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pack.go
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pack.go
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package pack
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"sync"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/restic"
"github.com/restic/restic/internal/crypto"
)
// Packer is used to create a new Pack.
type Packer struct {
blobs []restic.Blob
bytes uint
k *crypto.Key
wr io.Writer
m sync.Mutex
}
// NewPacker returns a new Packer that can be used to pack blobs
// together. If wr is nil, a bytes.Buffer is used.
func NewPacker(k *crypto.Key, wr io.Writer) *Packer {
if wr == nil {
wr = bytes.NewBuffer(nil)
}
return &Packer{k: k, wr: wr}
}
// Add saves the data read from rd as a new blob to the packer. Returned is the
// number of bytes written to the pack.
func (p *Packer) Add(t restic.BlobType, id restic.ID, data []byte) (int, error) {
p.m.Lock()
defer p.m.Unlock()
c := restic.Blob{Type: t, ID: id}
n, err := p.wr.Write(data)
c.Length = uint(n)
c.Offset = p.bytes
p.bytes += uint(n)
p.blobs = append(p.blobs, c)
return n, errors.Wrap(err, "Write")
}
var entrySize = uint(binary.Size(restic.BlobType(0)) + binary.Size(uint32(0)) + len(restic.ID{}))
// headerEntry is used with encoding/binary to read and write header entries
type headerEntry struct {
Type uint8
Length uint32
ID restic.ID
}
// Finalize writes the header for all added blobs and finalizes the pack.
// Returned are the number of bytes written, including the header. If the
// underlying writer implements io.Closer, it is closed.
func (p *Packer) Finalize() (uint, error) {
p.m.Lock()
defer p.m.Unlock()
bytesWritten := p.bytes
hdrBuf := bytes.NewBuffer(nil)
bytesHeader, err := p.writeHeader(hdrBuf)
if err != nil {
return 0, err
}
encryptedHeader := make([]byte, 0, hdrBuf.Len()+p.k.Overhead()+p.k.NonceSize())
nonce := crypto.NewRandomNonce()
encryptedHeader = append(encryptedHeader, nonce...)
encryptedHeader = p.k.Seal(encryptedHeader, nonce, hdrBuf.Bytes(), nil)
// append the header
n, err := p.wr.Write(encryptedHeader)
if err != nil {
return 0, errors.Wrap(err, "Write")
}
hdrBytes := restic.CiphertextLength(int(bytesHeader))
if n != hdrBytes {
return 0, errors.New("wrong number of bytes written")
}
bytesWritten += uint(hdrBytes)
// write length
err = binary.Write(p.wr, binary.LittleEndian, uint32(restic.CiphertextLength(len(p.blobs)*int(entrySize))))
if err != nil {
return 0, errors.Wrap(err, "binary.Write")
}
bytesWritten += uint(binary.Size(uint32(0)))
p.bytes = uint(bytesWritten)
if w, ok := p.wr.(io.Closer); ok {
return bytesWritten, w.Close()
}
return bytesWritten, nil
}
// writeHeader constructs and writes the header to wr.
func (p *Packer) writeHeader(wr io.Writer) (bytesWritten uint, err error) {
for _, b := range p.blobs {
entry := headerEntry{
Length: uint32(b.Length),
ID: b.ID,
}
switch b.Type {
case restic.DataBlob:
entry.Type = 0
case restic.TreeBlob:
entry.Type = 1
default:
return 0, errors.Errorf("invalid blob type %v", b.Type)
}
err := binary.Write(wr, binary.LittleEndian, entry)
if err != nil {
return bytesWritten, errors.Wrap(err, "binary.Write")
}
bytesWritten += entrySize
}
return
}
// Size returns the number of bytes written so far.
func (p *Packer) Size() uint {
p.m.Lock()
defer p.m.Unlock()
return p.bytes
}
// Count returns the number of blobs in this packer.
func (p *Packer) Count() int {
p.m.Lock()
defer p.m.Unlock()
return len(p.blobs)
}
// Blobs returns the slice of blobs that have been written.
func (p *Packer) Blobs() []restic.Blob {
p.m.Lock()
defer p.m.Unlock()
return p.blobs
}
// Writer return the underlying writer.
func (p *Packer) Writer() io.Writer {
return p.wr
}
func (p *Packer) String() string {
return fmt.Sprintf("<Packer %d blobs, %d bytes>", len(p.blobs), p.bytes)
}
var (
// size of the header-length field at the end of the file
headerLengthSize = binary.Size(uint32(0))
// we require at least one entry in the header, and one blob for a pack file
minFileSize = entrySize + crypto.Extension + uint(headerLengthSize)
)
const (
maxHeaderSize = 16 * 1024 * 1024
// number of header enries to download as part of header-length request
eagerEntries = 15
)
// readRecords reads up to max records from the underlying ReaderAt, returning
// the raw header, the total number of records in the header, and any error.
