#!/bin/sh

unset _NGX_RESOLVER_STACK _NGX_RESOLVER_TIMEOUT
## here should be SANE defaults (!)
_NGX_RESOLVER_STACK=ipv4
_NGX_RESOLVER_TIMEOUT=10s

if [ -z "${NGX_RESOLVER_STACK:-}" ] ; then
	NGX_RESOLVER_STACK=${_NGX_RESOLVER_STACK}
else
	NGX_RESOLVER_STACK=$(printf '%s' "${NGX_RESOLVER_STACK}" | tr '[:upper:]' '[:lower:]')
	case "${NGX_RESOLVER_STACK}" in
	none | ipv4 | ipv6 | any ) ;;
	## adjust
	0 | no )
		NGX_RESOLVER_STACK=none
	;;
	4 | ip4 | v4 )
		NGX_RESOLVER_STACK=ipv4
	;;
	6 | ip6 | v6 )
		NGX_RESOLVER_STACK=ipv6
	;;
	all | dual )
		NGX_RESOLVER_STACK=any
	;;
	* )
		log_always "NGX_RESOLVER_STACK: unrecognized value: ${NGX_RESOLVER_STACK}"
		log_always "setting NGX_RESOLVER_STACK=${_NGX_RESOLVER_STACK}"
		NGX_RESOLVER_STACK=${_NGX_RESOLVER_STACK}
	;;
	esac
fi
export NGX_RESOLVER_STACK

if [ "${NGX_RESOLVER_STACK}" = 'none' ] ; then
	unset NGX_RESOLV_CONF NGX_RESOLVER_TIMEOUT NGX_RESOLVERS
else
	if [ -z "${NGX_RESOLVER_TIMEOUT:-}" ] ; then
		NGX_RESOLVER_TIMEOUT=${_NGX_RESOLVER_TIMEOUT}
	else
		case "${NGX_RESOLVER_TIMEOUT}" in
		[1-9] | [1-9][0-9] )
			## convert implicit "seconds" to explicit
			NGX_RESOLVER_TIMEOUT="${NGX_RESOLVER_TIMEOUT}s"
		;;
		## adjust
		[1-9][Ss] | [1-9][0-9][Ss] )
			NGX_RESOLVER_TIMEOUT="${NGX_RESOLVER_TIMEOUT%?}s"
		;;
		[1-9][Mm][Ss] | [1-9][0-9][Mm][Ss] | [1-9][0-9][0-9][Mm][Ss] | [1-9][0-9][0-9][0-9][Mm][Ss] | [1-9][0-9][0-9][0-9][0-9][Mm][Ss] )
			NGX_RESOLVER_TIMEOUT="${NGX_RESOLVER_TIMEOUT%??}ms"
		;;
		* )
			log_always "NGX_RESOLVER_TIMEOUT: unrecognized value: ${NGX_RESOLVER_TIMEOUT}"
			log_always "setting NGX_RESOLVER_TIMEOUT=${_NGX_RESOLVER_TIMEOUT}"
			NGX_RESOLVER_TIMEOUT=${_NGX_RESOLVER_TIMEOUT}
		;;
		esac
	fi
	export NGX_RESOLVER_TIMEOUT

	unset _resolv_conf
	while [ -z "${NGX_RESOLVERS+x}" ] ; do
		_resolv_conf="${NGX_RESOLV_CONF-/etc/resolv.conf}"
		[ -n "${_resolv_conf}" ] || break
		[ -f "${_resolv_conf}" ] || break
		[ -s "${_resolv_conf}" ] || break

		unset i
		while read -r i ; do
			[ -n "$i" ] || continue

			case "$i" in
			## NB: /etc/resolv.conf allows (!) IPv6 addresses in dotted form (RFC 2373) but this is discouraged
			*:* )
				## TODO: IPv6 address validation
				i="[$i]"

				case "${NGX_RESOLVER_STACK}" in
				any | ipv6 )
					NGX_RESOLVERS=$(append_list "${NGX_RESOLVERS}" "$i")
				;;
				esac
			;;
			* )
				if ! is_ipv4_address "$i" ; then
					log_always "invalid IPv4 address: $i"
					continue
				fi

				case "${NGX_RESOLVER_STACK}" in
				any | ipv4 )
					NGX_RESOLVERS=$(append_list "${NGX_RESOLVERS}" "$i")
				;;
				esac
			;;
			esac
		done <<-EOF
		$(mawk '$1 == "nameserver" {print $2}' < "${_resolv_conf}")
		EOF
		unset i
	done
	unset _resolv_conf

	[ -z "${NGX_RESOLVERS}" ] || export NGX_RESOLVERS
fi

unset _NGX_RESOLVER_STACK _NGX_RESOLVER_TIMEOUT