formats/packfile: type Hash instead of strings

1 files changed, 401 insertions, 0 deletions

diff --git a/formats/packfile/reader.go b/formats/packfile/reader.go
new file mode 100644
index 0000000..ccf4822
--- /dev/null
+++ b/formats/packfile/reader.go
@@ -0,0 +1,401 @@
+package packfile
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+
+	"github.com/klauspost/compress/zlib"
+)
+
+const MaxObjectsLimit = 1000000
+
+var ErrMaxSize = fmt.Errorf("Max size exceeded for in-memory client")
+
+type TrackingByteReader struct {
+	r    io.Reader
+	n, l int
+}
+
+func (t *TrackingByteReader) Pos() int { return t.n }
+
+func (t *TrackingByteReader) Read(p []byte) (n int, err error) {
+	n, err = t.r.Read(p)
+	if err != nil {
+		return 0, err
+	}
+	t.n += n
+	if t.n >= t.l {
+		return n, ErrMaxSize
+	}
+	return n, err
+}
+
+func (t *TrackingByteReader) ReadByte() (c byte, err error) {
+	var p [1]byte
+	n, err := t.r.Read(p[:])
+	if err != nil {
+		return 0, err
+	}
+	if n > 1 {
+		return 0, fmt.Errorf("read %d bytes, should have read just 1", n)
+	}
+	t.n += n // n is 1
+	return p[0], nil
+}
+
+type PackfileReader struct {
+	r *TrackingByteReader
+
+	objects map[Hash]packfileObject
+	offsets map[int]Hash
+	deltas  []packfileDelta
+
+	contentCallback ContentCallback
+}
+
+type packfileObject struct {
+	bytes []byte
+	typ   int8
+}
+
+type packfileDelta struct {
+	hash  Hash
+	delta []byte
+}
+
+func NewPackfileReader(r io.Reader, l int, fn ContentCallback) (*PackfileReader, error) {
+	return &PackfileReader{
+		r:               &TrackingByteReader{r: r, n: 0, l: l},
+		objects:         make(map[Hash]packfileObject, 0),
+		offsets:         make(map[int]Hash, 0),
+		contentCallback: fn,
+	}, nil
+}
+
+func (pr *PackfileReader) Pos() int { return pr.r.Pos() }
+
+func (pr *PackfileReader) Read() (*Packfile, error) {
+	packfile := NewPackfile()
+
+	if err := pr.validateHeader(); err != nil {
+		if err == io.EOF {
+			// This is an empty repo. It's OK.
+			return packfile, nil
+		}
+		return nil, err
+	}
+
+	ver, err := pr.readInt32()
+	if err != nil {
+		return nil, err
+	}
+
+	count, err := pr.readInt32()
+	if err != nil {
+		return nil, err
+	}
+
+	packfile.Version = uint32(ver)
+	packfile.ObjectCount = int(count)
+
+	if packfile.ObjectCount > MaxObjectsLimit {
+		return nil, NewError("too many objects (%d)", packfile.ObjectCount)
+	}
+
+	if err := pr.readObjects(packfile); err != nil {
+		return nil, err
+	}
+
+	packfile.Size = int64(pr.r.Pos())
+
+	return packfile, nil
+}
+
+func (pr *PackfileReader) validateHeader() error {
+	var header = make([]byte, 4)
+	if _, err := pr.r.Read(header); err != nil {
+		return err
+	}
+
+	if !bytes.Equal(header, []byte{'P', 'A', 'C', 'K'}) {
+		return NewError("Pack file does not start with 'PACK'")
+	}
+
+	return nil
+}
+
+func (pr *PackfileReader) readInt32() (uint32, error) {
+	var value uint32
+	if err := binary.Read(pr.r, binary.BigEndian, &value); err != nil {
+		return 0, err
+	}
+
+	return value, nil
+}
+
+func (pr *PackfileReader) readObjects(packfile *Packfile) error {
+	// This code has 50-80 µs of overhead per object not counting zlib inflation.
+	// Together with zlib inflation, it's 400-410 µs for small objects.
+	// That's 1 sec for ~2450 objects, ~4.20 MB, or ~250 ms per MB,
+	// of which 12-20 % is _not_ zlib inflation (ie. is our code).
