How to Upload Multipart Form Data with HttpClient in C# 4.5?

Using C# HttpClient 4.5 to Upload Multipart Form Data

The .NET 4.5 HttpClient class simplifies uploading files and structured data via a single HTTP multipart/form-data request. This guide demonstrates the process:

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

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

This code snippet creates an HttpClient and a MultipartFormDataContent object, defining the boundary for the multipart request. The image data is added as a StreamContent, specifying the form field name ("bilddatei") and filename ("upload.jpg").

The PostAsync method sends the data to the specified URL. The response body is then parsed, and a regular expression extracts the uploaded file's URL. Error handling (e.g., checking response.IsSuccessStatusCode) could be added for robustness.

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