package backend import ( "crypto/rand" "crypto/sha256" "encoding/hex" "errors" "fmt" "io" "io/ioutil" "log" "os" "os/exec" "path/filepath" "strings" "github.com/pkg/sftp" ) const ( tempfileRandomSuffixLength = 10 ) type SFTP struct { c *sftp.Client p string ver uint id ID cmd *exec.Cmd } func start_client(program string, args ...string) (*SFTP, error) { // Connect to a remote host and request the sftp subsystem via the 'ssh' // command. This assumes that passwordless login is correctly configured. cmd := exec.Command(program, args...) // send errors from ssh to stderr cmd.Stderr = os.Stderr // get stdin and stdout wr, err := cmd.StdinPipe() if err != nil { log.Fatal(err) } rd, err := cmd.StdoutPipe() if err != nil { log.Fatal(err) } // start the process if err := cmd.Start(); err != nil { log.Fatal(err) } // open the SFTP session client, err := sftp.NewClientPipe(rd, wr) if err != nil { log.Fatal(err) } return &SFTP{c: client, cmd: cmd}, nil } // OpenSFTP opens an sftp backend. When the command is started via // exec.Command, it is expected to speak sftp on stdin/stdout. The backend // is expected at the given path. func OpenSFTP(dir string, program string, args ...string) (*SFTP, error) { sftp, err := start_client(program, args...) if err != nil { return nil, err } // test if all necessary dirs and files are there items := []string{ dir, filepath.Join(dir, dataPath), filepath.Join(dir, snapshotPath), filepath.Join(dir, treePath), filepath.Join(dir, lockPath), filepath.Join(dir, keyPath), filepath.Join(dir, tempPath), } for _, d := range items { if _, err := sftp.c.Lstat(d); err != nil { return nil, fmt.Errorf("%s does not exist", d) } } // read version file f, err := sftp.c.Open(filepath.Join(dir, versionFileName)) if err != nil { return nil, fmt.Errorf("unable to read version file: %v\n", err) } var version uint n, err := fmt.Fscanf(f, "%d", &version) if err != nil { return nil, err } if n != 1 { return nil, errors.New("could not read version from file") } err = f.Close() if err != nil { return nil, err } // check version if version != BackendVersion { return nil, fmt.Errorf("wrong version %d", version) } // read ID f, err = sftp.c.Open(filepath.Join(dir, idFileName)) if err != nil { return nil, err } buf, err := ioutil.ReadAll(f) if err != nil { return nil, err } err = f.Close() if err != nil { return nil, err } id, err := ParseID(strings.TrimSpace(string(buf))) if err != nil { return nil, err } sftp.id = id sftp.p = dir return sftp, nil } // CreateSFTP creates all the necessary files and directories for a new sftp // backend at dir. func CreateSFTP(dir string, program string, args ...string) (*SFTP, error) { sftp, err := start_client(program, args...) if err != nil { return nil, err } versionFile := filepath.Join(dir, versionFileName) idFile := filepath.Join(dir, idFileName) dirs := []string{ dir, filepath.Join(dir, dataPath), filepath.Join(dir, snapshotPath), filepath.Join(dir, treePath), filepath.Join(dir, lockPath), filepath.Join(dir, keyPath), filepath.Join(dir, tempPath), } // test if files already exist _, err = sftp.c.Lstat(versionFile) if err == nil { return nil, errors.New("version file already exists") } _, err = sftp.c.Lstat(idFile) if err == nil { return nil, errors.New("id file already exists") } // test if directories already exist for _, d := range dirs[1:] { if _, err := sftp.c.Lstat(d); err == nil { return nil, fmt.Errorf("dir %s already exists", d) } } // create paths for data, refs and temp blobs for _, d := range dirs { err = sftp.mkdirAll(d, dirMode) if err != nil { return nil, err } } // create version file f, err := sftp.c.Create(versionFile) if err != nil { return nil, err } _, err = fmt.Fprintf(f, "%d\n", BackendVersion) if err != nil { return nil, err } err = f.Close() if err != nil { return nil, err } // create ID file id := make([]byte, sha256.Size) _, err = rand.Read(id) if err != nil { return nil, err } f, err = sftp.c.Create(idFile) if err != nil { return nil, err } _, err = fmt.Fprintf(f, "%s\n", ID(id).String()) if err != nil { return nil, err } err = f.Close() if err != nil { return nil, err } err = sftp.c.Close() if err != nil { return nil, err } err = sftp.cmd.Wait() if err != nil { return nil, err } // open backend return OpenSFTP(dir, program, args...) } // Location returns this backend's location (the directory name). func (r *SFTP) Location() string { return r.p } // Return temp directory in correct directory for this backend. func (r *SFTP) tempFile() (string, *sftp.File, error) { // choose random suffix buf := make([]byte, tempfileRandomSuffixLength) n, err := io.ReadFull(rand.Reader, buf) if err != nil { return "", nil, err } if n != len(buf) { return "", nil, errors.New("unable to generate enough random bytes for temp file") } // construct tempfile name name := filepath.Join(r.p, tempPath, fmt.Sprintf("temp-%s", hex.EncodeToString(buf))) // create file in temp dir f, err := r.c.Create(name) if err != nil { return "", nil, err } return name, f, nil } func (r *SFTP) mkdirAll(dir string, mode os.FileMode) error { // check if directory already exists fi, err := r.c.Lstat(dir) if err == nil { if fi.IsDir() { return nil } return fmt.Errorf("mkdirAll(%s): entry exists but is not a directory", dir) } // create parent directories errMkdirAll := r.mkdirAll(filepath.Dir(dir), dirMode) // create directory errMkdir := r.c.Mkdir(dir) // test if directory was created successfully fi, err = r.c.Lstat(dir) if err != nil { // return previous