plumbing: packfile, Add a buffer to crc writer

plumbing/format/packfile/scanner.go

@@ -63,10 +63,7 @@ func NewScanner(r io.Reader) *Scanner {
 
 	crc := crc32.NewIEEE()
 	return &Scanner{
-		r: &teeReader{
-			newByteReadSeeker(seeker),
-			crc,
-		},
+		r:          newTeeReader(newByteReadSeeker(seeker), crc),
 		crc:        crc,
 		IsSeekable: ok,
 	}
@@ -143,6 +140,8 @@ func (s *Scanner) readCount() (uint32, error) {
 
 // NextObjectHeader returns the ObjectHeader for the next object in the reader
 func (s *Scanner) NextObjectHeader() (*ObjectHeader, error) {
+	defer s.Flush()
+
 	if err := s.doPending(); err != nil {
 		return nil, err
 	}
@@ -271,6 +270,7 @@ func (s *Scanner) NextObject(w io.Writer) (written int64, crc32 uint32, err erro
 
 	s.pendingObject = nil
 	written, err = s.copyObject(w)
+	s.Flush()
 	crc32 = s.crc.Sum32()
 	return
 }
@@ -339,6 +339,16 @@ func (s *Scanner) Close() error {
 	return err
 }
 
+// Flush finishes writing the buffer to crc hasher in case we are using
+// a teeReader. Otherwise it is a no-op.
+func (s *Scanner) Flush() error {
+	tee, ok := s.r.(*teeReader)
+	if ok {
+		return tee.Flush()
+	}
+	return nil
+}
+
 type trackableReader struct {
 	count int64
 	io.Reader
@@ -400,10 +410,21 @@ type reader interface {
 
 type teeReader struct {
 	reader
-	w hash.Hash32
+	w         hash.Hash32
+	bufWriter *bufio.Writer
+}
+
+func newTeeReader(r reader, h hash.Hash32) *teeReader {
+	return &teeReader{
+		reader:    r,
+		w:         h,
+		bufWriter: bufio.NewWriter(h),
+	}
 }
 
 func (r *teeReader) Read(p []byte) (n int, err error) {
+	r.Flush()
+
 	n, err = r.reader.Read(p)
 	if n > 0 {
 		if n, err := r.w.Write(p[:n]); err != nil {
@@ -416,11 +437,12 @@ func (r *teeReader) Read(p []byte) (n int, err error) {
 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 b, r.bufWriter.WriteByte(b)
 	}
 
 	return
 }
+
+func (r *teeReader) Flush() (err error) {
+	return r.bufWriter.Flush()
+}

plumbing/format/packfile/scanner_test.go

@@ -41,14 +41,16 @@ func (s *ScannerSuite) TestNextObjectHeaderWithoutHeader(c *C) {
 }
 
 func (s *ScannerSuite) TestNextObjectHeaderREFDelta(c *C) {
-	s.testNextObjectHeader(c, "ref-delta", expectedHeadersREF)
+	s.testNextObjectHeader(c, "ref-delta", expectedHeadersREF, expectedCRCREF)
 }
 
 func (s *ScannerSuite) TestNextObjectHeaderOFSDelta(c *C) {
-	s.testNextObjectHeader(c, "ofs-delta", expectedHeadersOFS)
+	s.testNextObjectHeader(c, "ofs-delta", expectedHeadersOFS, expectedCRCOFS)
 }
 
-func (s *ScannerSuite) testNextObjectHeader(c *C, tag string, expected []ObjectHeader) {
+func (s *ScannerSuite) testNextObjectHeader(c *C, tag string,
+	expected []ObjectHeader, expectedCRC []uint32) {
+
 	r := fixtures.Basic().ByTag(tag).One().Packfile()
 	p := NewScanner(r)
 
@@ -61,9 +63,10 @@ func (s *ScannerSuite) testNextObjectHeader(c *C, tag string, expected []ObjectH
 		c.Assert(*h, DeepEquals, expected[i])
 
 		buf := bytes.NewBuffer(nil)
-		n, _, err := p.NextObject(buf)
+		n, crcFromScanner, err := p.NextObject(buf)
 		c.Assert(err, IsNil)
 		c.Assert(n, Equals, h.Length)
+		c.Assert(crcFromScanner, Equals, expectedCRC[i])
 	}
 
 	n, err := p.Checksum()
@@ -149,6 +152,40 @@ var expectedHeadersOFS = []ObjectHeader{
 	{Type: plumbing.OFSDeltaObject, Offset: 84760, Length: 4, OffsetReference: 84741},
 }
 
+var expectedCRCOFS = []uint32{
+	0xaa07ba4b,
+	0xf706df58,
+	0x12438846,
+	0x2905a38c,
+	0xd9429436,
+	0xbecfde4e,
+	0x780e4b3e,
+	0xdc18344f,
+	0xcf4e4280,
+	0x1f08118a,
+	0xafded7b8,
+	0xcc1428ed,
+	0x1631d22f,
+	0xbfff5850,
+	0xd108e1d8,
+	0x8e97ba25,
+	0x7316ff70,
+	0xdb4fce56,
+	0x901cce2c,
+	0xec4552b0,
+	0x847905bf,
+	0x3689459a,
+	0xe67af94a,
+	0xc2314a2e,
+	0xcd987848,
+	0x8a853a6d,
+	0x70c6518,
+	0x4f4108e2,
+	0xd6fe09e9,
+	0xf07a2804,
+	0x1d75d6be,
+}
+
 var expectedHeadersREF = []ObjectHeader{
 	{Type: plumbing.CommitObject, Offset: 12, Length: 254},
 	{Type: plumbing.REFDeltaObject, Offset: 186, Length: 93,
@@ -188,3 +225,37 @@ var expectedHeadersREF = []ObjectHeader{
 		Reference: plumbing.NewHash("eba74343e2f15d62adedfd8c883ee0262b5c8021")},
 	{Type: plumbing.TreeObject, Offset: 85485, Length: 73},
 }
+
+var expectedCRCREF = []uint32{
+	0xaa07ba4b,
+	0xfb4725a4,
+	0x12438846,
+	0x2905a38c,
+	0xd9429436,
+	0xbecfde4e,
+	0xdc18344f,
+	0x780e4b3e,
+	0xcf4e4280,
+	0x1f08118a,
+	0xafded7b8,
+	0xcc1428ed,
+	0x1631d22f,
+	0x847905bf,
+	0x3e20f31d,
+	0x3689459a,
+	0xd108e1d8,
+	0x71143d4a,
+	0xe67af94a,
+	0x739fb89f,
+	0xc2314a2e,
+	0x87864926,
+	0x415d752f,
+	0xf72fb182,
+	0x3ffa37d4,
+	0xcd987848,
+	0x2f20ac8f,
+	0xf2f0575,
+	0x7d8726e1,
+	0x740bf39,
+	0x26af4735,
+}