safe-http-client

SafeHttpClient.cs

/// <summary>
/// This static wrapper around HttpClient allows to avoid issue with exhausting
/// outgoing sockets via reusing single instance of that. Additionally, it addresses
/// issue caused by resusing connections -- skipping DNS changes via limiting connection
/// lifespan.
/// See for details:
/// https://blogs.msdn.microsoft.com/shacorn/2016/10/21/best-practices-for-using-httpclient-on-services/
/// http://byterot.blogspot.ru/2016/07/singleton-httpclient-dns.html
/// </summary>
public class SafeHttpClient
{
    private static class ServicePointManagerConfigurator
    {
	private static object _syncRoot = new object();
	private static HashSet<string> _configuredHosts = new HashSet<string>();

	public static void EnsureConfigured(Uri uri)
	{
	    string host = uri.Host;

	    lock (_syncRoot)
	    {
		if (!_configuredHosts.Contains(host))
		{
		    Trace.WriteLine($"Configure {host} host to limit connection lifetime to pick up DNS changes");

		    // limit connection lifespan to DNS refresh timeout (2 minutes)
		    ServicePointManager.FindServicePoint(uri).ConnectionLeaseTimeout = ServicePointManager.DnsRefreshTimeout;

		    _configuredHosts.Add(host);
		}
	    }
	}
    }

    private HttpClient _httpClient = new HttpClient();

    public static readonly SafeHttpClient Instance = new SafeHttpClient();

    private SafeHttpClient() { }

    public Task<HttpResponseMessage> SendAsync(HttpRequestMessage request)
    {
	ServicePointManagerConfigurator.EnsureConfigured(request.RequestUri);

	return _httpClient.SendAsync(request);
    }
}