restic/backend/sftp.go

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package backend
import (
"crypto/rand"
"encoding/hex"
"errors"
"fmt"
"io"
"io/ioutil"
"log"
"os"
"os/exec"
"path/filepath"
"strconv"
"strings"
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"github.com/juju/arrar"
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"github.com/pkg/sftp"
)
const (
// dirMode = 0700
// blobPath = "blobs"
// snapshotPath = "snapshots"
// treePath = "trees"
// lockPath = "locks"
// keyPath = "keys"
// tempPath = "tmp"
// versionFileName = "version"
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
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// exec.Command, it is expected to speak sftp on stdin/stdout. The backend
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// 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, blobPath),
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, blobPath),
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 blobs, refs and temp
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
}
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// open backend
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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 Blob:
n = blobPath
case Snapshot:
n = snapshotPath
case Tree:
n = treePath
case Lock:
n = lockPath
case Key:
n = keyPath
}
return filepath.Join(r.p, n)
}
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// 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.
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func (r *SFTP) Create(t Type, data []byte) (ID, error) {
// TODO: make sure that tempfile is removed upon error
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// 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
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filename, file, err := r.tempFile()
if err != nil {
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return nil, arrar.Annotate(err, "create tempfile")
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}
// write data to tempfile
_, err = file.Write(data)
if err != nil {
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return nil, arrar.Annotate(err, "writing data to tempfile")
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}
err = file.Close()
if err != nil {
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return nil, arrar.Annotate(err, "close tempfile")
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}
// return id
err = r.renameFile(filename, t, id)
if err != nil {
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return nil, arrar.Annotate(err, "rename file")
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}
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() {
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if file != nil {
file.Close()
}
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}()
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if err == nil {
return true, nil
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}
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return false, err
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}
// 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()
}