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ca4bd7d7c7
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10 changed files with 944 additions and 0 deletions
183
internal/resolv/resolv.go
Normal file
183
internal/resolv/resolv.go
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@ -0,0 +1,183 @@
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package resolv
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import (
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"bufio"
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"errors"
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"fmt"
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"net"
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"os"
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"slices"
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"strings"
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"sync"
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)
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const DefaultPath = "/run/dns/resolv.conf"
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var (
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ErrInvalidAddress = errors.New("invalid nameserver address")
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ErrAlreadyExists = errors.New("nameserver already exists")
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ErrNotFound = errors.New("nameserver not found")
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)
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type Manager struct {
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path string
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mu sync.Mutex
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}
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func New(path string) *Manager {
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if path == "" {
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path = DefaultPath
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}
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return &Manager{path: path}
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}
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func (m *Manager) List() ([]string, error) {
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m.mu.Lock()
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defer m.mu.Unlock()
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_, servers, err := m.read()
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if err != nil {
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return nil, err
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}
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return servers, nil
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}
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func (m *Manager) Add(addr string) error {
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addr = strings.TrimSpace(addr)
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if !isValidIP(addr) {
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return fmt.Errorf("%w: %q", ErrInvalidAddress, addr)
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}
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m.mu.Lock()
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defer m.mu.Unlock()
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lines, servers, err := m.read()
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if err != nil {
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return err
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}
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if slices.Contains(servers, addr) {
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return fmt.Errorf("%w: %s", ErrAlreadyExists, addr)
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}
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lines = append(lines, "nameserver "+addr)
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return m.write(lines)
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}
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func (m *Manager) Remove(addr string) error {
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addr = strings.TrimSpace(addr)
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if !isValidIP(addr) {
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return fmt.Errorf("%w: %q", ErrInvalidAddress, addr)
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}
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m.mu.Lock()
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defer m.mu.Unlock()
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lines, _, err := m.read()
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if err != nil {
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return err
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}
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out := make([]string, 0, len(lines))
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removed := false
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for _, line := range lines {
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if !removed && parseNameserver(line) == addr {
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removed = true
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continue
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}
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out = append(out, line)
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}
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if !removed {
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return fmt.Errorf("%w: %s", ErrNotFound, addr)
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}
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return m.write(out)
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}
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func (m *Manager) read() ([]string, []string, error) {
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f, err := os.Open(m.path)
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if err != nil {
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if os.IsNotExist(err) {
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return nil, nil, nil
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}
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return nil, nil, err
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}
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defer f.Close()
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var lines, servers []string
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sc := bufio.NewScanner(f)
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for sc.Scan() {
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line := sc.Text()
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lines = append(lines, line)
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if ns := parseNameserver(line); ns != "" {
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servers = append(servers, ns)
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}
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}
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if err := sc.Err(); err != nil {
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return nil, nil, err
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}
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return lines, servers, nil
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}
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func (m *Manager) write(lines []string) error {
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dir := dirOf(m.path)
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tmp, err := os.CreateTemp(dir, ".resolv.conf.tmp.*")
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if err != nil {
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return err
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}
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tmpName := tmp.Name()
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cleanup := func() { _ = os.Remove(tmpName) }
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w := bufio.NewWriter(tmp)
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for _, line := range lines {
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if _, err := w.WriteString(line); err != nil {
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tmp.Close()
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cleanup()
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return err
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}
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if _, err := w.WriteString("\n"); err != nil {
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tmp.Close()
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cleanup()
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return err
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}
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}
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if err := w.Flush(); err != nil {
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tmp.Close()
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cleanup()
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return err
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}
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if err := tmp.Sync(); err != nil {
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tmp.Close()
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cleanup()
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return err
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}
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if err := tmp.Close(); err != nil {
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cleanup()
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return err
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}
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if err := os.Rename(tmpName, m.path); err != nil {
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cleanup()
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return err
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}
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return nil
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}
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func parseNameserver(line string) string {
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s := strings.TrimSpace(line)
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if s == "" || strings.HasPrefix(s, "#") || strings.HasPrefix(s, ";") {
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return ""
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}
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fields := strings.Fields(s)
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if len(fields) < 2 || fields[0] != "nameserver" {
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return ""
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}
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return fields[1]
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}
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func isValidIP(s string) bool {
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return s != "" && net.ParseIP(s) != nil
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}
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func dirOf(path string) string {
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if i := strings.LastIndex(path, "/"); i >= 0 {
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return path[:i]
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}
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return "."
