Unable to use IFormFile with ApiController in 2.1

[Eilon]

From @mitchellj on Thursday, 09 August 2018 20:06:10

When we are trying to use IFormFile it works perfectly when we are not using [ApiController], as soon as we introduce ApiController one of two things happens

1. If we do not prefix with [FromForm] we get a Serialization exception which generates a Bad Request response.
2. If we do prefix FromForm to the IFormFile then it becomes null

In order to get IFormFile to work we need to remove ApiController completely in which case the IFormFile becomes completely propagated correctly.

Copied from original issue: dotnet/aspnetcore#3403

[mkArtakMSFT]

Thanks for contacting us, @mitchellj.
This is because we do not special case the IFormFile type and treat it as a complex type. ApiController conventions for complex types are that by default they're treated as FromBody.
@pranavkm, seems this is a good candidate to be special-cased.

[pranavkm]

1. Do you have your compatibility version set to 2.1? See https://docs.microsoft.com/en-us/aspnet/core/migration/20_21?view=aspnetcore-2.1#changes-to-startup
2. We had an issue specifically with collection of IFormFile - BindingSource for IEnumerable<IFormFile> ApiController parameters on is incorrectly inferred as FromBody #7770 that was fixed in 2.2

[Schmaga]

I ran into the same problem. And strangely, when not using any controller parameter and trying to access or iterate Request.Form.Files the thread would just die without ever responding to the browser or even entering any exception handling blocks that are around the code. Feels kind of weird. My ASP.NET Core version was 2.1.2.

Until this is solved, I was able to help myself with a workaround by explicitly stating the name of the form parameter using the [FromForm] attribute like this:

public async Task<IActionResult> UploadLogo([FromForm(Name = "file")] IFormFile file)        
{
     ...
}

After that for some reason the binding worked. I discovered this behavior by accident after having a hard time getting the file upload from an angular 6 application to work. Hope it helps someone else. The link to the corresponding stackoverflow answer is: https://stackoverflow.com/a/52017637/8007572

[pranavkm]

@Schmaga did the compat switch work for you?

[mitchellj]

Sorry I was out of the country for a while, I will be back in a couple of days and try the compat switches and report back. Compatibility was NOT set previously so that is most likely the issue will confirm though.