Merge pull request #906 from src-d/perf/packfile-reads

Improve packfile reading performance

13 files changed, 1713 insertions, 1203 deletions

diff --git a/plumbing/format/packfile/common.go b/plumbing/format/packfile/common.go
index beb015d..2b4aceb 100644
--- a/plumbing/format/packfile/common.go
+++ b/plumbing/format/packfile/common.go
@@ -23,24 +23,28 @@ const (
 	maskType        = uint8(112) // 0111 0000
 )
 
-// UpdateObjectStorage updates the given storer.EncodedObjectStorer with the contents of the
+// UpdateObjectStorage updates the storer with the objects in the given
 // packfile.
-func UpdateObjectStorage(s storer.EncodedObjectStorer, packfile io.Reader) error {
-	if sw, ok := s.(storer.PackfileWriter); ok {
-		return writePackfileToObjectStorage(sw, packfile)
+func UpdateObjectStorage(s storer.Storer, packfile io.Reader) error {
+	if pw, ok := s.(storer.PackfileWriter); ok {
+		return WritePackfileToObjectStorage(pw, packfile)
 	}
 
-	stream := NewScanner(packfile)
-	d, err := NewDecoder(stream, s)
+	p, err := NewParserWithStorage(NewScanner(packfile), s)
 	if err != nil {
 		return err
 	}
 
