add changes to maintain perms and owner of logfile

chown.go

@@ -0,0 +1,12 @@
+// +build !linux
+
+package lumberjack
+
+import (
+	"os"
+	"syscall"
+)
+
+func chown(_ string, _ os.FileInfo) error {
+	return nil
+}

chown_linux.go

@@ -0,0 +1,19 @@
+package lumberjack
+
+import (
+	"os"
+	"syscall"
+)
+
+// os_Chown is a var so we can mock it out during tests.
+var os_Chown = os.Chown
+
+func chown(name string, info os.FileInfo) error {
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, info.Mode())
+	if err != nil {
+		return err
+	}
+	f.Close()
+	stat := info.Sys().(*syscall.Stat_t)
+	return os_Chown(name, int(stat.Uid), int(stat.Gid))
+}

chown_test.go

@@ -0,0 +1,67 @@
+// +build linux
+
+package lumberjack
+
+import (
+	"os"
+	"syscall"
+	"testing"
+)
+
+func TestMaintainOwner(t *testing.T) {
+	fakeC := fakeChown{}
+	os_Chown = fakeC.Set
+	os_Stat = fakeStat
+	defer func() {
+		os_Chown = os.Chown
+		os_Stat = os.Stat
+	}()
+	currentTime = fakeTime
+	dir := makeTempDir("TestMaintainOwner", t)
+	defer os.RemoveAll(dir)
+
+	filename := logFile(dir)
+
+	l := &Logger{
+		Filename:   filename,
+		MaxBackups: 1,
+		MaxSize:    100, // megabytes
+	}
+	defer l.Close()
+	b := []byte("boo!")
+	n, err := l.Write(b)
+	isNil(err, t)
+	equals(len(b), n, t)
+
+	newFakeTime()
+
+	err = l.Rotate()
+	isNil(err, t)
+
+	equals(555, fakeC.uid, t)
+	equals(666, fakeC.gid, t)
+}
+
+type fakeChown struct {
+	name string
+	uid  int
+	gid  int
+}
+
+func (f *fakeChown) Set(name string, uid, gid int) error {
+	f.name = name
+	f.uid = uid
+	f.gid = gid
+	return nil
+}
+
+func fakeStat(name string) (os.FileInfo, error) {
+	info, err := os.Stat(name)
+	if err != nil {
+		return info, err
+	}
+	stat := info.Sys().(*syscall.Stat_t)
+	stat.Uid = 555
+	stat.Gid = 666
+	return info, nil
+}

lumberjack.go

@@ -101,6 +101,9 @@ var (
 	// currentTime exists so it can be mocked out by tests.
 	currentTime = time.Now
 
+	// os_Stat exists so it can be mocked out by tests.
+	os_Stat = os.Stat
+
 	// megabyte is the conversion factor between MaxSize and bytes.  It is a
 	// variable so tests can mock it out and not need to write megabytes of data
 	// to disk.
@@ -191,19 +194,27 @@ func (l *Logger) openNew() error {
 	}
 
 	name := l.filename()
-	_, err = os.Stat(name)
+	mode := os.FileMode(0644)
+	info, err := os_Stat(name)
 	if err == nil {
+		// Copy the mode off the old logfile.
+		mode = info.Mode()
 		// move the existing file
 		newname := backupName(name, l.LocalTime)
 		if err := os.Rename(name, newname); err != nil {
 			return fmt.Errorf("can't rename log file: %s", err)
 		}
+
+		// this is a no-op anywhere but linux
+		if err := chown(name, info); err != nil {
+			return err
+		}
 	}
 
 	// we use truncate here because this should only get called when we've moved
 	// the file ourselves. if someone else creates the file in the meantime,
 	// just wipe out the contents.
-	f, err := os.OpenFile(l.filename(), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
 	if err != nil {
 		return fmt.Errorf("can't open new logfile: %s", err)
 	}
@@ -234,7 +245,7 @@ func backupName(name string, local bool) string {
 // put it over the MaxSize, a new file is created.
 func (l *Logger) openExistingOrNew(writeLen int) error {
 	filename := l.filename()
-	info, err := os.Stat(filename)
+	info, err := os_Stat(filename)
 	if os.IsNotExist(err) {
 		return l.openNew()
 	}

lumberjack_test.go

@@ -493,7 +493,6 @@ func TestRotate(t *testing.T) {
 	existsWithLen(filename2, n, t)
 	existsWithLen(filename, 0, t)
 	fileCount(dir, 2, t)
-
 	newFakeTime()
 
 	err = l.Rotate()
@@ -574,6 +573,43 @@ localtime = true`[1:]
 	equals(0, len(md.Undecoded()), t)
 }
 
+func TestMaintainMode(t *testing.T) {
+	currentTime = fakeTime
+	dir := makeTempDir("TestMaintainMode", t)
+	defer os.RemoveAll(dir)
+
+	filename := logFile(dir)
+
+	mode := os.FileMode(0770)
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, mode)
+	isNil(err, t)
+	f.Close()
+
+	l := &Logger{
+		Filename:   filename,
+		MaxBackups: 1,
+		MaxSize:    100, // megabytes
+	}
+	defer l.Close()
+	b := []byte("boo!")
+	n, err := l.Write(b)
+	isNil(err, t)
+	equals(len(b), n, t)
+
+	newFakeTime()
+
+	err = l.Rotate()
+	isNil(err, t)
+
+	filename2 := backupFile(dir)
+	info, err := os.Stat(filename)
+	isNil(err, t)
+	info2, err := os.Stat(filename2)
+	isNil(err, t)
+	equals(mode, info.Mode(), t)
+	equals(mode, info2.Mode(), t)
+}
+
 // makeTempDir creates a file with a semi-unique name in the OS temp directory.
 // It should be based on the name of the test, to keep parallel tests from
 // colliding, and must be cleaned up after the test is finished.