rspec/rules/S4470/rule.adoc

It is well documented that while ``HttpClient`` implements ``IDisposable``, it is intended to be reused, which means not wrapping it in a ``using`` statement.

As noted in the documentation:
____
HttpClient is intended to be instantiated once and re-used throughout the life of an application. Instantiating an HttpClient class for every request will exhaust the number of sockets available under heavy loads. This will result in SocketException errors.
____

This rule raises an issue when an instance of a ``HttpClient`` is created within a ``using`` statement.


== Noncompliant Code Example

----
namespace MyLibrary
{
    public class Foo
    {
        public async Task Bar()
        {
            using (var client = new HttpClient()) // Noncompliant
            {
                await client.GetAsync("https://www.sonarqube.org/");
            }
        }
    }
}
----


== Compliant Solution

----
namespace MyLibrary
{
    public class Foo
    {
        private static HttpClient client = new HttpClient();

        public async Task Bar()
        {
            await client.GetAsync("https://www.sonarqube.org/");
        }
    }
}
----


== See

* https://msdn.microsoft.com/en-us/library/system.net.http.httpclient(v=vs.110).aspx?f=255&mspperror=-2147217396#Anchor_5[HttpClient Class]
* https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/calling-a-web-api-from-a-net-client[Call a Web API From a .NET Client (C#)]
* https://github.com/mspnp/performance-optimization/blob/master/ImproperInstantiation/docs/LoadTesting.md[Microsoft Patterns & Practices]