Http MultipartFormDataContent

c#, filestream, httpclient, multipartform-data, post

Solution

Posting MultipartFormDataContent in C# is simple but may be confusing the first time. Here is the code that works for me when posting a .png .txt etc.

// 2. Create the url 
string url = "https://myurl.com/api/...";
string filename = "myFile.png";
// In my case this is the JSON that will be returned from the post
string result = "";
// 1. Create a MultipartPostMethod
// "NKdKd9Yk" is the boundary parameter

using (var formContent = new MultipartFormDataContent("NKdKd9Yk"))
{
    formContent.Headers.ContentType.MediaType = "multipart/form-data";
    // 3. Add the filename C:\\... + fileName is the path your file
    Stream fileStream = System.IO.File.OpenRead("C:\\Users\\username\\Pictures\\" + fileName);
    formContent.Add(new StreamContent(fileStream), fileName, fileName);

    using (var client = new HttpClient())
    {
        // Bearer Token header if needed
        client.DefaultRequestHeaders.Add("Authorization", "Bearer " + _bearerToken);
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("multipart/form-data"));

        try
        {
            // 4.. Execute the MultipartPostMethod
            var message = await client.PostAsync(url, formContent);
            // 5.a Receive the response
            result = await message.Content.ReadAsStringAsync();                
        }
        catch (Exception ex)
        {
            // Do what you want if it fails.
            throw ex;
        }
    }    
}

// 5.b Process the reponse Get a usable object from the JSON that is returned
MyObject myObject = JsonConvert.DeserializeObject<MyObject>(result);

In my case I need to do something with the object after it posts so I convert it to that object with JsonConvert.

Problem

I have been asked to do the following in C#: ``` /** * 1. Create a MultipartPostMethod * 2. Construct the web URL to connect to the SDP Server * 3. Add the filename to be attached as a parameter to the MultipartPostMethod with parameter name "filename" * 4. Execute the MultipartPostMethod * 5. Receive and process the response as required * / ``` I have written some code that has no errors, however, the file is not attached. Can someone have a look at my C# code to see if I have written the code incorrectly? Here is my code: ``` var client = new HttpClient(); const string weblinkUrl = "http://testserver.com/attach?"; var method = new MultipartFormDataContent(); const string fileName = "C:\file.txt"; var streamContent = new StreamContent(File.Open(fileName, FileMode.Open)); method.Add(streamContent, "filename"); var result = client.PostAsync(weblinkUrl, method); MessageBox.Show(result.Result.ToString()); ```

Original source

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