os: make Chtimes accept empty time values to skip file time modification

Empty time value time.Time{} leaves the corresponding time of the file
unchanged.

Fixes #32558

Change-Id: I1aff42f30668ff505ecec2e9509d8f2b8e4b1b6a
Reviewed-on: https://go-review.googlesource.com/c/go/+/219638
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/internal/syscall/unix/at_aix.go

@@ -11,4 +11,5 @@ package unix
 const (
 	AT_REMOVEDIR        = 0x1
 	AT_SYMLINK_NOFOLLOW = 0x1
+	UTIME_OMIT          = -0x3
 )

src/internal/syscall/unix/at_js.go

@@ -0,0 +1,13 @@
+// Copyright 2020 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 unix
+
+const (
+	// UTIME_OMIT is the sentinel value to indicate that a time value should not
+	// be changed. It is useful for example to indicate for example with UtimesNano
+	// to avoid changing AccessTime or ModifiedTime.
+	// Its value must match syscall/fs_js.go
+	UTIME_OMIT = -0x2
+)

src/internal/syscall/unix/at_solaris.go

@@ -16,4 +16,6 @@ func syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err
 const (
 	AT_REMOVEDIR        = 0x1
 	AT_SYMLINK_NOFOLLOW = 0x1000
+
+	UTIME_OMIT = -0x2
 )

src/internal/syscall/unix/at_sysnum_darwin.go

@@ -6,3 +6,5 @@ package unix
 
 const AT_REMOVEDIR = 0x80
 const AT_SYMLINK_NOFOLLOW = 0x0020
+
+const UTIME_OMIT = -0x2

src/internal/syscall/unix/at_sysnum_dragonfly.go

@@ -12,3 +12,5 @@ const fstatatTrap uintptr = syscall.SYS_FSTATAT
 
 const AT_REMOVEDIR = 0x2
 const AT_SYMLINK_NOFOLLOW = 0x1
+
+const UTIME_OMIT = -0x1

src/internal/syscall/unix/at_sysnum_freebsd.go

@@ -10,6 +10,8 @@ const (
 	AT_REMOVEDIR        = 0x800
 	AT_SYMLINK_NOFOLLOW = 0x200
 
+	UTIME_OMIT = -0x2
+
 	unlinkatTrap       uintptr = syscall.SYS_UNLINKAT
 	openatTrap         uintptr = syscall.SYS_OPENAT
 	posixFallocateTrap uintptr = syscall.SYS_POSIX_FALLOCATE

src/internal/syscall/unix/at_sysnum_linux.go

@@ -14,4 +14,6 @@ const (
 	AT_FDCWD            = -0x64
 	AT_REMOVEDIR        = 0x200
 	AT_SYMLINK_NOFOLLOW = 0x100
+
+	UTIME_OMIT = 0x3ffffffe
 )

src/internal/syscall/unix/at_sysnum_netbsd.go

@@ -12,3 +12,5 @@ const fstatatTrap uintptr = syscall.SYS_FSTATAT
 
 const AT_REMOVEDIR = 0x800
 const AT_SYMLINK_NOFOLLOW = 0x200
+
+const UTIME_OMIT = (1 << 30) - 2

src/internal/syscall/unix/at_sysnum_openbsd.go

@@ -12,3 +12,5 @@ const fstatatTrap uintptr = syscall.SYS_FSTATAT
 
 const AT_REMOVEDIR = 0x08
 const AT_SYMLINK_NOFOLLOW = 0x02
+
+const UTIME_OMIT = -0x1

src/internal/syscall/unix/at_wasip1.go

@@ -0,0 +1,13 @@
+// Copyright 2020 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 unix
+
+const (
+	// UTIME_OMIT is the sentinel value to indicate that a time value should not
+	// be changed. It is useful for example to indicate for example with UtimesNano
+	// to avoid changing AccessTime or ModifiedTime.
+	// Its value must match syscall/fs_wasip1.go
+	UTIME_OMIT = -0x2
+)

src/os/file_plan9.go

@@ -447,6 +447,7 @@ func chmod(name string, mode FileMode) error {
 
 // Chtimes changes the access and modification times of the named
 // file, similar to the Unix utime() or utimes() functions.
+// A zero time.Time value will leave the corresponding file time unchanged.
 //
 // The underlying filesystem may truncate or round the values to a
 // less precise time unit.
@@ -457,6 +458,12 @@ func Chtimes(name string, atime time.Time, mtime time.Time) error {
 	d.Null()
 	d.Atime = uint32(atime.Unix())
 	d.Mtime = uint32(mtime.Unix())
+	if atime.IsZero() {
+		d.Atime = 0xFFFFFFFF
+	}
+	if mtime.IsZero() {
+		d.Mtime = 0xFFFFFFFF
+	}
 
 	var buf [syscall.STATFIXLEN]byte
 	n, err := d.Marshal(buf[:])

