ddns-scripts: fix IPv6 updates to IPv4-only DDNS providers

When use_ipv6 is enabled but the DDNS provider only supports IPv4 (e.g., DuckDNS), the update would fail. This patch adds DNS resolution checks to detect if the update URL host supports IPv6 (AAAA records). If not, it automatically falls back to IPv4 for the transfer.

Changes:
- Added IPv6 capability detection for update URL hosts
- Modified do_transfer() to check for AAAA records before forcing IPv6
- Implements fallback to IPv4 when host doesn't support IPv6
- Affects wget, curl, and uclient-fetch transfer methods

Signed-off-by: Rogan Lynch <[email protected]>

Author: roganlynch

net/ddns-scripts/files/usr/lib/ddns/dynamic_dns_functions.sh

@@ -677,12 +677,38 @@ do_transfer() {
 	local __ERR=0
 	local __CNT=0	# error counter
 	local __PROG  __RUNPROG
+	local __URL_HOST __DNS_HAS_AAAA=0
 
 	[ $# -ne 1 ] && write_log 12 "Error in 'do_transfer()' - wrong number of parameters"
 
 	# Use ip_network as default for bind_network if not separately specified
 	[ -z "$bind_network" ] && [ "$ip_source" = "network" ] && [ "$ip_network" ] && bind_network="$ip_network"
 
+	# Check if URL host supports IPv6 when use_ipv6 is enabled
+	if [ $use_ipv6 -eq 1 ]; then
+		# Extract hostname from URL
+		__URL_HOST=$(echo "$__URL" | sed -e 's|^[^/]*//||' -e 's|/.*$||' -e 's|:.*$||')
+		__DNS_HAS_AAAA=0
+		
+		# Try to resolve IPv6 address for the host
+		if [ -n "$BIND_HOST" ]; then
+			$BIND_HOST -t AAAA "$__URL_HOST" >$DATFILE 2>$ERRFILE && grep -q "has IPv6 address" $DATFILE && __DNS_HAS_AAAA=1
+		elif [ -n "$KNOT_HOST" ]; then
+			$KNOT_HOST -t AAAA "$__URL_HOST" >$DATFILE 2>$ERRFILE && grep -q "has IPv6 address" $DATFILE && __DNS_HAS_AAAA=1
+		elif [ -n "$DRILL" ]; then
+			$DRILL AAAA "$__URL_HOST" >$DATFILE 2>$ERRFILE && grep -E "^$__URL_HOST\.|^$__URL_HOST[[:space:]]" $DATFILE | grep -q "$IPV6_REGEX" && __DNS_HAS_AAAA=1
+		elif [ -n "$HOSTIP" ]; then
+			$HOSTIP -6 "$__URL_HOST" >$DATFILE 2>$ERRFILE && grep -q "$IPV6_REGEX" $DATFILE && __DNS_HAS_AAAA=1
+		elif [ -n "$NSLOOKUP" ]; then
+			$NSLOOKUP "$__URL_HOST" >$DATFILE 2>$ERRFILE && grep -q "$IPV6_REGEX" $DATFILE && __DNS_HAS_AAAA=1
+		fi
+		
+		# If host doesn't support IPv6, we'll use IPv4 instead
+		if [ $__DNS_HAS_AAAA -eq 0 ]; then
+			write_log 6 "Update URL host '$__URL_HOST' does not support IPv6, using IPv4 for transfer"
+		fi
+	fi
+
 	# lets prefer GNU Wget because it does all for us - IPv4/IPv6/HTTPS/PROXY/force IP version
 	if [ -n "$WGET_SSL" ] && [ $USE_CURL -eq 0 ]; then 			# except global option use_curl is set to "1"
 		__PROG="$WGET --hsts-file=/tmp/.wget-hsts -nv -t 1 -O $DATFILE -o $ERRFILE"	# non_verbose no_retry outfile errfile
@@ -698,7 +724,15 @@ do_transfer() {
 		fi
 		# force ip version to use
 		if [ $force_ipversion -eq 1 ]; then
-			[ $use_ipv6 -eq 0 ] && __PROG="$__PROG -4" || __PROG="$__PROG -6"	# force IPv4/IPv6
+				if [ $use_ipv6 -eq 0 ]; then
+					__PROG="$__PROG -4"
+				elif [ $__DNS_HAS_AAAA -eq 1 ]; then
+					__PROG="$__PROG -6"	# only force IPv6 if host supports it
+				else
+					__PROG="$__PROG -4"	# fallback to IPv4 if host doesn't support IPv6
+				fi
+		elif [ $use_ipv6 -eq 1 ] && [ $__DNS_HAS_AAAA -eq 1 ]; then
+			__PROG="$__PROG -6"	# use IPv6 if available
 		fi
 		# set certificate parameters
 		if [ $use_https -eq 1 ]; then
@@ -742,7 +776,15 @@ do_transfer() {
 		fi
 		# force ip version to use
 		if [ $force_ipversion -eq 1 ]; then
-			[ $use_ipv6 -eq 0 ] && __PROG="$__PROG -4" || __PROG="$__PROG -6"	# force IPv4/IPv6
+				if [ $use_ipv6 -eq 0 ]; then
+					__PROG="$__PROG -4"
+				elif [ $__DNS_HAS_AAAA -eq 1 ]; then
+					__PROG="$__PROG -6"	# only force IPv6 if host supports it
+				else
+					__PROG="$__PROG -4"	# fallback to IPv4 if host doesn't support IPv6
+				fi
+		elif [ $use_ipv6 -eq 1 ] && [ $__DNS_HAS_AAAA -eq 1 ]; then
+			__PROG="$__PROG -6"	# use IPv6 if available
 		fi
 		# set certificate parameters
 		if [ $use_https -eq 1 ]; then
@@ -778,7 +820,15 @@ do_transfer() {
 			write_log 14 "uclient-fetch: FORCE binding to specific address not supported"
 		# force ip version to use
 		if [ $force_ipversion -eq 1 ]; then
-			[ $use_ipv6 -eq 0 ] && __PROG="$__PROG -4" || __PROG="$__PROG -6"       # force IPv4/IPv6
+				if [ $use_ipv6 -eq 0 ]; then
+					__PROG="$__PROG -4"
+				elif [ $__DNS_HAS_AAAA -eq 1 ]; then
+					__PROG="$__PROG -6"	# only force IPv6 if host supports it
+				else
+					__PROG="$__PROG -4"	# fallback to IPv4 if host doesn't support IPv6
+				fi
+		elif [ $use_ipv6 -eq 1 ] && [ $__DNS_HAS_AAAA -eq 1 ]; then
+			__PROG="$__PROG -6"	# use IPv6 if available
 		fi
 		# https possibly not supported
 		[ $use_https -eq 1 -a -z "$UCLIENT_FETCH_SSL" ] && \