Refactor pkg/networkfs

Solves #11591

Signed-off-by: bobby abbott <ttobbaybbob@gmail.com>

etchosts/etchosts.go

@@ -0,0 +1,67 @@
+package etchosts
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"regexp"
+)
+
+type Record struct {
+	Hosts string
+	IP    string
+}
+
+func (r Record) WriteTo(w io.Writer) (int64, error) {
+	n, err := fmt.Fprintf(w, "%s\t%s\n", r.IP, r.Hosts)
+	return int64(n), err
+}
+
+var defaultContent = []Record{
+	{Hosts: "localhost", IP: "127.0.0.1"},
+	{Hosts: "localhost ip6-localhost ip6-loopback", IP: "::1"},
+	{Hosts: "ip6-localnet", IP: "fe00::0"},
+	{Hosts: "ip6-mcastprefix", IP: "ff00::0"},
+	{Hosts: "ip6-allnodes", IP: "ff02::1"},
+	{Hosts: "ip6-allrouters", IP: "ff02::2"},
+}
+
+func Build(path, IP, hostname, domainname string, extraContent []Record) error {
+	content := bytes.NewBuffer(nil)
+	if IP != "" {
+		var mainRec Record
+		mainRec.IP = IP
+		if domainname != "" {
+			mainRec.Hosts = fmt.Sprintf("%s.%s %s", hostname, domainname, hostname)
+		} else {
+			mainRec.Hosts = hostname
+		}
+		if _, err := mainRec.WriteTo(content); err != nil {
+			return err
+		}
+	}
+
+	for _, r := range defaultContent {
+		if _, err := r.WriteTo(content); err != nil {
+			return err
+		}
+	}
+
+	for _, r := range extraContent {
+		if _, err := r.WriteTo(content); err != nil {
+			return err
+		}
+	}
+
+	return ioutil.WriteFile(path, content.Bytes(), 0644)
+}
+
+func Update(path, IP, hostname string) error {
+	old, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	var re = regexp.MustCompile(fmt.Sprintf("(\\S*)(\\t%s)", regexp.QuoteMeta(hostname)))
+	return ioutil.WriteFile(path, re.ReplaceAll(old, []byte(IP+"$2")), 0644)
+}