parse DNSOptions

Signed-off-by: Haiyan Meng <hmeng@redhat.com>

server/utils.go

@@ -3,8 +3,11 @@ package server
 import (
 	"errors"
 	"fmt"
+	"io"
+	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 )
 
 func getGPRCVersion() (string, error) {
@@ -24,3 +27,67 @@ func getGPRCVersion() (string, error) {
 	}
 	return out, nil
 }
+
+func copyFile(src, dest string) error {
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	out, err := os.Create(dest)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	if _, err := io.Copy(out, in); err != nil {
+		return err
+	}
+	return nil
+}
+
+func removeFile(path string) error {
+	if _, err := os.Stat(path); err == nil {
+		if err := os.Remove(path); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func parseDNSOptions(servers, searches []string, path string) error {
+	nServers := len(servers)
+	nSearches := len(searches)
+	if nServers == 0 && nSearches == 0 {
+		return copyFile("/etc/resolv.conf", path)
+	}
+
+	if nSearches > maxDNSSearches {
+		return fmt.Errorf("DNSOption.Searches has more than 6 domains")
+	}
+
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if nSearches > 0 {
+		data := fmt.Sprintf("search %s\n", strings.Join(searches, " "))
+		_, err = f.Write([]byte(data))
+		if err != nil {
+			return err
+		}
+	}
+
+	if nServers > 0 {
+		data := fmt.Sprintf("nameserver %s\n", strings.Join(servers, "\nnameserver "))
+		_, err = f.Write([]byte(data))
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}