--- /dev/null
+// Copyright 2023 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 fs
+
+import (
+ "time"
+)
+
+// FormatFileInfo returns a formatted version of info for human readability.
+// Implementations of FileInfo can call this from a String method.
+// The output for a file named "hello.go", 100 bytes, mode 0o644, created
+// January 1, 1970 at noon is
+//
+// -rw-r--r-- 100 1970-01-01 12:00:00 hello.go
+func FormatFileInfo(info FileInfo) string {
+ name := info.Name()
+ b := make([]byte, 0, 40+len(name))
+ b = append(b, info.Mode().String()...)
+ b = append(b, ' ')
+
+ size := info.Size()
+ var usize uint64
+ if size >= 0 {
+ usize = uint64(size)
+ } else {
+ b = append(b, '-')
+ usize = uint64(-size)
+ }
+ var buf [20]byte
+ i := len(buf) - 1
+ for usize >= 10 {
+ q := usize / 10
+ buf[i] = byte('0' + usize - q*10)
+ i--
+ usize = q
+ }
+ buf[i] = byte('0' + usize)
+ b = append(b, buf[i:]...)
+ b = append(b, ' ')
+
+ b = append(b, info.ModTime().Format(time.DateTime)...)
+ b = append(b, ' ')
+
+ b = append(b, name...)
+ if info.IsDir() {
+ b = append(b, '/')
+ }
+
+ return string(b)
+}
+
+// FormatDirEntry returns a formatted version of dir for human readability.
+// Implementations of DirEntry can call this from a String method.
+// The outputs for a directory named subdir and a file named hello.go are:
+//
+// d subdir/
+// - hello.go
+func FormatDirEntry(dir DirEntry) string {
+ name := dir.Name()
+ b := make([]byte, 0, 5+len(name))
+
+ // The Type method does not return any permission bits,
+ // so strip them from the string.
+ mode := dir.Type().String()
+ mode = mode[:len(mode)-9]
+
+ b = append(b, mode...)
+ b = append(b, ' ')
+ b = append(b, name...)
+ if dir.IsDir() {
+ b = append(b, '/')
+ }
+ return string(b)
+}
--- /dev/null
+// Copyright 2023 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 fs_test
+
+import (
+ . "io/fs"
+ "testing"
+ "time"
+)
+
+// formatTest implements FileInfo to test FormatFileInfo,
+// and implements DirEntry to test FormatDirEntry.
+type formatTest struct {
+ name string
+ size int64
+ mode FileMode
+ modTime time.Time
+ isDir bool
+}
+
+func (fs *formatTest) Name() string {
+ return fs.name
+}
+
+func (fs *formatTest) Size() int64 {
+ return fs.size
+}
+
+func (fs *formatTest) Mode() FileMode {
+ return fs.mode
+}
+
+func (fs *formatTest) ModTime() time.Time {
+ return fs.modTime
+}
+
+func (fs *formatTest) IsDir() bool {
+ return fs.isDir
+}
+
+func (fs *formatTest) Sys() any {
+ return nil
+}
+
+func (fs *formatTest) Type() FileMode {
+ return fs.mode.Type()
+}
+
+func (fs *formatTest) Info() (FileInfo, error) {
+ return fs, nil
+}
+
+var formatTests = []struct {
+ input formatTest
+ wantFileInfo string
+ wantDirEntry string
+}{
+ {
+ formatTest{
+ name: "hello.go",
+ size: 100,
+ mode: 0o644,
+ modTime: time.Date(1970, time.January, 1, 12, 0, 0, 0, time.UTC),
+ isDir: false,
+ },
+ "-rw-r--r-- 100 1970-01-01 12:00:00 hello.go",
+ "- hello.go",
+ },
+ {
+ formatTest{
+ name: "home/gopher",
+ size: 0,
+ mode: ModeDir | 0o755,
+ modTime: time.Date(1970, time.January, 1, 12, 0, 0, 0, time.UTC),
+ isDir: true,
+ },
+ "drwxr-xr-x 0 1970-01-01 12:00:00 home/gopher/",
+ "d home/gopher/",
+ },
+ {
+ formatTest{
+ name: "big",
+ size: 0x7fffffffffffffff,
+ mode: ModeIrregular | 0o644,
+ modTime: time.Date(1970, time.January, 1, 12, 0, 0, 0, time.UTC),
+ isDir: false,
+ },
+ "?rw-r--r-- 9223372036854775807 1970-01-01 12:00:00 big",
+ "? big",
+ },
+ {
+ formatTest{
+ name: "small",
+ size: -0x8000000000000000,
+ mode: ModeSocket | ModeSetuid | 0o644,
+ modTime: time.Date(1970, time.January, 1, 12, 0, 0, 0, time.UTC),
+ isDir: false,
+ },
+ "Surw-r--r-- -9223372036854775808 1970-01-01 12:00:00 small",
+ "S small",
+ },
+}
+
+func TestFormatFileInfo(t *testing.T) {
+ for i, test := range formatTests {
+ got := FormatFileInfo(&test.input)
+ if got != test.wantFileInfo {
+ t.Errorf("%d: FormatFileInfo(%#v) = %q, want %q", i, test.input, got, test.wantFileInfo)
+ }
+ }
+}
+
+func TestFormatDirEntry(t *testing.T) {
+ for i, test := range formatTests {
+ got := FormatDirEntry(&test.input)
+ if got != test.wantDirEntry {
+ t.Errorf("%d: FormatDirEntry(%#v) = %q, want %q", i, test.input, got, test.wantDirEntry)
+ }
+ }
+
+}