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}
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158
internal/resolv/resolv_test.go
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158
internal/resolv/resolv_test.go
Normal file
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@ -0,0 +1,158 @@
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package resolv
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import (
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"errors"
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"os"
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"path/filepath"
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"reflect"
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"sync"
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"testing"
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)
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func newTestManager(t *testing.T, initial string) (*Manager, string) {
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t.Helper()
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dir := t.TempDir()
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path := filepath.Join(dir, "resolv.conf")
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if initial != "" {
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if err := os.WriteFile(path, []byte(initial), 0o644); err != nil {
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t.Fatalf("seed: %v", err)
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}
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}
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return New(path), path
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}
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func readFile(t *testing.T, path string) string {
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t.Helper()
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b, err := os.ReadFile(path)
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if err != nil {
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t.Fatalf("read: %v", err)
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}
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return string(b)
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}
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func TestList_EmptyMissingFile(t *testing.T) {
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m, _ := newTestManager(t, "")
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got, err := m.List()
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if err != nil {
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t.Fatalf("List: %v", err)
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}
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if len(got) != 0 {
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t.Fatalf("want empty, got %v", got)
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}
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}
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func TestList_ParsesNameserversIgnoresOther(t *testing.T) {
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const initial = `# comment
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; another comment
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search example.com
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nameserver 1.1.1.1
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options rotate
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nameserver 8.8.8.8
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nameserver 2001:4860:4860::8888
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`
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m, _ := newTestManager(t, initial)
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got, err := m.List()
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if err != nil {
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t.Fatalf("List: %v", err)
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}
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want := []string{"1.1.1.1", "8.8.8.8", "2001:4860:4860::8888"}
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if !reflect.DeepEqual(got, want) {
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t.Fatalf("want %v, got %v", want, got)
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}
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}
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func TestAdd_AppendsAndPersists(t *testing.T) {
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m, path := newTestManager(t, "search example.com\nnameserver 1.1.1.1\n")
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if err := m.Add("8.8.8.8"); err != nil {
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t.Fatalf("Add: %v", err)
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}
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got, _ := m.List()
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want := []string{"1.1.1.1", "8.8.8.8"}
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if !reflect.DeepEqual(got, want) {
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t.Fatalf("list want %v, got %v", want, got)
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}
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content := readFile(t, path)
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if want := "search example.com\nnameserver 1.1.1.1\nnameserver 8.8.8.8\n"; content != want {
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t.Fatalf("file mismatch:\nwant: %q\ngot: %q", want, content)
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}
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}
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func TestAdd_RejectsInvalid(t *testing.T) {
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m, _ := newTestManager(t, "")
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for _, addr := range []string{"", "not-an-ip", "999.999.999.999", "1.1.1"} {
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if err := m.Add(addr); !errors.Is(err, ErrInvalidAddress) {
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t.Fatalf("Add(%q): want ErrInvalidAddress, got %v", addr, err)
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}
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}
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}
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func TestAdd_DuplicateRejected(t *testing.T) {
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m, _ := newTestManager(t, "nameserver 1.1.1.1\n")
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if err := m.Add("1.1.1.1"); !errors.Is(err, ErrAlreadyExists) {
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t.Fatalf("want ErrAlreadyExists, got %v", err)
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}
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}
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func TestRemove_DeletesEntry(t *testing.T) {
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const initial = "search example.com\nnameserver 1.1.1.1\nnameserver 8.8.8.8\n"
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m, path := newTestManager(t, initial)
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if err := m.Remove("1.1.1.1"); err != nil {
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t.Fatalf("Remove: %v", err)
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}
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got, _ := m.List()
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if want := []string{"8.8.8.8"}; !reflect.DeepEqual(got, want) {
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t.Fatalf("want %v, got %v", want, got)
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}
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content := readFile(t, path)
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if want := "search example.com\nnameserver 8.8.8.8\n"; content != want {
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t.Fatalf("file mismatch:\nwant: %q\ngot: %q", want, content)
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}
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}
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func TestRemove_NotFound(t *testing.T) {
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m, _ := newTestManager(t, "nameserver 1.1.1.1\n")
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if err := m.Remove("8.8.8.8"); !errors.Is(err, ErrNotFound) {
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t.Fatalf("want ErrNotFound, got %v", err)
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}
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}
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func TestRemove_InvalidAddress(t *testing.T) {
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m, _ := newTestManager(t, "")
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if err := m.Remove("nope"); !errors.Is(err, ErrInvalidAddress) {
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t.Fatalf("want ErrInvalidAddress, got %v", err)
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}
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}
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func TestConcurrentAddsConsistent(t *testing.T) {
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m, _ := newTestManager(t, "")
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addrs := []string{
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"1.1.1.1", "8.8.8.8", "9.9.9.9", "8.8.4.4",
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"1.0.0.1", "208.67.222.222", "208.67.220.220", "64.6.64.6",
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}
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var wg sync.WaitGroup
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for _, a := range addrs {
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wg.Add(1)
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go func(a string) {
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defer wg.Done()
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if err := m.Add(a); err != nil {
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t.Errorf("Add(%s): %v", a, err)
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}
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}(a)
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}
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wg.Wait()
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got, err := m.List()
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if err != nil {
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t.Fatalf("List: %v", err)
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}
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if len(got) != len(addrs) {
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t.Fatalf("want %d entries, got %d (%v)", len(addrs), len(got), got)
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}
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seen := make(map[string]bool, len(got))
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for _, s := range got {
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if seen[s] {
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t.Fatalf("duplicate %s in %v", s, got)
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}
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seen[s] = true
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}
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}
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