Upload Binary Data using HTTP POST is a practical and efficient method for transferring files between client and server applications. In this blog, you’ll learn how to upload binary data from a web client to a server endpoint using C# and ASP.NET. This approach is particularly valuable when enabling communication between different technologies—such as posting an image from a Flash application to an ASP.NET backend—making cross-platform file transfers smooth and reliable.

Upload Binary Data using HTTP POST in C#

Here’s how you can read a binary file from a file upload control and post it to a target URL using the HttpWebRequest class:

private bool UploadFile(string PostURL)
{
    try
    {
        int contentLength = fileUpload.PostedFile.ContentLength;
        byte[] data = new byte[contentLength];
        fileUpload.PostedFile.InputStream.Read(data, 0, contentLength);

        // Prepare web request...
        HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(PostURL);
        webRequest.Method = "POST";
        webRequest.ContentType = "application/octet-stream"; //Update MIME type
        webRequest.ContentLength = data.Length;
        using (Stream postStream = webRequest.GetRequestStream())
        {
            // Send the data.
            postStream.Write(data, 0, data.Length);
            postStream.Close();
         }
         return true;
    }
    catch (Exception ex)
    {
         //Log exception here...
         return false;
     }
}

Tip: Always validate and sanitize uploaded data before processing it on the server.

Handling Binary Data on the Receiving Server

On the receiving side (target URL), you can read the raw binary stream from the HTTP request like this:

byte[] Image = ReadFully(Request.InputStream);

.................

public static byte[] ReadFully(Stream input)
{
     byte[] buffer = new byte[16 * 1024];
     using (MemoryStream ms = new MemoryStream())
     {
         int read;
         while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
         {
             ms.Write(buffer, 0, read);
         }
         return ms.ToArray();
     }
}

Once retrieved, you can process or store the file as needed (e.g., saving the image to disk or a database).

Use Cases & Scenarios

• Cross-platform communication (e.g., Flash or JavaScript sending files to a .NET backend)

• Mobile or desktop clients posting captured media files to a web API

• Internal services exchanging binary content without complex form-data encoding

Best Practices

• Use HTTPS to encrypt data in transit

• Validate MIME types and file extensions

• Limit file sizes to prevent abuse

• Avoid multipart/form-data unless you’re sending additional fields; application/octet-stream is simpler and cleaner for raw binary uploads