Resource leak by not closing the client

The HTTP client is not explicitly closed, leading to possible leaks. The JAX-RS ClientBuilder is dynamically resolved, which in my case uses RestEasy instead of Jersey. In that case it uses a finalizer to log a warning that the client wasn’t closed, which is a requirement of the API. It would also be nice if these were pooled.

These issues makes it a little uncomfortable to use this SDK in a production with a reasonable email volume.

 * Client is the main entry point to the fluent API used to build and execute client
 * requests in order to consume responses returned.
 * <p/>
 * Clients are heavy-weight objects that manage the client-side communication
 * infrastructure. Initialization as well as disposal of a {@code Client} instance
 * may be a rather expensive operation. It is therefore advised to construct only
 * a small number of {@code Client} instances in the application. Client instances
 * must be {@link #close() properly closed} before being disposed to avoid leaking
 * resources.

https://github.com/sargue/mailgun/blob/abd667ceac159ae0d208b7e1d571cca8959c4bc7/src/main/java/net/sargue/mailgun/Mail.java#L143-L158

[ben-manes]

@kopax, I was using simpleJavaMail, which is a really excellent library. However, the SMTP endpoint is very flaky at scale and requires retries. Mailgun’s support wasn’t helpful except acknowledging that they do some nasty things in their load balancer to cycle IPs for defensive reasons. They said the HTTP api was faster and more robust, so I had to port over.

I wrote an Email class similar to @sargue’s MailBuilder class to aggregate the contents into a multipart. This goes to a Retrofit interface, which is backed by a shared OkHttp client. Not much work thanks to this library and the api docs to clarify their endpoint.

mailgun.zip

[ben-manes]

My requirements are the same and not bulk mail, but it amounts to around 800k/month. This is for example a company sending an invoice to their customer.

I did not include the code using this client, which adds those to the Email class, invokes the Mailgun.send method, and handles all of the metrics / retrials / etc. You would use this as,

Email email = new Email()
    .from(...).to(...)
    .text("Hello World")
    .attachment(filename, file, mediaType);
mailgun.send(domain, email);

Anyone is welcome to formalize into a reusable client, like @sargue’s nice library. It was not much work on my part, Retrofit does all the heavy lifting and this is just an example of how quickly one can bootstrap a usage.