refactor: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

Reference: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

ipn/ipnlocal/peerapi_test.go

@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
-	"io/ioutil"
 	"math/rand"
 	"net/http"
 	"net/http/httptest"
@@ -87,7 +86,7 @@ func fileHasContents(name string, want string) check {
 			return
 		}
 		path := filepath.Join(root, name)
-		got, err := ioutil.ReadFile(path)
+		got, err := os.ReadFile(path)
 		if err != nil {
 			t.Errorf("fileHasContents: %v", err)
 			return
@@ -517,7 +516,7 @@ func TestDeletedMarkers(t *testing.T) {
 	}
 	wantEmptyTempDir := func() {
 		t.Helper()
-		if fis, err := ioutil.ReadDir(dir); err != nil {
+		if fis, err := os.ReadDir(dir); err != nil {
 			t.Fatal(err)
 		} else if len(fis) > 0 && runtime.GOOS != "windows" {
 			for _, fi := range fis {

ipn/ipnlocal/ssh.go

@@ -18,7 +18,6 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -80,7 +79,7 @@ func (b *LocalBackend) hostKeyFileOrCreate(keyDir, typ string) ([]byte, error) {
 	defer keyGenMu.Unlock()
 
 	path := filepath.Join(keyDir, "ssh_host_"+typ+"_key")
-	v, err := ioutil.ReadFile(path)
+	v, err := os.ReadFile(path)
 	if err == nil {
 		return v, nil
 	}
@@ -121,7 +120,7 @@ func (b *LocalBackend) hostKeyFileOrCreate(keyDir, typ string) ([]byte, error) {
 func (b *LocalBackend) getSystemSSH_HostKeys() (ret map[string]ssh.Signer) {
 	for _, typ := range keyTypes {
 		filename := "/etc/ssh/ssh_host_" + typ + "_key"
-		hostKey, err := ioutil.ReadFile(filename)
+		hostKey, err := os.ReadFile(filename)
 		if err != nil || len(bytes.TrimSpace(hostKey)) == 0 {
 			continue
 		}

ipn/ipnserver/server.go

@@ -12,7 +12,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -215,7 +214,7 @@ func (s *Server) blockWhileInUse(conn io.Reader, ci connIdentity) {
 	s.logf("blocking client while server in use; connIdentity=%v", ci)
 	connDone := make(chan struct{})
 	go func() {
-		io.Copy(ioutil.Discard, conn)
+		io.Copy(io.Discard, conn)
 		close(connDone)
 	}()
 	ch := make(chan struct{}, 1)
@@ -1175,7 +1174,7 @@ func findTrueNASTaildropDir(name string) (dir string, err error) {
 	}
 
 	// but if running on the host, it may be something like /mnt/Primary/Taildrop
-	fis, err := ioutil.ReadDir("/mnt")
+	fis, err := os.ReadDir("/mnt")
 	if err != nil {
 		return "", fmt.Errorf("error reading /mnt: %w", err)
 	}

ipn/localapi/cert.go

@@ -23,7 +23,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -293,7 +292,7 @@ func (h *Handler) getCertPEM(ctx context.Context, logf logger.Logf, traceACME fu
 	if err := encodeECDSAKey(&privPEM, certPrivKey); err != nil {
 		return nil, err
 	}
-	if err := ioutil.WriteFile(keyFile(dir, domain), privPEM.Bytes(), 0600); err != nil {
+	if err := os.WriteFile(keyFile(dir, domain), privPEM.Bytes(), 0600); err != nil {
 		return nil, err
 	}
 
@@ -316,7 +315,7 @@ func (h *Handler) getCertPEM(ctx context.Context, logf logger.Logf, traceACME fu
 			return nil, err
 		}
 	}
-	if err := ioutil.WriteFile(certFile(dir, domain), certPEM.Bytes(), 0644); err != nil {
+	if err := os.WriteFile(certFile(dir, domain), certPEM.Bytes(), 0644); err != nil {
 		return nil, err
 	}
 
@@ -372,7 +371,7 @@ func parsePrivateKey(der []byte) (crypto.Signer, error) {
 
 func acmeKey(dir string) (crypto.Signer, error) {
 	pemName := filepath.Join(dir, "acme-account.key.pem")
-	if v, err := ioutil.ReadFile(pemName); err == nil {
+	if v, err := os.ReadFile(pemName); err == nil {
 		priv, _ := pem.Decode(v)
 		if priv == nil || !strings.Contains(priv.Type, "PRIVATE") {
 			return nil, errors.New("acme/autocert: invalid account key found in cache")
@@ -388,7 +387,7 @@ func acmeKey(dir string) (crypto.Signer, error) {
 	if err := encodeECDSAKey(&pemBuf, privKey); err != nil {
 		return nil, err
 	}
-	if err := ioutil.WriteFile(pemName, pemBuf.Bytes(), 0600); err != nil {
+	if err := os.WriteFile(pemName, pemBuf.Bytes(), 0600); err != nil {
 		return nil, err
 	}
 	return privKey, nil

ipn/prefs.go

@@ -9,7 +9,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net/netip"
 	"os"
@@ -618,7 +617,7 @@ func PrefsFromBytes(b []byte) (*Prefs, error) {
 // LoadPrefs loads a legacy relaynode config file into Prefs
 // with sensible migration defaults set.
 func LoadPrefs(filename string) (*Prefs, error) {
-	data, err := ioutil.ReadFile(filename)
+	data, err := os.ReadFile(filename)
 	if err != nil {
 		return nil, fmt.Errorf("LoadPrefs open: %w", err) // err includes path
 	}

ipn/prefs_test.go

@@ -8,7 +8,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"net/netip"
 	"os"
 	"reflect"
@@ -474,7 +473,7 @@ func TestLoadPrefsNotExist(t *testing.T) {
 // TestLoadPrefsFileWithZeroInIt verifies that LoadPrefs hanldes corrupted input files.
 // See issue #954 for details.
 func TestLoadPrefsFileWithZeroInIt(t *testing.T) {
-	f, err := ioutil.TempFile("", "TestLoadPrefsFileWithZeroInIt")
+	f, err := os.CreateTemp("", "TestLoadPrefsFileWithZeroInIt")
 	if err != nil {
 		t.Fatal(err)
 	}

ipn/store/stores.go

@@ -9,7 +9,6 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -128,7 +127,7 @@ func NewFileStore(logf logger.Logf, path string) (ipn.StateStore, error) {
 		return nil, fmt.Errorf("creating state directory: %w", err)
 	}
 
-	bs, err := ioutil.ReadFile(path)
+	bs, err := os.ReadFile(path)
 
 	// Treat an empty file as a missing file.
 	// (https://github.com/tailscale/tailscale/issues/895#issuecomment-723255589)