Adds mail server and dns check + enhance ping

- Add ipv4|v6 selection for ping
- Add dns field check
- Add imaps and smtp checks

check.sh

@@ -401,11 +401,20 @@ check_audiostream_mpv() {
 check_ping() {
 	ns=$1
 	count=$2
+	proto="$3"
 	if [ -z "$count" ]
 	then
 		count=5
 	fi
-	ping -i 0.2 -c $count $ns 2>/dev/null >/dev/null
+	case "$proto" in
+		ipv4)
+			proto="-4";;
+		ipv6)
+			proto="-6";;
+		*)
+			proto="";;
+	esac
+	ping $proto -i 0.2 -c $count $ns 2>/dev/null >/dev/null
 	res=$?
 	if [ "$res" -ne 0 ]
 	then
@@ -415,6 +424,69 @@ check_ping() {
 	fi
 }
 
+check_dns() {
+	hostname=$1
+	field=$2
+	expt=$3
+	result=$(dig +short "$hostname" "$field")
+	if echo "$result" | grep -e "$expt" >/dev/null
+	then
+		success "DNS replied '$expt' for '$field $hostname'"
+	else
+		fail "Unexpected DNS reply '$result' expecting '$expt' for '$hostname $field'"
+	fi
+}
+
+check_smtp() {
+	hostname=$1
+	port=$2
+	if [ -z "$port" ]
+	then
+		port=587
+	fi
+	code=$(nc -q0 "$hostname" "$port" < /dev/null | cut -d " " -f1)
+	if [ "$code" = "220" ]
+	then
+		success "SMTP@$hostname server replied 220 status"
+	else
+		fail "Unexpected reply from smtp@$hostname '$code'"
+	fi
+}
+
+check_smtp_id() {
+	hostname=$1
+	idstr=$2
+	port=$3
+	if [ -z "$port" ]
+	then
+		port=587
+	fi
+	rep=$(nc -q0 "$hostname" "$port" < /dev/null)
+	if echo "$rep" | grep -e "^220 $idstr" > /dev/null
+	then
+		success "SMTP@$hostname server replie '$idstr'"
+	else
+		fail "Unexpected reply from smtp@$hostname '$rep'"
+	fi
+}
+
+check_imaps() {
+	hostname=$1
+	port=$2
+	if [ -z "$port" ]
+	then
+		port=993
+	fi
+	rep=$(echo "01 LOGOUT" | openssl s_client -quiet -verify_quiet -connect "${hostname}:$port" -servername "$hostname")
+
+	if echo "$rep" | grep "^01 OK" > /dev/null
+	then
+		success "IMAPS@$hostname '$(echo "$rep" | grep "^01 OK")'"
+	else
+		fail "Unexpected reply from imaps@$hostname '$rep'"
+	fi
+}
+
 check_git_repo() {
 	tmpdir=$(mktemp -d -t check_git.XXXXXXXXX)
 	git clone $1 $tmpdir 2>/dev/null 1>/dev/null