From 7f4c77577efc3400a7ddabb8ae85176c1d2b8b65 Mon Sep 17 00:00:00 2001
From: Shulhan <ms@kilabit.info>
Date: Sun, 2 Apr 2023 01:24:07 +0700
Subject: lib/net: add method WriteTo to ResolvConf

The WriteTo method write the ResolvConf as text.
---
 lib/net/resolvconf.go              | 50 ++++++++++++++++++++++++++++++++++++++
 lib/net/resolvconf_example_test.go | 43 +++++++++++++++++++++++++++++++-
 2 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/lib/net/resolvconf.go b/lib/net/resolvconf.go
index faf12c50..d35dda38 100644
--- a/lib/net/resolvconf.go
+++ b/lib/net/resolvconf.go
@@ -5,7 +5,11 @@
 package net
 
 import (
+	"bytes"
+	"fmt"
+	"io"
 	"os"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -353,3 +357,49 @@ func (rc *ResolvConf) PopulateQuery(dname string) (queries []string) {
 	}
 	return queries
 }
+
+// WriteTo write the ResolvConf into w.
+func (rc *ResolvConf) WriteTo(w io.Writer) (n int, err error) {
+	var bb bytes.Buffer
+
+	if len(rc.Domain) > 0 {
+		fmt.Fprintf(&bb, "domain %s\n", rc.Domain)
+	}
+
+	var k string
+
+	if len(rc.Search) > 0 {
+		fmt.Fprint(&bb, `search`)
+		for _, k = range rc.Search {
+			bb.WriteString(` ` + k)
+		}
+		bb.WriteByte('\n')
+	}
+	for _, k = range rc.NameServers {
+		fmt.Fprintf(&bb, "nameserver %s\n", k)
+	}
+
+	if rc.NDots > 0 {
+		fmt.Fprintf(&bb, "options ndots:%d\n", rc.NDots)
+	}
+	if rc.Timeout > 0 {
+		fmt.Fprintf(&bb, "options timeout:%d\n", rc.Timeout)
+	}
+	if rc.Attempts > 0 {
+		fmt.Fprintf(&bb, "options attempts:%d\n", rc.Attempts)
+	}
+
+	if len(rc.OptMisc) > 0 {
+		var keys []string
+		for k = range rc.OptMisc {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+
+		for _, k = range keys {
+			fmt.Fprintf(&bb, "options %s\n", k)
+		}
+	}
+
+	return w.Write(bb.Bytes())
+}
diff --git a/lib/net/resolvconf_example_test.go b/lib/net/resolvconf_example_test.go
index a3e8cb6e..c33630ad 100644
--- a/lib/net/resolvconf_example_test.go
+++ b/lib/net/resolvconf_example_test.go
@@ -4,7 +4,11 @@
 
 package net
 
-import "fmt"
+import (
+	"bytes"
+	"fmt"
+	"log"
+)
 
 func ExampleResolvConf_PopulateQuery() {
 	var (
@@ -24,3 +28,40 @@ func ExampleResolvConf_PopulateQuery() {
 	//[vpn vpn.my.internal]
 	//[a.machine]
 }
+
+func ExampleResolvConf_WriteTo() {
+	var (
+		rc = &ResolvConf{
+			Domain:      `internal`,
+			Search:      []string{`a.internal`, `b.internal`},
+			NameServers: []string{`127.0.0.1`, `192.168.1.1`},
+			NDots:       1,
+			Timeout:     5,
+			Attempts:    3,
+			OptMisc: map[string]bool{
+				`rotate`: true,
+				`debug`:  true,
+			},
+		}
+
+		bb  bytes.Buffer
+		err error
+	)
+
+	_, err = rc.WriteTo(&bb)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(bb.String())
+	// Output:
+	// domain internal
+	// search a.internal b.internal
+	// nameserver 127.0.0.1
+	// nameserver 192.168.1.1
+	// options ndots:1
+	// options timeout:5
+	// options attempts:3
+	// options debug
+	// options rotate
+}
-- 
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