Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I am developing some REST API with C# and Net Core
I have a function in my repository which accepts a parameter of type IFormFile .

public async Task<bool> UploadFile(IFormFile file)
    // do some stuff and save the file to azure storage
This function is called by a controller method which pass it the uploaded file 
public class FileController : Controller
    public async Task<IActionResult> UploadDoc(IFormFile file
        // Call the repository function to save the file on azure
        var res = await documentRepository.UploadFile(file);
Now I have another function that calls an external API which returns a file as a byte array. I'd like to save this byte array using the repository.UploadFile method but I can't cast the byte array object to IFormFile.

Is it possible?
You can convert the byte array to a MemoryStream:
var stream = new MemoryStream(byteArray);
..and then pass that to the constructor of the FromFile class:
IFormFile file = new FormFile(stream, 0, byteArray.Length, "name", "fileName");
                It error like after I tried your code, please kindly give some advise.  'Could not load type 'Microsoft.AspNetCore.Http.Internal.FormFile' from assembly 'Microsoft.AspNetCore.Http  thanks you.
– Mr.Buntha Khin
                Apr 30, 2021 at 9:21
Your repo shouldn't be using IFormFile. That's an abstraction that only applies to one particular method of HTTP file transfer (namely a multipart/form-data encoded request body). Something like your repo should have no knowledge of the source of the file (HTTP), nor how it was transmitted (multipart/form-data vs application/json for example).
Instead, you should use Stream for your param. In your UploadDoc action, then, you can simply do:
using (var stream = file.OpenReadStream())
    await documentRepository.UploadFile(stream);
And, where you have just a byte array:
using (var stream = new MemoryStream(byteArray))
    await documentRepository.UploadFile(stream);
You might also consider adding an overload of UploadFile that takes a byte[], as creating a new memory stream from a byte array just to have a stream is a waste of resources. However, a byte[] has to be handled differently than a Stream, so it may require some duplication of logic to go that route. You'll need to evaluate the tradeoffs.
Create a new MemoryStream based on the byte array.
Create a new FormFile object based on the MemoryStream.
Make sure to append the ContentDisposition header, otherwise you will be unable to operate your FormFile object as a C# exception will be thrown.
The complete code:
        using (var stream = new MemoryStream(byteArray))
            var file = new FormFile(stream, 0, byteArray.Length, name, fileName)
                Headers = new HeaderDictionary(),
                ContentType = contentType,
            System.Net.Mime.ContentDisposition cd = new System.Net.Mime.ContentDisposition
                FileName = file.FileName
            file.ContentDisposition = cd.ToString();
                Does this only work in the controllers? I'm trying to do this in a class library, and no matter what NuGet package I install, FormFile is not part of the assembly.  I've tried Microsoft.AspNetCore.Http.FormFile, and Microsoft.AspNetCore.Http.Internal.FormFile.  I'm currently still on .Net Core 3.1.
– King Wilder
                Nov 22, 2021 at 22:04
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.