-	_, err = d.Decode()
+	_, err = p.Parse()
 	return err
 }
 
-func writePackfileToObjectStorage(sw storer.PackfileWriter, packfile io.Reader) (err error) {
+// WritePackfileToObjectStorage writes all the packfile objects into the given
+// object storage.
+func WritePackfileToObjectStorage(
+	sw storer.PackfileWriter,
+	packfile io.Reader,
+) (err error) {
 	w, err := sw.PackfileWriter()
 	if err != nil {
 		return err
diff --git a/plumbing/format/packfile/decoder.go b/plumbing/format/packfile/decoder.go
deleted file mode 100644
index f706e5d..0000000
--- a/plumbing/format/packfile/decoder.go
+++ /dev/null
@@ -1,495 +0,0 @@
-package packfile
-
-import (
-	"bytes"
-
-	"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"
-)
-
-// Format specifies if the packfile uses ref-deltas or ofs-deltas.
-type Format int
-
-// Possible values of the Format type.
-const (
-	UnknownFormat Format = iota
-	OFSDeltaFormat
-	REFDeltaFormat
-)
-
-var (
-	// ErrMaxObjectsLimitReached is returned by Decode when the number
-	// of objects in the packfile is higher than
-	// Decoder.MaxObjectsLimit.
-	ErrMaxObjectsLimitReached = NewError("max. objects limit reached")
-	// ErrInvalidObject is returned by Decode when an invalid object is
-	// found in the packfile.
-	ErrInvalidObject = NewError("invalid git object")
-	// ErrPackEntryNotFound is returned by Decode when a reference in
-	// the packfile references and unknown object.
-	ErrPackEntryNotFound = NewError("can't find a pack entry")
-	// ErrZLib is returned by Decode when there was an error unzipping
-	// the packfile contents.
-	ErrZLib = NewError("zlib reading error")
-	// ErrCannotRecall is returned by RecallByOffset or RecallByHash if the object
-	// to recall cannot be returned.
-	ErrCannotRecall = NewError("cannot recall object")
-	// ErrResolveDeltasNotSupported is returned if a NewDecoder is used with a
-	// non-seekable scanner and without a plumbing.ObjectStorage
-	ErrResolveDeltasNotSupported = NewError("resolve delta is not supported")
-	// ErrNonSeekable is returned if a ReadObjectAt method is called without a
-	// seekable scanner
-	ErrNonSeekable = NewError("non-seekable scanner")
-	// ErrRollback error making Rollback over a transaction after an error
-	ErrRollback = NewError("rollback error, during set error")
-	// ErrAlreadyDecoded is returned if NewDecoder is called for a second time
-	ErrAlreadyDecoded = NewError("packfile was already decoded")
-)
-
-// Decoder reads and decodes packfiles from an input Scanner, if an ObjectStorer
-// was provided the decoded objects are store there. If not the decode object
-// is destroyed. The Offsets and CRCs are calculated whether an
-// ObjectStorer was provided or not.
-type Decoder struct {
-	deltaBaseCache cache.Object
-
-	s  *Scanner
-	o  storer.EncodedObjectStorer
-	tx storer.Transaction
-
-	isDecoded bool
-
-	// hasBuiltIndex indicates if the index is fully built or not. If it is not,
-	// will be built incrementally while decoding.
-	hasBuiltIndex bool
-	idx           *Index
-
-	offsetToType map[int64]plumbing.ObjectType
-	decoderType  plumbing.ObjectType
-}
-
-// NewDecoder returns a new Decoder that decodes a Packfile using the given
-// Scanner and stores the objects in the provided EncodedObjectStorer. ObjectStorer can be nil, in this
-// If the passed EncodedObjectStorer is nil, objects are not stored, but
-// offsets on the Packfile and CRCs are calculated.
-//
-// If EncodedObjectStorer is nil and the Scanner is not Seekable, ErrNonSeekable is
-// returned.
-//
-// If the ObjectStorer implements storer.Transactioner, a transaction is created
-// during the Decode execution. If anything fails, Rollback is called
-func NewDecoder(s *Scanner, o storer.EncodedObjectStorer) (*Decoder, error) {
-	return NewDecoderForType(s, o, plumbing.AnyObject,
-		cache.NewObjectLRUDefault())
-}
-
-// NewDecoderWithCache is a version of NewDecoder where cache can be specified.
-func NewDecoderWithCache(s *Scanner, o storer.EncodedObjectStorer,
-	cacheObject cache.Object) (*Decoder, error) {
-
-	return NewDecoderForType(s, o, plumbing.AnyObject, cacheObject)
-}
-
-// NewDecoderForType returns a new Decoder but in this case for a specific object type.
-// When an object is read using this Decoder instance and it is not of the same type of
-// the specified one, nil will be returned. This is intended to avoid the content
-// deserialization of all the objects.
-//
-// cacheObject is a cache.Object implementation that is used to speed up the
-// process. If cache is not needed you can pass nil. To create an LRU cache
-// object with the default size you can use the helper cache.ObjectLRUDefault().
-func NewDecoderForType(s *Scanner, o storer.EncodedObjectStorer,
-	t plumbing.ObjectType, cacheObject cache.Object) (*Decoder, error) {
-
-	if t == plumbing.OFSDeltaObject ||
-		t == plumbing.REFDeltaObject ||
-		t == plumbing.InvalidObject {
-		return nil, plumbing.ErrInvalidType
-	}
-
-	if !canResolveDeltas(s, o) {
-		return nil, ErrResolveDeltasNotSupported
-	}
-
-	return &Decoder{
-		s:              s,
-		o:              o,
-		deltaBaseCache: cacheObject,
-
-		idx:          NewIndex(0),
-		offsetToType: make(map[int64]plumbing.ObjectType),
-		decoderType:  t,
-	}, nil
-}
-
-func canResolveDeltas(s *Scanner, o storer.EncodedObjectStorer) bool {
-	return s.IsSeekable || o != nil
-}
-
-// Decode reads a packfile and stores it in the value pointed to by s. The
-// offsets and the CRCs are calculated by this method
-func (d *Decoder) Decode() (checksum plumbing.Hash, err error) {
-	defer func() { d.isDecoded = true }()
-
-	if d.isDecoded {
-		return plumbing.ZeroHash, ErrAlreadyDecoded
-	}
-
-	if err := d.doDecode(); err != nil {
-		return plumbing.ZeroHash, err
-	}
-
-	return d.s.Checksum()
-}
-
-func (d *Decoder) doDecode() error {
-	_, count, err := d.s.Header()
-	if err != nil {
-		return err
-	}
-
-	if !d.hasBuiltIndex {
-		d.idx = NewIndex(int(count))
-	}
-	defer func() { d.hasBuiltIndex = true }()
-
-	_, isTxStorer := d.o.(storer.Transactioner)
-	switch {
-	case d.o == nil:
-		return d.decodeObjects(int(count))
-	case isTxStorer:
-		return d.decodeObjectsWithObjectStorerTx(int(count))
-	default:
-		return d.decodeObjectsWithObjectStorer(int(count))
-	}
-}
-
-func (d *Decoder) decodeObjects(count int) error {
-	for i := 0; i < count; i++ {
-		if _, err := d.DecodeObject(); err != nil {
-			return err
-		}
-	}
-
-	return nil
-}
-
-func (d *Decoder) decodeObjectsWithObjectStorer(count int) error {
-	for i := 0; i < count; i++ {
-		obj, err := d.DecodeObject()
-		if err != nil {
-			return err
-		}
-
-		if _, err := d.o.SetEncodedObject(obj); err != nil {
-			return err
-		}
-	}
-
-	return nil
-}
-
-func (d *Decoder) decodeObjectsWithObjectStorerTx(count int) error {
-	d.tx = d.o.(storer.Transactioner).Begin()
-
-	for i := 0; i < count; i++ {
-		obj, err := d.DecodeObject()
-		if err != nil {
-			return err
-		}
-
-		if _, err := d.tx.SetEncodedObject(obj); err != nil {
-			if rerr := d.tx.Rollback(); rerr != nil {
-				return ErrRollback.AddDetails(
-					"error: %s, during tx.Set error: %s", rerr, err,
-				)
-			}
-
-			return err
-		}
-
-	}
-
-	return d.tx.Commit()
-}
-
-// DecodeObject reads the next object from the scanner and returns it. This
-// method can be used in replacement of the Decode method, to work in a
-// interactive way. If you created a new decoder instance using NewDecoderForType
-// constructor, if the object decoded is not equals to the specified one, nil will
-// be returned
-func (d *Decoder) DecodeObject() (plumbing.EncodedObject, error) {
-	return d.doDecodeObject(d.decoderType)
-}
-
-func (d *Decoder) doDecodeObject(t plumbing.ObjectType) (plumbing.EncodedObject, error) {
-	h, err := d.s.NextObjectHeader()
-	if err != nil {
-		return nil, err
-	}
-
-	if t == plumbing.AnyObject {
-		return d.decodeByHeader(h)
-	}
-
-	return d.decodeIfSpecificType(h)
-}
-
-func (d *Decoder) decodeIfSpecificType(h *ObjectHeader) (plumbing.EncodedObject, error) {
-	var (
-		obj      plumbing.EncodedObject
-		realType plumbing.ObjectType
-		err      error
-	)
-	switch h.Type {
-	case plumbing.OFSDeltaObject:
-		realType, err = d.ofsDeltaType(h.OffsetReference)
-	case plumbing.REFDeltaObject:
-		realType, err = d.refDeltaType(h.Reference)
-		if err == plumbing.ErrObjectNotFound {
-			obj, err = d.decodeByHeader(h)
-			if err != nil {
-				realType = obj.Type()
-			}
-		}
-	default:
-		realType = h.Type
-	}
-
-	if err != nil {
-		return nil, err
-	}
-
-	d.offsetToType[h.Offset] = realType
-
-	if d.decoderType == realType {
-		if obj != nil {
-			return obj, nil
-		}
-
