Download file with WebClient or HttpClient?

Question

I am trying to download file from a URL and I have to choose between WebClient and HttpClient. I have referenced this article and several other articles on the internet. Everywhere, it is suggested to go for HttpClient due to its great async support and other .Net 4.5 privileges. But I am still not totally convinced and need more inputs.

I am using below code to download file from internet:

WebClient:

WebClient client = new WebClient();
client.DownloadFile(downloadUrl, filePath);

HttpClient:

using (HttpClient client = new HttpClient())
{        
    using (HttpResponseMessage response = await client.GetAsync(url))
    using (Stream streamToReadFrom = await response.Content.ReadAsStreamAsync())
    {
    }
}

From my perspective, I can see only one disadvantage in using WebClient, that would be the non async call, blocking the calling thread. But what if I am not worried about the blocking of thread or use client.DownloadFileAsync() to leverage the async support?

On the other hand, if I use HttpClient, ain't I loading every single byte of a file into memory and then writing it to a local file? If the file size is too large, won't memory overhead be expensive? Which could be avoided if we use WebClient, since it will directly write to local file and not consume system memory.

So, if performance is my utter priority, which approach should I use for download? I would like to be clarified if my above assumption is wrong, and I am open to alternate approach as well.

Answer 1

You can do it natively with .Net 4.5+. I tried doing it your way and then I just found a method in Intellisense that seemed to make sense.

https://learn.microsoft.com/en-us/dotnet/api/system.io.stream.copytoasync?view=netframework-4.7.2

uri = new Uri(generatePdfsRetrieveUrl + pdfGuid + ".pdf");
HttpClient client = new HttpClient();
var response = await client.GetAsync(uri);
using (var fs = new FileStream(
    HostingEnvironment.MapPath(string.Format("~/Downloads/{0}.pdf", pdfGuid)), 
    FileMode.CreateNew))
{
    await response.Content.CopyToAsync(fs);
}

Answer 2

Here is my approach.

If you are calling a WebApi to get a file, then from a controller method you can use HttpClient GET request and return file stream using FileStreamResult return type.

public async Task<ActionResult> GetAttachment(int FileID)
{
    UriBuilder uriBuilder = new UriBuilder();
    uriBuilder.Scheme = "https";
    uriBuilder.Host = "api.example.com";

    var Path = "/files/download";
    uriBuilder.Path = Path;
    using (HttpClient client = new HttpClient())
    {
        client.BaseAddress = new Uri(uriBuilder.ToString());
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Add("authorization", access_token); //if any
        client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = await client.GetAsync(uriBuilder.ToString());

            if (response.IsSuccessStatusCode)
            {
                System.Net.Http.HttpContent content = response.Content;
                var contentStream = await content.ReadAsStreamAsync(); // get the actual content stream
                return File(contentStream, content_type, filename);
            }
            else
            {
                throw new FileNotFoundException();
            }
    }
}

Answer 3

To use HttpClient on my existing code that used WebClient, I wrote a small extension method to use it on the same way I used DownloadFileTaskAsync on my code.

using (var client = new System.Net.Http.HttpClient()) // WebClient
{
    var fileName = @"C:\temp\imgd.jpg";
    var uri = new Uri("https://yourwebsite.com/assets/banners/Default.jpg");

    await client.DownloadFileTaskAsync(uri, fileName);
}

To use it we can have this extension method:

public static class HttpClientUtils
{
    public static async Task DownloadFileTaskAsync(this HttpClient client, Uri uri, string FileName)
    {
        using (var s = await client.GetStreamAsync(uri))
        {
            using (var fs = new FileStream(FileName, FileMode.CreateNew))
            {
                await s.CopyToAsync(fs);
            }
        }
    }
}

Answer 4

Here’s one way to use it to download a URL and save it to a file: (I am using windows 7, therefore no WindowsRT available to me, so I’m also using System.IO.)

public static class WebUtils
{
    private static Lazy<IWebProxy> proxy = new Lazy<IWebProxy>(() => string.IsNullOrEmpty(Settings.Default.WebProxyAddress) ? null : new WebProxy { Address = new Uri(Settings.Default.WebProxyAddress), UseDefaultCredentials = true });

    public static IWebProxy Proxy
    {
        get { return WebUtils.proxy.Value; }
    }

    public static Task DownloadAsync(string requestUri, string filename)
    {
        if (requestUri == null)
            throw new ArgumentNullException(“requestUri”);

        return DownloadAsync(new Uri(requestUri), filename);
    }

    public static async Task DownloadAsync(Uri requestUri, string filename)
    {
        if (filename == null)
            throw new ArgumentNullException("filename");

        if (Proxy != null)
            WebRequest.DefaultWebProxy = Proxy;

        using (var httpClient = new HttpClient())
        {
            using (var request = new HttpRequestMessage(HttpMethod.Get, requestUri))
            {
                using (Stream contentStream = await (await httpClient.SendAsync(request)).Content.ReadAsStreamAsync(), stream = new FileStream(filename, FileMode.Create, FileAccess.Write, FileShare.None, Constants.LargeBufferSize, true))
                {
                    await contentStream.CopyToAsync(stream);
                }
            }
        }
    }
} 

Note that code is saving the address of the proxy server I use (at work) in a setting, and using that if such setting is specified. Otherwise, it should tell you all you need to know regarding using the HttpClient beta to download and save a file.