// If the header contains fewer than max entries, the header is truncated to
// the appropriate size.
func readRecords(rd io.ReaderAt, size int64, max int) ([]byte, int, error) {
var bufsize int
bufsize += max * int(entrySize)
bufsize += crypto.Extension
bufsize += headerLengthSize
if bufsize > int(size) {
bufsize = int(size)
}
b := make([]byte, bufsize)
off := size - int64(bufsize)
if _, err := rd.ReadAt(b, off); err != nil {
return nil, 0, err
}
hlen := binary.LittleEndian.Uint32(b[len(b)-headerLengthSize:])
b = b[:len(b)-headerLengthSize]
debug.Log("header length: %v", hlen)
var err error
switch {
case hlen == 0:
err = InvalidFileError{Message: "header length is zero"}
case hlen < crypto.Extension:
err = InvalidFileError{Message: "header length is too small"}
case (hlen-crypto.Extension)%uint32(entrySize) != 0:
err = InvalidFileError{Message: "header length is invalid"}
case int64(hlen) > size-int64(headerLengthSize):
err = InvalidFileError{Message: "header is larger than file"}
case int64(hlen) > maxHeaderSize:
err = InvalidFileError{Message: "header is larger than maxHeaderSize"}
}
if err != nil {
return nil, 0, errors.Wrap(err, "readHeader")
}
total := (int(hlen) - crypto.Extension) / int(entrySize)
if total < max {
// truncate to the beginning of the pack header
b = b[len(b)-int(hlen):]
}
return b, total, nil
}
// readHeader reads the header at the end of rd. size is the length of the
// whole data accessible in rd.
func readHeader(rd io.ReaderAt, size int64) ([]byte, error) {
debug.Log("size: %v", size)
if size < int64(minFileSize) {
err := InvalidFileError{Message: "file is too small"}
return nil, errors.Wrap(err, "readHeader")
}
// assuming extra request is significantly slower than extra bytes download,
// eagerly download eagerEntries header entries as part of header-length request.
// only make second request if actual number of entries is greater than eagerEntries
b, c, err := readRecords(rd, size, eagerEntries)
if err != nil {
return nil, err
}
if c <= eagerEntries {
// eager read sufficed, return what we got
return b, nil
}
b, _, err = readRecords(rd, size, c)
if err != nil {
return nil, err
}
return b, nil
}
// InvalidFileError is return when a file is found that is not a pack file.
type InvalidFileError struct {
Message string
}
func (e InvalidFileError) Error() string {
return e.Message
}
// List returns the list of entries found in a pack file.
func List(k *crypto.Key, rd io.ReaderAt, size int64) (entries []restic.Blob, err error) {
buf, err := readHeader(rd, size)
if err != nil {
return nil, err
}
if len(buf) < k.NonceSize()+k.Overhead() {
return nil, errors.New("invalid header, too small")
}
nonce, buf := buf[:k.NonceSize()], buf[k.NonceSize():]
buf, err = k.Open(buf[:0], nonce, buf, nil)
if err != nil {
return nil, err
}
hdrRd := bytes.NewReader(buf)
entries = make([]restic.Blob, 0, uint(len(buf))/entrySize)
pos := uint(0)
for {
e := headerEntry{}
err = binary.Read(hdrRd, binary.LittleEndian, &e)
if errors.Cause(err) == io.EOF {
break
}
if err != nil {
return nil, errors.Wrap(err, "binary.Read")
}
entry := restic.Blob{
Length: uint(e.Length),
ID: e.ID,
Offset: pos,
}
switch e.Type {
case 0:
entry.Type = restic.DataBlob
case 1:
entry.Type = restic.TreeBlob
default:
return nil, errors.Errorf("invalid type %d", e.Type)
}
entries = append(entries, entry)
pos += uint(e.Length)
}
return entries, nil
}