1 files changed, 505 insertions, 0 deletions
diff --git a/plumbing/format/packfile/parser.go b/plumbing/format/packfile/parser.go
new file mode 100644
index 0000000..581c334
--- /dev/null
+++ b/plumbing/format/packfile/parser.go
@@ -0,0 +1,505 @@
+package packfile
+
+import (
+	"bytes"
+	"errors"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/cache"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+var (
+	// ErrReferenceDeltaNotFound is returned when the reference delta is not
+	// found.
+	ErrReferenceDeltaNotFound = errors.New("reference delta not found")
+
+	// ErrNotSeekableSource is returned when the source for the parser is not
+	// seekable and a storage was not provided, so it can't be parsed.
+	ErrNotSeekableSource = errors.New("parser source is not seekable and storage was not provided")
+
+	// ErrDeltaNotCached is returned when the delta could not be found in cache.
+	ErrDeltaNotCached = errors.New("delta could not be found in 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, content []byte) 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 {
+	storage          storer.EncodedObjectStorer
+	scanner          *Scanner
+	count            uint32
+	oi               []*objectInfo
+	oiByHash         map[plumbing.Hash]*objectInfo
+	oiByOffset       map[int64]*objectInfo
+	hashOffset       map[plumbing.Hash]int64
+	pendingRefDeltas map[plumbing.Hash][]*objectInfo
+	checksum         plumbing.Hash
+
+	cache *cache.ObjectLRU
+	// delta content by offset, only used if source is not seekable
+	deltas map[int64][]byte
+
+	ob []Observer
+}
+
+// NewParser creates a new Parser. The Scanner source must be seekable.
+// If it's not, NewParserWithStorage should be used instead.
+func NewParser(scanner *Scanner, ob ...Observer) (*Parser, error) {
+	return NewParserWithStorage(scanner, nil, ob...)
+}
+
+// NewParserWithStorage creates a new Parser. The scanner source must either
+// be seekable or a storage must be provided.
+func NewParserWithStorage(
+	scanner *Scanner,
+	storage storer.EncodedObjectStorer,
+	ob ...Observer,
+) (*Parser, error) {
+	if !scanner.IsSeekable && storage == nil {
+		return nil, ErrNotSeekableSource
+	}
+
+	var deltas map[int64][]byte
+	if !scanner.IsSeekable {
+		deltas = make(map[int64][]byte)
+	}
+
+	return &Parser{
+		storage:          storage,
+		scanner:          scanner,
+		ob:               ob,
+		count:            0,
+		cache:            cache.NewObjectLRUDefault(),
+		pendingRefDeltas: make(map[plumbing.Hash][]*objectInfo),
+		deltas:           deltas,
+	}, nil
+}
+
+func (p *Parser) forEachObserver(f func(o Observer) error) error {
+	for _, o := range p.ob {
+		if err := f(o); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (p *Parser) onHeader(count uint32) error {
+	return p.forEachObserver(func(o Observer) error {
+		return o.OnHeader(count)
+	})
+}
+
+func (p *Parser) onInflatedObjectHeader(
+	t plumbing.ObjectType,
+	objSize int64,
+	pos int64,
+) error {
+	return p.forEachObserver(func(o Observer) error {
+		return o.OnInflatedObjectHeader(t, objSize, pos)
+	})
+}
+
+func (p *Parser) onInflatedObjectContent(
+	h plumbing.Hash,
+	pos int64,
+	crc uint32,
+	content []byte,
+) error {
+	return p.forEachObserver(func(o Observer) error {
+		return o.OnInflatedObjectContent(h, pos, crc, content)
+	})
+}
+
+func (p *Parser) onFooter(h plumbing.Hash) error {
+	return p.forEachObserver(func(o Observer) error {
+		return o.OnFooter(h)
+	})
+}
+
+// Parse start decoding phase of the packfile.
