Properly handle dokku data removal

- remove deployed applications during dpkg purge
- disable all core plugins during dpkg purge
- ensure init files are removed
- ensure motd is removed
- remove all core plugins, dokku config files (including tls/sshcommand entries etc.) during purge
- remove all empty directories and broken symlinks in the DOKKU_ROOT and DOKKU_LIB_ROOT directories during purge

Note that we do not delete the dokku user itself as there might be other data we don't know about in this directory.

debian/postrm

@@ -1,7 +1,39 @@
 #!/bin/bash
 set -eo pipefail; [[ $TRACE ]] && set -x
 
-if [[ "$1" == "purge" ]] && [[ -e /usr/share/debconf/confmodule ]]; then
-    . /usr/share/debconf/confmodule
-    db_purge
-fi
+readonly DOKKU_ROOT="${DOKKU_ROOT:-/home/dokku}"
+readonly DOKKU_LIB_ROOT="${DOKKU_LIB_PATH:-/var/lib/dokku}"
+
+main() {
+  rm -f /etc/init/dokku-installer.conf
+  rm -f /etc/init/dokku-redeploy.conf
+  rm -f /etc/systemd/system/dokku-installer.conf
+  rm -f /etc/systemd/system/dokku-redeploy.service
+  rm -f /etc/update-motd.d/99-dokku
+
+  if [[ "$1" == "purge" ]]; then
+    rm -f ${DOKKU_ROOT}/.dokkurc ${DOKKU_ROOT}/dokkurc ${DOKKU_ROOT}/tls
+    rm -f ${DOKKU_ROOT}/.ssh/authorized_keys ${DOKKU_ROOT}/.sshcommand
+    rm -f ${DOKKU_ROOT}/ENV ${DOKKU_ROOT}/HOSTNAME ${DOKKU_ROOT}/VERSION
+    rm -rf ${DOKKU_ROOT}/.cache
+    rm -rf ${DOKKU_LIB_ROOT}/core-plugins
+
+    rm -f ${DOKKU_LIB_ROOT}/plugins/config.toml
+    if [[ -d ${DOKKU_LIB_ROOT} ]]; then
+      find -L ${DOKKU_LIB_ROOT} -type l -delete
+      find ${DOKKU_LIB_ROOT} -type d -empty -delete
+    fi
+
+    if [[ -d ${DOKKU_ROOT} ]]; then
+      find -L ${DOKKU_ROOT} -type l -delete
+      find ${DOKKU_ROOT} -type d -empty -delete
+    fi
+
+    if [[ -e /usr/share/debconf/confmodule ]]; then
+      . /usr/share/debconf/confmodule
+      db_purge
+    fi
+  fi
+}
+
+main "$@"

debian/prerm

@@ -0,0 +1,55 @@
+#!/bin/bash
+set -eo pipefail; [[ $TRACE ]] && set -x
+
+readonly DOKKU_ROOT="${DOKKU_ROOT:-/home/dokku}"
+readonly DOKKU_LIB_ROOT="${DOKKU_LIB_PATH:-/var/lib/dokku}"
+
+ps_backtrace() {
+  if [ $# -lt 1 ]; then
+    echo "Usage: $0 PID" > /dev/stderr
+    exit 1
+  fi
+
+  declare -i pid=$1;
+  ppid=0;
+  header_modifier="";
+  while : ; do
+    if [ $ppid -ne 0 ]; then
+      header_modifier=h;
+    fi;
+    ppid=$(ps -o ppid= $pid);
+    ps uww $header_modifier -p $pid;
+    if [ $pid -eq 1 ]; then
+      break;
+    fi;
+    pid=$ppid;
+  done;
+}
+
+main() {
+  # HACK: Ensure that we only delete data when purging dokku from the system
+  if ps_backtrace $BASHPID 2> /dev/null | grep dpkg | grep -- "--purge" > /dev/null; then
+    echo "Processing purge"
+
+    echo "Destroying deployed applications"
+    for app in $(DOKKU_QUIET_OUTPUT=1 dokku apps); do
+      dokku --force apps:destroy $app
+    done
+
+    # HACK: Only disable core plugins, as we don't know what data users store in non-core plugin directories
+    echo "Disabling all core plugins"
+    find ${DOKKU_LIB_ROOT}/core-plugins/available -mindepth 1 -maxdepth 1 -type d -printf '%f\n' | while read -r plugin; do
+      if [ ! -d ${DOKKU_LIB_ROOT}/plugins/available/$plugin ]; then
+        rm ${DOKKU_LIB_ROOT}/plugins/available/$plugin;
+        PLUGIN_PATH=${DOKKU_LIB_ROOT}/core-plugins plugn disable $plugin
+        PLUGIN_PATH=${DOKKU_LIB_ROOT}/plugins plugn disable $plugin
+      fi
+    done
+  else
+    echo "Processing $1"
+  fi
+
+  dokku cleanup
+}
+
+main "$@"