diff options
Diffstat (limited to 'formats/packfile/scanner.go')
| -rw-r--r-- | formats/packfile/scanner.go | 418 |
1 files changed, 0 insertions, 418 deletions
diff --git a/formats/packfile/scanner.go b/formats/packfile/scanner.go deleted file mode 100644 index 69cc7d0..0000000 --- a/formats/packfile/scanner.go +++ /dev/null @@ -1,418 +0,0 @@ -package packfile - -import ( - "bufio" - "bytes" - "compress/zlib" - "fmt" - "hash" - "hash/crc32" - "io" - "io/ioutil" - - "gopkg.in/src-d/go-git.v4/core" - "gopkg.in/src-d/go-git.v4/utils/binary" -) - -var ( - // ErrEmptyPackfile is returned by ReadHeader when no data is found in the packfile - ErrEmptyPackfile = NewError("empty packfile") - // ErrBadSignature is returned by ReadHeader when the signature in the packfile is incorrect. - ErrBadSignature = NewError("malformed pack file signature") - // ErrUnsupportedVersion is returned by ReadHeader when the packfile version is - // different than VersionSupported. - ErrUnsupportedVersion = NewError("unsupported packfile version") - // ErrSeekNotSupported returned if seek is not support - ErrSeekNotSupported = NewError("not seek support") -) - -const ( - // VersionSupported is the packfile version supported by this parser. - VersionSupported uint32 = 2 -) - -// ObjectHeader contains the information related to the object, this information -// is collected from the previous bytes to the content of the object. -type ObjectHeader struct { - Type core.ObjectType - Offset int64 - Length int64 - Reference core.Hash - OffsetReference int64 -} - -type Scanner struct { - r reader - crc hash.Hash32 - - // pendingObject is used to detect if an object has been read, or still - // is waiting to be read - pendingObject *ObjectHeader - version, objects uint32 - - // lsSeekable says if this scanner can do Seek or not, to have a Scanner - // seekable a r implementing io.Seeker is required - IsSeekable bool -} - -// NewScanner returns a new Scanner based on a reader, if the given reader -// implements io.ReadSeeker the Scanner will be also Seekable -func NewScanner(r io.Reader) *Scanner { - seeker, ok := r.(io.ReadSeeker) - if !ok { - seeker = &trackableReader{Reader: r} - } - - crc := crc32.NewIEEE() - return &Scanner{ - r: &teeReader{ - newByteReadSeeker(seeker), - crc, - }, - crc: crc, - IsSeekable: ok, - } -} - -// Header reads the whole packfile header (signature, version and object count). -// It returns the version and the object count and performs checks on the -// validity of the signature and the version fields. -func (s *Scanner) Header() (version, objects uint32, err error) { - if s.version != 0 { - return s.version, s.objects, nil - } - - sig, err := s.readSignature() - if err != nil { - if err == io.EOF { - err = ErrEmptyPackfile - } - - return - } - - if !s.isValidSignature(sig) { - err = ErrBadSignature - return - } - - version, err = s.readVersion() - s.version = version - if err != nil { - return - } - - if !s.isSupportedVersion(version) { - err = ErrUnsupportedVersion.AddDetails("%d", version) - return - } - - objects, err = s.readCount() - s.objects = objects - return -} - -// readSignature reads an returns the signature field in the packfile. -func (s *Scanner) readSignature() ([]byte, error) { - var sig = make([]byte, 4) - if _, err := io.ReadFull(s.r, sig); err != nil { - return []byte{}, err - } - - return sig, nil -} - -// isValidSignature returns if sig is a valid packfile signature. -func (s *Scanner) isValidSignature(sig []byte) bool { - return bytes.Equal(sig, []byte{'P', 'A', 'C', 'K'}) -} - -// readVersion reads and returns the version field of a packfile. -func (s *Scanner) readVersion() (uint32, error) { - return binary.ReadUint32(s.r) -} - -// isSupportedVersion returns whether version v is supported by the parser. -// The current supported version is VersionSupported, defined above. -func (s *Scanner) isSupportedVersion(v uint32) bool { - return v == VersionSupported -} - -// readCount reads and returns the count of objects field of a packfile. -func (s *Scanner) readCount() (uint32, error) { - return binary.ReadUint32(s.r) -} - -// NextObjectHeader returns the ObjectHeader for the next object in the reader -func (s *Scanner) NextObjectHeader() (*ObjectHeader, error) { - if err := s.doPending(); err != nil { - return nil, err - } - - s.crc.Reset() - - h := &ObjectHeader{} - s.pendingObject = h - - var err error - h.Offset, err = s.r.Seek(0, io.SeekCurrent) - if err != nil { - return nil, err - } - - h.Type, h.Length, err = s.readObjectTypeAndLength() - if err != nil { - return nil, err - } - - switch h.Type { - case core.OFSDeltaObject: - no, err := binary.ReadVariableWidthInt(s.r) - if err != nil { - return nil, err - } - - h.OffsetReference = h.Offset - no - case core.REFDeltaObject: - var err error - h.Reference, err = binary.ReadHash(s.r) - if err != nil { - return nil, err - } - } - - return h, nil -} - -func (s *Scanner) doPending() error { - if s.version == 0 { - var err error - s.version, s.objects, err = s.Header() - if err != nil { - return err - } - } - - return s.discardObjectIfNeeded() -} - -func (s *Scanner) discardObjectIfNeeded() error { - if s.pendingObject == nil { - return nil - } - - h := s.pendingObject - n, _, err := s.NextObject(ioutil.Discard) - if err != nil { - return err - } - - if n != h.Length { - return fmt.Errorf( - "error discarding object, discarded %d, expected %d", - n, h.Length, - ) - } - - return nil -} - -// ReadObjectTypeAndLength reads and returns the object type and the -// length field from an object entry in a packfile. -func (s *Scanner) readObjectTypeAndLength() (core.ObjectType, int64, error) { - t, c, err := s.readType() - if err != nil { - return t, 0, err - } - - l, err := s.readLength(c) - - return t, l, err -} - -const ( - maskType = uint8(112) // 0111 0000 - maskFirstLength = uint8(15) // 0000 1111 - maskContinue = uint8(128) // 1000 000 - firstLengthBits = uint8(4) // the first byte has 4 bits to store the length - maskLength = uint8(127) // 0111 1111 - lengthBits = uint8(7) // subsequent bytes has 7 bits to store the length -) - -func (s *Scanner) readType() (core.ObjectType, byte, error) { - var c byte - var err error - if c, err = s.r.ReadByte(); err != nil { - return core.ObjectType(0), 0, err - } - - typ := parseType(c) - - return typ, c, nil -} - -func parseType(b byte) core.ObjectType { - return core.ObjectType((b & maskType) >> firstLengthBits) -} - -// the length is codified in the last 4 bits of the first byte and in -// the last 7 bits of subsequent bytes. Last byte has a 0 MSB. -func (s *Scanner) readLength(first byte) (int64, error) { - length := int64(first & maskFirstLength) - - c := first - shift := firstLengthBits - var err error - for c&maskContinue > 0 { - if c, err = s.r.ReadByte(); err != nil { - return 0, err - } - - length += int64(c&maskLength) << shift - shift += lengthBits - } - - return length, nil -} - -// NextObject writes the content of the next object into the reader, returns -// the number of bytes written, the CRC32 of the content and an error, if any -func (s *Scanner) NextObject(w io.Writer) (written int64, crc32 uint32, err error) { - defer s.crc.Reset() - - s.pendingObject = nil - written, err = s.copyObject(w) - crc32 = s.crc.Sum32() - return -} - -// ReadRegularObject reads and write a non-deltified object -// from it zlib stream in an object entry in the packfile. -func (s *Scanner) copyObject(w io.Writer) (int64, error) { - zr, err := zlib.NewReader(s.r) - if err != nil { - return -1, fmt.Errorf("zlib reading error: %s", err) - } - - defer func() { - closeErr := zr.Close() - if err == nil { - err = closeErr - } - }() - - return io.Copy(w, zr) -} - -// Seek sets a new offset from start, returns the old position before the change -func (s *Scanner) Seek(offset int64) (previous int64, err error) { - // if seeking we asume that you are not interested on the header - if s.version == 0 { - s.version = VersionSupported - } - - previous, err = s.r.Seek(0, io.SeekCurrent) - if err != nil { - return -1, err - } - - _, err = s.r.Seek(offset, io.SeekStart) - return previous, err -} - -// Checksum returns the checksum of the packfile -func (s *Scanner) Checksum() (core.Hash, error) { - err := s.discardObjectIfNeeded() - if err != nil { - return core.ZeroHash, err - } - - return binary.ReadHash(s.r) -} - -// Close reads the reader until io.EOF -func (s *Scanner) Close() error { - _, err := io.Copy(ioutil.Discard, s.r) - return err -} - -type trackableReader struct { - count int64 - io.Reader -} - -// Read reads up to len(p) bytes into p. -func (r *trackableReader) Read(p []byte) (n int, err error) { - n, err = r.Reader.Read(p) - r.count += int64(n) - - return -} - -// Seek only supports io.SeekCurrent, any other operation fails -func (r *trackableReader) Seek(offset int64, whence int) (int64, error) { - if whence != io.SeekCurrent { - return -1, ErrSeekNotSupported - } - - return r.count, nil -} - -func newByteReadSeeker(r io.ReadSeeker) *bufferedSeeker { - return &bufferedSeeker{ - r: r, - Reader: *bufio.NewReader(r), - } -} - -type bufferedSeeker struct { - r io.ReadSeeker - bufio.Reader -} - -func (r *bufferedSeeker) Seek(offset int64, whence int) (int64, error) { - if whence == io.SeekCurrent { - current, err := r.r.Seek(offset, whence) - if err != nil { - return current, err - } - - return current - int64(r.Buffered()), nil - } - - defer r.Reader.Reset(r.r) - return r.r.Seek(offset, whence) -} - -type reader interface { - io.Reader - io.ByteReader - io.Seeker -} - -type teeReader struct { - reader - w hash.Hash32 -} - -func (r *teeReader) Read(p []byte) (n int, err error) { - n, err = r.reader.Read(p) - if n > 0 { - if n, err := r.w.Write(p[:n]); err != nil { - return n, err - } - } - return -} - -func (r *teeReader) ReadByte() (b byte, err error) { - b, err = r.reader.ReadByte() - if err == nil { - _, err := r.w.Write([]byte{b}) - if err != nil { - return 0, err - } - } - - return -} |