Bug: The way httpclient is being used in the MandrillApi could lead to several issues

[codingmoh]

Hello there,

while browsing through the source code I've noticed, that the httpclient is being instantiated in the constructor of the MandrillApi, this could be causing several issues, like socket exhaustion and outdated dns configuration.

From MSDN Documentation:

While this class implements IDisposable, declaring and instantiating it within a using statement is not preferred because when the HttpClient object gets disposed of, the underlying socket is not immediately released, which can lead to a socket exhaustion problem. For more information about this issue, see the blog post You're using HttpClient wrong and it's destabilizing your software.

See: https://docs.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/use-httpclientfactory-to-implement-resilient-http-requests#issues-with-the-original-httpclient-class-available-in-net-core
And here: https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/

Another potential issue I've discovered is that the HttpClient is being used without a retry policy. I/O Operations and request (esp. HttpRequests) could always fail due to various reasons. This could be easily solved by using the polly library:
https://docs.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/implement-http-call-retries-exponential-backoff-polly

Suggestion for fixing this:

• Either inject httpclientfactory or httpclient
• Use Polly library to allow automatic retries