1 files changed, 76 insertions, 0 deletions
diff --git a/src/io/fs/format.go b/src/io/fs/format.go
new file mode 100644
index 0000000..60b40df
--- /dev/null
+++ b/src/io/fs/format.go
@@ -0,0 +1,76 @@
+// 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)
+}