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restic/internal/fs/fs_reader.go
Michael Eischer 48dbefc37e fs / archiver: convert to handle based interface
The actual implementation still relies on file paths, but with the
abstraction layer in place, an FS implementation can ensure atomic file
accesses in the future.
2024-11-16 12:56:23 +01:00

305 lines
6.8 KiB
Go

package fs
import (
"fmt"
"io"
"os"
"path"
"sync"
"syscall"
"time"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/restic"
)
// Reader is a file system which provides a directory with a single file. When
// this file is opened for reading, the reader is passed through. The file can
// be opened once, all subsequent open calls return syscall.EIO. For Lstat(),
// the provided FileInfo is returned.
type Reader struct {
Name string
io.ReadCloser
// for FileInfo
Mode os.FileMode
ModTime time.Time
Size int64
AllowEmptyFile bool
open sync.Once
}
// statically ensure that Local implements FS.
var _ FS = &Reader{}
// VolumeName returns leading volume name, for the Reader file system it's
// always the empty string.
func (fs *Reader) VolumeName(_ string) string {
return ""
}
func (fs *Reader) fi() os.FileInfo {
return fakeFileInfo{
name: fs.Name,
size: fs.Size,
mode: fs.Mode,
modtime: fs.ModTime,
}
}
func (fs *Reader) OpenFile(name string, flag int, _ bool) (f File, err error) {
if flag & ^(O_RDONLY|O_NOFOLLOW) != 0 {
return nil, pathError("open", name,
fmt.Errorf("invalid combination of flags 0x%x", flag))
}
switch name {
case fs.Name:
fs.open.Do(func() {
f = newReaderFile(fs.ReadCloser, fs.fi(), fs.AllowEmptyFile)
})
if f == nil {
return nil, pathError("open", name, syscall.EIO)
}
return f, nil
case "/", ".":
f = fakeDir{
entries: []os.FileInfo{fs.fi()},
}
return f, nil
}
return nil, pathError("open", name, syscall.ENOENT)
}
// Lstat returns the FileInfo structure describing the named file.
// If the file is a symbolic link, the returned FileInfo
// describes the symbolic link. Lstat makes no attempt to follow the link.
// If there is an error, it will be of type *os.PathError.
func (fs *Reader) Lstat(name string) (os.FileInfo, error) {
getDirInfo := func(name string) os.FileInfo {
fi := fakeFileInfo{
name: fs.Base(name),
size: 0,
mode: os.ModeDir | 0755,
modtime: time.Now(),
}
return fi
}
switch name {
case fs.Name:
return fs.fi(), nil
case "/", ".":
return getDirInfo(name), nil
}
dir := fs.Dir(fs.Name)
for {
if dir == "/" || dir == "." {
break
}
if name == dir {
return getDirInfo(name), nil
}
dir = fs.Dir(dir)
}
return nil, pathError("lstat", name, os.ErrNotExist)
}
func (fs *Reader) DeviceID(_ os.FileInfo) (deviceID uint64, err error) {
return 0, errors.New("Device IDs are not supported")
}
func (fs *Reader) ExtendedStat(fi os.FileInfo) ExtendedFileInfo {
return ExtendedFileInfo{
FileInfo: fi,
}
}
// Join joins any number of path elements into a single path, adding a
// Separator if necessary. Join calls Clean on the result; in particular, all
// empty strings are ignored. On Windows, the result is a UNC path if and only
// if the first path element is a UNC path.
func (fs *Reader) Join(elem ...string) string {
return path.Join(elem...)
}
// Separator returns the OS and FS dependent separator for dirs/subdirs/files.
func (fs *Reader) Separator() string {
return "/"
}
// IsAbs reports whether the path is absolute. For the Reader, this is always the case.
func (fs *Reader) IsAbs(_ string) bool {
return true
}
// Abs returns an absolute representation of path. If the path is not absolute
// it will be joined with the current working directory to turn it into an
// absolute path. The absolute path name for a given file is not guaranteed to
// be unique. Abs calls Clean on the result.
