How to upload files to Asp.Net MVC 4.0 action running in IIS Express with HttpClient class included in .Net 4.0

Question

I have a C/S application. I implemented the server with Asp.Net MVC 4.0, and the client runs on .Net 4.5.

I have a Controller Action in the server side looks like this:

public JsonResult Upload(string arg1, int arg2)
{
    //do something about arg1 and arg2 here
    ...

    var files = Request.Files;
    if (files.Count > 0)
    {
        foreach(var file in files)
        {
            var ms = new MemoryStream();
            file.InputStream.CopyTo(ms);
            //save it to somewhere
            ...
        }
    }

    ...
}

I created a test html page to test it in browser. It worked as expected.

In the client side, I use HttpClient class and it worked perfectly where no file uploading involved. However after days of researching I still have no luck to resolve this in my debug machine which runs IIS Express. I found that all clues leads to MultipartFormDataContent , but still can't get it work, even if I copy those sample codes, the server side still can't get a thing, all args are empty, and no files is there in the Request.Files . I used to have my own http helper class based on HttpWebRequest , which works for file uploading, but I prefer to use HttpClient in this new project.

So, How do I upload files to the server with HttpClient?

Answer 1

After debugging with Fiddler, comparing raw http message with WinMerge, I found the differences between Firefox and my program:

Firefox (removed some headers to make things simpe):

POST http://localhost:53400/Input/Upload HTTP/1.1
Host: localhost:53400
Content-Type: multipart/form-data; boundary=---------------------------1590871622043
Content-Length: ****

-----------------------------1590871622043
Content-Disposition: form-data; name="arg1"

abc
-----------------------------1590871622043
Content-Disposition: form-data; name="arg2"

3
-----------------------------1590871622043
Content-Disposition: form-data; name="uploadfile"; filename="wave.wav"
Content-Type: audio/wav

//file data here
-----------------------------1590871622043--

My Program with MultipartFormDataContent :

POST http://localhost:53400/Input/Save HTTP/1.1
Content-Type: multipart/form-data; boundary="caac5ea7-8ab4-4682-be40-ecb3ddf3e70a"
Host: localhost:53400
Content-Length: ****

--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=arg1

abc
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=arg2

3
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=uploadfile; filename=wave.wav; filename*=utf-8''wave.wav

//file data here
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a--

The last thing I would notice is that in these Content-Disposition lines, Firefox quotes all values, but my program does not. One could easily assume that it would not matter, but in the end, I found that is the exact cause.

Now that I know the reason, here comes the code that works, as easy as quoting the names:

var multipart = new MultipartFormDataContent();
multipart.Add(new StringContent("abc"), '"' + "arg1" + '"');
multipart.Add(new StringContent("3"), '"' + "arg2" + '"');

// byte[] fileData;
multipart.Add(new ByteArrayContent(fileData), '"' + "uploadfile"+ '"', '"' + "wave.wav" + '"');
//HttpClient http; string url;
var response = await http.PostAsync(url, multipart);
response.EnsureSuccessStatusCode();
//...