Webapi Cannot Parse Multipart/Form-Data Post

API controller POST method multipart/form-data using boundary get message inside the body

There isn't built-in support of multi-part/form-data Media Type in .Net5 by default. So, the input formatter should be attached to the MvcBuilder.

Considering the fact that you can't manipulate client-side, ApiMultipartFormDataFormatter which enables this type of input formatting can be utilized.

1. Add the Package:

Install-Package ApiMultipartFormDataFormatter -Version 3.0.0

2. Configure the Formatter in Startup.cs

   public void ConfigureServices(IServiceCollection services)
   {
       services.AddControllers(options =>
       {
           options.InputFormatters.Add(new MultipartFormDataFormatter());
       });
   }
   

3. Assuming the mentioned well formed json is something like below class:

   public class CustomContent
   {
       public string Name { get; set; }
   }
   

   So, we need to wrap it up into another class that contains this as a parameter.
   Note: The library doesn't support deserialization by this moment So, a getter-only property is added to the model which returns the deserialized object.

   public class ViewModel
   {
       // Equivalent to ZZZZZZZZZZ
       public string SerializedContent { get; set; }
       public CustomContent Content => !string.IsNullOrEmpty(SerializedContent)
           ? JsonConvert.DeserializeObject<CustomContent>(SerializedContent)
           : null;
   }
   

4. Reform the Action to accept the wrapper model.

   [HttpPost]
   [Route("[action]")]
   public IActionResult Parse(ViewModel vm)
   {            
       return Ok($"Received Name: {vm?.Content?.Name}");
   }
   

The working cURL request of the corresponding example is:

curl --location --request POST 'http://localhost:25599/api/MultiPart/Parse' 

\
--header 'Content-Type: multipart/form-data; boundary=boundary' \
--data-raw '--boundary
Content-Disposition: form-data; name="SerializedContent"
Content-Type: application/json
Content-Length: 100

{
    "Name" : "Foo"
}
--boundary--'

The response should be equal to Received Name: Foo.

How to set up a Web API controller for multipart/form-data

I normally use the HttpPostedFileBase parameter only in Mvc Controllers. When dealing with ApiControllers try checking the HttpContext.Current.Request.Files property for incoming files instead:

[HttpPost]
public string UploadFile()
{
    var file = HttpContext.Current.Request.Files.Count > 0 ?
        HttpContext.Current.Request.Files[0] : null;

    if (file != null && file.ContentLength > 0)
    {
        var fileName = Path.GetFileName(file.FileName);

        var path = Path.Combine(
            HttpContext.Current.Server.MapPath("~/uploads"),
            fileName
        );

        file.SaveAs(path);
    }

    return file != null ? "/uploads/" + file.FileName : null;
}

ASP.NET How read a multipart form data in Web API?

This should help you get started:

 var uploadPath = HostingEnvironment.MapPath("/") + @"/Uploads";
 Directory.CreateDirectory(uploadPath);
 var provider = new MultipartFormDataStreamProvider(uploadPath);
 await Request.Content.ReadAsMultipartAsync(provider);

 // Files
 //
 foreach (MultipartFileData file in provider.FileData)
 {
     Debug.WriteLine(file.Headers.ContentDisposition.FileName);
     Debug.WriteLine("File path: " + file.LocalFileName);
 }

 // Form data
 //
 foreach (var key in provider.FormData.AllKeys)
 {
     foreach (var val in provider.FormData.GetValues(key))
     {
          Debug.WriteLine(string.Format("{0}: {1}", key, val));
     }
 }

multipart/form-data post api not working on hcloud

In that action(Post method) i am sending data in string format , on server side(hcloud) url scanner refused the action because some special character.

Now passing the data in josn format, it works fine

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