cmd/go/internal/renameio: allow write file with the specified permissions

Now renameio package creates file use ioutil.TempFile, which calls
OpenFile with mode 0600, we should support creates a file with given
permission bits.

Fixes #31871

Change-Id: I0436e9f7081f2fce18bf9f3b14d55b02d4d995fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/175958
Run-TryBot: Baokun Lee <nototon@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/cache/cache.go

@@ -278,7 +278,7 @@ func (c *Cache) Trim() {
 
 	// Ignore errors from here: if we don't write the complete timestamp, the
 	// cache will appear older than it is, and we'll trim it again next time.
-	renameio.WriteFile(filepath.Join(c.dir, "trim.txt"), []byte(fmt.Sprintf("%d", now.Unix())))
+	renameio.WriteFile(filepath.Join(c.dir, "trim.txt"), []byte(fmt.Sprintf("%d", now.Unix())), 0666)
 }
 
 // trimSubdir trims a single cache subdirectory.

src/cmd/go/internal/modfetch/cache.go

@@ -488,7 +488,7 @@ func writeDiskCache(file string, data []byte) error {
 		return err
 	}
 
-	if err := renameio.WriteFile(file, data); err != nil {
+	if err := renameio.WriteFile(file, data, 0666); err != nil {
 		return err
 	}
 
@@ -550,7 +550,7 @@ func rewriteVersionList(dir string) {
 		return
 	}
 
-	if err := renameio.WriteFile(listFile, buf.Bytes()); err != nil {
+	if err := renameio.WriteFile(listFile, buf.Bytes(), 0666); err != nil {
 		base.Fatalf("go: failed to write version list: %v", err)
 	}
 }

src/cmd/go/internal/modfetch/fetch.go

@@ -248,7 +248,7 @@ func downloadZip(mod module.Version, zipfile string) (err error) {
 	}
 	checkModSum(mod, hash)
 
-	if err := renameio.WriteFile(zipfile+"hash", []byte(hash)); err != nil {
+	if err := renameio.WriteFile(zipfile+"hash", []byte(hash), 0666); err != nil {
 		return err
 	}
 	if err := os.Rename(f.Name(), zipfile); err != nil {
@@ -565,7 +565,7 @@ func WriteGoSum() {
 		}
 	}
 
-	if err := renameio.WriteFile(GoSumFile, buf.Bytes()); err != nil {
+	if err := renameio.WriteFile(GoSumFile, buf.Bytes(), 0666); err != nil {
 		base.Fatalf("go: writing go.sum: %v", err)
 	}
 

src/cmd/go/internal/modload/init.go

@@ -715,7 +715,7 @@ func WriteGoMod() {
 
 	}
 
-	if err := renameio.WriteFile(file, new); err != nil {
+	if err := renameio.WriteFile(file, new, 0666); err != nil {
 		base.Fatalf("error writing go.mod: %v", err)
 	}
 	modFileData = new

src/cmd/go/internal/renameio/renameio.go

@@ -8,13 +8,14 @@ package renameio
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
+	"math/rand"
 	"os"
 	"path/filepath"
+	"strconv"
 	"time"
 )
 
-const patternSuffix = "*.tmp"
+const patternSuffix = ".tmp"
 
 // Pattern returns a glob pattern that matches the unrenamed temporary files
 // created when writing to filename.
@@ -27,14 +28,14 @@ func Pattern(filename string) string {
 // final name.
 //
 // That ensures that the final location, if it exists, is always a complete file.
-func WriteFile(filename string, data []byte) (err error) {
-	return WriteToFile(filename, bytes.NewReader(data))
+func WriteFile(filename string, data []byte, perm os.FileMode) (err error) {
+	return WriteToFile(filename, bytes.NewReader(data), perm)
 }
 
 // WriteToFile is a variant of WriteFile that accepts the data as an io.Reader
 // instead of a slice.
-func WriteToFile(filename string, data io.Reader) (err error) {
-	f, err := ioutil.TempFile(filepath.Dir(filename), filepath.Base(filename)+patternSuffix)
+func WriteToFile(filename string, data io.Reader, perm os.FileMode) (err error) {
+	f, err := tempFile(filepath.Dir(filename), filepath.Base(filename), perm)
 	if err != nil {
 		return err
 	}
@@ -79,3 +80,16 @@ func WriteToFile(filename string, data io.Reader) (err error) {
 		time.Sleep(5 * time.Millisecond)
 	}
 }
+
+// tempFile creates a new temporary file with given permission bits.
+func tempFile(dir, prefix string, perm os.FileMode) (f *os.File, err error) {
+	for i := 0; i < 10000; i++ {
+		name := filepath.Join(dir, prefix+strconv.Itoa(rand.Intn(1000000000))+patternSuffix)
+		f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
+		if os.IsExist(err) {
+			continue
+		}
+		break
+	}
+	return
+}

src/cmd/go/internal/renameio/renameio_test.go

+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package renameio writes files atomically by renaming temporary files.
+
+//+build !nacl,!plan9,!windows,!js
+
+package renameio
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+)
+
+func TestWriteFileModeAppliesUmask(t *testing.T) {
+	dir, err := ioutil.TempDir("", "renameio")
+	if err != nil {
+		t.Fatalf("Failed to create temporary directory: %v", err)
+	}
+
+	const mode = 0644
+	const umask = 0007
+	defer syscall.Umask(syscall.Umask(umask))
+
+	file := filepath.Join(dir, "testWrite")
+	err = WriteFile(file, []byte("go-build"), mode)
+	if err != nil {
+		t.Fatalf("Failed to write file: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	fi, err := os.Stat(file)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for mode %#o): %s", file, mode, err)
+	}
+
+	if fi.Mode()&os.ModePerm != 0640 {
+		t.Errorf("Stat %q: mode %#o want %#o", file, fi.Mode()&os.ModePerm, 0640)
+	}
+}