libnm: add flag to map zero to NULL in _nm_utils_ipaddr_canonical_or_invalid()

This seems a questionable thing to do, and should be made clearer by
having a parameter (that makes you think about what is happening here).

Also, the normalization for vxlan.remote does not perform this mapping,
so the parameter is there so that the approach can handle both flavors.

src/libnm-core-impl/nm-setting-ip-config.c

@@ -5788,7 +5788,8 @@ _nm_sett_info_property_override_create_array_ip_config(int addr_family)
             .to_dbus_fcn   = _nm_setting_property_to_dbus_fcn_direct,
             .from_dbus_fcn = _nm_setting_property_from_dbus_fcn_direct_ip_config_gateway),
         .direct_offset = NM_STRUCT_OFFSET_ENSURE_TYPE(char *, NMSettingIPConfigPrivate, gateway),
-        .direct_set_string_ip_address_addr_family = addr_family + 1);
+        .direct_set_string_ip_address_addr_family                  = addr_family + 1,
+        .direct_set_string_ip_address_addr_family_map_zero_to_null = TRUE);
 
     _nm_properties_override_gobj(
         properties_override,
@@ -5996,7 +5997,8 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
         g_free(priv->gateway);
         priv->gateway =
             _nm_utils_ipaddr_canonical_or_invalid(NM_SETTING_IP_CONFIG_GET_FAMILY(setting),
-                                                  g_value_get_string(value));
+                                                  g_value_get_string(value),
+                                                  TRUE);
         break;
     case PROP_ROUTES:
         g_ptr_array_unref(priv->routes);

src/libnm-core-impl/nm-setting.c

@@ -669,9 +669,11 @@ _property_direct_set_string(const NMSettInfoProperty *property_info, char **dst,
     if (property_info->direct_set_string_ip_address_addr_family != 0) {
         s = _nm_utils_ipaddr_canonical_or_invalid(
             property_info->direct_set_string_ip_address_addr_family - 1,
-            src);
+            src,
+            property_info->direct_set_string_ip_address_addr_family_map_zero_to_null);
         goto out_take;
-    }
+    } else
+        nm_assert(!property_info->direct_set_string_ip_address_addr_family_map_zero_to_null);
 
     if (NM_FLAGS_HAS(property_info->param_spec->flags, NM_SETTING_PARAM_SECRET))
         return nm_strdup_reset_secret(dst, src);

src/libnm-core-impl/nm-utils-private.h

@@ -44,7 +44,8 @@ void _nm_utils_bytes_from_dbus(GVariant *dbus_value, GValue *prop_value);
 
 char *_nm_utils_hwaddr_canonical_or_invalid(const char *mac, gssize length);
 
-char *_nm_utils_ipaddr_canonical_or_invalid(int addr_family, const char *ip);
+char *
+_nm_utils_ipaddr_canonical_or_invalid(int addr_family, const char *ip, gboolean map_zero_to_null);
 
 gboolean _nm_utils_hwaddr_link_local_valid(const char *mac);
 

src/libnm-core-impl/nm-utils.c

@@ -3911,7 +3911,7 @@ _nm_utils_hwaddr_canonical_or_invalid(const char *mac, gssize length)
 }
 
 char *
-_nm_utils_ipaddr_canonical_or_invalid(int addr_family, const char *ip)
+_nm_utils_ipaddr_canonical_or_invalid(int addr_family, const char *ip, gboolean map_zero_to_null)
 {
     NMIPAddr addr_bin;
 
@@ -3923,7 +3923,7 @@ _nm_utils_ipaddr_canonical_or_invalid(int addr_family, const char *ip)
     if (!nm_utils_parse_inaddr_bin(addr_family, ip, &addr_family, &addr_bin))
         return g_strdup(ip);
 
-    if (nm_ip_addr_is_null(addr_family, &addr_bin))
+    if (map_zero_to_null && nm_ip_addr_is_null(addr_family, &addr_bin))
         return NULL;
 
     return nm_utils_inet_ntop_dup(addr_family, &addr_bin);

src/libnm-core-impl/tests/test-setting.c

@@ -4592,6 +4592,9 @@ test_setting_metadata(void)
                                AF_INET + 1,
                                AF_INET6 + 1));
 
+            if (sip->direct_set_string_ip_address_addr_family == 0)
+                g_assert(!sip->direct_set_string_ip_address_addr_family_map_zero_to_null);
+
             /* currently, we have no cases where special options are mixed. There is no problem to support
              * that, but as it's not needed, don't do it for now. */
             g_assert_cmpint(n_special_options, <=, 1);

src/libnm-core-intern/nm-core-internal.h

@@ -768,11 +768,16 @@ struct _NMSettInfoProperty {
     guint8 direct_set_string_mac_address_len : 5;
 
     /* If non-zero, this is the addr-family (AF_UNSPEC/AF_INET/AF_INET6) for normalizing an IP
-     * address. Note that AF_UNSPEC is zero, so to differentiate between zero and AF_UNSPEC
+     * address with _nm_utils_ipaddr_canonical_or_invalid().
+     * Note that AF_UNSPEC is zero, so to differentiate between zero and AF_UNSPEC
      * this value is actually the address family + 1. So either zero or AF_UNSPEC+1, AF_INET+1,
      * or AF_INET6+1. */
     guint8 direct_set_string_ip_address_addr_family : 5;
 
+    /* Only makes sense together with direct_set_string_ip_address_addr_family. This flag
+     * is passed to _nm_utils_ipaddr_canonical_or_invalid(). */
+    bool direct_set_string_ip_address_addr_family_map_zero_to_null : 1;
+
     /* Usually, properties that are set to the default value for the GParamSpec
      * are not serialized to GVariant (and NULL is returned by to_dbus_data().
      * Set this flag to force always converting the property even if the value