--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/vendor/github.com/spf13/afero/unionFile.go	Sat Sep 29 18:09:54 2018 +0200
@@ -0,0 +1,305 @@
+package afero
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+// The UnionFile implements the afero.File interface and will be returned
+// when reading a directory present at least in the overlay or opening a file
+// for writing.
+//
+// The calls to
+// Readdir() and Readdirnames() merge the file os.FileInfo / names from the
+// base and the overlay - for files present in both layers, only those
+// from the overlay will be used.
+//
+// When opening files for writing (Create() / OpenFile() with the right flags)
+// the operations will be done in both layers, starting with the overlay. A
+// successful read in the overlay will move the cursor position in the base layer
+// by the number of bytes read.
+type UnionFile struct {
+	Base   File
+	Layer  File
+	Merger DirsMerger
+	off    int
+	files  []os.FileInfo
+}
+
+func (f *UnionFile) Close() error {
+	// first close base, so we have a newer timestamp in the overlay. If we'd close
+	// the overlay first, we'd get a cacheStale the next time we access this file
+	// -> cache would be useless ;-)
+	if f.Base != nil {
+		f.Base.Close()
+	}
+	if f.Layer != nil {
+		return f.Layer.Close()
+	}
+	return BADFD
+}
+
+func (f *UnionFile) Read(s []byte) (int, error) {
+	if f.Layer != nil {
+		n, err := f.Layer.Read(s)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			// advance the file position also in the base file, the next
+			// call may be a write at this position (or a seek with SEEK_CUR)
+			if _, seekErr := f.Base.Seek(int64(n), os.SEEK_CUR); seekErr != nil {
+				// only overwrite err in case the seek fails: we need to
+				// report an eventual io.EOF to the caller
+				err = seekErr
+			}
+		}
+		return n, err
+	}
+	if f.Base != nil {
+		return f.Base.Read(s)
+	}
+	return 0, BADFD
+}
+
+func (f *UnionFile) ReadAt(s []byte, o int64) (int, error) {
+	if f.Layer != nil {
+		n, err := f.Layer.ReadAt(s, o)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o+int64(n), os.SEEK_SET)
+		}
+		return n, err
+	}
+	if f.Base != nil {
+		return f.Base.ReadAt(s, o)
+	}
+	return 0, BADFD
+}
+
+func (f *UnionFile) Seek(o int64, w int) (pos int64, err error) {
+	if f.Layer != nil {
+		pos, err = f.Layer.Seek(o, w)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o, w)
+		}
+		return pos, err
+	}
+	if f.Base != nil {
+		return f.Base.Seek(o, w)
+	}
+	return 0, BADFD
+}
+
+func (f *UnionFile) Write(s []byte) (n int, err error) {
+	if f.Layer != nil {
+		n, err = f.Layer.Write(s)
+		if err == nil && f.Base != nil { // hmm, do we have fixed size files where a write may hit the EOF mark?
+			_, err = f.Base.Write(s)
+		}
+		return n, err
+	}
+	if f.Base != nil {
+		return f.Base.Write(s)
+	}
+	return 0, BADFD
+}
+
+func (f *UnionFile) WriteAt(s []byte, o int64) (n int, err error) {
+	if f.Layer != nil {
+		n, err = f.Layer.WriteAt(s, o)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteAt(s, o)
+		}
+		return n, err
+	}
+	if f.Base != nil {
+		return f.Base.WriteAt(s, o)
+	}
+	return 0, BADFD
+}
+
+func (f *UnionFile) Name() string {
+	if f.Layer != nil {
+		return f.Layer.Name()
+	}
+	return f.Base.Name()
+}
+
+// DirsMerger is how UnionFile weaves two directories together.
+// It takes the FileInfo slices from the layer and the base and returns a
+// single view.