-		return d.decodeByHeader(h)
-	}
-
-	return nil, nil
-}
-
-func (d *Decoder) ofsDeltaType(offset int64) (plumbing.ObjectType, error) {
-	t, ok := d.offsetToType[offset]
-	if !ok {
-		return plumbing.InvalidObject, plumbing.ErrObjectNotFound
-	}
-
-	return t, nil
-}
-
-func (d *Decoder) refDeltaType(ref plumbing.Hash) (plumbing.ObjectType, error) {
-	e, ok := d.idx.LookupHash(ref)
-	if !ok {
-		return plumbing.InvalidObject, plumbing.ErrObjectNotFound
-	}
-
-	return d.ofsDeltaType(int64(e.Offset))
-}
-
-func (d *Decoder) decodeByHeader(h *ObjectHeader) (plumbing.EncodedObject, error) {
-	obj := d.newObject()
-	obj.SetSize(h.Length)
-	obj.SetType(h.Type)
-
-	var crc uint32
-	var err error
-	switch h.Type {
-	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
-		crc, err = d.fillRegularObjectContent(obj)
-	case plumbing.REFDeltaObject:
-		crc, err = d.fillREFDeltaObjectContent(obj, h.Reference)
-	case plumbing.OFSDeltaObject:
-		crc, err = d.fillOFSDeltaObjectContent(obj, h.OffsetReference)
-	default:
-		err = ErrInvalidObject.AddDetails("type %q", h.Type)
-	}
-
-	if err != nil {
-		return obj, err
-	}
-
-	if !d.hasBuiltIndex {
-		d.idx.Add(obj.Hash(), uint64(h.Offset), crc)
-	}
-
-	return obj, nil
-}
-
-func (d *Decoder) newObject() plumbing.EncodedObject {
-	if d.o == nil {
-		return &plumbing.MemoryObject{}
-	}
-
-	return d.o.NewEncodedObject()
-}
-
-// DecodeObjectAt reads an object at the given location. Every EncodedObject
-// returned is added into a internal index. This is intended to be able to regenerate
-// objects from deltas (offset deltas or reference deltas) without an package index
-// (.idx file). If Decode wasn't called previously objects offset should provided
-// using the SetOffsets method. It decodes the object regardless of the Decoder
-// type.
-func (d *Decoder) DecodeObjectAt(offset int64) (plumbing.EncodedObject, error) {
-	if !d.s.IsSeekable {
-		return nil, ErrNonSeekable
-	}
-
-	beforeJump, err := d.s.SeekFromStart(offset)
-	if err != nil {
-		return nil, err
-	}
-
-	defer func() {
-		_, seekErr := d.s.SeekFromStart(beforeJump)
-		if err == nil {
-			err = seekErr
-		}
-	}()
-
-	return d.doDecodeObject(plumbing.AnyObject)
-}
-
-func (d *Decoder) fillRegularObjectContent(obj plumbing.EncodedObject) (uint32, error) {
-	w, err := obj.Writer()
-	if err != nil {
-		return 0, err
-	}
-
-	_, crc, err := d.s.NextObject(w)
-	return crc, err
-}
-
-func (d *Decoder) fillREFDeltaObjectContent(obj plumbing.EncodedObject, ref plumbing.Hash) (uint32, error) {
-	buf := bufPool.Get().(*bytes.Buffer)
-	buf.Reset()
-	_, crc, err := d.s.NextObject(buf)
-	if err != nil {
-		return 0, err
-	}
-
-	base, ok := d.cacheGet(ref)
-	if !ok {
-		base, err = d.recallByHash(ref)
-		if err != nil {
-			return 0, err
-		}
-	}
-
-	obj.SetType(base.Type())
-	err = ApplyDelta(obj, base, buf.Bytes())
-	d.cachePut(obj)
-	bufPool.Put(buf)
-
-	return crc, err
-}
-
-func (d *Decoder) fillOFSDeltaObjectContent(obj plumbing.EncodedObject, offset int64) (uint32, error) {
-	buf := bytes.NewBuffer(nil)
-	_, crc, err := d.s.NextObject(buf)
-	if err != nil {
-		return 0, err
-	}
-
-	e, ok := d.idx.LookupOffset(uint64(offset))
-	var base plumbing.EncodedObject
-	if ok {
-		base, ok = d.cacheGet(e.Hash)
-	}
-
-	if !ok {
-		base, err = d.recallByOffset(offset)
-		if err != nil {
-			return 0, err
-		}
-
-		d.cachePut(base)
-	}
-
-	obj.SetType(base.Type())
-	err = ApplyDelta(obj, base, buf.Bytes())
-	d.cachePut(obj)
-
-	return crc, err
-}
-
-func (d *Decoder) cacheGet(h plumbing.Hash) (plumbing.EncodedObject, bool) {
-	if d.deltaBaseCache == nil {
-		return nil, false
-	}
-
-	return d.deltaBaseCache.Get(h)
-}
-
-func (d *Decoder) cachePut(obj plumbing.EncodedObject) {
-	if d.deltaBaseCache == nil {
-		return
-	}
-
-	d.deltaBaseCache.Put(obj)
-}
-
-func (d *Decoder) recallByOffset(o int64) (plumbing.EncodedObject, error) {
-	if d.s.IsSeekable {
-		return d.DecodeObjectAt(o)
-	}
-
-	if e, ok := d.idx.LookupOffset(uint64(o)); ok {
-		return d.recallByHashNonSeekable(e.Hash)
-	}
-
-	return nil, plumbing.ErrObjectNotFound
-}
-
-func (d *Decoder) recallByHash(h plumbing.Hash) (plumbing.EncodedObject, error) {
-	if d.s.IsSeekable {
-		if e, ok := d.idx.LookupHash(h); ok {
-			return d.DecodeObjectAt(int64(e.Offset))
-		}
-	}
-
-	return d.recallByHashNonSeekable(h)
-}
-
-// recallByHashNonSeekable if we are in a transaction the objects are read from
-// the transaction, if not are directly read from the ObjectStorer
-func (d *Decoder) recallByHashNonSeekable(h plumbing.Hash) (obj plumbing.EncodedObject, err error) {
-	if d.tx != nil {
-		obj, err = d.tx.EncodedObject(plumbing.AnyObject, h)
-	} else {
-		obj, err = d.o.EncodedObject(plumbing.AnyObject, h)
-	}
-
-	if err != plumbing.ErrObjectNotFound {
-		return obj, err
-	}
-
-	return nil, plumbing.ErrObjectNotFound
-}
-
-// SetIndex sets an index for the packfile. It is recommended to set this.
-// The index might be read from a file or reused from a previous Decoder usage
-// (see Index function).
-func (d *Decoder) SetIndex(idx *Index) {
-	d.hasBuiltIndex = true
-	d.idx = idx
-}
-
-// Index returns the index for the packfile. If index was set with SetIndex,
-// Index will return it. Otherwise, it will return an index that is built while
-// decoding. If neither SetIndex was called with a full index or Decode called
-// for the whole packfile, then the returned index will be incomplete.
-func (d *Decoder) Index() *Index {
-	return d.idx
-}
-
-// Close closes the Scanner. usually this mean that the whole reader is read and
-// discarded
-func (d *Decoder) Close() error {
-	return d.s.Close()
-}
diff --git a/plumbing/format/packfile/decoder_test.go b/plumbing/format/packfile/decoder_test.go
deleted file mode 100644
index b5bc7b7..0000000
--- a/plumbing/format/packfile/decoder_test.go
+++ /dev/null
@@ -1,396 +0,0 @@
-package packfile_test
-
-import (
-	"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/format/idxfile"
-	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
-	"gopkg.in/src-d/go-git.v4/plumbing/storer"
-	"gopkg.in/src-d/go-git.v4/storage/filesystem"
-	"gopkg.in/src-d/go-git.v4/storage/memory"
-
-	. "gopkg.in/check.v1"
-	"gopkg.in/src-d/go-billy.v4/memfs"
-	"gopkg.in/src-d/go-git-fixtures.v3"
-)
-
-type ReaderSuite struct {
-	fixtures.Suite
-}
-
-var _ = Suite(&ReaderSuite{})
-
-func (s *ReaderSuite) TestNewDecodeNonSeekable(c *C) {
-	scanner := packfile.NewScanner(nil)
-	d, err := packfile.NewDecoder(scanner, nil)
-
-	c.Assert(d, IsNil)
-	c.Assert(err, NotNil)
-}
-
-func (s *ReaderSuite) TestDecode(c *C) {
-	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		scanner := packfile.NewScanner(f.Packfile())
-		storage := memory.NewStorage()
-
-		d, err := packfile.NewDecoder(scanner, storage)
-		c.Assert(err, IsNil)
-		defer d.Close()
-
-		ch, err := d.Decode()
-		c.Assert(err, IsNil)
-		c.Assert(ch, Equals, f.PackfileHash)
-
-		assertObjects(c, storage, expectedHashes)
-	})
-}
-
-func (s *ReaderSuite) TestDecodeByTypeRefDelta(c *C) {
-	f := fixtures.Basic().ByTag("ref-delta").One()
-
-	storage := memory.NewStorage()
-	scanner := packfile.NewScanner(f.Packfile())
-	d, err := packfile.NewDecoderForType(scanner, storage, plumbing.CommitObject,
-		cache.NewObjectLRUDefault())
-	c.Assert(err, IsNil)
-
-	// Index required to decode by ref-delta.
-	d.SetIndex(getIndexFromIdxFile(f.Idx()))
-
-	defer d.Close()
-
-	_, count, err := scanner.Header()
-	c.Assert(err, IsNil)
-
-	var i uint32
-	for i = 0; i < count; i++ {
-		obj, err := d.DecodeObject()
-		c.Assert(err, IsNil)
-
-		if obj != nil {
-			c.Assert(obj.Type(), Equals, plumbing.CommitObject)
-		}
-	}
-}
-
-func (s *ReaderSuite) TestDecodeByTypeRefDeltaError(c *C) {
-	fixtures.Basic().ByTag("ref-delta").Test(c, func(f *fixtures.Fixture) {
-		storage := memory.NewStorage()
-		scanner := packfile.NewScanner(f.Packfile())
-		d, err := packfile.NewDecoderForType(scanner, storage,
-			plumbing.CommitObject, cache.NewObjectLRUDefault())
-		c.Assert(err, IsNil)
-
-		defer d.Close()
-
-		_, count, err := scanner.Header()
-		c.Assert(err, IsNil)
-
-		isError := false
-		var i uint32
-		for i = 0; i < count; i++ {
-			_, err := d.DecodeObject()
-			if err != nil {
-				isError = true
-				break
-			}
-		}
-		c.Assert(isError, Equals, true)
-	})
-
-}
-
-func (s *ReaderSuite) TestDecodeByType(c *C) {
-	ts := []plumbing.ObjectType{
-		plumbing.CommitObject,
-		plumbing.TagObject,
-		plumbing.TreeObject,
-		plumbing.BlobObject,
-	}
-
-	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		for _, t := range ts {
-			storage := memory.NewStorage()
-			scanner := packfile.NewScanner(f.Packfile())
