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), io.SeekCurrent); 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), io.SeekStart) } 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) { 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. // At the end of the directory view, the error is io.EOF if c > 0. 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...) } files := f.files[f.off:] if c <= 0 { return files, nil } if len(files) == 0 { return nil, io.EOF } if c > len(files) { c = len(files) } defer func() { f.off += c }() return files[: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 copyFile(base Fs, layer Fs, name string, bfh File) error { // 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), 0o777) // 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()) } func copyToLayer(base Fs, layer Fs, name string) error { bfh, err := base.Open(name) if err != nil { return err } defer bfh.Close() return copyFile(base, layer, name, bfh) } func copyFileToLayer(base Fs, layer Fs, name string, flag int, perm os.FileMode) error { bfh, err := base.OpenFile(name, flag, perm) if err != nil { return err } defer bfh.Close() return copyFile(base, layer, name, bfh) }