diff options
Diffstat (limited to 'formats/packfile/scanner.go')
| -rw-r--r-- | formats/packfile/scanner.go | 126 |
1 files changed, 23 insertions, 103 deletions
diff --git a/formats/packfile/scanner.go b/formats/packfile/scanner.go index a5e4215..69cc7d0 100644 --- a/formats/packfile/scanner.go +++ b/formats/packfile/scanner.go @@ -4,7 +4,6 @@ import ( "bufio" "bytes" "compress/zlib" - "encoding/binary" "fmt" "hash" "hash/crc32" @@ -12,6 +11,7 @@ import ( "io/ioutil" "gopkg.in/src-d/go-git.v4/core" + "gopkg.in/src-d/go-git.v4/utils/binary" ) var ( @@ -129,7 +129,7 @@ func (s *Scanner) isValidSignature(sig []byte) bool { // readVersion reads and returns the version field of a packfile. func (s *Scanner) readVersion() (uint32, error) { - return s.readInt32() + return binary.ReadUint32(s.r) } // isSupportedVersion returns whether version v is supported by the parser. @@ -140,17 +140,7 @@ func (s *Scanner) isSupportedVersion(v uint32) bool { // readCount reads and returns the count of objects field of a packfile. func (s *Scanner) readCount() (uint32, error) { - return s.readInt32() -} - -// ReadInt32 reads 4 bytes and returns them as a Big Endian int32. -func (s *Scanner) readInt32() (uint32, error) { - var v uint32 - if err := binary.Read(s.r, binary.BigEndian, &v); err != nil { - return 0, err - } - - return v, nil + return binary.ReadUint32(s.r) } // NextObjectHeader returns the ObjectHeader for the next object in the reader @@ -177,15 +167,15 @@ func (s *Scanner) NextObjectHeader() (*ObjectHeader, error) { switch h.Type { case core.OFSDeltaObject: - no, err := s.readNegativeOffset() + no, err := binary.ReadVariableWidthInt(s.r) if err != nil { return nil, err } - h.OffsetReference = h.Offset + no + h.OffsetReference = h.Offset - no case core.REFDeltaObject: var err error - h.Reference, err = s.readHash() + h.Reference, err = binary.ReadHash(s.r) if err != nil { return nil, err } @@ -240,10 +230,19 @@ func (s *Scanner) readObjectTypeAndLength() (core.ObjectType, int64, error) { 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.readByte(); err != nil { + if c, err = s.r.ReadByte(); err != nil { return core.ObjectType(0), 0, err } @@ -252,6 +251,10 @@ func (s *Scanner) readType() (core.ObjectType, byte, error) { 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) { @@ -260,8 +263,8 @@ func (s *Scanner) readLength(first byte) (int64, error) { c := first shift := firstLengthBits var err error - for moreBytesInLength(c) { - if c, err = s.readByte(); err != nil { + for c&maskContinue > 0 { + if c, err = s.r.ReadByte(); err != nil { return 0, err } @@ -324,73 +327,7 @@ func (s *Scanner) Checksum() (core.Hash, error) { return core.ZeroHash, err } - return s.readHash() -} - -// ReadHash reads a hash. -func (s *Scanner) readHash() (core.Hash, error) { - var h core.Hash - if _, err := io.ReadFull(s.r, h[:]); err != nil { - return core.ZeroHash, err - } - - return h, nil -} - -// ReadNegativeOffset reads and returns an offset from a OFS DELTA -// object entry in a packfile. OFS DELTA offsets are specified in Git -// VLQ special format: -// -// Ordinary VLQ has some redundancies, example: the number 358 can be -// encoded as the 2-octet VLQ 0x8166 or the 3-octet VLQ 0x808166 or the -// 4-octet VLQ 0x80808166 and so forth. -// -// To avoid these redundancies, the VLQ format used in Git removes this -// prepending redundancy and extends the representable range of shorter -// VLQs by adding an offset to VLQs of 2 or more octets in such a way -// that the lowest possible value for such an (N+1)-octet VLQ becomes -// exactly one more than the maximum possible value for an N-octet VLQ. -// In particular, since a 1-octet VLQ can store a maximum value of 127, -// the minimum 2-octet VLQ (0x8000) is assigned the value 128 instead of -// 0. Conversely, the maximum value of such a 2-octet VLQ (0xff7f) is -// 16511 instead of just 16383. Similarly, the minimum 3-octet VLQ -// (0x808000) has a value of 16512 instead of zero, which means -// that the maximum 3-octet VLQ (0xffff7f) is 2113663 instead of -// just 2097151. And so forth. -// -// This is how the offset is saved in C: -// -// dheader[pos] = ofs & 127; -// while (ofs >>= 7) -// dheader[--pos] = 128 | (--ofs & 127); -// -func (s *Scanner) readNegativeOffset() (int64, error) { - var c byte - var err error - - if c, err = s.readByte(); err != nil { - return 0, err - } - - var offset = int64(c & maskLength) - for moreBytesInLength(c) { - offset++ - if c, err = s.readByte(); err != nil { - return 0, err - } - offset = (offset << lengthBits) + int64(c&maskLength) - } - - return -offset, nil -} - -func (s *Scanner) readByte() (byte, error) { - b, err := s.r.ReadByte() - if err != nil { - return 0, err - } - - return b, err + return binary.ReadHash(s.r) } // Close reads the reader until io.EOF @@ -399,23 +336,6 @@ func (s *Scanner) Close() error { return err } -func moreBytesInLength(c byte) bool { - return c&maskContinue > 0 -} - -var ( - maskContinue = uint8(128) // 1000 0000 - maskType = uint8(112) // 0111 0000 - maskFirstLength = uint8(15) // 0000 1111 - 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 parseType(b byte) core.ObjectType { - return core.ObjectType((b & maskType) >> firstLengthBits) -} - type trackableReader struct { count int64 io.Reader |