources:

    • Route values
    • Query string
    • Header
    • Body (as JSON)
    • Services provided by dependency injection
    • Custom

    NOTE: Binding from forms is not natively supported in .NET 6

    You can either leverage custom binding or use special types handling:

    app.MapPost("/upload", (HttpRequest request) =>
{
    //Do something with the file
    var files = request.Form.Files;
    return Results.Ok();
})
.Accepts("multipart/form-data")
.Produces(200);

    UPD

    Since Minimal APIs should be able to bind IFormFile/IFormFileCollection directly:

    app.MapPost("/upload", async (IFormFile file) =>
{
    // ...
});

app.MapPost("/upload_many", async (IFormFileCollection myFiles) =>
{
    foreach (var file in myFiles)
    {
        // ...
    }
});
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  2. 0

    Just noting here, you can upload a file with any ContentType like the following sample code.

    In this example I chose a text/plain ContentType,
    but you can choose your own by editing the .Accepts<IFormFile>("text/plain"); line to your desired ContentType.

    app.MapPost("/upload",
    async (HttpRequest request) =>
    {
        using (var reader = new StreamReader(request.Body, System.Text.Encoding.UTF8))
        {

            // Read the raw file as a `string`.
            string fileContent = await reader.ReadToEndAsync();

            // Do something with `fileContent`...
    
            return "File Was Processed Sucessfully!";
        }
    }).Accepts<IFormFile>("text/plain");

    It is also well supported by Swagger UI:

    enter image description here

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  3. 0 
    app.MapPost("/upload",
    async Task<IResult> (HttpRequest request) =>
    {
        if (!request.HasFormContentType)
            return Results.BadRequest();

        var form = await request.ReadFormAsync();

        if (form.Files.Any() == false)
            return Results.BadRequest("There are no files");

        var file = form.Files.FirstOrDefault();

        if (file is null || file.Length == 0)
            return Results.BadRequest("File cannot be empty");

        using var stream = file.OpenReadStream();

        var reader = new StreamReader(stream);
        var text = await reader.ReadToEndAsync();

        return Results.Ok(text);
    }).Accepts<IFormFile>("multipart/form-data");
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  4. 0

    This has been addressed with .NET 7. Support for IFormFile and IFormFileCollection has been added. You should be able to use it in your MediatR pipelines.

    Ref: .NET 7 Minimal API Support for File Upload Bindings

    var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello World!");

app.MapPost("/upload", async (IFormFile file) =>
{
    var tempFile = Path.GetTempFileName();
    app.Logger.LogInformation(tempFile);
    using var stream = File.OpenWrite(tempFile);
    await file.CopyToAsync(stream);
});

app.MapPost("/upload_many", async (IFormFileCollection myFiles) =>
{
    foreach (var file in myFiles)
    {
        var tempFile = Path.GetTempFileName();
        app.Logger.LogInformation(tempFile);
        using var stream = File.OpenWrite(tempFile);
        await file.CopyToAsync(stream);
    }
});

app.Run();
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