fix: an upgrade keeps the configuration and asks nothing.

debian-package/debian/changelog

@@ -1,3 +1,16 @@
+vpn-router (0.5.8-1) unstable; urgency=medium
+
+  fix: an upgrade keeps the configuration and asks nothing.
+
+  * postinst passes on only the debconf answers that were given. The
+    defaults of questions never asked, such as platform none, no longer
+    replace settings of vpn-router.json.
+  * Without an answer that changes it, the configuration ucf is given is
+    vpn-router.json byte for byte, so an upgrade has no conflict to ask
+    about; settings the file leaves out keep their defaults when it is read.
+
+ -- Slawomir Koszewski <slawek@koszewscy.waw.pl>  Sat, 24 Oct 2026 20:00:00 +0200
+
 vpn-router (0.5.7-1) unstable; urgency=medium
 
   feature: users have a first name, a last name and an e-mail address.

debian-package/debian/postinst

@@ -2,28 +2,39 @@
 set -e
 . /usr/share/debconf/confmodule
 
+# The answer to a question in ANSWER, or "" when the question has not been seen; the
+# default debconf holds for an unseen question is not an answer.
+answer() {
+    ANSWER=""
+    db_fget "$1" seen
+    if [ "$RET" = "true" ]; then
+        db_get "$1"
+        ANSWER="$RET"
+    fi
+}
+
 case "$1" in
     configure)
         # --- Read the installer's answers ---
-        db_get vpn-router/platform;         VPN_ROUTER_PLATFORM="$RET"
-        db_get vpn-router/mode;             VPN_ROUTER_MODE="$RET"
-        db_get vpn-router/int_addr;         VPN_ROUTER_INT_ADDR="$RET"
-        db_get vpn-router/external_interface; VPN_ROUTER_EXTERNAL_INTERFACE="$RET"
-        db_get vpn-router/internal_interface; VPN_ROUTER_INTERNAL_INTERFACE="$RET"
-        db_get vpn-router/local_fqdn;       VPN_ROUTER_LOCAL_FQDN="$RET"
-        db_get vpn-router/local_id_mode;    VPN_ROUTER_LOCAL_ID_MODE="$RET"
-        db_get vpn-router/local_cidrs;      VPN_ROUTER_LOCAL_CIDRS="$RET"
-        db_get vpn-router/int_gateway_ip;   VPN_ROUTER_INT_GATEWAY_IP="$RET"
-        db_get vpn-router/remote_addrs;     VPN_ROUTER_REMOTE_ADDRS="$RET"
-        db_get vpn-router/remote_id;        VPN_ROUTER_REMOTE_ID="$RET"
-        db_get vpn-router/remote_cidrs;     VPN_ROUTER_REMOTE_CIDRS="$RET"
-        db_get vpn-router/psk;              VPN_ROUTER_PSK="$RET"
-        db_get vpn-router/p2s_enabled;      VPN_ROUTER_P2S_ENABLED="$RET"
-        db_get vpn-router/p2s_address_pool; VPN_ROUTER_P2S_ADDRESS_POOL="$RET"
-        db_get vpn-router/p2s_ca_name;      VPN_ROUTER_P2S_CA_NAME="$RET"
-        db_get vpn-router/wg_enabled;       VPN_ROUTER_WG_ENABLED="$RET"
-        db_get vpn-router/wg_address;       VPN_ROUTER_WG_ADDRESS="$RET"
-        db_get vpn-router/wg_listen_port;   VPN_ROUTER_WG_LISTEN_PORT="$RET"
+        answer vpn-router/platform;         VPN_ROUTER_PLATFORM="$ANSWER"
+        answer vpn-router/mode;             VPN_ROUTER_MODE="$ANSWER"
+        answer vpn-router/int_addr;         VPN_ROUTER_INT_ADDR="$ANSWER"
+        answer vpn-router/external_interface; VPN_ROUTER_EXTERNAL_INTERFACE="$ANSWER"
+        answer vpn-router/internal_interface; VPN_ROUTER_INTERNAL_INTERFACE="$ANSWER"
+        answer vpn-router/local_fqdn;       VPN_ROUTER_LOCAL_FQDN="$ANSWER"
+        answer vpn-router/local_id_mode;    VPN_ROUTER_LOCAL_ID_MODE="$ANSWER"
+        answer vpn-router/local_cidrs;      VPN_ROUTER_LOCAL_CIDRS="$ANSWER"
+        answer vpn-router/int_gateway_ip;   VPN_ROUTER_INT_GATEWAY_IP="$ANSWER"
+        answer vpn-router/remote_addrs;     VPN_ROUTER_REMOTE_ADDRS="$ANSWER"
+        answer vpn-router/remote_id;        VPN_ROUTER_REMOTE_ID="$ANSWER"
+        answer vpn-router/remote_cidrs;     VPN_ROUTER_REMOTE_CIDRS="$ANSWER"
+        answer vpn-router/psk;              VPN_ROUTER_PSK="$ANSWER"
+        answer vpn-router/p2s_enabled;      VPN_ROUTER_P2S_ENABLED="$ANSWER"
+        answer vpn-router/p2s_address_pool; VPN_ROUTER_P2S_ADDRESS_POOL="$ANSWER"
+        answer vpn-router/p2s_ca_name;      VPN_ROUTER_P2S_CA_NAME="$ANSWER"
+        answer vpn-router/wg_enabled;       VPN_ROUTER_WG_ENABLED="$ANSWER"
+        answer vpn-router/wg_address;       VPN_ROUTER_WG_ADDRESS="$ANSWER"
+        answer vpn-router/wg_listen_port;   VPN_ROUTER_WG_LISTEN_PORT="$ANSWER"
 
         export VPN_ROUTER_PLATFORM VPN_ROUTER_MODE VPN_ROUTER_INT_ADDR \
                VPN_ROUTER_EXTERNAL_INTERFACE \