chore: Very very rough impl

pkg/resolver/nameserver.go

@@ -0,0 +1,33 @@
+package resolver
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+// GetDefaultNameserver reads `/etc/resolv.conf` to determine the default
+// nameserver configured. Returns an error if unable to parse or
+// no nameserver specified. It returns as soon as it finds a line
+// with `nameserver` prefix.
+// An example format:
+// `nameserver 127.0.0.1`
+
+func GetDefaultNameserver() (string, error) {
+	file, err := os.Open("/etc/resolv.conf")
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		if strings.HasPrefix(scanner.Text(), "nameserver") {
+			return strings.Fields(scanner.Text())[1], nil
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
+	return "", err
+}