src/os/file_posix.go

@@ -173,14 +173,22 @@ func (f *File) Sync() error {
 
 // Chtimes changes the access and modification times of the named
 // file, similar to the Unix utime() or utimes() functions.
+// A zero time.Time value will leave the corresponding file time unchanged.
 //
 // The underlying filesystem may truncate or round the values to a
 // less precise time unit.
 // If there is an error, it will be of type *PathError.
 func Chtimes(name string, atime time.Time, mtime time.Time) error {
 	var utimes [2]syscall.Timespec
-	utimes[0] = syscall.NsecToTimespec(atime.UnixNano())
-	utimes[1] = syscall.NsecToTimespec(mtime.UnixNano())
+	set := func(i int, t time.Time) {
+		if t.IsZero() {
+			utimes[i] = syscall.Timespec{Sec: _UTIME_OMIT, Nsec: _UTIME_OMIT}
+		} else {
+			utimes[i] = syscall.NsecToTimespec(t.UnixNano())
+		}
+	}
+	set(0, atime)
+	set(1, mtime)
 	if e := syscall.UtimesNano(fixLongPath(name), utimes[0:]); e != nil {
 		return &PathError{Op: "chtimes", Path: name, Err: e}
 	}

src/os/file_unix.go

@@ -14,6 +14,8 @@ import (
 	"syscall"
 )
 
+const _UTIME_OMIT = unix.UTIME_OMIT
+
 // fixLongPath is a noop on non-Windows platforms.
 func fixLongPath(path string) string {
 	return path

src/os/file_windows.go

@@ -15,6 +15,8 @@ import (
 	"unsafe"
 )
 
+const _UTIME_OMIT = 0
+
 // file is the real representation of *File.
 // The extra level of indirection ensures that no clients of os
 // can overwrite this data, which could cause the finalizer

src/os/os_test.go

@@ -1386,6 +1386,128 @@ func TestChtimes(t *testing.T) {
 	testChtimes(t, f.Name())
 }
 
+func TestChtimesWithZeroTimes(t *testing.T) {
+	file := newFile("chtimes-with-zero", t)
+	_, err := file.Write([]byte("hello, world\n"))
+	if err != nil {
+		t.Fatalf("Write: %s", err)
+	}
+	fName := file.Name()
+	defer Remove(file.Name())
+	err = file.Close()
+	if err != nil {
+		t.Errorf("%v", err)
+	}
+	fs, err := Stat(fName)
+	if err != nil {
+		t.Fatal(err)
+	}
+	startAtime := Atime(fs)
+	startMtime := fs.ModTime()
+	switch runtime.GOOS {
+	case "js":
+		startAtime = startAtime.Truncate(time.Second)
+		startMtime = startMtime.Truncate(time.Second)
+	}
+	at0 := startAtime
+	mt0 := startMtime
+	t0 := startMtime.Truncate(time.Second).Add(1 * time.Hour)
+
+	tests := []struct {
+		aTime     time.Time
+		mTime     time.Time
+		wantATime time.Time
+		wantMTime time.Time
+	}{
+		{
+			aTime:     time.Time{},
+			mTime:     time.Time{},
+			wantATime: startAtime,
+			wantMTime: startMtime,
+		},
+		{
+			aTime:     t0.Add(200 * time.Second),
+			mTime:     time.Time{},
+			wantATime: t0.Add(200 * time.Second),
+			wantMTime: startMtime,
+		},
+		{
+			aTime:     time.Time{},
+			mTime:     t0.Add(100 * time.Second),
+			wantATime: t0.Add(200 * time.Second),
+			wantMTime: t0.Add(100 * time.Second),
+		},
+		{
+			aTime:     t0.Add(300 * time.Second),
+			mTime:     t0.Add(100 * time.Second),
+			wantATime: t0.Add(300 * time.Second),
+			wantMTime: t0.Add(100 * time.Second),
+		},
+	}
+
+	for _, tt := range tests {
+		// Now change the times accordingly.
+		if err := Chtimes(fName, tt.aTime, tt.mTime); err != nil {
+			t.Error(err)
+		}
+
+		// Finally verify the expectations.
+		fs, err = Stat(fName)
+		if err != nil {
+			t.Error(err)
+		}
+		at0 = Atime(fs)
+		mt0 = fs.ModTime()
+
+		if got, want := at0, tt.wantATime; !got.Equal(want) {
+			errormsg := fmt.Sprintf("AccessTime mismatch with values ATime:%q-MTime:%q\ngot:  %q\nwant: %q", tt.aTime, tt.mTime, got, want)
+			switch runtime.GOOS {
+			case "plan9":
+				// Mtime is the time of the last change of
+				// content.  Similarly, atime is set whenever
+				// the contents are accessed; also, it is set
+				// whenever mtime is set.
+			case "windows":
+				t.Error(errormsg)
+			default: // unix's
+				if got, want := at0, tt.wantATime; !got.Equal(want) {
+					mounts, err := ReadFile("/bin/mounts")
+					if err != nil {
+						mounts, err = ReadFile("/etc/mtab")
+					}
+					if strings.Contains(string(mounts), "noatime") {
+						t.Log(errormsg)
+						t.Log("A filesystem is mounted with noatime; ignoring.")
+					} else {
+						switch runtime.GOOS {
+						case "netbsd", "dragonfly":
+							// On a 64-bit implementation, birth time is generally supported and cannot be changed.
+							// When supported, atime update is restricted and depends on the file system and on the
+							// OS configuration.
+							if strings.Contains(runtime.GOARCH, "64") {
+								t.Log(errormsg)
+								t.Log("Filesystem might not support atime changes; ignoring.")
+							}
+						default:
+							t.Error(errormsg)
+						}
+					}
+				}
+			}
+		}
+		if got, want := mt0, tt.wantMTime; !got.Equal(want) {
+			errormsg := fmt.Sprintf("ModTime mismatch with values ATime:%q-MTime:%q\ngot:  %q\nwant: %q", tt.aTime, tt.mTime, got, want)
+			switch runtime.GOOS {
+			case "dragonfly":
+				t.Log(errormsg)
+				t.Log("Mtime is always updated; ignoring.")
+			default:
+				t.Error(errormsg)
+			}
+		}
+	}
+}
+
 // Use TempDir (via newDir) to make sure we're on a local file system,
 // so that timings are not distorted by latency and caching.
 // On NFS, timings can be off due to caching of meta-data on

