Code maintenance: rework ovpn host extraction

internal/updater/openvpn.go

@@ -1,26 +1,50 @@
 package updater
 
 import (
+	"errors"
+	"fmt"
+	"net"
 	"strings"
 )
 
-func extractRemoteLinesFromOpenvpn(content []byte) (remoteLines []string) {
-	lines := strings.Split(string(content), "\n")
-	for _, line := range lines {
-		if strings.HasPrefix(line, "remote ") {
-			remoteLines = append(remoteLines, line)
-		}
+var (
+	errRemoteHostNotFound = errors.New("remote host not found")
+)
+
+func extractHostFromOVPN(b []byte) (host, warning string, err error) {
+	const (
+		rejectIP     = true
+		rejectDomain = false
+	)
+	hosts := extractRemoteHostsFromOpenvpn(b, rejectIP, rejectDomain)
+	if len(hosts) == 0 {
+		return "", "", errRemoteHostNotFound
+	} else if len(hosts) > 1 {
+		warning = fmt.Sprintf(
+			"only using the first host %q and discarding %d other hosts",
+			hosts[0], len(hosts)-1)
 	}
-	return remoteLines
+	return hosts[0], warning, nil
 }
 
-func extractHostnamesFromRemoteLines(remoteLines []string) (hostnames []string) {
-	for _, remoteLine := range remoteLines {
-		fields := strings.Fields(remoteLine)
-		if len(fields[1]) == 0 {
+func extractRemoteHostsFromOpenvpn(content []byte,
+	rejectIP, rejectDomain bool) (hosts []string) {
+	lines := strings.Split(string(content), "\n")
+	for _, line := range lines {
+		if !strings.HasPrefix(line, "remote ") {
 			continue
 		}
-		hostnames = append(hostnames, fields[1])
+		fields := strings.Fields(line)
+		if len(fields) == 1 || len(fields[1]) == 0 {
+			continue
+		}
+		host := fields[1]
+		parsedIP := net.ParseIP(host)
+		if (rejectIP && parsedIP != nil) ||
+			(rejectDomain && parsedIP == nil) {
+			continue
+		}
+		hosts = append(hosts, host)
 	}
-	return hostnames
+	return hosts
 }