WebAPI File Uploading - Without writing files to disk

Question

All the documentation / tutorials / questions about processing a file uploaded using FormData to a ASP.NET WebAPI handler use MultipartFormDataStreamProvider to process the multipart stream to split it into the relevant form fields and files.

var root = HttpContext.Current.Server.MapPath("~/App_Data");
var provider = new MultipartFormDataStreamProvider(root);

await Request.Content.ReadAsMultipartAsync(provider);

foreach (MultipartFileData file in provider.FileData)
{
   // File
}

However, the files are automatically written to a directory during processsing.

It seems a lot of hassle when I could just use HttpContext.Current.Request.Files[0].InputStream to access a given file stream directly in memory.

How can WebAPI just access the file stream directly without the IO overhead of using MultipartFormDataStreamProvider?

Official tutorial: http://www.asp.net/web-api/overview/advanced/sending-html-form-data,-part-2

Solution

Solved:

Use the existing simple MultipartMemoryStreamProvider. No custom classes or providers required. This differers from the duplicate question which solved the solution by writing a custom provider.

Then use it in a WebAPI handler as so:

public async Task<IHttpActionResult> UploadFile()
{
    if (!Request.Content.IsMimeMultipartContent())
    {
        return StatusCode(HttpStatusCode.UnsupportedMediaType);
    }        
  
    var filesReadToProvider = await Request.Content.ReadAsMultipartAsync();
    
    foreach (var stream in filesReadToProvider.Contents)
    {
        var fileBytes = await stream.ReadAsByteArrayAsync();
    }
    return StatusCode(HttpStatusCode.OK);
}

Comments

[Jon Susiak]

I think This Question should answer your needs.

[simbolo]

Thanks @JonSusiak - I wish I found that a few hours ago, I ended up doing the exact same thing by examining the source code or MultipartFormDataStreamProvider and using the MultipartStreamProvider provider to give me the file upload in a MemoryStream rather than writing it to disk. Was just getting round to posting the answer.

[Merenzo]

@simbolo - why didn't you use HttpContext.Current.Request.Files[0].InputStream? Could you explain the disadvantage?

[xdiegom]

Microsoft has a really good example for how to upload files: docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/…

[guiomie]

Where can I find IHttpActionResult ?

[simbolo]

@guiomie simple google: msdn.microsoft.com/en-us/library/…

[mbx-mbx]

Could this code please be updated so that it compiles? Not all code paths return a value. Thanks.

[George Harnwell]

@Magrangs - you simply need to return a Http Result such as return Ok();

[Henrik Høyer]

end the method with: return Request.CreateResponse(HttpStatusCode.OK);

[Unbreakable]

Can I simply send even big files to this function, or I need to define some boundary and other fancy stuff in the client side which sends the file?

[A X]

This doesn't work though - it gets screwed up from an encoding perspective

[David]

With asp.net 4.7 I am still getting exception Exception. Exception type full name: System.NullReferenceException.] - [System.NullReferenceException: Object reference not set to an instance of an object

[Brett JB]

Hi @simbolo, I am also wanting to do this and have managed to extract the file data using your approach. I also have additional form data as well though. Do you have any ideas how I can get to that? The filestoreadprovider is a collection of HttpContent objects, which I have managed to make into a list and walk through, but I cant seem to get at the data. Any Ideas? (Before I throw this out as seperate question..) Thanks...

[Brent Woodle]

The MultipartMemoryStreamProvider doesn't have an API for accessing form data that is included in the request like MultipartFormDataStreamProvider.FormData does.