1 files changed, 360 insertions, 0 deletions
diff --git a/plumbing/format/packfile/parser.go b/plumbing/format/packfile/parser.go
new file mode 100644
index 0000000..696f5ba
--- /dev/null
+++ b/plumbing/format/packfile/parser.go
@@ -0,0 +1,360 @@
+package packfile
+
+import (
+	"bytes"
+	"errors"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/cache"
+)
+
+// Observer interface is implemented by index encoders.
+type Observer interface {
+	// OnHeader is called when a new packfile is opened.
+	OnHeader(count uint32) error
+	// OnInflatedObjectHeader is called for each object header read.
+	OnInflatedObjectHeader(t plumbing.ObjectType, objSize int64, pos int64) error
+	// OnInflatedObjectContent is called for each decoded object.
+	OnInflatedObjectContent(h plumbing.Hash, pos int64, crc uint32) error
+	// OnFooter is called when decoding is done.
+	OnFooter(h plumbing.Hash) error
+}
+
+// Parser decodes a packfile and calls any observer associated to it. Is used
+// to generate indexes.
+type Parser struct {
+	scanner    *Scanner
+	count      uint32
+	oi         []*objectInfo
+	oiByHash   map[plumbing.Hash]*objectInfo
+	oiByOffset map[int64]*objectInfo
+	hashOffset map[plumbing.Hash]int64
+	checksum   plumbing.Hash
+
+	cache *cache.ObjectLRU
+
+	ob []Observer
+}
+
+// NewParser creates a new Parser struct.
+func NewParser(scanner *Scanner, ob ...Observer) *Parser {
+	return &Parser{
+		scanner: scanner,
+		ob:      ob,
+		count:   0,
+		cache:   cache.NewObjectLRUDefault(),
+	}
+}
+
+// Parse start decoding phase of the packfile.
+func (p *Parser) Parse() (plumbing.Hash, error) {
+	err := p.init()
+	if err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	err = p.firstPass()
+	if err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	err = p.resolveDeltas()
+	if err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	for _, o := range p.ob {
+		err := o.OnFooter(p.checksum)
+		if err != nil {
+			return plumbing.ZeroHash, err
+		}
+	}
+
+	return p.checksum, nil
+}
+
+func (p *Parser) init() error {
+	_, c, err := p.scanner.Header()
+	if err != nil {
+		return err
+	}
+
+	for _, o := range p.ob {
+		err := o.OnHeader(c)
+		if err != nil {
+			return err
+		}
+	}
+
+	p.count = c
+	p.oiByHash = make(map[plumbing.Hash]*objectInfo, p.count)
+	p.oiByOffset = make(map[int64]*objectInfo, p.count)
+	p.oi = make([]*objectInfo, p.count)
+
+	return nil
+}
+
+func (p *Parser) firstPass() error {
+	buf := new(bytes.Buffer)
+
+	for i := uint32(0); i < p.count; i++ {
+		buf.Truncate(0)
+
+		oh, err := p.scanner.NextObjectHeader()
+		if err != nil {
+			return err
+		}
+
+		delta := false
+		var ota *objectInfo
+		switch t := oh.Type; t {
+		case plumbing.OFSDeltaObject, plumbing.REFDeltaObject:
+			delta = true
+
+			var parent *objectInfo
+			var ok bool
+
+			if t == plumbing.OFSDeltaObject {
+				parent, ok = p.oiByOffset[oh.OffsetReference]
+			} else {
+				parent, ok = p.oiByHash[oh.Reference]
+			}
+
+			if !ok {
+				// TODO improve error
+				return errors.New("Reference delta not found")
+			}
+
+			ota = newDeltaObject(oh.Offset, oh.Length, t, parent)
+
+			parent.Children = append(parent.Children, ota)
+		default:
+			ota = newBaseObject(oh.Offset, oh.Length, t)
+		}
+
+		size, crc, err := p.scanner.NextObject(buf)
+		if err != nil {
+			return err
+		}
+
+		ota.Crc32 = crc
+		ota.PackSize = size
+		ota.Length = oh.Length
+
+		if !delta {
+			ota.Write(buf.Bytes())
+			ota.SHA1 = ota.Sum()
+		}
+
+		p.oiByOffset[oh.Offset] = ota
+		p.oiByHash[oh.Reference] = ota
+
+		p.oi[i] = ota
+	}
+
+	checksum, err := p.scanner.Checksum()