-			d, err := packfile.NewDecoderForType(scanner, storage, t,
-				cache.NewObjectLRUDefault())
-			c.Assert(err, IsNil)
-
-			// when the packfile is ref-delta based, the offsets are required
-			if f.Is("ref-delta") {
-				d.SetIndex(getIndexFromIdxFile(f.Idx()))
-			}
-
-			defer d.Close()
-
-			_, count, err := scanner.Header()
-			c.Assert(err, IsNil)
-
-			var i uint32
-			for i = 0; i < count; i++ {
-				obj, err := d.DecodeObject()
-				c.Assert(err, IsNil)
-
-				if obj != nil {
-					c.Assert(obj.Type(), Equals, t)
-				}
-			}
-		}
-	})
-}
-func (s *ReaderSuite) TestDecodeByTypeConstructor(c *C) {
-	f := fixtures.Basic().ByTag("packfile").One()
-	storage := memory.NewStorage()
-	scanner := packfile.NewScanner(f.Packfile())
-
-	_, err := packfile.NewDecoderForType(scanner, storage,
-		plumbing.OFSDeltaObject, cache.NewObjectLRUDefault())
-	c.Assert(err, Equals, plumbing.ErrInvalidType)
-
-	_, err = packfile.NewDecoderForType(scanner, storage,
-		plumbing.REFDeltaObject, cache.NewObjectLRUDefault())
-
-	c.Assert(err, Equals, plumbing.ErrInvalidType)
-
-	_, err = packfile.NewDecoderForType(scanner, storage, plumbing.InvalidObject,
-		cache.NewObjectLRUDefault())
-	c.Assert(err, Equals, plumbing.ErrInvalidType)
-}
-
-func (s *ReaderSuite) TestDecodeMultipleTimes(c *C) {
-	f := fixtures.Basic().ByTag("packfile").One()
-	scanner := packfile.NewScanner(f.Packfile())
-	storage := memory.NewStorage()
-
-	d, err := packfile.NewDecoder(scanner, storage)
-	c.Assert(err, IsNil)
-	defer d.Close()
-
-	ch, err := d.Decode()
-	c.Assert(err, IsNil)
-	c.Assert(ch, Equals, f.PackfileHash)
-
-	ch, err = d.Decode()
-	c.Assert(err, Equals, packfile.ErrAlreadyDecoded)
-	c.Assert(ch, Equals, plumbing.ZeroHash)
-}
-
-func (s *ReaderSuite) TestDecodeInMemory(c *C) {
-	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		scanner := packfile.NewScanner(f.Packfile())
-		d, err := packfile.NewDecoder(scanner, nil)
-		c.Assert(err, IsNil)
-
-		ch, err := d.Decode()
-		c.Assert(err, IsNil)
-		c.Assert(ch, Equals, f.PackfileHash)
-	})
-}
-
-type nonSeekableReader struct {
-	r io.Reader
-}
-
-func (nsr nonSeekableReader) Read(b []byte) (int, error) {
-	return nsr.r.Read(b)
-}
-
-func (s *ReaderSuite) TestDecodeNoSeekableWithTxStorer(c *C) {
-	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		reader := nonSeekableReader{
-			r: f.Packfile(),
-		}
-
-		scanner := packfile.NewScanner(reader)
-
-		var storage storer.EncodedObjectStorer = memory.NewStorage()
-		_, isTxStorer := storage.(storer.Transactioner)
-		c.Assert(isTxStorer, Equals, true)
-
-		d, err := packfile.NewDecoder(scanner, storage)
-		c.Assert(err, IsNil)
-		defer d.Close()
-
-		ch, err := d.Decode()
-		c.Assert(err, IsNil)
-		c.Assert(ch, Equals, f.PackfileHash)
-
-		assertObjects(c, storage, expectedHashes)
-	})
-}
-
-func (s *ReaderSuite) TestDecodeNoSeekableWithoutTxStorer(c *C) {
-	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		reader := nonSeekableReader{
-			r: f.Packfile(),
-		}
-
-		scanner := packfile.NewScanner(reader)
-
-		var storage storer.EncodedObjectStorer
-		storage, _ = filesystem.NewStorage(memfs.New())
-		_, isTxStorer := storage.(storer.Transactioner)
-		c.Assert(isTxStorer, Equals, false)
-
-		d, err := packfile.NewDecoder(scanner, storage)
-		c.Assert(err, IsNil)
-		defer d.Close()
-
-		ch, err := d.Decode()
-		c.Assert(err, IsNil)
-		c.Assert(ch, Equals, f.PackfileHash)
-
-		assertObjects(c, storage, expectedHashes)
-	})
-}
-
-var expectedHashes = []string{
-	"918c48b83bd081e863dbe1b80f8998f058cd8294",
-	"af2d6a6954d532f8ffb47615169c8fdf9d383a1a",
-	"1669dce138d9b841a518c64b10914d88f5e488ea",
-	"a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
-	"b8e471f58bcbca63b07bda20e428190409c2db47",
-	"35e85108805c84807bc66a02d91535e1e24b38b9",
-	"b029517f6300c2da0f4b651b8642506cd6aaf45d",
-	"32858aad3c383ed1ff0a0f9bdf231d54a00c9e88",
-	"d3ff53e0564a9f87d8e84b6e28e5060e517008aa",
-	"c192bd6a24ea1ab01d78686e417c8bdc7c3d197f",
-	"d5c0f4ab811897cadf03aec358ae60d21f91c50d",
-	"49c6bb89b17060d7b4deacb7b338fcc6ea2352a9",
-	"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b",
-	"9dea2395f5403188298c1dabe8bdafe562c491e3",
-	"586af567d0bb5e771e49bdd9434f5e0fb76d25fa",
-	"9a48f23120e880dfbe41f7c9b7b708e9ee62a492",
-	"5a877e6a906a2743ad6e45d99c1793642aaf8eda",
-	"c8f1d8c61f9da76f4cb49fd86322b6e685dba956",
-	"a8d315b2b1c615d43042c3a62402b8a54288cf5c",
-	"a39771a7651f97faf5c72e08224d857fc35133db",
-	"880cd14280f4b9b6ed3986d6671f907d7cc2a198",
-	"fb72698cab7617ac416264415f13224dfd7a165e",
-	"4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd",
-	"eba74343e2f15d62adedfd8c883ee0262b5c8021",
-	"c2d30fa8ef288618f65f6eed6e168e0d514886f4",
-	"8dcef98b1d52143e1e2dbc458ffe38f925786bf2",
-	"aa9b383c260e1d05fbbf6b30a02914555e20c725",
-	"6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
-	"dbd3641b371024f44d0e469a9c8f5457b0660de1",
-	"e8d3ffab552895c19b9fcf7aa264d277cde33881",
-	"7e59600739c96546163833214c36459e324bad0a",
-}
-
-func (s *ReaderSuite) TestDecodeCRCs(c *C) {
-	f := fixtures.Basic().ByTag("ofs-delta").One()
-
-	scanner := packfile.NewScanner(f.Packfile())
-	storage := memory.NewStorage()
-
-	d, err := packfile.NewDecoder(scanner, storage)
-	c.Assert(err, IsNil)
-	_, err = d.Decode()
-	c.Assert(err, IsNil)
-
-	var sum uint64
-	idx := d.Index().ToIdxFile()
-	for _, e := range idx.Entries {
-		sum += uint64(e.CRC32)
-	}
-
-	c.Assert(int(sum), Equals, 78022211966)
-}
-
-func (s *ReaderSuite) TestDecodeObjectAt(c *C) {
-	f := fixtures.Basic().One()
-	scanner := packfile.NewScanner(f.Packfile())
-	d, err := packfile.NewDecoder(scanner, nil)
-	c.Assert(err, IsNil)
-
-	// when the packfile is ref-delta based, the offsets are required
-	if f.Is("ref-delta") {
-		d.SetIndex(getIndexFromIdxFile(f.Idx()))
-	}
-
-	// the objects at reference 186, is a delta, so should be recall,
-	// without being read before.
-	obj, err := d.DecodeObjectAt(186)
-	c.Assert(err, IsNil)
-	c.Assert(obj.Hash().String(), Equals, "6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
-}
-
-func (s *ReaderSuite) TestDecodeObjectAtForType(c *C) {
-	f := fixtures.Basic().One()
-	scanner := packfile.NewScanner(f.Packfile())
-	d, err := packfile.NewDecoderForType(scanner, nil, plumbing.TreeObject,
-		cache.NewObjectLRUDefault())
-	c.Assert(err, IsNil)
-
-	// when the packfile is ref-delta based, the offsets are required
-	if f.Is("ref-delta") {
-		d.SetIndex(getIndexFromIdxFile(f.Idx()))
-	}
-
-	// the objects at reference 186, is a delta, so should be recall,
-	// without being read before.
-	obj, err := d.DecodeObjectAt(186)
-	c.Assert(err, IsNil)
-	c.Assert(obj.Type(), Equals, plumbing.CommitObject)
-	c.Assert(obj.Hash().String(), Equals, "6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
-}
-
-func (s *ReaderSuite) TestIndex(c *C) {
-	f := fixtures.Basic().One()
-	scanner := packfile.NewScanner(f.Packfile())
-	d, err := packfile.NewDecoder(scanner, nil)
-	c.Assert(err, IsNil)
-
-	c.Assert(d.Index().ToIdxFile().Entries, HasLen, 0)
-
-	_, err = d.Decode()
-	c.Assert(err, IsNil)
-
-	c.Assert(len(d.Index().ToIdxFile().Entries), Equals, 31)
-}
-
-func (s *ReaderSuite) TestSetIndex(c *C) {
-	f := fixtures.Basic().One()
-	scanner := packfile.NewScanner(f.Packfile())
-	d, err := packfile.NewDecoder(scanner, nil)
-	c.Assert(err, IsNil)
-
-	idx := packfile.NewIndex(1)
-	h := plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5")
-	idx.Add(h, uint64(42), 0)
-	d.SetIndex(idx)
-
-	idxf := d.Index().ToIdxFile()
-	c.Assert(idxf.Entries, HasLen, 1)
-	c.Assert(idxf.Entries[0].Offset, Equals, uint64(42))
-}
-
-func assertObjects(c *C, s storer.EncodedObjectStorer, expects []string) {
-
-	i, err := s.IterEncodedObjects(plumbing.AnyObject)
-	c.Assert(err, IsNil)
-
-	var count int
-	err = i.ForEach(func(plumbing.EncodedObject) error { count++; return nil })
-	c.Assert(err, IsNil)
-	c.Assert(count, Equals, len(expects))
-
-	for _, exp := range expects {
-		obt, err := s.EncodedObject(plumbing.AnyObject, plumbing.NewHash(exp))
-		c.Assert(err, IsNil)
-		c.Assert(obt.Hash().String(), Equals, exp)
-	}
-}
-
-func getIndexFromIdxFile(r io.Reader) *packfile.Index {
-	idxf := idxfile.NewIdxfile()
-	d := idxfile.NewDecoder(r)
-	if err := d.Decode(idxf); err != nil {
-		panic(err)
-	}
-
-	return packfile.NewIndexFromIdxFile(idxf)
-}
diff --git a/plumbing/format/packfile/encoder_advanced_test.go b/plumbing/format/packfile/encoder_advanced_test.go
index 8cc7180..fc1419e 100644
--- a/plumbing/format/packfile/encoder_advanced_test.go
+++ b/plumbing/format/packfile/encoder_advanced_test.go
@@ -2,14 +2,16 @@ package packfile_test
 