+
+	for i := 0; i < packfile.ObjectCount; i++ {
+		var pos = pr.Pos()
+		obj, err := pr.readObject(packfile)
+		if err != nil && err != io.EOF {
+			return err
+		}
+
+		pr.offsets[pos] = obj.hash
+
+		if err == io.EOF {
+			break
+		}
+	}
+
+	return nil
+}
+
+func (pr *PackfileReader) readObject(packfile *Packfile) (*objectReader, error) {
+	o, err := newObjectReader(pr, packfile)
+	if err != nil {
+		return nil, err
+	}
+
+	switch o.typ {
+	case OBJ_REF_DELTA:
+		err = o.readREFDelta()
+	case OBJ_OFS_DELTA:
+		err = o.readOFSDelta()
+	case OBJ_COMMIT, OBJ_TREE, OBJ_BLOB, OBJ_TAG:
+		err = o.readObject()
+	default:
+		err = NewError("Invalid git object tag %q", o.typ)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return o, err
+}
+
+const (
+	OBJ_COMMIT    = 1
+	OBJ_TREE      = 2
+	OBJ_BLOB      = 3
+	OBJ_TAG       = 4
+	OBJ_OFS_DELTA = 6
+	OBJ_REF_DELTA = 7
+)
+
+const SIZE_LIMIT uint64 = 1 << 32 // 4GB
+
+type objectReader struct {
+	pr    *PackfileReader
+	pf    *Packfile
+	hash  Hash
+	steps int
+
+	typ  int8
+	size uint64
+}
+
+func newObjectReader(pr *PackfileReader, pf *Packfile) (*objectReader, error) {
+	o := &objectReader{pr: pr, pf: pf}
+
+	var buf [1]byte
+	if _, err := o.Read(buf[:]); err != nil {
+		return nil, err
+	}
+
+	o.typ = int8((buf[0] >> 4) & 7)
+	o.size = uint64(buf[0] & 15)
+	o.steps++ // byte we just read to get `o.typ` and `o.size`
+
+	var shift uint = 4
+	for buf[0]&0x80 == 0x80 {
+		if _, err := o.Read(buf[:]); err != nil {
+			return nil, err
+		}
+
+		o.size += uint64(buf[0]&0x7f) << shift
+		o.steps++ // byte we just read to update `o.size`
+		shift += 7
+	}
+
+	return o, nil
+}
+
+func (o *objectReader) readREFDelta() error {
+	var ref Hash
+	if _, err := o.Read(ref[:]); err != nil {
+		return err
+	}
+
+	buf, err := o.inflate()
+	if err != nil {
+		return err
+	}
+
+	referenced, ok := o.pr.objects[ref]
+	if !ok {
+		o.pr.deltas = append(o.pr.deltas, packfileDelta{hash: ref, delta: buf[:]})
+	} else {
+		patched := PatchDelta(referenced.bytes, buf[:])
+		if patched == nil {
+			return NewError("error while patching %x", ref)
+		}
+		o.typ = referenced.typ
+		err = o.addObject(patched)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func decodeOffset(src io.ByteReader, steps int) (int, error) {
+	b, err := src.ReadByte()
+	if err != nil {
+		return 0, err
+	}
+	var offset = int(b & 0x7f)
+	for (b & 0x80) != 0 {
+		offset += 1 // WHY?
+		b, err = src.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		offset = (offset << 7) + int(b&0x7f)
+	}
+	// offset needs to be aware of the bytes we read for `o.typ` and `o.size`
+	offset += steps
+	return -offset, nil
+}
+
+func (o *objectReader) readOFSDelta() error {
+	var pos = o.pr.Pos()
+
+	// read negative offset
+	offset, err := decodeOffset(o.pr.r, o.steps)
+	if err != nil {
+		return err
+	}
+
+	buf, err := o.inflate()
+	if err != nil {
+		return err
+	}
+
+	ref := o.pr.offsets[pos+offset]
+	referenced, ok := o.pr.objects[ref]
+	if !ok {
+		return NewError("can't find a pack entry at %d", pos+offset)
+	} else {
+		patched := PatchDelta(referenced.bytes, buf)
+		if patched == nil {
+			return NewError("error while patching %q", ref)
+		}
+		o.typ = referenced.typ
+		err = o.addObject(patched)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (o *objectReader) readObject() error {
+	buf, err := o.inflate()
+	if err != nil {
+		return err
+	}
+
+	return o.addObject(buf)
+}
+
+func (o *objectReader) addObject(bytes []byte) error {
+	var hash Hash
+
+	switch o.typ {
+	case OBJ_COMMIT:
+		c, err := ParseCommit(bytes)
+		if err != nil {
+			return err
+		}
+		o.pf.Commits[c.Hash()] = c
+		hash = c.Hash()
+	case OBJ_TREE:
+		c, err := NewTree(bytes)
+		if err != nil {
+			return err
+		}
+		o.pf.Trees[c.Hash()] = c
+		hash = c.Hash()
+	case OBJ_BLOB:
+		c, err := NewBlob(bytes)
+		if err != nil {
+			return err
+		}
+		o.pf.Blobs[c.Hash()] = c
+		hash = c.Hash()
+
+		if o.pr.contentCallback != nil {
+			o.pr.contentCallback(hash, bytes)
+		}
+	}
+
+	o.pr.objects[hash] = packfileObject{bytes: bytes, typ: o.typ}
+	o.hash = hash
+
+	return nil
+}
+
+func (o *objectReader) inflate() ([]byte, error) {
+	zr, err := zlib.NewReader(o.pr.r)
+	if err != nil {
+		if err == zlib.ErrHeader {
+			return nil, zlib.ErrHeader
+		} else {
+			return nil, NewError("error opening packfile's object zlib: %v", err)
+		}
+	}
+	defer zr.Close()
+
+	if o.size > SIZE_LIMIT {
+		return nil, NewError("the object size exceeed the allowed limit: %d", o.size)
+	}
+
+	var buf bytes.Buffer
+	io.Copy(&buf, zr) // also: io.CopyN(&buf, zr, int64(o.size))
+
+	var bufLen = buf.Len()
+	if bufLen != int(o.size) {
+		return nil, NewError("inflated size mismatch, expected %d, got %d", o.size, bufLen)
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (o *objectReader) Read(p []byte) (int, error) {
+	return o.pr.r.Read(p)
+}
+
+func (o *objectReader) ReadByte() (byte, error) {
+	return o.pr.r.ReadByte()
+}
+
+type ReaderError struct {
+	Msg string // description of error
+}
+
+func NewError(format string, args ...interface{}) error {
+	return &ReaderError{Msg: fmt.Sprintf(format, args...)}
+}
+
+func (e *ReaderError) Error() string { return e.Msg }