C# File Upload: Web Method Not Accepting Form Data Sent Along With Uploaded File

Question

My web method:

    [HttpPost]
    public async Task<IActionResult> UploadFile2(IFormFile file, int idPackage)
    {
        string output = $"{file.FileName} - {file.Length} - {idPackage}";
        return Ok(output);
    }

My Postman request:

POST https://localhost:7006/api/upload/UploadFile2 HTTP/1.1
User-Agent: PostmanRuntime/7.29.2
Accept: */*
Postman-Token: fc51918c-f03f-4e29-9726-6a5159dcb035
Host: localhost:7006
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Content-Type: multipart/form-data; boundary=--------------------------368567246425722572627984
Content-Length: 363

----------------------------368567246425722572627984
Content-Disposition: form-data; name="idPackage"

1247
----------------------------368567246425722572627984
Content-Disposition: form-data; name="file"; filename="dummy.dat"
Content-Type: application/octet-stream

dummy data from the dummy file
----------------------------368567246425722572627984--

The file parameter correctly receives the uploaded file as input.

The idPackage parameter remains the default value of 0, even though I am sending along 1247 for this value.

What could possibly be causing this?

Update 1

This very same web request does work in another project of mine, I just found out.

It has to be some sort of server side setting, related to how requests are handled, although I currently have no idea which one.

Update 2

I figured it had to be the Newtonsoft JSON resolver configuration that I have in my other project.

Turns out that wasn't it. Still no idea what it could be, then.

Is there any way of debugging how C# processes a web request under the hood?

K. A. · Accepted Answer · 2022-11-07 20:39:52Z

1

Maybe I'm going to say something stupid, but try to create a DTO class

DTO:

public class UploadFileDTO 
{
     public IFormFile File { get; set; } 
     public int IdPackage { get; set; }
}

Method

    [HttpPost]
    public async Task<IActionResult> UploadFile2([FromForm] UploadFileDTO input)
    {
        string output = $"{input.File.FileName} - {input.File.Length} - {input.IdPackage}";
        return Ok(output);
    }

Source: How to upload an IFormFile with additional parameters

answered Nov 7, 2022 at 20:39

K. A.

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1 Comment

Jay Over a year ago

Coincidentally, I had just found the same SO thread. I could do that, and it might solve my problem. However, that still leaves me with the question of why it does work in an older production project, but not in a newer sandbox project. It's insufferable not to know the cause. Imagine updating your .NET version and your Nuget packages, and then it breaks your current upload implementation. I'll definitely give the DTO-way a shot, though.

Jay · Accepted Answer · 2022-11-07 21:02:06Z

0

I just solved this by adding the [FromForm] attribute in front of the extra parameter.

[HttpPost]
public async Task<IActionResult> UploadFile2(IFormFile file, [FromForm]int idPackage)
{
    string output = $"{file.FileName} - {file.Length} - {idPackage}";
    return Ok(output);
}

Why this didn't need to be done in my older production project, but not my newer sandbox project... I do not know.

I'm guessing they changed something with newer .NET versions and/or Nuget packages.

I found the solution by coming across this guy's code snippet.

answered Nov 7, 2022 at 21:02

Jay

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