Add command to mail the output of a backup run

This commit introduces the 'run-report' command and a new config file
'config/recipient' which indicates the recipient of the report.

Since lifeboat was always intended to be run via a cronjob, we assumed
mail functionality would come from the specific crond implementation.
This is well-supported throughout, but not a feature that systemd's
timers (yet?) have. Since one of our systems is now running systemd, we
needed a decent alternative.

A wrapper script was considered, but at that point we could also just as
simply include mail support in lifeboat itself. We have chosen to
implement this by calling out to sendmail, which seems to be a de-facto
standard (postfix has sendmail compatibility, as does msmtp). It should
be available on a wide range of systems.

For now, hardcode the message headers and send mail to one recipient
only. Set the X-Report header for simple filtering by mail clients.

2 files changed, 28 insertions, 1 deletions

diff --git a/lifeboat b/lifeboat
index e84c916..b8724fc 100755
--- a/lifeboat
+++ b/lifeboat
@@ -18,6 +18,22 @@ usage() {
 	exit 1
 }
 
+report_backup() {
+	cd "$LIFEBOAT_ROOT/$repo"
+
+	test -r config/recipient || errx "Could not read recipient from config/recipient"
+	read -r recipient < config/recipient
+	test -n "$recipient" || errx "No recipient given in config/recipient"
+
+	cat <<-EOF | sendmail "$recipient"
+		From: Lifeboat <lifeboat@$(hostname -f)>
+		Subject: lifeboat: backup for $(hostname) on $(date)
+		X-Report: lifeboat
+
+		$(run_backup 2>&1)
+	EOF
+}
+
 run_backup() {
 	cd "$LIFEBOAT_ROOT/$repo"
 
@@ -75,5 +91,6 @@ export RESTIC_PASSWORD_FILE=$LIFEBOAT_ROOT/$repo/credentials/restic
 
 case "$1" in
 	run) run_backup;;
+	run-report) report_backup;;
 	*) restic "$@";;
 esac
diff --git a/lifeboat.1 b/lifeboat.1
index 1cbf61c..5d76ea1 100644
--- a/lifeboat.1
+++ b/lifeboat.1
@@ -1,4 +1,4 @@
-.Dd January 17, 2020
+.Dd April 30, 2021
 .Dt LIFEBOAT 1
 .Os
 .Sh NAME
@@ -24,6 +24,11 @@ or as follows:
 .Bl -tag -width Ds
 .It Sy run
 Create a snapshot for the specified repository.
+.It Sy run-report
+Like
+.Sy run ,
+but send any program output to the mail address specified in
+.Pa config/recipient .
 .El
 .Sh DIRECTORY STRUCTURE
 .Nm
@@ -78,6 +83,11 @@ if the combined size of the repository is below 10G:
 .Bd -literal -offset indent
 nas:backups/	10485760
 .Ed
+.It Sy config/recipient
+A file containing the mail address of the recipient for backup reports.
+Only needed for the
+.Sy run-report
+command.
 .It Sy credentials/restic
 A file containing the password for the
 .Xr restic 1