//
// For the Reader, all paths are absolute.
func (fs *Reader) Abs(p string) (string, error) {
return path.Clean(p), nil
}
// Clean returns the cleaned path. For details, see filepath.Clean.
func (fs *Reader) Clean(p string) string {
return path.Clean(p)
}
// Base returns the last element of p.
func (fs *Reader) Base(p string) string {
return path.Base(p)
}
// Dir returns p without the last element.
func (fs *Reader) Dir(p string) string {
return path.Dir(p)
}
func newReaderFile(rd io.ReadCloser, fi os.FileInfo, allowEmptyFile bool) *readerFile {
return &readerFile{
ReadCloser: rd,
AllowEmptyFile: allowEmptyFile,
fakeFile: fakeFile{
FileInfo: fi,
name: fi.Name(),
},
}
}
type readerFile struct {
io.ReadCloser
AllowEmptyFile, bytesRead bool
fakeFile
}
// ErrFileEmpty is returned inside a *os.PathError by Read() for the file
// opened from the fs provided by Reader when no data could be read and
// AllowEmptyFile is not set.
var ErrFileEmpty = errors.New("no data read")
func (r *readerFile) Read(p []byte) (int, error) {
n, err := r.ReadCloser.Read(p)
if n > 0 {
r.bytesRead = true
}
// return an error if we did not read any data
if err == io.EOF && !r.AllowEmptyFile && !r.bytesRead {
return n, pathError("read", r.fakeFile.name, ErrFileEmpty)
}
return n, err
}
func (r *readerFile) Close() error {
return r.ReadCloser.Close()
}
// ensure that readerFile implements File
var _ File = &readerFile{}
// fakeFile implements all File methods, but only returns errors for anything
// except Stat()
type fakeFile struct {
name string
os.FileInfo
}
// ensure that fakeFile implements File
var _ File = fakeFile{}
func (f fakeFile) MakeReadable() error {
return nil
}
func (f fakeFile) Readdirnames(_ int) ([]string, error) {
return nil, pathError("readdirnames", f.name, os.ErrInvalid)
}
func (f fakeFile) Read(_ []byte) (int, error) {
return 0, pathError("read", f.name, os.ErrInvalid)
}
func (f fakeFile) Close() error {
return nil
}
func (f fakeFile) Stat() (os.FileInfo, error) {
return f.FileInfo, nil
}
func (f fakeFile) ToNode(_ bool) (*restic.Node, error) {
node := buildBasicNode(f.name, f.FileInfo)
// fill minimal info with current values for uid, gid
node.UID = uint32(os.Getuid())
node.GID = uint32(os.Getgid())
node.ChangeTime = node.ModTime
return node, nil
}
// fakeDir implements Readdirnames and Readdir, everything else is delegated to fakeFile.
type fakeDir struct {
entries []os.FileInfo
fakeFile
}
func (d fakeDir) Readdirnames(n int) ([]string, error) {
if n > 0 {
return nil, pathError("readdirnames", d.name, errors.New("not implemented"))
}
names := make([]string, 0, len(d.entries))
for _, entry := range d.entries {
names = append(names, entry.Name())
}
return names, nil
}
// fakeFileInfo implements the bare minimum of os.FileInfo.
type fakeFileInfo struct {
name string
size int64
mode os.FileMode
modtime time.Time
}
func (fi fakeFileInfo) Name() string {
return fi.name
}
func (fi fakeFileInfo) Size() int64 {
return fi.size
}
func (fi fakeFileInfo) Mode() os.FileMode {
return fi.mode
}
func (fi fakeFileInfo) ModTime() time.Time {
return fi.modtime
}
func (fi fakeFileInfo) IsDir() bool {
return fi.mode&os.ModeDir > 0
}
func (fi fakeFileInfo) Sys() interface{} {
return nil
}
func pathError(op, name string, err error) *os.PathError {
return &os.PathError{Op: op, Path: name, Err: err}
}