Sending file in API request .NET

Question

I have an enpoint that I send request via Postman form-data. Request has 2 keys.

message : string
file: File

this works ok. So, I want to send the same request in C# code. In c# I just need to choose file from local, somehow convert it to proper format, assign it to file property in request Model, I mean I can not change the logic how request is sent. I must not write additional logic to HttpRequest or MultipartFormDataContent etc (I can not even see this part how it is sent). Just need to add Model to this request body. I have model RequestModel

public class RequestModel
{
[JsonProperty("message")]
public string Message {get; set; }

[JsonProperty("file")]
public whateverType File {get; set; }
}

message part works, so I need to assign local file to File property. how can I do that. I tried almost everything but it does not work. Thanks.

Does this answer your question? How to upload files in asp.net core? — Neil
– Neil, Commented Feb 5, 2022 at 16:54
This SO thread is similar for asp.net core: stackoverflow.com/questions/54411250/… — Steve Wong
– Steve Wong, Commented Feb 5, 2022 at 16:57
in .net 6. these answers do not solve my problem. simply I need to convert the way postman converts. when i choose file in postman how it converts this file? what is the equivalent of converted type in c#? — sultanriveriere
– sultanriveriere, Commented Feb 5, 2022 at 17:09

AliReza Sabouri · Accepted Answer · 2022-02-05 19:05:47Z

0

You don't need to keep the file in your model.

this is an example to post a model just by knowing the file name.

var model = new RequestModel();

// ... fill the model with some data
model.Message = "test";
model.File = @"c:\test.jpg";

using var httpClient = new HttpClient();
{
    var form = new MultipartFormDataContent();
    form.Add(new StringContent(model.Message), nameof(RequestModel.Message));

    var bytes = File.ReadAllBytes(model.File);
    form.Add(new ByteArrayContent(bytes, 0, bytes.Length), "profile_pic", "hello1.jpg");
    var response = await httpClient.PostAsync("PostUrl", form);
    response.EnsureSuccessStatusCode();
    var sd = response.Content.ReadAsStringAsync().Result; // you should use await if your method is async ...
}

public class RequestModel
{
    public string Message { get; set; }

    public string File { get; set; } // simply use file-path
}

edited Feb 5, 2022 at 19:05

answered Feb 5, 2022 at 17:10

AliReza Sabouri

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19 Comments

sultanriveriere Over a year ago

I choose file from local directory (I do not need [FromForm]) and the main part is the body of this method.

sultanriveriere Over a year ago

i have tried this: error:Could not create an instance of type Microsoft.AspNetCore.Http.IFormFile.

sultanriveriere Over a year ago

ContentType = '((Microsoft.AspNetCore.Http.FormFile)model.attachment).ContentType' threw an exception of type 'System.NullReferenceException'

AliReza Sabouri Over a year ago

You should create an instance of FormFile not IFormFile

sultanriveriere Over a year ago

yep, i'm creating an instance of FormFile

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