This patch contains some minor code style improvements, to leave the
linter happier and generally follow best practices in some areas where
things snuck through.
This patch adds support for TLS-wrapped submission connections.
Instead of clients establishing a connection over plain text and then
using STARTTLS to switch over a TLS connection, this new mode allows the
clients to connect directly over TLS, like it's done in HTTPS.
This is not an official standard yet, but it's reasonably common in
practice, and provides some advantages over the traditional submission
port.
The default port is 465, commonly used for this; chasquid defaults to
systemd file descriptor passing as for the other protocols (for now).
When testing, we don't want the server to do SPF lookups, as those cause
real DNS queries which can be problematic and add a dependency on the
environment.
This patch adds an internal boolean to disable the SPF lookups, which is
only set from the tests.
glog works fine and has great features, but it does not play along well
with systemd or standard log rotators (as it does the rotation itself).
So this patch replaces glog with a new logging module "log", which by
default logs to stderr, in a systemd-friendly manner.
Logging to files or syslog is still supported.
The submission port is expected to be used only by authenticated
clients, so this patch makes chasquid enforce this, which also helps
to reduce spam.
https://www.rfc-editor.org/rfc/rfc6409.txt
This patch moves chasquid's Server and Conn structures to their own
smtpsrv package, to make chasquid.go a bit more readable. It also helps
clarify the relation between Server and Conn.
There are no functional changes.
Note that git can still track the history across this commit (e.g. git
gui blame shows the right data).
