3 files changed, 65 insertions, 15 deletions

diff --git a/fs/fs.go b/fs/fs.go
index cbfeb44..b06ded8 100644
--- a/fs/fs.go
+++ b/fs/fs.go
@@ -29,10 +29,13 @@ type RegularFile interface {
 type Dir interface {
 	File
 	Readdir() ([]File, error)
+	GetChild(name string) (File, error) // Must return os.ErrNotExist, if child doesn't exist
 
 	CreateChildFile(name string, exec bool) (RegularFile, error)
 	CreateChildDir(name string) (Dir, error)
 	CreateChildSymlink(name string, target string) (Symlink, error)
+
+	RenameChild(oldname, newname string) error
 }
 
 type Symlink interface {
diff --git a/fs/memory.go b/fs/memory.go
index 5f5d327..221ff36 100644
--- a/fs/memory.go
+++ b/fs/memory.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"errors"
 	"io"
+	"os"
 	"time"
 )
 
@@ -14,7 +15,13 @@ type memfsBase struct {
 	mtime  time.Time
 }
 
+type memfsChild interface {
+	File
+	setName(string)
+}
+
 func (b memfsBase) Name() string       { return b.name }
+func (b *memfsBase) setName(n string)  { b.name = n }
 func (b memfsBase) Executable() bool   { return b.exec }
 func (b memfsBase) ModTime() time.Time { return b.mtime }
 
@@ -45,13 +52,13 @@ func (f memfsFile) Write(p []byte) (int, error) {
 	return f.content.Write(p)
 }
 
-func (memfsBase) Close() error {
+func (memfsFile) Close() error {
 	return nil
 }
 
 type memfsDir struct {
 	memfsBase
-	children map[string]File
+	children map[string]memfsChild
 }
 
 func (memfsDir) Type() FileType { return FDir }
@@ -66,6 +73,14 @@ func (d memfsDir) Readdir() ([]File, error) {
 	return l, nil
 }
 
+func (d memfsDir) GetChild(name string) (File, error) {
+	c, ok := d.children[name]
+	if !ok {
+		return nil, os.ErrNotExist
+	}
+	return c, nil
+}
+
 func (d memfsDir) createChildBase(name string, exec bool) memfsBase {
 	return memfsBase{
 		parent: &d,
@@ -80,17 +95,17 @@ func (d memfsDir) CreateChildFile(name string, exec bool) (RegularFile, error) {
 		memfsBase: d.createChildBase(name, exec),
 		content:   new(bytes.Buffer),
 	}
-	d.children[name] = child
-	return child, nil
+	d.children[name] = &child
+	return &child, nil
 }
 
 func (d memfsDir) CreateChildDir(name string) (Dir, error) {
 	child := memfsDir{
 		memfsBase: d.createChildBase(name, true),
-		children:  make(map[string]File),
+		children:  make(map[string]memfsChild),
 	}
-	d.children[name] = child
-	return child, nil
+	d.children[name] = &child
+	return &child, nil
 }
 
 func (d memfsDir) CreateChildSymlink(name string, target string) (Symlink, error) {
@@ -98,23 +113,37 @@ func (d memfsDir) CreateChildSymlink(name string, target string) (Symlink, error
 		memfsBase: d.createChildBase(name, false),
 		target:    target,
 	}
-	d.children[name] = child
-	return child, nil
+	d.children[name] = &child
+	return &child, nil
 }
 
 func (d *memfsDir) deleteChild(name string) {
 	delete(d.children, name)
 }
 
+func (d *memfsDir) RenameChild(oldname, newname string) error {
+	c, ok := d.children[oldname]
+	if !ok {
+		return os.ErrNotExist
+	}
+
+	c.setName(newname)
+
+	delete(d.children, oldname)
+	d.children[newname] = c
+
+	return nil
+}
+
 func NewMemoryFSRoot(name string) Dir {
-	return memfsDir{
+	return &memfsDir{
 		memfsBase: memfsBase{
 			parent: nil,
 			name:   name,
 			exec:   true,
 			mtime:  time.Now(),
 		},
-		children: make(map[string]File),
+		children: make(map[string]memfsChild),
 	}
 }
 
diff --git a/fs/os.go b/fs/os.go
index f251c66..0a4f614 100644
--- a/fs/os.go
+++ b/fs/os.go
@@ -3,9 +3,14 @@ package fs
 import (
 	"io"
 	"os"
+	"strings"
 	"time"
 )
 
+func pathJoin(parts ...string) string {
+	return strings.Join(parts, string(os.PathSeparator))
+}
+
 func openOSFile(path string) (osFile, error) {
 	fi, err := os.Lstat(path)
 	if err != nil {
@@ -79,7 +84,7 @@ func (f osFile) Readdir() (list []File, err error) {
 		}
 
 		list = append(list, osFile{
-			fullpath: f.fullpath + string(os.PathSeparator) + fi.Name(),
+			fullpath: pathJoin(f.fullpath, fi.Name()),
 			fi:       fi,
 		})
 	}
@@ -87,6 +92,15 @@ func (f osFile) Readdir() (list []File, err error) {
 	return
 }
 
+func (f osFile) GetChild(name string) (File, error) {
+	path := pathJoin(f.fullpath, name)
+	fi, err := os.Lstat(path)
+	if err != nil {
+		return nil, err
+	}
+	return osFile{path, fi}, nil
+}
+
 func perms(executable bool) os.FileMode {
 	if executable {
 		return 0755
@@ -96,7 +110,7 @@ func perms(executable bool) os.FileMode {
 }
 
 func (f osFile) CreateChildFile(name string, exec bool) (RegularFile, error) {
-	p := f.fullpath + string(os.PathSeparator) + name
+	p := pathJoin(f.fullpath, name)
 
 	fh, err := os.OpenFile(p, os.O_RDWR|os.O_CREATE, perms(exec))
 	if err != nil {
@@ -108,7 +122,7 @@ func (f osFile) CreateChildFile(name string, exec bool) (RegularFile, error) {
 }
 
 func (f osFile) CreateChildDir(name string) (Dir, error) {
-	p := f.fullpath + string(os.PathSeparator) + name
+	p := pathJoin(f.fullpath, name)
 
 	if err := os.Mkdir(p, perms(true)); err != nil {
 		return nil, err
@@ -118,7 +132,7 @@ func (f osFile) CreateChildDir(name string) (Dir, error) {
 }
 
 func (f osFile) CreateChildSymlink(name string, target string) (Symlink, error) {
-	p := f.fullpath + string(os.PathSeparator) + name
+	p := pathJoin(f.fullpath, name)
 
 	err := os.Symlink(target, p)
 	if err != nil {
@@ -128,6 +142,10 @@ func (f osFile) CreateChildSymlink(name string, target string) (Symlink, error)
 	return openOSFile(p)
 }
 
+func (f osFile) RenameChild(oldname, newname string) error {
+	return os.Rename(pathJoin(f.fullpath, oldname), pathJoin(f.fullpath, newname))
+}
+
 func (f osFile) Readlink() (string, error) {
 	return os.Readlink(f.fullpath)
 }