Question

I am referring to this article to understand file downloads using C#.

Code uses traditional method to read Stream like

((bytesSize = strResponse.Read(downBuffer, 0, downBuffer.Length)) > 0

How can I divide a file to be downloaded into multiple segments, so that I can download separate segments in parallel and merge them?

using (WebClient wcDownload = new WebClient())
{
    try
    {
        // Create a request to the file we are downloading
        webRequest = (HttpWebRequest)WebRequest.Create(txtUrl.Text);
        // Set default authentication for retrieving the file
        webRequest.Credentials = CredentialCache.DefaultCredentials;
        // Retrieve the response from the server
        webResponse = (HttpWebResponse)webRequest.GetResponse();
        // Ask the server for the file size and store it
        Int64 fileSize = webResponse.ContentLength;

        // Open the URL for download 
        strResponse = wcDownload.OpenRead(txtUrl.Text);
        // Create a new file stream where we will be saving the data (local drive)
        strLocal = new FileStream(txtPath.Text, FileMode.Create, FileAccess.Write, FileShare.None);

        // It will store the current number of bytes we retrieved from the server
        int bytesSize = 0;
        // A buffer for storing and writing the data retrieved from the server
        byte[] downBuffer = new byte[2048];

        // Loop through the buffer until the buffer is empty
        while ((bytesSize = strResponse.Read(downBuffer, 0, downBuffer.Length)) > 0)
        {
            // Write the data from the buffer to the local hard drive
            strLocal.Write(downBuffer, 0, bytesSize);
            // Invoke the method that updates the form's label and progress bar
            this.Invoke(new UpdateProgessCallback(this.UpdateProgress), new object[] { strLocal.Length, fileSize });
        }
    }

Answer 1

you need several threads to accomplish that.
first you start the first download thread, creating a webclient and getting the file size. then you can start several new thread, which add a download range header.
you need a logic which takes care about the downloaded parts, and creates new download parts when one finished.

http://msdn.microsoft.com/de-de/library/system.net.httpwebrequest.addrange.aspx

I noticed that the WebClient implementation has sometimes a strange behaviour, so I still recommend implementing an own HTTP client if you really want to write a “big” download program.

ps: thanks to user svick