 import (
 	"bytes"
+	"io"
 	"math/rand"
 	"testing"
 
+	"gopkg.in/src-d/go-billy.v4/memfs"
 	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
 	. "gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
 	"gopkg.in/src-d/go-git.v4/plumbing/storer"
 	"gopkg.in/src-d/go-git.v4/storage/filesystem"
-	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
 	"gopkg.in/src-d/go-git-fixtures.v3"
@@ -34,7 +36,6 @@ func (s *EncoderAdvancedSuite) TestEncodeDecode(c *C) {
 		c.Assert(err, IsNil)
 		s.testEncodeDecode(c, storage, 10)
 	})
-
 }
 
 func (s *EncoderAdvancedSuite) TestEncodeDecodeNoDeltaCompression(c *C) {
@@ -52,8 +53,11 @@ func (s *EncoderAdvancedSuite) TestEncodeDecodeNoDeltaCompression(c *C) {
 	})
 }
 
-func (s *EncoderAdvancedSuite) testEncodeDecode(c *C, storage storer.Storer, packWindow uint) {
-
+func (s *EncoderAdvancedSuite) testEncodeDecode(
+	c *C,
+	storage storer.Storer,
+	packWindow uint,
+) {
 	objIter, err := storage.IterEncodedObjects(plumbing.AnyObject)
 	c.Assert(err, IsNil)
 
@@ -80,16 +84,35 @@ func (s *EncoderAdvancedSuite) testEncodeDecode(c *C, storage storer.Storer, pac
 	encodeHash, err := enc.Encode(hashes, packWindow)
 	c.Assert(err, IsNil)
 
-	scanner := NewScanner(buf)
-	storage = memory.NewStorage()
-	d, err := NewDecoder(scanner, storage)
+	fs := memfs.New()
+	f, err := fs.Create("packfile")
+	c.Assert(err, IsNil)
+
+	_, err = f.Write(buf.Bytes())
+	c.Assert(err, IsNil)
+
+	_, err = f.Seek(0, io.SeekStart)
+	c.Assert(err, IsNil)
+
+	w := new(idxfile.Writer)
+	parser, err := NewParser(NewScanner(f), w)
+	c.Assert(err, IsNil)
+
+	_, err = parser.Parse()
 	c.Assert(err, IsNil)
-	decodeHash, err := d.Decode()
+	index, err := w.Index()
 	c.Assert(err, IsNil)
 
+	_, err = f.Seek(0, io.SeekStart)
+	c.Assert(err, IsNil)
+
+	p := NewPackfile(index, fs, f)
+
+	decodeHash, err := p.ID()
+	c.Assert(err, IsNil)
 	c.Assert(encodeHash, Equals, decodeHash)
 
-	objIter, err = storage.IterEncodedObjects(plumbing.AnyObject)
+	objIter, err = p.GetAll()
 	c.Assert(err, IsNil)
 	obtainedObjects := map[plumbing.Hash]bool{}
 	err = objIter.ForEach(func(o plumbing.EncodedObject) error {
diff --git a/plumbing/format/packfile/encoder_test.go b/plumbing/format/packfile/encoder_test.go
index 84d03fb..80b916d 100644
--- a/plumbing/format/packfile/encoder_test.go
+++ b/plumbing/format/packfile/encoder_test.go
@@ -2,8 +2,12 @@ package packfile
 
 import (
 	"bytes"
+	"io"
+	stdioutil "io/ioutil"
 
+	"gopkg.in/src-d/go-billy.v4/memfs"
 	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
 	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
@@ -130,24 +134,20 @@ func (s *EncoderSuite) simpleDeltaTest(c *C) {
 	})
 	c.Assert(err, IsNil)
 
-	scanner := NewScanner(s.buf)
-
-	storage := memory.NewStorage()
-	d, err := NewDecoder(scanner, storage)
-	c.Assert(err, IsNil)
-
-	decHash, err := d.Decode()
+	p, cleanup := packfileFromReader(c, s.buf)
+	defer cleanup()
+	decHash, err := p.ID()
 	c.Assert(err, IsNil)
 
 	c.Assert(encHash, Equals, decHash)
 
-	decSrc, err := storage.EncodedObject(srcObject.Type(), srcObject.Hash())
+	decSrc, err := p.Get(srcObject.Hash())
 	c.Assert(err, IsNil)
-	c.Assert(decSrc, DeepEquals, srcObject)
+	objectsEqual(c, decSrc, srcObject)
 
-	decTarget, err := storage.EncodedObject(targetObject.Type(), targetObject.Hash())
+	decTarget, err := p.Get(targetObject.Hash())
 	c.Assert(err, IsNil)
-	c.Assert(decTarget, DeepEquals, targetObject)
+	objectsEqual(c, decTarget, targetObject)
 }
 
 func (s *EncoderSuite) deltaOverDeltaTest(c *C) {
@@ -173,27 +173,24 @@ func (s *EncoderSuite) deltaOverDeltaTest(c *C) {
 	})
 	c.Assert(err, IsNil)
 
-	scanner := NewScanner(s.buf)
-	storage := memory.NewStorage()
-	d, err := NewDecoder(scanner, storage)
-	c.Assert(err, IsNil)
-
-	decHash, err := d.Decode()
+	p, cleanup := packfileFromReader(c, s.buf)
+	defer cleanup()
+	decHash, err := p.ID()
 	c.Assert(err, IsNil)
 
 	c.Assert(encHash, Equals, decHash)
 
-	decSrc, err := storage.EncodedObject(srcObject.Type(), srcObject.Hash())
+	decSrc, err := p.Get(srcObject.Hash())
 	c.Assert(err, IsNil)
-	c.Assert(decSrc, DeepEquals, srcObject)
+	objectsEqual(c, decSrc, srcObject)
 
-	decTarget, err := storage.EncodedObject(targetObject.Type(), targetObject.Hash())
+	decTarget, err := p.Get(targetObject.Hash())
 	c.Assert(err, IsNil)
-	c.Assert(decTarget, DeepEquals, targetObject)
+	objectsEqual(c, decTarget, targetObject)
 
-	decOtherTarget, err := storage.EncodedObject(otherTargetObject.Type(), otherTargetObject.Hash())
+	decOtherTarget, err := p.Get(otherTargetObject.Hash())
 	c.Assert(err, IsNil)
-	c.Assert(decOtherTarget, DeepEquals, otherTargetObject)
+	objectsEqual(c, decOtherTarget, otherTargetObject)
 }
 
 func (s *EncoderSuite) deltaOverDeltaCyclicTest(c *C) {
@@ -248,29 +245,74 @@ func (s *EncoderSuite) deltaOverDeltaCyclicTest(c *C) {
 	})
 	c.Assert(err, IsNil)
 
-	scanner := NewScanner(s.buf)
-	storage := memory.NewStorage()
-	d, err := NewDecoder(scanner, storage)
+	p, cleanup := packfileFromReader(c, s.buf)
+	defer cleanup()
+	decHash, err := p.ID()
 	c.Assert(err, IsNil)
 
-	decHash, err := d.Decode()
+	c.Assert(encHash, Equals, decHash)
+
+	decSrc, err := p.Get(o1.Hash())
 	c.Assert(err, IsNil)
+	objectsEqual(c, decSrc, o1)
 
-	c.Assert(encHash, Equals, decHash)
+	decTarget, err := p.Get(o2.Hash())
+	c.Assert(err, IsNil)
+	objectsEqual(c, decTarget, o2)
+
+	decOtherTarget, err := p.Get(o3.Hash())
+	c.Assert(err, IsNil)
+	objectsEqual(c, decOtherTarget, o3)
+
+	decAnotherTarget, err := p.Get(o4.Hash())
+	c.Assert(err, IsNil)
+	objectsEqual(c, decAnotherTarget, o4)
+}
 
