--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/vendor/github.com/spf13/afero/cacheOnReadFs.go	Sat Sep 29 18:09:54 2018 +0200
@@ -0,0 +1,290 @@
+package afero
+
+import (
+	"os"
+	"syscall"
+	"time"
+)
+
+// If the cache duration is 0, cache time will be unlimited, i.e. once
+// a file is in the layer, the base will never be read again for this file.
+//
+// For cache times greater than 0, the modification time of a file is
+// checked. Note that a lot of file system implementations only allow a
+// resolution of a second for timestamps... or as the godoc for os.Chtimes()
+// states: "The underlying filesystem may truncate or round the values to a
+// less precise time unit."
+//
+// This caching union will forward all write calls also to the base file
+// system first. To prevent writing to the base Fs, wrap it in a read-only
+// filter - Note: this will also make the overlay read-only, for writing files
+// in the overlay, use the overlay Fs directly, not via the union Fs.
+type CacheOnReadFs struct {
+	base      Fs
+	layer     Fs
+	cacheTime time.Duration
+}
+
+func NewCacheOnReadFs(base Fs, layer Fs, cacheTime time.Duration) Fs {
+	return &CacheOnReadFs{base: base, layer: layer, cacheTime: cacheTime}
+}
+
+type cacheState int
+
+const (
+	// not present in the overlay, unknown if it exists in the base:
+	cacheMiss cacheState = iota
+	// present in the overlay and in base, base file is newer:
+	cacheStale
+	// present in the overlay - with cache time == 0 it may exist in the base,
+	// with cacheTime > 0 it exists in the base and is same age or newer in the
+	// overlay
+	cacheHit
+	// happens if someone writes directly to the overlay without
+	// going through this union
+	cacheLocal
+)
+
+func (u *CacheOnReadFs) cacheStatus(name string) (state cacheState, fi os.FileInfo, err error) {
+	var lfi, bfi os.FileInfo
+	lfi, err = u.layer.Stat(name)
+	if err == nil {
+		if u.cacheTime == 0 {
+			return cacheHit, lfi, nil
+		}
+		if lfi.ModTime().Add(u.cacheTime).Before(time.Now()) {
+			bfi, err = u.base.Stat(name)
+			if err != nil {
+				return cacheLocal, lfi, nil
+			}
+			if bfi.ModTime().After(lfi.ModTime()) {
+				return cacheStale, bfi, nil
+			}
+		}
+		return cacheHit, lfi, nil
+	}
+
+	if err == syscall.ENOENT || os.IsNotExist(err) {
+		return cacheMiss, nil, nil
+	}
+
+	return cacheMiss, nil, err
+}
+
+func (u *CacheOnReadFs) copyToLayer(name string) error {
+	return copyToLayer(u.base, u.layer, name)
+}
+
+func (u *CacheOnReadFs) Chtimes(name string, atime, mtime time.Time) error {
+	st, _, err := u.cacheStatus(name)
+	if err != nil {
+		return err
+	}
+	switch st {
+	case cacheLocal:
+	case cacheHit:
+		err = u.base.Chtimes(name, atime, mtime)
+	case cacheStale, cacheMiss:
+		if err := u.copyToLayer(name); err != nil {
+			return err
+		}
+		err = u.base.Chtimes(name, atime, mtime)
+	}
+	if err != nil {
+		return err
+	}
+	return u.layer.Chtimes(name, atime, mtime)
+}
+
+func (u *CacheOnReadFs) Chmod(name string, mode os.FileMode) error {
+	st, _, err := u.cacheStatus(name)
+	if err != nil {
+		return err
+	}
+	switch st {
+	case cacheLocal:
+	case cacheHit:
+		err = u.base.Chmod(name, mode)
+	case cacheStale, cacheMiss:
+		if err := u.copyToLayer(name); err != nil {
+			return err
+		}
+		err = u.base.Chmod(name, mode)
+	}
+	if err != nil {
+		return err
+	}
+	return u.layer.Chmod(name, mode)
+}
+
+func (u *CacheOnReadFs) Stat(name string) (os.FileInfo, error) {
+	st, fi, err := u.cacheStatus(name)
+	if err != nil {
+		return nil, err
+	}
+	switch st {
+	case cacheMiss:
+		return u.base.Stat(name)
+	default: // cacheStale has base, cacheHit and cacheLocal the layer os.FileInfo
+		return fi, nil
