.deb/.rpm: add osmocom user during package install

Create osmocom user & group during package installation.
Fix the configuration dir/files permission to match.

Related: OS#4107
Tweaked-By: Oliver Smith <osmith@sysmocom.de>
Change-Id: I7826fedb1b055a282954e5774615245092ddae5d

debian/control

@@ -17,7 +17,7 @@ Vcs-Browser: https://gitea.osmocom.org/cellular-infrastructure/osmo-sip-connecto
 
 Package: osmo-sip-connector
 Architecture: any
-Depends: ${shlibs:Depends}, ${misc:Depends}
+Depends: ${shlibs:Depends}, ${misc:Depends}, adduser
 Description: MNCC to SIP bridge for osmo-nitb
  Use the osmo-nitb MNCC interface and bridge it to SIP.
 

debian/postinst

@@ -0,0 +1,39 @@
+#!/bin/sh -e
+# Create 'osmocom' user and group (if it doesn't exist yet) and adjust permissions
+# of directories which are not automatically adjusted by systemd from previous (root-owned)
+# install.
+
+# N. B: the user is intentionally NOT removed during package uninstall:
+# see https://wiki.debian.org/AccountHandlingInMaintainerScripts for reasoning.
+chperms() {
+	# chperms <user> <group> <perms> <file>
+	if ! OVERRIDE=`dpkg-statoverride --list $4 2>&1`; then
+		if [ -e $4 ]; then
+			chown $1:$2 $4
+			chmod $3 $4
+		fi
+	fi
+}
+
+case "$1" in
+  configure)
+    if ! getent passwd osmocom > /dev/null; then
+        adduser --quiet \
+                --system \
+                --group \
+                --no-create-home \
+                --disabled-password \
+                --home /var/lib/osmocom \
+                --gecos "Open Source Mobile Communications" \
+                osmocom
+    fi
+# Set permissions according to https://www.debian.org/doc/debian-policy/ch-files.html#s-permissions-owners
+    chperms osmocom osmocom 0660 /etc/osmocom/osmo-sip-connector.cfg
+    chperms root osmocom 2775 /etc/osmocom
+
+  ;;
+esac
+
+# dh_installdeb(1) will replace this with shell code automatically
+# generated by other debhelper scripts.
+#DEBHELPER#