-	decSrc, err := storage.EncodedObject(o1.Type(), o1.Hash())
+func objectsEqual(c *C, o1, o2 plumbing.EncodedObject) {
+	c.Assert(o1.Type(), Equals, o2.Type())
+	c.Assert(o1.Hash(), Equals, o2.Hash())
+	c.Assert(o1.Size(), Equals, o2.Size())
+
+	r1, err := o1.Reader()
 	c.Assert(err, IsNil)
-	c.Assert(decSrc, DeepEquals, o1)
 
-	decTarget, err := storage.EncodedObject(o2.Type(), o2.Hash())
+	b1, err := stdioutil.ReadAll(r1)
 	c.Assert(err, IsNil)
-	c.Assert(decTarget, DeepEquals, o2)
 
-	decOtherTarget, err := storage.EncodedObject(o3.Type(), o3.Hash())
+	r2, err := o2.Reader()
 	c.Assert(err, IsNil)
-	c.Assert(decOtherTarget, DeepEquals, o3)
 
-	decAnotherTarget, err := storage.EncodedObject(o4.Type(), o4.Hash())
+	b2, err := stdioutil.ReadAll(r2)
 	c.Assert(err, IsNil)
-	c.Assert(decAnotherTarget, DeepEquals, o4)
+
+	c.Assert(bytes.Compare(b1, b2), Equals, 0)
+}
+
+func packfileFromReader(c *C, buf *bytes.Buffer) (*Packfile, func()) {
+	fs := memfs.New()
+	file, err := fs.Create("packfile")
+	c.Assert(err, IsNil)
+
+	_, err = file.Write(buf.Bytes())
+	c.Assert(err, IsNil)
+
+	_, err = file.Seek(0, io.SeekStart)
+	c.Assert(err, IsNil)
+
+	scanner := NewScanner(file)
+
+	w := new(idxfile.Writer)
+	p, err := NewParser(scanner, w)
+	c.Assert(err, IsNil)
+
+	_, err = p.Parse()
+	c.Assert(err, IsNil)
+
+	index, err := w.Index()
+	c.Assert(err, IsNil)
+
+	return NewPackfile(index, fs, file), func() {
+		c.Assert(file.Close(), IsNil)
+	}
 }
diff --git a/plumbing/format/packfile/fsobject.go b/plumbing/format/packfile/fsobject.go
new file mode 100644
index 0000000..6fd3ca5
--- /dev/null
+++ b/plumbing/format/packfile/fsobject.go
@@ -0,0 +1,106 @@
+package packfile
+
+import (
+	"io"
+
+	billy "gopkg.in/src-d/go-billy.v4"
+	"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/format/idxfile"
+)
+
+// FSObject is an object from the packfile on the filesystem.
+type FSObject struct {
+	hash   plumbing.Hash
+	h      *ObjectHeader
+	offset int64
+	size   int64
+	typ    plumbing.ObjectType
+	index  idxfile.Index
+	fs     billy.Filesystem
+	path   string
+	cache  cache.Object
+}
+
+// NewFSObject creates a new filesystem object.
+func NewFSObject(
+	hash plumbing.Hash,
+	finalType plumbing.ObjectType,
+	offset int64,
+	contentSize int64,
+	index idxfile.Index,
+	fs billy.Filesystem,
+	path string,
+	cache cache.Object,
+) *FSObject {
+	return &FSObject{
+		hash:   hash,
+		offset: offset,
+		size:   contentSize,
+		typ:    finalType,
+		index:  index,
+		fs:     fs,
+		path:   path,
+		cache:  cache,
+	}
+}
+
+// Reader implements the plumbing.EncodedObject interface.
+func (o *FSObject) Reader() (io.ReadCloser, error) {
+	f, err := o.fs.Open(o.path)
+	if err != nil {
+		return nil, err
+	}
+
+	p := NewPackfileWithCache(o.index, nil, f, o.cache)
+	r, err := p.getObjectContent(o.offset)
+	if err != nil {
+		_ = f.Close()
+		return nil, err
+	}
+
+	if err := f.Close(); err != nil {
+		return nil, err
+	}
+
+	return r, nil
+}
+
+// SetSize implements the plumbing.EncodedObject interface. This method
+// is a noop.
+func (o *FSObject) SetSize(int64) {}
+
+// SetType implements the plumbing.EncodedObject interface. This method is
+// a noop.
+func (o *FSObject) SetType(plumbing.ObjectType) {}
+
+// Hash implements the plumbing.EncodedObject interface.
+func (o *FSObject) Hash() plumbing.Hash { return o.hash }
+
+// Size implements the plumbing.EncodedObject interface.
+func (o *FSObject) Size() int64 { return o.size }
+
+// Type implements the plumbing.EncodedObject interface.
+func (o *FSObject) Type() plumbing.ObjectType {
+	return o.typ
+}
+
+// Writer implements the plumbing.EncodedObject interface. This method always
+// returns a nil writer.
+func (o *FSObject) Writer() (io.WriteCloser, error) {
+	return nil, nil
+}
+
+type objectReader struct {
+	io.ReadCloser
+	f billy.File
+}
+
+func (r *objectReader) Close() error {
+	if err := r.ReadCloser.Close(); err != nil {
+		_ = r.f.Close()
+		return err
+	}
+
+	return r.f.Close()
+}
diff --git a/plumbing/format/packfile/index.go b/plumbing/format/packfile/index.go
deleted file mode 100644
index 021b2d1..0000000
--- a/plumbing/format/packfile/index.go
+++ /dev/null
@@ -1,125 +0,0 @@
-package packfile
-
-import (
-	"sort"
-
-	"gopkg.in/src-d/go-git.v4/plumbing"
-	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
-)
-
-// Index is an in-memory representation of a packfile index.
-// This uses idxfile.Idxfile under the hood to obtain indexes from .idx files
-// or to store them.
-type Index struct {
-	byHash   map[plumbing.Hash]*idxfile.Entry
-	byOffset []*idxfile.Entry // sorted by their offset
-}
-
-// NewIndex creates a new empty index with the given size. Size is a hint and
-// can be 0. It is recommended to set it to the number of objects to be indexed
-// if it is known beforehand (e.g. reading from a packfile).
-func NewIndex(size int) *Index {
-	return &Index{
-		byHash:   make(map[plumbing.Hash]*idxfile.Entry, size),
-		byOffset: make([]*idxfile.Entry, 0, size),
-	}
-}
-
-// NewIndexFromIdxFile creates a new Index from an idxfile.IdxFile.
-func NewIndexFromIdxFile(idxf *idxfile.Idxfile) *Index {
-	idx := &Index{
-		byHash:   make(map[plumbing.Hash]*idxfile.Entry, idxf.ObjectCount),
-		byOffset: make([]*idxfile.Entry, 0, idxf.ObjectCount),
-	}
-	sorted := true
-	for i, e := range idxf.Entries {
-		idx.addUnsorted(e)
-		if i > 0 && idx.byOffset[i-1].Offset >= e.Offset {
-			sorted = false
-		}
-	}
-
-	// If the idxfile was loaded from a regular packfile index
-	// then it will already be in offset order, in which case we
-	// can avoid doing a relatively expensive idempotent sort.
-	if !sorted {
-		sort.Sort(orderByOffset(idx.byOffset))
-	}
-
-	return idx
-}
-
-// orderByOffset is a sort.Interface adapter that arranges
-// a slice of entries by their offset.
-type orderByOffset []*idxfile.Entry
-
-func (o orderByOffset) Len() int           { return len(o) }
-func (o orderByOffset) Less(i, j int) bool { return o[i].Offset < o[j].Offset }
-func (o orderByOffset) Swap(i, j int)      { o[i], o[j] = o[j], o[i] }
-
-// Add adds a new Entry with the given values to the index.
-func (idx *Index) Add(h plumbing.Hash, offset uint64, crc32 uint32) {
-	e := &idxfile.Entry{
-		Hash:   h,
-		Offset: offset,
-		CRC32:  crc32,
-	}
-	idx.byHash[e.Hash] = e
-
-	// Find the right position in byOffset.
-	// Look for the first position whose offset is *greater* than e.Offset.
-	i := sort.Search(len(idx.byOffset), func(i int) bool {