+func (p *Parser) Parse() (plumbing.Hash, error) {
+	if err := p.init(); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	if err := p.indexObjects(); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	var err error
+	p.checksum, err = p.scanner.Checksum()
+	if err != nil && err != io.EOF {
+		return plumbing.ZeroHash, err
+	}
+
+	if err := p.resolveDeltas(); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	if len(p.pendingRefDeltas) > 0 {
+		return plumbing.ZeroHash, ErrReferenceDeltaNotFound
+	}
+
+	if err := p.onFooter(p.checksum); 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
+	}
+
+	if err := p.onHeader(c); 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) indexObjects() error {
+	buf := new(bytes.Buffer)
+
+	for i := uint32(0); i < p.count; i++ {
+		buf.Reset()
+
+		oh, err := p.scanner.NextObjectHeader()
+		if err != nil {
+			return err
+		}
+
+		delta := false
+		var ota *objectInfo
+		switch t := oh.Type; t {
+		case plumbing.OFSDeltaObject:
+			delta = true
+
+			parent, ok := p.oiByOffset[oh.OffsetReference]
+			if !ok {
+				return plumbing.ErrObjectNotFound
+			}
+
+			ota = newDeltaObject(oh.Offset, oh.Length, t, parent)
+			parent.Children = append(parent.Children, ota)
+		case plumbing.REFDeltaObject:
+			delta = true
+
+			parent, ok := p.oiByHash[oh.Reference]
+			if ok {
+				ota = newDeltaObject(oh.Offset, oh.Length, t, parent)
+				parent.Children = append(parent.Children, ota)
+			} else {
+				ota = newBaseObject(oh.Offset, oh.Length, t)
+				p.pendingRefDeltas[oh.Reference] = append(
+					p.pendingRefDeltas[oh.Reference],
+					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
+
+		data := buf.Bytes()
+		if !delta {
+			if _, err := ota.Write(data); err != nil {
+				return err
+			}
+			ota.SHA1 = ota.Sum()
+			p.oiByHash[ota.SHA1] = ota
+		}
+
+		if p.storage != nil && !delta {
+			obj := new(plumbing.MemoryObject)
+			obj.SetSize(oh.Length)
+			obj.SetType(oh.Type)
+			if _, err := obj.Write(data); err != nil {
+				return err
+			}
+
+			if _, err := p.storage.SetEncodedObject(obj); err != nil {
+				return err
+			}
+		}
+
+		if delta && !p.scanner.IsSeekable {
+			p.deltas[oh.Offset] = make([]byte, len(data))
+			copy(p.deltas[oh.Offset], data)
+		}
+
+		p.oiByOffset[oh.Offset] = ota
+		p.oi[i] = ota
+	}
+
+	return nil
+}
+
+func (p *Parser) resolveDeltas() error {
+	for _, obj := range p.oi {
+		content, err := p.get(obj)
+		if err != nil {
+			return err
+		}
+
+		if err := p.onInflatedObjectHeader(obj.Type, obj.Length, obj.Offset); err != nil {
+			return err
+		}
+
+		if err := p.onInflatedObjectContent(obj.SHA1, obj.Offset, obj.Crc32, content); err != nil {
+			return err
+		}
+
+		if !obj.IsDelta() && len(obj.Children) > 0 {
+			for _, child := range obj.Children {
+				if _, err := p.resolveObject(child, content); err != nil {
+					return err
+				}
+			}
+
+			// Remove the delta from the cache.
+			if obj.DiskType.IsDelta() && !p.scanner.IsSeekable {
+				delete(p.deltas, obj.Offset)
+			}
+		}
+
+		obj.Content = nil
+	}
+
+	return nil
+}
+
+func (p *Parser) get(o *objectInfo) ([]byte, error) {
+	if len(o.Content) > 0 {
+		return o.Content, nil
+	}
+
+	e, ok := p.cache.Get(o.SHA1)
+	// If it's not on the cache and is not a delta we can try to find it in the
+	// storage, if there's one.
+	if !ok && p.storage != nil && !o.Type.IsDelta() {
+		var err error
+		e, err = p.storage.EncodedObject(plumbing.AnyObject, o.SHA1)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	if e != nil {
+		r, err := e.Reader()
+		if err != nil {
+			return nil, err
+		}
+
+		buf := make([]byte, e.Size())
+		if _, err = r.Read(buf); err != nil {
+			return nil, err
+		}
+
+		return buf, nil
+	}
+
+	var data []byte
+	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
+		}
+	} else {
+		var err error
+		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
+	}
+
+	if pending, ok := p.pendingRefDeltas[o.SHA1]; ok {
+		for _, po := range pending {
+			po.Parent = o
+			o.Children = append(o.Children, po)
+		}
+		delete(p.pendingRefDeltas, o.SHA1)
+	}
+
+	if p.storage != nil {
+		obj := new(plumbing.MemoryObject)
+		obj.SetSize(o.Size())
+		obj.SetType(o.Type)
+		if _, err := obj.Write(data); err != nil {
+			return nil, err
+		}
+
+		if _, err := p.storage.SetEncodedObject(obj); err != nil {
+			return nil, err
+		}
+	}
+
+	return data, nil
+}
+
+func (p *Parser) readData(o *objectInfo) ([]byte, error) {
+	if !p.scanner.IsSeekable && o.DiskType.IsDelta() {
+		data, ok := p.deltas[o.Offset]
+		if !ok {
+			return nil, ErrDeltaNotCached
+		}
+
+		return data, nil
+	}
+
+	// TODO: skip header. Header size can be calculated with the offset of the
+	// next offset in the first pass.
+	if _, err := p.scanner.SeekFromStart(o.Offset); err != nil {
+		return nil, err
+	}
+
+	if _, err := p.scanner.NextObjectHeader(); err != nil {
+		return nil, err
+	}
+
+	buf := new(bytes.Buffer)
+	if _, _, err := p.scanner.NextObject(buf); 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
+	ota.Hasher = plumbing.NewHasher(ota.Type, int64(len(patched)))
+	if _, err := ota.Write(patched); err != nil {
+		return nil, err
+	}
+	ota.SHA1 = ota.Sum()
+	ota.Length = int64(len(patched))
+
+	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
+
+	Content []byte
+}
+
+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) Write(b []byte) (int, error) {
+	o.Content = make([]byte, len(b))
+	copy(o.Content, b)
+	return o.Hasher.Write(b)
+}
+
+func (o *objectInfo) IsDelta() bool {
+	return o.Type.IsDelta()
+}
+
+func (o *objectInfo) Size() int64 {
+	return o.Length
+}