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Upload a File - Rest API - C#

  • May 27, 2025
  • 1 reply
  • 42 views
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I'm trying to use .net core 3, to invoke the Box REST API, to upload a small file.

The .net core code is based on the information provided on: Upload a file.

I haven't been successful so far, and all my attempts have resulted in a 400: Bad Request error.

 

This is code snippet:

 

var client = _clientFactory.CreateClient("box-upload");

var dto = new UploadFileContent() {
 attributes = new UploadFileContentAttributes() {
  name = fileDto.file.FileName,
   parent = new UploadFileContentParent() {
    id = fileDto.folderId
   }
 }
};
var content = new MultipartFormDataContent();
content.Headers.ContentType = MediaTypeHeaderValue.Parse("multipart/form-data");

var jsonContent = new StringContent(JsonConvert.SerializeObject(dto), Encoding.UTF8, "application/json");
jsonContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
content.Add(jsonContent, "attributes");

if (!string.IsNullOrWhiteSpace(token))
 client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(BearerToken, token);

var streamContent = new StreamContent(fileDto.file.OpenReadStream());
content.Add(streamContent, "file");

var response = await client.PostAsync(url, content);

 

What am i missing?

Thank you in advance.

 

 

    1 reply

    C
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    • community-manager
    • Author
    • Known Participant
    • 34746 replies
    • May 27, 2025

    There were a few details missing, the code is now working:

     

     

    var token = await GetToken();

if (string.IsNullOrWhiteSpace(token)) throw new Exception("Could not obtain Token");

var client = _clientFactory.CreateClient("box-upload");

using var content = new MultipartFormDataContent();
var attributes = new UploadFileContentAttributes {
 name = fileDto.file.FileName,
  parent = new UploadFileContentParent {
   id = fileDto.folderId
  }
};

using var jsonContent =
 new StringContent(JsonConvert.SerializeObject(attributes), Encoding.UTF8, "application/json");
content.Add(jsonContent, "attributes");

client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(BearerToken, token);

byte[] data;
using(var br = new BinaryReader(fileDto.file.OpenReadStream())) {
 data = br.ReadBytes((int) fileDto.file.OpenReadStream().Length);
}

using var bytes = new ByteArrayContent(data);

content.Add(bytes, "file", fileDto.file.FileName);

var response = await client.PostAsync(url, content);

if (!response.IsSuccessStatusCode) throw new Exception(response.ToString());

var jsonString = await response.Content.ReadAsStringAsync();

     


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