-		return idx.byOffset[i].Offset > offset
-	})
-	if i == len(idx.byOffset) {
-		// Simple case: add it to the end.
-		idx.byOffset = append(idx.byOffset, e)
-		return
-	}
-	// Harder case: shift existing entries down by one to make room.
-	// Append a nil entry first so we can use existing capacity in case
-	// the index was carefully preallocated.
-	idx.byOffset = append(idx.byOffset, nil)
-	copy(idx.byOffset[i+1:], idx.byOffset[i:len(idx.byOffset)-1])
-	idx.byOffset[i] = e
-}
-
-func (idx *Index) addUnsorted(e *idxfile.Entry) {
-	idx.byHash[e.Hash] = e
-	idx.byOffset = append(idx.byOffset, e)
-}
-
-// LookupHash looks an entry up by its hash. An idxfile.Entry is returned and
-// a bool, which is true if it was found or false if it wasn't.
-func (idx *Index) LookupHash(h plumbing.Hash) (*idxfile.Entry, bool) {
-	e, ok := idx.byHash[h]
-	return e, ok
-}
-
-// LookupHash looks an entry up by its offset in the packfile. An idxfile.Entry
-// is returned and a bool, which is true if it was found or false if it wasn't.
-func (idx *Index) LookupOffset(offset uint64) (*idxfile.Entry, bool) {
-	i := sort.Search(len(idx.byOffset), func(i int) bool {
-		return idx.byOffset[i].Offset >= offset
-	})
-	if i >= len(idx.byOffset) || idx.byOffset[i].Offset != offset {
-		return nil, false // not present
-	}
-	return idx.byOffset[i], true
-}
-
-// Size returns the number of entries in the index.
-func (idx *Index) Size() int {
-	return len(idx.byHash)
-}
-
-// ToIdxFile converts the index to an idxfile.Idxfile, which can then be used
-// to serialize.
-func (idx *Index) ToIdxFile() *idxfile.Idxfile {
-	idxf := idxfile.NewIdxfile()
-	for _, e := range idx.byHash {
-		idxf.Entries = append(idxf.Entries, e)
-	}
-
-	return idxf
-}
diff --git a/plumbing/format/packfile/index_test.go b/plumbing/format/packfile/index_test.go
deleted file mode 100644
index 8de886d..0000000
--- a/plumbing/format/packfile/index_test.go
+++ /dev/null
@@ -1,133 +0,0 @@
-package packfile
-
-import (
-	"strconv"
-	"strings"
-	"testing"
-
-	"gopkg.in/src-d/go-git.v4/plumbing"
-
-	. "gopkg.in/check.v1"
-)
-
-type IndexSuite struct{}
-
-var _ = Suite(&IndexSuite{})
-
-func (s *IndexSuite) TestLookupOffset(c *C) {
-	idx := NewIndex(0)
-
-	for o1 := 0; o1 < 10000; o1 += 100 {
-		for o2 := 0; o2 < 10000; o2 += 100 {
-			if o2 >= o1 {
-				e, ok := idx.LookupOffset(uint64(o2))
-				c.Assert(ok, Equals, false)
-				c.Assert(e, IsNil)
-			} else {
-				e, ok := idx.LookupOffset(uint64(o2))
-				c.Assert(ok, Equals, true)
-				c.Assert(e, NotNil)
-				c.Assert(e.Hash, Equals, toHash(o2))
-				c.Assert(e.Offset, Equals, uint64(o2))
-			}
-		}
-
-		h1 := toHash(o1)
-		idx.Add(h1, uint64(o1), 0)
-
-		for o2 := 0; o2 < 10000; o2 += 100 {
-			if o2 > o1 {
-				e, ok := idx.LookupOffset(uint64(o2))
-				c.Assert(ok, Equals, false)
-				c.Assert(e, IsNil)
-			} else {
-				e, ok := idx.LookupOffset(uint64(o2))
-				c.Assert(ok, Equals, true)
-				c.Assert(e, NotNil)
-				c.Assert(e.Hash, Equals, toHash(o2))
-				c.Assert(e.Offset, Equals, uint64(o2))
-			}
-		}
-	}
-}
-
-func (s *IndexSuite) TestLookupHash(c *C) {
-	idx := NewIndex(0)
-
-	for o1 := 0; o1 < 10000; o1 += 100 {
-		for o2 := 0; o2 < 10000; o2 += 100 {
-			if o2 >= o1 {
-				e, ok := idx.LookupHash(toHash(o2))
-				c.Assert(ok, Equals, false)
-				c.Assert(e, IsNil)
-			} else {
-				e, ok := idx.LookupHash(toHash(o2))
-				c.Assert(ok, Equals, true)
-				c.Assert(e, NotNil)
-				c.Assert(e.Hash, Equals, toHash(o2))
-				c.Assert(e.Offset, Equals, uint64(o2))
-			}
-		}
-
-		h1 := toHash(o1)
-		idx.Add(h1, uint64(o1), 0)
-
-		for o2 := 0; o2 < 10000; o2 += 100 {
-			if o2 > o1 {
-				e, ok := idx.LookupHash(toHash(o2))
-				c.Assert(ok, Equals, false)
-				c.Assert(e, IsNil)
-			} else {
-				e, ok := idx.LookupHash(toHash(o2))
-				c.Assert(ok, Equals, true)
-				c.Assert(e, NotNil)
-				c.Assert(e.Hash, Equals, toHash(o2))
-				c.Assert(e.Offset, Equals, uint64(o2))
-			}
-		}
-	}
-}
-
-func (s *IndexSuite) TestSize(c *C) {
-	idx := NewIndex(0)
-
-	for o1 := 0; o1 < 1000; o1++ {
-		c.Assert(idx.Size(), Equals, o1)
-		h1 := toHash(o1)
-		idx.Add(h1, uint64(o1), 0)
-	}
-}
-
-func (s *IndexSuite) TestIdxFileEmpty(c *C) {
-	idx := NewIndex(0)
-	idxf := idx.ToIdxFile()
-	idx2 := NewIndexFromIdxFile(idxf)
-	c.Assert(idx, DeepEquals, idx2)
-}
-
-func (s *IndexSuite) TestIdxFile(c *C) {
-	idx := NewIndex(0)
-	for o1 := 0; o1 < 1000; o1++ {
-		h1 := toHash(o1)
-		idx.Add(h1, uint64(o1), 0)
-	}
-
-	idx2 := NewIndexFromIdxFile(idx.ToIdxFile())
-	c.Assert(idx, DeepEquals, idx2)
-}
-
-func toHash(i int) plumbing.Hash {
-	is := strconv.Itoa(i)
-	padding := strings.Repeat("a", 40-len(is))
-	return plumbing.NewHash(padding + is)
-}
-
-func BenchmarkIndexConstruction(b *testing.B) {
-	b.ReportAllocs()
-
-	idx := NewIndex(0)
-	for o := 0; o < 1e6*b.N; o += 100 {
-		h1 := toHash(o)
-		idx.Add(h1, uint64(o), 0)
-	}
-}
diff --git a/plumbing/format/packfile/packfile.go b/plumbing/format/packfile/packfile.go
new file mode 100644
index 0000000..5feb781
--- /dev/null
+++ b/plumbing/format/packfile/packfile.go
@@ -0,0 +1,505 @@
+package packfile
+
+import (
+	"bytes"
+	"io"
+	"os"
+
+	billy "gopkg.in/src-d/go-billy.v4"
+	"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/format/idxfile"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+var (
+	// ErrInvalidObject is returned by Decode when an invalid object is
+	// found in the packfile.
+	ErrInvalidObject = NewError("invalid git object")
+	// ErrZLib is returned by Decode when there was an error unzipping
+	// the packfile contents.
+	ErrZLib = NewError("zlib reading error")
+)
+
+// Packfile allows retrieving information from inside a packfile.
+type Packfile struct {
+	idxfile.Index
+	fs             billy.Filesystem
+	file           billy.File
+	s              *Scanner
+	deltaBaseCache cache.Object
+	offsetToType   map[int64]plumbing.ObjectType
+}
+
+// NewPackfileWithCache creates a new Packfile with the given object cache.
+// If the filesystem is provided, the packfile will return FSObjects, otherwise
+// it will return MemoryObjects.
+func NewPackfileWithCache(
+	index idxfile.Index,
+	fs billy.Filesystem,
+	file billy.File,
+	cache cache.Object,
+) *Packfile {
+	s := NewScanner(file)
+	return &Packfile{
+		index,
+		fs,
+		file,
+		s,
+		cache,
+		make(map[int64]plumbing.ObjectType),
+	}
+}
+
+// NewPackfile returns a packfile representation for the given packfile file
+// and packfile idx.
