The `MailerImpl` gains a few new fields (`retryBase`, & `retryMax`). These are used with `core.RetryBackoff` in `reconnect()` to implement exponential backoff in a reconnect attempt loop. Both `expiration-mailer` and `notify-mailer` are modified to add CLI args for these 2 flags and to wire them into the `MailerImpl` via its `New()` constructor.
In `MailerImpl`'s `SendMail()` function it now detects when `sendOne` returns an `io.EOF` error indicating that the server closed the connection unexpectedly. When this case occurs `reconnect()` is invoked. If the reconnect succeeds then we invoke `sendOne` again to try and complete the message sending operation that was interrupted by the disconnect.
For integration testing purposes I modified the `mail-test-srv` to support a `-closeChance` parameter between 0 and 100. This controls what % of `MAIL` commands will result in the server immediately closing the client connection before further processing. This allows us to simulate a flaky mailserver. `test/startservers.py` is modified to start the `mail-test-srv` with a 35% close chance to thoroughly test the reconnection logic during the existing `expiration-mailer` integration tests. I took this as a chance to do some slight clean-up of the `mail-test-srv` code (mostly removing global state).
For unit testing purposes I modified the mailer `TestConnect` test to abstract out a server that can operate similar to `mail-test-serv` (e.g. can close connections artificially).
This is testing a server that **closes** a connection, and not a server that **goes away/goes down**. E.g. the `core.RetryBackoff` sleeps themselves are not being tested. The client is disconnected and attempts a reconnection which always succeeds on the first try. To test a "gone away" server would require a more substantial rewrite of the unit tests and the `mail-test-srv`/integration tests. I think this matches the experience we have with MailChimp/Mandril closing long lived connections.
This creates a new server, 'mail-test-srv', which is a simplistic SMTP
server that accepts mail and can report the received mail over HTTP.
An integration test is added that uses the new server to test the expiry
mailer.
The FAKECLOCK environment variable is used to force the expiry mailer to
think that the just-issued certificate is about to expire.
Additionally, the expiry mailer is modified to cleanly shut down its
SMTP connections.
Daniel
Daniel McCarney
Kane York