[enh] add --dry-run option to dyndns update

data/actionsmap/yunohost.yml

@@ -1537,6 +1537,10 @@ dyndns:
                     full: --force
                     help: Force the update (for debugging only)
                     action: store_true
+                -D:
+                    full: --dry-run
+                    help: Only display the generated zone
+                    action: store_true
                 -6:
                     full: --ipv6
                     help: IPv6 address to send

src/yunohost/dyndns.py

@@ -33,7 +33,7 @@ import subprocess
 from moulinette import m18n
 from moulinette.core import MoulinetteError
 from moulinette.utils.log import getActionLogger
-from moulinette.utils.filesystem import write_to_file
+from moulinette.utils.filesystem import write_to_file, read_file
 from moulinette.utils.network import download_json
 from moulinette.utils.process import check_output
 
@@ -176,7 +176,7 @@ def dyndns_subscribe(operation_logger, subscribe_host="dyndns.yunohost.org", dom
 
 @is_unit_operation()
 def dyndns_update(operation_logger, dyn_host="dyndns.yunohost.org", domain=None, key=None,
-                  ipv4=None, ipv6=None, force=False):
+                  ipv4=None, ipv6=None, force=False, dry_run=False):
     """
     Update IP on DynDNS platform
 
@@ -249,7 +249,7 @@ def dyndns_update(operation_logger, dyn_host="dyndns.yunohost.org", domain=None,
     logger.debug("Requested IPv4/v6 are (%s, %s)" % (ipv4, ipv6))
 
     # no need to update
-    if not force and (old_ipv4 == ipv4 and old_ipv6 == ipv6):
+    if (not force and not dry_run) and (old_ipv4 == ipv4 and old_ipv6 == ipv6):
         logger.info("No updated needed.")
         return
     else:
@@ -296,13 +296,18 @@ def dyndns_update(operation_logger, dyn_host="dyndns.yunohost.org", domain=None,
 
     logger.debug("Now pushing new conf to DynDNS host...")
 
-    try:
-        command = ["/usr/bin/nsupdate", "-k", key, DYNDNS_ZONE]
-        subprocess.check_call(command)
-    except subprocess.CalledProcessError:
-        raise YunohostError('dyndns_ip_update_failed')
+    if not dry_run:
+        try:
+            command = ["/usr/bin/nsupdate", "-k", key, DYNDNS_ZONE]
+            subprocess.check_call(command)
+        except subprocess.CalledProcessError:
+            raise YunohostError('dyndns_ip_update_failed')
 
-    logger.success(m18n.n('dyndns_ip_updated'))
+        logger.success(m18n.n('dyndns_ip_updated'))
+    else:
+        print(read_file(DYNDNS_ZONE))
+        print("")
+        print("Warning: dry run, this is only the generated config, it won't be applied")
 
 
 def dyndns_installcron():