From 66bd06748c953a4d46cedee71ca6386e11f6898e Mon Sep 17 00:00:00 2001
From: "Perez Domingo, Victor" <victor.perez@tecnalia.com>
Date: Sun, 17 Jan 2021 14:41:40 +0100
Subject: [PATCH] Fix #12, MemFS ReadDir sorted by filename

---
 memfs/memory.go      |  9 +++++++++
 memfs/memory_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/memfs/memory.go b/memfs/memory.go
index d4ac056..6054d22 100644
--- a/memfs/memory.go
+++ b/memfs/memory.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"time"
 
@@ -117,6 +118,12 @@ func (fs *Memory) Lstat(filename string) (os.FileInfo, error) {
 	return f.Stat()
 }
 
+type ByName []os.FileInfo
+
+func (a ByName) Len() int           { return len(a) }
+func (a ByName) Less(i, j int) bool { return a[i].Name() < a[j].Name() }
+func (a ByName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
 func (fs *Memory) ReadDir(path string) ([]os.FileInfo, error) {
 	if f, has := fs.s.Get(path); has {
 		if target, isLink := fs.resolveLink(path, f); isLink {
@@ -130,6 +137,8 @@ func (fs *Memory) ReadDir(path string) ([]os.FileInfo, error) {
 		entries = append(entries, fi)
 	}
 
+	sort.Sort(ByName(entries))
+
 	return entries, nil
 }
 
diff --git a/memfs/memory_test.go b/memfs/memory_test.go
index 1ec74b8..95edcc9 100644
--- a/memfs/memory_test.go
+++ b/memfs/memory_test.go
@@ -44,3 +44,27 @@ func (s *MemorySuite) TestNegativeOffsets(c *C) {
 	_, err = f.Write(buf)
 	c.Assert(err, ErrorMatches, "writeat negative: negative offset")
 }
+
+func (s *MemorySuite) TestOrder(c *C) {
+	var err error
+
+	files := []string{
+		"a",
+		"b",
+		"c",
+	}
+	for _, f := range files {
+		_, err = s.FS.Create(f)
+		c.Assert(err, IsNil)
+	}
+
+	attemps := 30
+	for n := 0; n < attemps; n++ {
+		actual, err := s.FS.ReadDir("")
+		c.Assert(err, IsNil)
+
+		for i, f := range files {
+			c.Assert(actual[i].Name(), Equals, f)
+		}
+	}
+}