package backend import ( "crypto/rand" "encoding/hex" "errors" "fmt" "io" "io/ioutil" "log" "os" "os/exec" "path/filepath" "strconv" "strings" "github.com/juju/arrar" "github.com/pkg/sftp" ) const ( tempfileRandomSuffixLength = 10 ) type SFTP struct { c *sftp.Client p string ver uint 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) } buf := make([]byte, 100) n, err := f.Read(buf) if err != nil && err != io.EOF { return nil, err } err = f.Close() if err != nil { return nil, err } version, err := strconv.Atoi(strings.TrimSpace(string(buf[:n]))) if err != nil { return nil, fmt.Errorf("unable to convert version to integer: %v\n", err) } // check version if version != BackendVersion { return nil, fmt.Errorf("wrong version %d", version) } 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) 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 version file already exists _, err = sftp.c.Lstat(versionFile) if err == nil { return nil, errors.New("version 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 { // TODO: implement client.MkdirAll() and set mode to dirMode _, err = sftp.c.Lstat(d) if err != nil { err = sftp.c.Mkdir(d) if err != nil { return nil, err } } } // create version file f, err := sftp.c.Create(versionFile) if err != nil { return nil, err } _, err = f.Write([]byte(strconv.Itoa(BackendVersion))) 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 } // Rename temp file to final name according to type and ID. func (r *SFTP) renameFile(filename string, t Type, id ID) error { return r.c.Rename(filename, filepath.Join(r.dir(t), id.String())) } // Construct directory for given Type. func (r *SFTP) dir(t Type) string { var n string switch t { case Data: n = dataPath case Snapshot: n = snapshotPath case Tree: n = treePath case Lock: n = lockPath case Key: n = keyPath } return filepath.Join(r.p, n) } // Create stores new content of type t and data and returns the ID. If the blob // is already present, returns ErrAlreadyPresent and the blob's ID. func (r *SFTP) Create(t Type, data []byte) (ID, error) { // TODO: make sure that tempfile is removed upon error // check if blob is already present in backend id := IDFromData(data) if ok, _ := r.Test(t, id); ok { return id, ErrAlreadyPresent } // create tempfile in backend filename, file, err := r.tempFile() if err != nil { return nil, arrar.Annotate(err, "create tempfile") } // write data to tempfile _, err = file.Write(data) if err != nil { return nil, arrar.Annotate(err, "writing data to tempfile") } err = file.Close() if err != nil { return nil, arrar.Annotate(err, "close tempfile") } // return id err = r.renameFile(filename, t, id) if err != nil { return nil, arrar.Annotate(err, "rename file") } return id, nil } // Construct path for given Type and ID. func (r *SFTP) filename(t Type, id ID) string { return filepath.Join(r.dir(t), id.String()) } // Get returns the content stored under the given ID. func (r *SFTP) Get(t Type, id ID) ([]byte, error) { // try to open file file, err := r.c.Open(r.filename(t, id)) defer file.Close() if err != nil { return nil, err } // read all buf, err := ioutil.ReadAll(file) if err != nil { return nil, err } return buf, 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 { return true, nil } return false, err } // 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, err := r.c.ReadDir(r.dir(t)) 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 } // 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() }