package packfile import ( "bufio" "bytes" "fmt" "hash" "hash/crc32" "io" "github.com/go-git/go-git/v5/plumbing" "github.com/go-git/go-git/v5/utils/binary" "github.com/go-git/go-git/v5/utils/ioutil" "github.com/go-git/go-git/v5/utils/sync" ) 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") ) // 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 plumbing.ObjectType Offset int64 Length int64 Reference plumbing.Hash OffsetReference int64 } type Scanner struct { r *scannerReader 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 { _, ok := r.(io.ReadSeeker) crc := crc32.NewIEEE() return &Scanner{ r: newScannerReader(r, crc), crc: crc, IsSeekable: ok, } } func (s *Scanner) Reset(r io.Reader) { _, ok := r.(io.ReadSeeker) s.r.Reset(r) s.crc.Reset() s.IsSeekable = ok s.pendingObject = nil s.version = 0 s.objects = 0 } // 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 a 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, signature) } // 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) } // SeekObjectHeader seeks to specified offset and returns the ObjectHeader // for the next object in the reader func (s *Scanner) SeekObjectHeader(offset int64) (*ObjectHeader, error) { // if seeking we assume that you are not interested in the header if s.version == 0 { s.version = VersionSupported } if _, err := s.r.Seek(offset, io.SeekStart); err != nil { return nil, err } h, err := s.nextObjectHeader() if err != nil { return nil, err } h.Offset = offset return h, nil } // 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 } offset, err := s.r.Seek(0, io.SeekCurrent) if err != nil { return nil, err } h, err := s.nextObjectHeader() if err != nil { return nil, err } h.Offset = offset return h, nil } // nextObjectHeader returns the ObjectHeader for the next object in the reader // without the Offset field func (s *Scanner) nextObjectHeader() (*ObjectHeader, error) { s.r.Flush() 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 plumbing.OFSDeltaObject: no, err := binary.ReadVariableWidthInt(s.r) if err != nil { return nil, err } h.OffsetReference = h.Offset - no case plumbing.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(io.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() (plumbing.ObjectType, int64, error) { t, c, err := s.readType() if err != nil { return t, 0, err } l, err := s.readLength(c) return t, l, err } func (s *Scanner) readType() (plumbing.ObjectType, byte, error) { var c byte var err error if c, err = s.r.ReadByte(); err != nil { return plumbing.ObjectType(0), 0, err } typ := parseType(c) return typ, c, nil } func parseType(b byte) plumbing.ObjectType { return plumbing.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) { s.pendingObject = nil written, err = s.copyObject(w) s.r.Flush() crc32 = s.crc.Sum32() s.crc.Reset() return } // ReadObject returns a reader for the object content and an error func (s *Scanner) ReadObject() (io.ReadCloser, error) { s.pendingObject = nil zr, err := sync.GetZlibReader(s.r) if err != nil { return nil, fmt.Errorf("zlib reset error: %s", err) } return ioutil.NewReadCloserWithCloser(zr.Reader, func() error { sync.PutZlibReader(zr) return nil }), nil } // 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) (n int64, err error) { zr, err := sync.GetZlibReader(s.r) defer sync.PutZlibReader(zr) if err != nil { return 0, fmt.Errorf("zlib reset error: %s", err) } defer ioutil.CheckClose(zr.Reader, &err) buf := sync.GetByteSlice() n, err = io.CopyBuffer(w, zr.Reader, *buf) sync.PutByteSlice(buf) return } // SeekFromStart sets a new offset from start, returns the old position before // the change. func (s *Scanner) SeekFromStart(offset int64) (previous int64, err error) { // if seeking we assume that you are not interested in 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() (plumbing.Hash, error) { err := s.discardObjectIfNeeded() if err != nil { return plumbing.ZeroHash, err } return binary.ReadHash(s.r) } // Close reads the reader until io.EOF func (s *Scanner) Close() error { buf := sync.GetByteSlice() _, err := io.CopyBuffer(io.Discard, s.r, *buf) sync.PutByteSlice(buf) return err } // Flush is a no-op (deprecated) func (s *Scanner) Flush() error { return nil } // scannerReader has the following characteristics: // - Provides an io.SeekReader impl for bufio.Reader, when the underlying // reader supports it. // - Keeps track of the current read position, for when the underlying reader // isn't an io.SeekReader, but we still want to know the current offset. // - Writes to the hash writer what it reads, with the aid of a smaller buffer. // The buffer helps avoid a performance penalty for performing small writes // to the crc32 hash writer. type scannerReader struct { reader io.Reader crc io.Writer rbuf *bufio.Reader wbuf *bufio.Writer offset int64 } func newScannerReader(r io.Reader, h io.Writer) *scannerReader { sr := &scannerReader{ rbuf: bufio.NewReader(nil), wbuf: bufio.NewWriterSize(nil, 64), crc: h, } sr.Reset(r) return sr } func (r *scannerReader) Reset(reader io.Reader) { r.reader = reader r.rbuf.Reset(r.reader) r.wbuf.Reset(r.crc) r.offset = 0 if seeker, ok := r.reader.(io.ReadSeeker); ok { r.offset, _ = seeker.Seek(0, io.SeekCurrent) } } func (r *scannerReader) Read(p []byte) (n int, err error) { n, err = r.rbuf.Read(p) r.offset += int64(n) if _, err := r.wbuf.Write(p[:n]); err != nil { return n, err } return } func (r *scannerReader) ReadByte() (b byte, err error) { b, err = r.rbuf.ReadByte() if err == nil { r.offset++ return b, r.wbuf.WriteByte(b) } return } func (r *scannerReader) Flush() error { return r.wbuf.Flush() } // Seek seeks to a location. If the underlying reader is not an io.ReadSeeker, // then only whence=io.SeekCurrent is supported, any other operation fails. func (r *scannerReader) Seek(offset int64, whence int) (int64, error) { var err error if seeker, ok := r.reader.(io.ReadSeeker); !ok { if whence != io.SeekCurrent || offset != 0 { return -1, ErrSeekNotSupported } } else { if whence == io.SeekCurrent && offset == 0 { return r.offset, nil } r.offset, err = seeker.Seek(offset, whence) r.rbuf.Reset(r.reader) } return r.offset, err }