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|
package afero
import (
"fmt"
"os"
"path/filepath"
"syscall"
"time"
)
var _ Lstater = (*CopyOnWriteFs)(nil)
// The CopyOnWriteFs is a union filesystem: a read only base file system with
// a possibly writeable layer on top. Changes to the file system will only
// be made in the overlay: Changing an existing file in the base layer which
// is not present in the overlay will copy the file to the overlay ("changing"
// includes also calls to e.g. Chtimes() and Chmod()).
//
// Reading directories is currently only supported via Open(), not OpenFile().
type CopyOnWriteFs struct {
base Fs
layer Fs
}
func NewCopyOnWriteFs(base Fs, layer Fs) Fs {
return &CopyOnWriteFs{base: base, layer: layer}
}
// Returns true if the file is not in the overlay
func (u *CopyOnWriteFs) isBaseFile(name string) (bool, error) {
if _, err := u.layer.Stat(name); err == nil {
return false, nil
}
_, err := u.base.Stat(name)
if err != nil {
if oerr, ok := err.(*os.PathError); ok {
if oerr.Err == os.ErrNotExist || oerr.Err == syscall.ENOENT || oerr.Err == syscall.ENOTDIR {
return false, nil
}
}
if err == syscall.ENOENT {
return false, nil
}
}
return true, err
}
func (u *CopyOnWriteFs) copyToLayer(name string) error {
return copyToLayer(u.base, u.layer, name)
}
func (u *CopyOnWriteFs) Chtimes(name string, atime, mtime time.Time) error {
b, err := u.isBaseFile(name)
if err != nil {
return err
}
if b {
if err := u.copyToLayer(name); err != nil {
return err
}
}
return u.layer.Chtimes(name, atime, mtime)
}
func (u *CopyOnWriteFs) Chmod(name string, mode os.FileMode) error {
b, err := u.isBaseFile(name)
if err != nil {
return err
}
if b {
if err := u.copyToLayer(name); err != nil {
return err
}
}
return u.layer.Chmod(name, mode)
}
func (u *CopyOnWriteFs) Stat(name string) (os.FileInfo, error) {
fi, err := u.layer.Stat(name)
if err != nil {
isNotExist := u.isNotExist(err)
if isNotExist {
return u.base.Stat(name)
}
return nil, err
}
return fi, nil
}
func (u *CopyOnWriteFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
llayer, ok1 := u.layer.(Lstater)
lbase, ok2 := u.base.(Lstater)
if ok1 {
fi, b, err := llayer.LstatIfPossible(name)
if err == nil {
return fi, b, nil
}
if !u.isNotExist(err) {
return nil, b, err
}
}
if ok2 {
fi, b, err := lbase.LstatIfPossible(name)
if err == nil {
return fi, b, nil
}
if !u.isNotExist(err) {
return nil, b, err
}
}
fi, err := u.Stat(name)
return fi, false, err
}
func (u *CopyOnWriteFs) isNotExist(err error) bool {
if e, ok := err.(*os.PathError); ok {
err = e.Err
}
if err == os.ErrNotExist || err == syscall.ENOENT || err == syscall.ENOTDIR {
return true
}
return false
}
// Renaming files present only in the base layer is not permitted
func (u *CopyOnWriteFs) Rename(oldname, newname string) error {
b, err := u.isBaseFile(oldname)
if err != nil {
return err
}
if b {
return syscall.EPERM
}
return u.layer.Rename(oldname, newname)
}
// Removing files present only in the base layer is not permitted. If
// a file is present in the base layer and the overlay, only the overlay
// will be removed.
func (u *CopyOnWriteFs) Remove(name string) error {
err := u.layer.Remove(name)
switch err {
case syscall.ENOENT:
_, err = u.base.Stat(name)
if err == nil {
return syscall.EPERM
}
return syscall.ENOENT
default:
return err
}
}
func (u *CopyOnWriteFs) RemoveAll(name string) error {
err := u.layer.RemoveAll(name)
switch err {
case syscall.ENOENT:
_, err = u.base.Stat(name)
if err == nil {
return syscall.EPERM
}
return syscall.ENOENT
default:
return err
}
}
func (u *CopyOnWriteFs) OpenFile(name string, flag int, perm os.FileMode) (File, error) {
b, err := u.isBaseFile(name)
if err != nil {
return nil, err
}
if flag&(os.O_WRONLY|os.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_TRUNC) != 0 {
if b {
if err = u.copyToLayer(name); err != nil {
return nil, err
}
return u.layer.OpenFile(name, flag, perm)
}
dir := filepath.Dir(name)
isaDir, err := IsDir(u.base, dir)
if err != nil && !os.IsNotExist(err) {
return nil, err
}
if isaDir {
if err = u.layer.MkdirAll(dir, 0777); err != nil {
return nil, err
}
return u.layer.OpenFile(name, flag, perm)
}
isaDir, err = IsDir(u.layer, dir)
if err != nil {
return nil, err
}
if isaDir {
return u.layer.OpenFile(name, flag, perm)
}
return nil, &os.PathError{Op: "open", Path: name, Err: syscall.ENOTDIR} // ...or os.ErrNotExist?
}
if b {
return u.base.OpenFile(name, flag, perm)
}
return u.layer.OpenFile(name, flag, perm)
}
// This function handles the 9 different possibilities caused
// by the union which are the intersection of the following...
// layer: doesn't exist, exists as a file, and exists as a directory
// base: doesn't exist, exists as a file, and exists as a directory
func (u *CopyOnWriteFs) Open(name string) (File, error) {
// Since the overlay overrides the base we check that first
b, err := u.isBaseFile(name)
if err != nil {
return nil, err
}
// If overlay doesn't exist, return the base (base state irrelevant)
if b {
return u.base.Open(name)
}
// If overlay is a file, return it (base state irrelevant)
dir, err := IsDir(u.layer, name)
if err != nil {
return nil, err
}
if !dir {
return u.layer.Open(name)
}
// Overlay is a directory, base state now matters.
// Base state has 3 states to check but 2 outcomes:
// A. It's a file or non-readable in the base (return just the overlay)
// B. It's an accessible directory in the base (return a UnionFile)
// If base is file or nonreadable, return overlay
dir, err = IsDir(u.base, name)
if !dir || err != nil {
return u.layer.Open(name)
}
// Both base & layer are directories
// Return union file (if opens are without error)
bfile, bErr := u.base.Open(name)
lfile, lErr := u.layer.Open(name)
// If either have errors at this point something is very wrong. Return nil and the errors
if bErr != nil || lErr != nil {
return nil, fmt.Errorf("BaseErr: %v\nOverlayErr: %v", bErr, lErr)
}
return &UnionFile{Base: bfile, Layer: lfile}, nil
}
func (u *CopyOnWriteFs) Mkdir(name string, perm os.FileMode) error {
dir, err := IsDir(u.base, name)
if err != nil {
return u.layer.MkdirAll(name, perm)
}
if dir {
return ErrFileExists
}
return u.layer.MkdirAll(name, perm)
}
func (u *CopyOnWriteFs) Name() string {
return "CopyOnWriteFs"
}
func (u *CopyOnWriteFs) MkdirAll(name string, perm os.FileMode) error {
dir, err := IsDir(u.base, name)
if err != nil {
return u.layer.MkdirAll(name, perm)
}
if dir {
// This is in line with how os.MkdirAll behaves.
return nil
}
return u.layer.MkdirAll(name, perm)
}
func (u *CopyOnWriteFs) Create(name string) (File, error) {
return u.OpenFile(name, os.O_CREATE|os.O_TRUNC|os.O_RDWR, 0666)
}
|
