How do I download a large file (via HTTP) in .NET?

Question

I need to download a large file (2 GB) over HTTP in a C# console application. Problem is, after about 1.2 GB, the application runs out of memory.

Here's the code I'm using:

WebClient request = new WebClient();
request.Credentials = new NetworkCredential(username, password);
byte[] fileData = request.DownloadData(baseURL + fName);

As you can see... I'm reading the file directly into memory. I'm pretty sure I could solve this if I were to read the data back from HTTP in chunks and write it to a file on disk.

How could I do this?

Answer 1

If you use WebClient.DownloadFile you could save it directly into a file.

Answer 2

The WebClient class is the one for simplified scenarios. Once you get past simple scenarios (and you have), you'll have to fall back a bit and use WebRequest.

With WebRequest, you'll have access to the response stream, and you'll be able to loop over it, reading a bit and writing a bit, until you're done.

From the Microsoft documentation:

We don't recommend that you use WebRequest or its derived classes for new development. Instead, use the System.Net.Http.HttpClient class.

Source: docs.microsoft.com/WebRequest

---

Example:

public void MyDownloadFile(Uri url, string outputFilePath)
{
    const int BUFFER_SIZE = 16 * 1024;
    using (var outputFileStream = File.Create(outputFilePath, BUFFER_SIZE))
    {
        var req = WebRequest.Create(url);
        using (var response = req.GetResponse())
        {
            using (var responseStream = response.GetResponseStream())
            {
                var buffer = new byte[BUFFER_SIZE];
                int bytesRead;
                do
                {
                    bytesRead = responseStream.Read(buffer, 0, BUFFER_SIZE);
                    outputFileStream.Write(buffer, 0, bytesRead);
                } while (bytesRead > 0);
            }
        }
    }
}

Note that if WebClient.DownloadFile works, then I'd call it the best solution. I wrote the above before the "DownloadFile" answer was posted. I also wrote it way too early in the morning, so a grain of salt (and testing) may be required.