text: // Copyright © 2015 Steve Francia <spf@spf13.com>.
  // Copyright 2013 tsuru authors. All rights reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  // http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  package mem
  
  import (
  	"bytes"
  	"errors"
  	"io"
  	"os"
  	"path/filepath"
  	"sync"
  	"sync/atomic"
  )
  
  import "time"
  
  const FilePathSeparator = string(filepath.Separator)
  
  type File struct {
  	// atomic requires 64-bit alignment for struct field access
  	at           int64
  	readDirCount int64
  	closed       bool
  	readOnly     bool
  	fileData     *FileData
  }
  
  func NewFileHandle(data *FileData) *File {
  	return &File{fileData: data}
  }
  
  func NewReadOnlyFileHandle(data *FileData) *File {
  	return &File{fileData: data, readOnly: true}
  }
  
  func (f File) Data() *FileData {
  	return f.fileData
  }
  
  type FileData struct {
  	sync.Mutex
  	name    string
  	data    []byte
  	memDir  Dir
  	dir     bool
  	mode    os.FileMode
  	modtime time.Time
  }
  
  func (d *FileData) Name() string {
  	d.Lock()
  	defer d.Unlock()
  	return d.name
  }
  
  func CreateFile(name string) *FileData {
  	return &FileData{name: name, mode: os.ModeTemporary, modtime: time.Now()}
  }
  
  func CreateDir(name string) *FileData {
  	return &FileData{name: name, memDir: &DirMap{}, dir: true}
  }
  
  func ChangeFileName(f *FileData, newname string) {
  	f.Lock()
  	f.name = newname
  	f.Unlock()
  }
  
  func SetMode(f *FileData, mode os.FileMode) {
  	f.Lock()
  	f.mode = mode
  	f.Unlock()
  }
  
  func SetModTime(f *FileData, mtime time.Time) {
  	f.Lock()
  	setModTime(f, mtime)
  	f.Unlock()
  }
  
  func setModTime(f *FileData, mtime time.Time) {
  	f.modtime = mtime
  }
  
  func GetFileInfo(f *FileData) *FileInfo {
  	return &FileInfo{f}
  }
  
  func (f *File) Open() error {
  	atomic.StoreInt64(&f.at, 0)
  	atomic.StoreInt64(&f.readDirCount, 0)
  	f.fileData.Lock()
  	f.closed = false
  	f.fileData.Unlock()
  	return nil
  }
  
  func (f *File) Close() error {
  	f.fileData.Lock()
  	f.closed = true
  	if !f.readOnly {
  		setModTime(f.fileData, time.Now())
  	}
  	f.fileData.Unlock()
  	return nil
  }
  
  func (f *File) Name() string {
  	return f.fileData.Name()
  }
  
  func (f *File) Stat() (os.FileInfo, error) {
  	return &FileInfo{f.fileData}, nil
  }
  
  func (f *File) Sync() error {
  	return nil
  }
  
  func (f *File) Readdir(count int) (res []os.FileInfo, err error) {
  	if !f.fileData.dir {
  		return nil, &os.PathError{Op: "readdir", Path: f.fileData.name, Err: errors.New("not a dir")}
  	}
  	var outLength int64
  
  	f.fileData.Lock()
  	files := f.fileData.memDir.Files()[f.readDirCount:]
  	if count > 0 {
  		if len(files) < count {
  			outLength = int64(len(files))
  		} else {
  			outLength = int64(count)
  		}
  		if len(files) == 0 {
  			err = io.EOF
  		}
  	} else {
  		outLength = int64(len(files))
  	}
  	f.readDirCount += outLength
  	f.fileData.Unlock()
  
  	res = make([]os.FileInfo, outLength)
  	for i := range res {
  		res[i] = &FileInfo{files[i]}
  	}
  
  	return res, err
  }
  
  func (f *File) Readdirnames(n int) (names []string, err error) {
  	fi, err := f.Readdir(n)
  	names = make([]string, len(fi))
  	for i, f := range fi {
  		_, names[i] = filepath.Split(f.Name())
  	}
  	return names, err
  }
  