errors return fmt.Errorf("mkdirAll(%s): unable to create directories: %v, %v", dir, errMkdirAll, errMkdir) } if !fi.IsDir() { return fmt.Errorf("mkdirAll(%s): entry exists but is not a directory", dir) } // set mode return r.c.Chmod(dir, mode) } // Rename temp file to final name according to type and ID. func (r *SFTP) renameFile(oldname string, t Type, id ID) error { filename := r.filename(t, id) // create directories if necessary if t == Data || t == Tree { err := r.mkdirAll(filepath.Dir(filename), dirMode) if err != nil { return err } } err := r.c.Rename(oldname, filename) if err != nil { return err } // set mode to read-only fi, err := r.c.Lstat(filename) if err != nil { return err } return r.c.Chmod(filename, fi.Mode()&os.FileMode(^uint32(0222))) } // Construct directory for given Type. func (r *SFTP) dirname(t Type, id ID) string { var n string switch t { case Data: n = dataPath if id != nil { n = filepath.Join(dataPath, fmt.Sprintf("%02x", id[0])) } case Snapshot: n = snapshotPath case Tree: n = treePath if id != nil { n = filepath.Join(treePath, fmt.Sprintf("%02x", id[0])) } case Lock: n = lockPath case Key: n = keyPath } return filepath.Join(r.p, n) } type sftpBlob struct { f *sftp.File name string hw *HashingWriter backend *SFTP tpe Type id ID size uint closed bool } func (sb *sftpBlob) Close() error { if sb.closed { return errors.New("Close() called on closed file") } sb.closed = true err := sb.f.Close() if err != nil { return fmt.Errorf("sftp: file.Close: %v", err) } // get ID sb.id = ID(sb.hw.Sum(nil)) // check for duplicate ID res, err := sb.backend.Test(sb.tpe, sb.id) if err != nil { return fmt.Errorf("testing presence of ID %v failed: %v", sb.id, err) } if res { return ErrAlreadyPresent } // rename file err = sb.backend.renameFile(sb.name, sb.tpe, sb.id) if err != nil { return err } return nil } func (sb *sftpBlob) Write(p []byte) (int, error) { n, err := sb.hw.Write(p) sb.size += uint(n) return n, err } func (sb *sftpBlob) Size() uint { return sb.size } func (sb *sftpBlob) ID() (ID, error) { if sb.id == nil { return nil, errors.New("blob is not closed, ID unavailable") } return sb.id, nil } // Create creates a new blob of type t. Blob implements io.WriteCloser. Once // Close() has been called, ID() can be used to retrieve the ID. If the blob is // already present, Close() returns ErrAlreadyPresent. func (r *SFTP) Create(t Type) (Blob, error) { // TODO: make sure that tempfile is removed upon error // create tempfile in backend filename, file, err := r.tempFile() if err != nil { return nil, err } blob := sftpBlob{ hw: NewHashingWriter(file, newHash()), f: file, name: filename, backend: r, tpe: t, } return &blob, nil } // Construct path for given Type and ID. func (r *SFTP) filename(t Type, id ID) string { return filepath.Join(r.dirname(t, id), id.String()) } // Get returns the content stored under the given ID. If the data doesn't match // the requested ID, ErrWrongData is returned. func (r *SFTP) Get(t Type, id ID) ([]byte, error) { if id == nil { return nil, errors.New("unable to load nil ID") } // try to open file file, err := r.c.Open(r.filename(t, id)) defer func() { // TODO: report bug against sftp client, ignore Close() for nil file if file != nil { file.Close() } }() if err != nil { return nil, err } // read all buf, err := ioutil.ReadAll(file) if err != nil { return nil, err } // check id if !Hash(buf).Equal(id) { return nil, ErrWrongData } return buf, nil } // GetReader returns a reader that yields the content stored under the given // ID. The content is not verified. The reader should be closed after draining // it. func (r *SFTP) GetReader(t Type, id ID) (io.ReadCloser, error) { if id == nil { return nil, errors.New("unable to load nil ID") } // try to open file file, err := r.c.Open(r.filename(t, id)) if err != nil { return nil, err } return file, nil } // Test returns true if a blob of the given type and ID exists in the backend. func (r *SFTP) Test(t Type, id ID) (bool, error) { file, err := r.c.Open(r.filename(t, id)) defer func() { if file != nil { file.Close() } }() if err != nil { if _, ok := err.(*sftp.StatusError); ok { return false, nil } return false, err } return true, nil } // Remove removes the content stored at ID. func (r *SFTP) Remove(t Type, id ID) error { return r.c.Remove(r.filename(t, id)) } // List lists all objects of a given type. func (r *SFTP) List(t Type) (IDs, error) { list := []os.FileInfo{} var err error if t == Data || t == Tree { // read first level basedir := r.dirname(t, nil) list1, err := r.c.ReadDir(basedir) if err != nil { return nil, err } // read files for _, dir := range list1 { entries, err := r.c.ReadDir(filepath.Join(basedir, dir.Name())) if err != nil { return nil, err } for _, entry := range entries { list = append(list, entry) } } } else { list, err = r.c.ReadDir(r.dirname(t, nil)) if err != nil { return nil, err } } ids := make(IDs, 0, len(list)) for _, item := range list { id, err := ParseID(item.Name()) // ignore everything that does not parse as an ID if err != nil { continue } ids = append(ids, id) } return ids, nil } // Version returns the version of this local backend. func (r *SFTP) Version() uint { return r.ver } // ID returns the ID of this local backend. func (r *SFTP) ID() ID { return r.id } // Close closes the sftp connection and terminates the underlying command. func (s *SFTP) Close() error { s.c.Close() // TODO: add timeout after which the process is killed return s.cmd.Wait() }