+type DirsMerger func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error)
+
+var defaultUnionMergeDirsFn = func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error) {
+	var files = make(map[string]os.FileInfo)
+
+	for _, fi := range lofi {
+		files[fi.Name()] = fi
+	}
+
+	for _, fi := range bofi {
+		if _, exists := files[fi.Name()]; !exists {
+			files[fi.Name()] = fi
+		}
+	}
+
+	rfi := make([]os.FileInfo, len(files))
+
+	i := 0
+	for _, fi := range files {
+		rfi[i] = fi
+		i++
+	}
+
+	return rfi, nil
+
+}
+
+// Readdir will weave the two directories together and
+// return a single view of the overlayed directories
+func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
+	var merge DirsMerger = f.Merger
+	if merge == nil {
+		merge = defaultUnionMergeDirsFn
+	}
+
+	if f.off == 0 {
+		var lfi []os.FileInfo
+		if f.Layer != nil {
+			lfi, err = f.Layer.Readdir(-1)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		var bfi []os.FileInfo
+		if f.Base != nil {
+			bfi, err = f.Base.Readdir(-1)
+			if err != nil {
+				return nil, err
+			}
+
+		}
+		merged, err := merge(lfi, bfi)
+		if err != nil {
+			return nil, err
+		}
+		f.files = append(f.files, merged...)
+	}
+	if c == -1 {
+		return f.files[f.off:], nil
+	}
+	defer func() { f.off += c }()
+	return f.files[f.off:c], nil
+}
+
+func (f *UnionFile) Readdirnames(c int) ([]string, error) {
+	rfi, err := f.Readdir(c)
+	if err != nil {
+		return nil, err
+	}
+	var names []string
+	for _, fi := range rfi {
+		names = append(names, fi.Name())
+	}
+	return names, nil
+}
+
+func (f *UnionFile) Stat() (os.FileInfo, error) {
+	if f.Layer != nil {
+		return f.Layer.Stat()
+	}
+	if f.Base != nil {
+		return f.Base.Stat()
+	}
+	return nil, BADFD
+}
+
+func (f *UnionFile) Sync() (err error) {
+	if f.Layer != nil {
+		err = f.Layer.Sync()
+		if err == nil && f.Base != nil {
+			err = f.Base.Sync()
+		}
+		return err
+	}
+	if f.Base != nil {
+		return f.Base.Sync()
+	}
+	return BADFD
+}
+
+func (f *UnionFile) Truncate(s int64) (err error) {
+	if f.Layer != nil {
+		err = f.Layer.Truncate(s)
+		if err == nil && f.Base != nil {
+			err = f.Base.Truncate(s)
+		}
+		return err
+	}
+	if f.Base != nil {
+		return f.Base.Truncate(s)
+	}
+	return BADFD
+}
+
+func (f *UnionFile) WriteString(s string) (n int, err error) {
+	if f.Layer != nil {
+		n, err = f.Layer.WriteString(s)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteString(s)
+		}
+		return n, err
+	}
+	if f.Base != nil {
+		return f.Base.WriteString(s)
+	}
+	return 0, BADFD
+}
+
+func copyToLayer(base Fs, layer Fs, name string) error {
+	bfh, err := base.Open(name)
+	if err != nil {
+		return err
+	}
+	defer bfh.Close()
+
+	// First make sure the directory exists
+	exists, err := Exists(layer, filepath.Dir(name))
+	if err != nil {
+		return err
+	}
+	if !exists {
+		err = layer.MkdirAll(filepath.Dir(name), 0777) // FIXME?
+		if err != nil {
+			return err
+		}
+	}
+
+	// Create the file on the overlay
+	lfh, err := layer.Create(name)
+	if err != nil {
+		return err
+	}
+	n, err := io.Copy(lfh, bfh)
+	if err != nil {
+		// If anything fails, clean up the file
+		layer.Remove(name)
+		lfh.Close()
+		return err
+	}
+
+	bfi, err := bfh.Stat()
+	if err != nil || bfi.Size() != n {
+		layer.Remove(name)
+		lfh.Close()
+		return syscall.EIO
+	}
+
+	err = lfh.Close()
+	if err != nil {
+		layer.Remove(name)
+		lfh.Close()
+		return err
+	}
+	return layer.Chtimes(name, bfi.ModTime(), bfi.ModTime())
+}