This patch updates the shell scripts with some of the common best
practices, which should make them more resilient to unusual failures and
unexpected environments (in particular, directories with spaces).
Most of these were identified by shellcheck.
The `which` command isn't guaranteed to be available, it is just
extremely common; `command -v` is the standard way to do find an
executable program. See https://lwn.net/Articles/874049/ for more
details.
This patch replaces the uses of `which` with `command -v`, which only
appears in a couple of tests.
Most integration tests depend on the $HOSTALIASES environment variable
being functional. That variable works on most systems, but not all. In
particular, systems with `systemd-resolved` can cause the variable to be
ignored.
This was reported by Alex Ellwein in
https://github.com/albertito/chasquid/issues/20.
This patch makes the affected tests to be skipped if $HOSTALIASES is not
working properly. It also removes unnecessary hosts files from tests
which don't need it, and documents this behaviour.
Thanks to Alex Ellwein and foxcpp@ for reporting and helping investigate
this issue!
This patch adds DKIM signing using https://github.com/driusan/dkim tools
to the example hook.
It also adds an optional integration test to exercise signing and
verification, and corresponding documentation.