+	p.checksum = checksum
+
+	if err == io.EOF {
+		return nil
+	}
+
+	return err
+}
+
+func (p *Parser) resolveDeltas() error {
+	for _, obj := range p.oi {
+		for _, o := range p.ob {
+			err := o.OnInflatedObjectHeader(obj.Type, obj.Length, obj.Offset)
+			if err != nil {
+				return err
+			}
+
+			err = o.OnInflatedObjectContent(obj.SHA1, obj.Offset, obj.Crc32)
+			if err != nil {
+				return err
+			}
+		}
+
+		if !obj.IsDelta() && len(obj.Children) > 0 {
+			var err error
+			base, err := p.get(obj)
+			if err != nil {
+				return err
+			}
+
+			for _, child := range obj.Children {
+				_, err = p.resolveObject(child, base)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+func (p *Parser) get(o *objectInfo) ([]byte, error) {
+	e, ok := p.cache.Get(o.SHA1)
+	if ok {
+		r, err := e.Reader()
+		if err != nil {
+			return nil, err
+		}
+
+		buf := make([]byte, e.Size())
+		_, err = r.Read(buf)
+		if err != nil {
+			return nil, err
+		}
+
+		return buf, nil
+	}
+
+	// Read from disk
+	if o.DiskType.IsDelta() {
+		base, err := p.get(o.Parent)
+		if err != nil {
+			return nil, err
+		}
+
+		data, err := p.resolveObject(o, base)
+		if err != nil {
+			return nil, err
+		}
+
+		if len(o.Children) > 0 {
+			m := &plumbing.MemoryObject{}
+			m.Write(data)
+			m.SetType(o.Type)
+			m.SetSize(o.Size())
+			p.cache.Put(m)
+		}
+
+		return data, nil
+	}
+
+	data, err := p.readData(o)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(o.Children) > 0 {
+		m := &plumbing.MemoryObject{}
+		m.Write(data)
+		m.SetType(o.Type)
+		m.SetSize(o.Size())
+		p.cache.Put(m)
+	}
+
+	return data, nil
+}
+
+func (p *Parser) resolveObject(
+	o *objectInfo,
+	base []byte) ([]byte, error) {
+
+	if !o.DiskType.IsDelta() {
+		return nil, nil
+	}
+
+	data, err := p.readData(o)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err = applyPatchBase(o, data, base)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}
+
+func (p *Parser) readData(o *objectInfo) ([]byte, error) {
+	buf := new(bytes.Buffer)
+
+	// TODO: skip header. Header size can be calculated with the offset of the
+	// next offset in the first pass.
+	p.scanner.SeekFromStart(o.Offset)
+	_, err := p.scanner.NextObjectHeader()
+	if err != nil {
+		return nil, err
+	}
+
+	buf.Truncate(0)
+
+	_, _, err = p.scanner.NextObject(buf)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+func applyPatchBase(ota *objectInfo, data, base []byte) ([]byte, error) {
+	patched, err := PatchDelta(base, data)
+	if err != nil {
+		return nil, err
+	}
+
+	ota.Type = ota.Parent.Type
+	hash := plumbing.ComputeHash(ota.Type, patched)
+
+	ota.SHA1 = hash
+
+	return patched, nil
+}
+
+type objectInfo struct {
+	plumbing.Hasher
+
+	Offset       int64
+	Length       int64
+	HeaderLength int64
+	PackSize     int64
+	Type         plumbing.ObjectType
+	DiskType     plumbing.ObjectType
+
+	Crc32 uint32
+
+	Parent   *objectInfo
+	Children []*objectInfo
+	SHA1     plumbing.Hash
+}
+
+func newBaseObject(offset, length int64, t plumbing.ObjectType) *objectInfo {
+	return newDeltaObject(offset, length, t, nil)
+}
+
+func newDeltaObject(
+	offset, length int64,
+	t plumbing.ObjectType,
+	parent *objectInfo,
+) *objectInfo {
+	children := make([]*objectInfo, 0)
+
+	obj := &objectInfo{
+		Hasher:   plumbing.NewHasher(t, length),
+		Offset:   offset,
+		Length:   length,
+		PackSize: 0,
+		Type:     t,
+		DiskType: t,
+		Crc32:    0,
+		Parent:   parent,
+		Children: children,
+	}
+
+	return obj
+}
+
+func (o *objectInfo) IsDelta() bool {
+	return o.Type.IsDelta()
+}
+
+func (o *objectInfo) Size() int64 {
+	return o.Length
+}