  func (f *File) Read(b []byte) (n int, err error) {
  	f.fileData.Lock()
  	defer f.fileData.Unlock()
  	if f.closed == true {
  		return 0, ErrFileClosed
  	}
  	if len(b) > 0 && int(f.at) == len(f.fileData.data) {
  		return 0, io.EOF
  	}
  	if int(f.at) > len(f.fileData.data) {
  		return 0, io.ErrUnexpectedEOF
  	}
  	if len(f.fileData.data)-int(f.at) >= len(b) {
  		n = len(b)
  	} else {
  		n = len(f.fileData.data) - int(f.at)
  	}
  	copy(b, f.fileData.data[f.at:f.at+int64(n)])
  	atomic.AddInt64(&f.at, int64(n))
  	return
  }
  
  func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
  	atomic.StoreInt64(&f.at, off)
  	return f.Read(b)
  }
  
  func (f *File) Truncate(size int64) error {
  	if f.closed == true {
  		return ErrFileClosed
  	}
  	if f.readOnly {
  		return &os.PathError{Op: "truncate", Path: f.fileData.name, Err: errors.New("file handle is read only")}
  	}
  	if size < 0 {
  		return ErrOutOfRange
  	}
  	if size > int64(len(f.fileData.data)) {
  		diff := size - int64(len(f.fileData.data))
  		f.fileData.data = append(f.fileData.data, bytes.Repeat([]byte{00}, int(diff))...)
  	} else {
  		f.fileData.data = f.fileData.data[0:size]
  	}
  	setModTime(f.fileData, time.Now())
  	return nil
  }
  
  func (f *File) Seek(offset int64, whence int) (int64, error) {
  	if f.closed == true {
  		return 0, ErrFileClosed
  	}
  	switch whence {
  	case 0:
  		atomic.StoreInt64(&f.at, offset)
  	case 1:
  		atomic.AddInt64(&f.at, int64(offset))
  	case 2:
  		atomic.StoreInt64(&f.at, int64(len(f.fileData.data))+offset)
  	}
  	return f.at, nil
  }
  
  func (f *File) Write(b []byte) (n int, err error) {
  	if f.readOnly {
  		return 0, &os.PathError{Op: "write", Path: f.fileData.name, Err: errors.New("file handle is read only")}
  	}
  	n = len(b)
  	cur := atomic.LoadInt64(&f.at)
  	f.fileData.Lock()
  	defer f.fileData.Unlock()
  	diff := cur - int64(len(f.fileData.data))
  	var tail []byte
  	if n+int(cur) < len(f.fileData.data) {
  		tail = f.fileData.data[n+int(cur):]
  	}
  	if diff > 0 {
  		f.fileData.data = append(bytes.Repeat([]byte{00}, int(diff)), b...)
  		f.fileData.data = append(f.fileData.data, tail...)
  	} else {
  		f.fileData.data = append(f.fileData.data[:cur], b...)
  		f.fileData.data = append(f.fileData.data, tail...)
  	}
  	setModTime(f.fileData, time.Now())
  
  	atomic.StoreInt64(&f.at, int64(len(f.fileData.data)))
  	return
  }
  
  func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
  	atomic.StoreInt64(&f.at, off)
  	return f.Write(b)
  }
  
  func (f *File) WriteString(s string) (ret int, err error) {
  	return f.Write([]byte(s))
  }
  
  func (f *File) Info() *FileInfo {
  	return &FileInfo{f.fileData}
  }
  
  type FileInfo struct {
  	*FileData
  }
  
  // Implements os.FileInfo
  func (s *FileInfo) Name() string {
  	s.Lock()
  	_, name := filepath.Split(s.name)
  	s.Unlock()
  	return name
  }
  func (s *FileInfo) Mode() os.FileMode {
  	s.Lock()
  	defer s.Unlock()
  	return s.mode
  }
  func (s *FileInfo) ModTime() time.Time {
  	s.Lock()
  	defer s.Unlock()
  	return s.modtime
  }
  func (s *FileInfo) IsDir() bool {
  	s.Lock()
  	defer s.Unlock()
  	return s.dir
  }
  func (s *FileInfo) Sys() interface{} { return nil }
  func (s *FileInfo) Size() int64 {
  	if s.IsDir() {
  		return int64(42)
  	}
  	s.Lock()
  	defer s.Unlock()
  	return int64(len(s.data))
  }
  
  var (
  	ErrFileClosed        = errors.New("File is closed")
  	ErrOutOfRange        = errors.New("Out of range")
  	ErrTooLarge          = errors.New("Too large")
  	ErrFileNotFound      = os.ErrNotExist
  	ErrFileExists        = os.ErrExist
  	ErrDestinationExists = os.ErrExist
  )
  