src/syscall/fs_js.go

@@ -273,6 +273,8 @@ func Lchown(path string, uid, gid int) error {
 }
 
 func UtimesNano(path string, ts []Timespec) error {
+	// UTIME_OMIT value must match internal/syscall/unix/at_js.go
+	const UTIME_OMIT = -0x2
 	if err := checkPath(path); err != nil {
 		return err
 	}
@@ -281,6 +283,18 @@ func UtimesNano(path string, ts []Timespec) error {
 	}
 	atime := ts[0].Sec
 	mtime := ts[1].Sec
+	if atime == UTIME_OMIT || mtime == UTIME_OMIT {
+		var st Stat_t
+		if err := Stat(path, &st); err != nil {
+			return err
+		}
+		if atime == UTIME_OMIT {
+			atime = st.Atime
+		}
+		if mtime == UTIME_OMIT {
+			mtime = st.Mtime
+		}
+	}
 	_, err := fsCall("utimes", path, atime, mtime)
 	return err
 }

src/syscall/fs_wasip1.go

@@ -663,17 +663,33 @@ func Lchown(path string, uid, gid int) error {
 }
 
 func UtimesNano(path string, ts []Timespec) error {
+	// UTIME_OMIT value must match internal/syscall/unix/at_wasip1.go
+	const UTIME_OMIT = -0x2
 	if path == "" {
 		return EINVAL
 	}
 	dirFd, pathPtr, pathLen := preparePath(path)
+	atime := TimespecToNsec(ts[0])
+	mtime := TimespecToNsec(ts[1])
+	if ts[0].Nsec == UTIME_OMIT || ts[1].Nsec == UTIME_OMIT {
+		var st Stat_t
+		if err := Stat(path, &st); err != nil {
+			return err
+		}
+		if ts[0].Nsec == UTIME_OMIT {
+			atime = int64(st.Atime)
+		}
+		if ts[1].Nsec == UTIME_OMIT {
+			mtime = int64(st.Mtime)
+		}
+	}
 	errno := path_filestat_set_times(
 		dirFd,
 		LOOKUP_SYMLINK_FOLLOW,
 		pathPtr,
 		pathLen,
-		timestamp(TimespecToNsec(ts[0])),
-		timestamp(TimespecToNsec(ts[1])),
+		timestamp(atime),
+		timestamp(mtime),
 		FILESTAT_SET_ATIM|FILESTAT_SET_MTIM,
 	)
 	return errnoErr(errno)

src/syscall/syscall_windows.go

@@ -635,8 +635,14 @@ func Utimes(path string, tv []Timeval) (err error) {
 		return e
 	}
 	defer Close(h)
-	a := NsecToFiletime(tv[0].Nanoseconds())
-	w := NsecToFiletime(tv[1].Nanoseconds())
+	a := Filetime{}
+	w := Filetime{}
+	if tv[0].Nanoseconds() != 0 {
+		a = NsecToFiletime(tv[0].Nanoseconds())
+	}
+	if tv[0].Nanoseconds() != 0 {
+		w = NsecToFiletime(tv[1].Nanoseconds())
+	}
 	return SetFileTime(h, nil, &a, &w)
 }
 
@@ -655,8 +661,14 @@ func UtimesNano(path string, ts []Timespec) (err error) {
 		return e
 	}
 	defer Close(h)
-	a := NsecToFiletime(TimespecToNsec(ts[0]))
-	w := NsecToFiletime(TimespecToNsec(ts[1]))
+	a := Filetime{}
+	w := Filetime{}
+	if TimespecToNsec(ts[0]) != 0 {
+		a = NsecToFiletime(TimespecToNsec(ts[0]))
+	}
+	if TimespecToNsec(ts[1]) != 0 {
+		w = NsecToFiletime(TimespecToNsec(ts[1]))
+	}
 	return SetFileTime(h, nil, &a, &w)
 }