Using HttpClient to Download a File with GetStreamAsync

I recently wanted to download a set of large files, normally I would use a bash script to do this, but there were some complications around the file and the directory structure that made it a bit more challenging for me in bash.

I decided to use C# instead. I was surprised that it was not so obvious how to do this. There are many methods on the HttpClient, but which should be used. So I wrote this post to remind my future self when I have forgotten how to do it.

I will start with what I think is the better way, but I haven’t run the memory tests needed to verify that.

HttpClient.GetStreamAsync

With the first approach, I use the HttpClient.GetStreamAsync method to get a Stream of the file I’m downloading, and then pass that stream to a FileStream to write the file to disk.

 1var httpClient = new HttpClient();
 2
 3string fileToDownload = "https://upload.wikimedia.org/wikipedia/commons/0/0e/Microsoft_.NET_logo.png"; 
 4
 5string fileName = fileToDownload.Split('/').Last();
 6
 7using var downloadStream = await httpClient.GetStreamAsync(fileToDownload);
 8using var fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write);
 9
10await downloadStream.CopyToAsync(fileStream);
11await fileStream.FlushAsync();
12fileStream.Close();

HttpClient.GetByteArrayAsync

Another approach is to read all the bytes of the file into memory and then write them to disk. If the stream works the way I think it does, then this is not as efficient as the previous approach.

1var httpClient = new HttpClient();
2
3string fileToDownload = "https://upload.wikimedia.org/wikipedia/commons/0/0e/Microsoft_.NET_logo.png"; 
4
5string fileName = fileToDownload.Split('/').Last();
6
7byte[] fileBytes = await httpClient.GetByteArrayAsync(fileToDownload);
8await File.WriteAllBytesAsync(fileName, fileBytes);

There other ways to do this, you could also using .GetAsync and access the response and content within it, but I think that is more complicated than it needs to be.