+	}
+}
+
+func (u *CacheOnReadFs) Rename(oldname, newname string) error {
+	st, _, err := u.cacheStatus(oldname)
+	if err != nil {
+		return err
+	}
+	switch st {
+	case cacheLocal:
+	case cacheHit:
+		err = u.base.Rename(oldname, newname)
+	case cacheStale, cacheMiss:
+		if err := u.copyToLayer(oldname); err != nil {
+			return err
+		}
+		err = u.base.Rename(oldname, newname)
+	}
+	if err != nil {
+		return err
+	}
+	return u.layer.Rename(oldname, newname)
+}
+
+func (u *CacheOnReadFs) Remove(name string) error {
+	st, _, err := u.cacheStatus(name)
+	if err != nil {
+		return err
+	}
+	switch st {
+	case cacheLocal:
+	case cacheHit, cacheStale, cacheMiss:
+		err = u.base.Remove(name)
+	}
+	if err != nil {
+		return err
+	}
+	return u.layer.Remove(name)
+}
+
+func (u *CacheOnReadFs) RemoveAll(name string) error {
+	st, _, err := u.cacheStatus(name)
+	if err != nil {
+		return err
+	}
+	switch st {
+	case cacheLocal:
+	case cacheHit, cacheStale, cacheMiss:
+		err = u.base.RemoveAll(name)
+	}
+	if err != nil {
+		return err
+	}
+	return u.layer.RemoveAll(name)
+}
+
+func (u *CacheOnReadFs) OpenFile(name string, flag int, perm os.FileMode) (File, error) {
+	st, _, err := u.cacheStatus(name)
+	if err != nil {
+		return nil, err
+	}
+	switch st {
+	case cacheLocal, cacheHit:
+	default:
+		if err := u.copyToLayer(name); err != nil {
+			return nil, err
+		}
+	}
+	if flag&(os.O_WRONLY|syscall.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_TRUNC) != 0 {
+		bfi, err := u.base.OpenFile(name, flag, perm)
+		if err != nil {
+			return nil, err
+		}
+		lfi, err := u.layer.OpenFile(name, flag, perm)
+		if err != nil {
+			bfi.Close() // oops, what if O_TRUNC was set and file opening in the layer failed...?
+			return nil, err
+		}
+		return &UnionFile{Base: bfi, Layer: lfi}, nil
+	}
+	return u.layer.OpenFile(name, flag, perm)
+}
+
+func (u *CacheOnReadFs) Open(name string) (File, error) {
+	st, fi, err := u.cacheStatus(name)
+	if err != nil {
+		return nil, err
+	}
+
+	switch st {
+	case cacheLocal:
+		return u.layer.Open(name)
+
+	case cacheMiss:
+		bfi, err := u.base.Stat(name)
+		if err != nil {
+			return nil, err
+		}
+		if bfi.IsDir() {
+			return u.base.Open(name)
+		}
+		if err := u.copyToLayer(name); err != nil {
+			return nil, err
+		}
+		return u.layer.Open(name)
+
+	case cacheStale:
+		if !fi.IsDir() {
+			if err := u.copyToLayer(name); err != nil {
+				return nil, err
+			}
+			return u.layer.Open(name)
+		}
+	case cacheHit:
+		if !fi.IsDir() {
+			return u.layer.Open(name)
+		}
+	}
+	// the dirs from cacheHit, cacheStale fall down here:
+	bfile, _ := u.base.Open(name)
+	lfile, err := u.layer.Open(name)
+	if err != nil && bfile == nil {
+		return nil, err
+	}
+	return &UnionFile{Base: bfile, Layer: lfile}, nil
+}
+
+func (u *CacheOnReadFs) Mkdir(name string, perm os.FileMode) error {
+	err := u.base.Mkdir(name, perm)
+	if err != nil {
+		return err
+	}
+	return u.layer.MkdirAll(name, perm) // yes, MkdirAll... we cannot assume it exists in the cache
+}
+
+func (u *CacheOnReadFs) Name() string {
+	return "CacheOnReadFs"
+}
+
+func (u *CacheOnReadFs) MkdirAll(name string, perm os.FileMode) error {
+	err := u.base.MkdirAll(name, perm)
+	if err != nil {
+		return err
+	}
+	return u.layer.MkdirAll(name, perm)
+}
+
+func (u *CacheOnReadFs) Create(name string) (File, error) {
+	bfh, err := u.base.Create(name)
+	if err != nil {
+		return nil, err
+	}
+	lfh, err := u.layer.Create(name)
+	if err != nil {
+		// oops, see comment about OS_TRUNC above, should we remove? then we have to
+		// remember if the file did not exist before
+		bfh.Close()
+		return nil, err
+	}
+	return &UnionFile{Base: bfh, Layer: lfh}, nil
+}