How to Upload Multipart/Form-Data Using HttpClient in C# 4.5?

Efficient Multipart/Form-Data Uploads using C# 4.5 and HttpClient

This guide demonstrates a straightforward method for uploading multipart/form-data using HttpClient in the .NET Framework 4.5. Many developers find readily available examples for this task lacking, so this solution provides a clear and practical approach.

Leveraging MultipartFormDataContent and HttpClient:

The core component is the MultipartFormDataContent object. This object allows you to structure your data as a multipart/form-data request, which is essential for uploading files. In this example, a binary file (represented as a byte array) is uploaded as a StreamContent with the name "bilddatei".

HTTP Request and Response Handling:

Once the MultipartFormDataContent is populated, it's sent via an asynchronous POST request using HttpClient.PostAsync. The server's response is then processed to extract relevant information—in this case, a URL.

Here's an example code snippet illustrating the process:

public static async Task<string> UploadFile(byte[] image)
{
    using (var client = new HttpClient())
    {
        using (var content = new MultipartFormDataContent("Upload----" + DateTime.Now.ToString(CultureInfo.InvariantCulture)))
        {
            content.Add(new StreamContent(new MemoryStream(image)), "bilddatei", "upload.jpg");

            using (var message = await client.PostAsync("http://www.directupload.net/index.php?mode=upload", content))
            {
                var responseBody = await message.Content.ReadAsStringAsync();
                return !string.IsNullOrEmpty(responseBody) ? Regex.Match(responseBody, @"http://\w*\.directupload\.net/images/\d*/\w*\.[a-z]{3}").Value : null;
            }
        }
    }
}

This concise code shows how to create the multipart content, execute the HTTP request, and parse the response to retrieve the uploaded file's URL. This provides a robust and efficient solution for handling multipart/form-data uploads in C# 4.5 using HttpClient.

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