+// If the filesystem is provided, the packfile will return FSObjects, otherwise
+// it will return MemoryObjects.
+func NewPackfile(index idxfile.Index, fs billy.Filesystem, file billy.File) *Packfile {
+	return NewPackfileWithCache(index, fs, file, cache.NewObjectLRUDefault())
+}
+
+// Get retrieves the encoded object in the packfile with the given hash.
+func (p *Packfile) Get(h plumbing.Hash) (plumbing.EncodedObject, error) {
+	offset, err := p.FindOffset(h)
+	if err != nil {
+		return nil, err
+	}
+
+	return p.GetByOffset(offset)
+}
+
+// GetByOffset retrieves the encoded object from the packfile with the given
+// offset.
+func (p *Packfile) GetByOffset(o int64) (plumbing.EncodedObject, error) {
+	hash, err := p.FindHash(o)
+	if err == nil {
+		if obj, ok := p.deltaBaseCache.Get(hash); ok {
+			return obj, nil
+		}
+	}
+
+	if _, err := p.s.SeekFromStart(o); err != nil {
+		if err == io.EOF || isInvalid(err) {
+			return nil, plumbing.ErrObjectNotFound
+		}
+
+		return nil, err
+	}
+
+	return p.nextObject()
+}
+
+func (p *Packfile) nextObjectHeader() (*ObjectHeader, error) {
+	h, err := p.s.NextObjectHeader()
+	p.s.pendingObject = nil
+	return h, err
+}
+
+func (p *Packfile) getObjectData(
+	h *ObjectHeader,
+) (typ plumbing.ObjectType, size int64, err error) {
+	switch h.Type {
+	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
+		typ = h.Type
+		size = h.Length
+	case plumbing.REFDeltaObject, plumbing.OFSDeltaObject:
+		buf := bufPool.Get().(*bytes.Buffer)
+		buf.Reset()
+		defer bufPool.Put(buf)
+
+		_, _, err = p.s.NextObject(buf)
+		if err != nil {
+			return
+		}
+
+		delta := buf.Bytes()
+		_, delta = decodeLEB128(delta) // skip src size
+		sz, _ := decodeLEB128(delta)
+		size = int64(sz)
+
+		var offset int64
+		if h.Type == plumbing.REFDeltaObject {
+			offset, err = p.FindOffset(h.Reference)
+			if err != nil {
+				return
+			}
+		} else {
+			offset = h.OffsetReference
+		}
+
+		if baseType, ok := p.offsetToType[offset]; ok {
+			typ = baseType
+		} else {
+			if _, err = p.s.SeekFromStart(offset); err != nil {
+				return
+			}
+
+			h, err = p.nextObjectHeader()
+			if err != nil {
+				return
+			}
+
+			typ, _, err = p.getObjectData(h)
+			if err != nil {
+				return
+			}
+		}
+	default:
+		err = ErrInvalidObject.AddDetails("type %q", h.Type)
+	}
+
+	return
+}
+
+func (p *Packfile) getObjectSize(h *ObjectHeader) (int64, error) {
+	switch h.Type {
+	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
+		return h.Length, nil
+	case plumbing.REFDeltaObject, plumbing.OFSDeltaObject:
+		buf := bufPool.Get().(*bytes.Buffer)
+		buf.Reset()
+		defer bufPool.Put(buf)
+
+		if _, _, err := p.s.NextObject(buf); err != nil {
+			return 0, err
+		}
+
+		delta := buf.Bytes()
+		_, delta = decodeLEB128(delta) // skip src size
+		sz, _ := decodeLEB128(delta)
+		return int64(sz), nil
+	default:
+		return 0, ErrInvalidObject.AddDetails("type %q", h.Type)
+	}
+}
+
+func (p *Packfile) getObjectType(h *ObjectHeader) (typ plumbing.ObjectType, err error) {
+	switch h.Type {
+	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
+		return h.Type, nil
+	case plumbing.REFDeltaObject, plumbing.OFSDeltaObject:
+		var offset int64
+		if h.Type == plumbing.REFDeltaObject {
+			offset, err = p.FindOffset(h.Reference)
+			if err != nil {
+				return
+			}
+		} else {
+			offset = h.OffsetReference
+		}
+
+		if baseType, ok := p.offsetToType[offset]; ok {
+			typ = baseType
+		} else {
+			if _, err = p.s.SeekFromStart(offset); err != nil {
+				return
+			}
+
+			h, err = p.nextObjectHeader()
+			if err != nil {
+				return
+			}
+
+			typ, err = p.getObjectType(h)
+			if err != nil {
+				return
+			}
+		}
+	default:
+		err = ErrInvalidObject.AddDetails("type %q", h.Type)
+	}
+
+	return
+}
+
+func (p *Packfile) nextObject() (plumbing.EncodedObject, error) {
+	h, err := p.nextObjectHeader()
+	if err != nil {
+		if err == io.EOF || isInvalid(err) {
+			return nil, plumbing.ErrObjectNotFound
+		}
+		return nil, err
+	}
+
+	// If we have no filesystem, we will return a MemoryObject instead
+	// of an FSObject.
+	if p.fs == nil {
+		return p.getNextObject(h)
+	}
+
+	hash, err := p.FindHash(h.Offset)
+	if err != nil {
+		return nil, err
+	}
+
+	size, err := p.getObjectSize(h)
+	if err != nil {
+		return nil, err
+	}
+
+	typ, err := p.getObjectType(h)
+	if err != nil {
+		return nil, err
+	}
+
+	p.offsetToType[h.Offset] = typ
+
+	return NewFSObject(
+		hash,
+		typ,
+		h.Offset,
+		size,
+		p.Index,
+		p.fs,
+		p.file.Name(),
+		p.deltaBaseCache,
+	), nil
+}
+
+func (p *Packfile) getObjectContent(offset int64) (io.ReadCloser, error) {
+	if _, err := p.s.SeekFromStart(offset); err != nil {
+		return nil, err
+	}
+
+	h, err := p.nextObjectHeader()
+	if err != nil {
+		return nil, err
+	}
+
+	obj, err := p.getNextObject(h)
+	if err != nil {
+		return nil, err
+	}
+
+	return obj.Reader()
+}
+
+func (p *Packfile) getNextObject(h *ObjectHeader) (plumbing.EncodedObject, error) {
+	var obj = new(plumbing.MemoryObject)
+	obj.SetSize(h.Length)
+	obj.SetType(h.Type)
+
+	var err error
+	switch h.Type {
+	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
+		err = p.fillRegularObjectContent(obj)
+	case plumbing.REFDeltaObject:
+		err = p.fillREFDeltaObjectContent(obj, h.Reference)
+	case plumbing.OFSDeltaObject:
+		err = p.fillOFSDeltaObjectContent(obj, h.OffsetReference)
+	default:
+		err = ErrInvalidObject.AddDetails("type %q", h.Type)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return obj, nil
+}
+
+func (p *Packfile) fillRegularObjectContent(obj plumbing.EncodedObject) error {
+	w, err := obj.Writer()
+	if err != nil {
+		return err
+	}
+
+	_, _, err = p.s.NextObject(w)
+	return err
+}
+
+func (p *Packfile) fillREFDeltaObjectContent(obj plumbing.EncodedObject, ref plumbing.Hash) error {
+	buf := bufPool.Get().(*bytes.Buffer)
+	buf.Reset()
+	_, _, err := p.s.NextObject(buf)
+	if err != nil {
+		return err
+	}
+
+	base, ok := p.cacheGet(ref)
+	if !ok {
+		base, err = p.Get(ref)
+		if err != nil {
+			return err
+		}
+	}
+
+	obj.SetType(base.Type())
+	err = ApplyDelta(obj, base, buf.Bytes())
+	p.cachePut(obj)
+	bufPool.Put(buf)
+
+	return err
+}
+
+func (p *Packfile) fillOFSDeltaObjectContent(obj plumbing.EncodedObject, offset int64) error {
+	buf := bytes.NewBuffer(nil)
+	_, _, err := p.s.NextObject(buf)
+	if err != nil {
+		return err
+	}
+
+	var base plumbing.EncodedObject
+	var ok bool
+	hash, err := p.FindHash(offset)
+	if err == nil {
+		base, ok = p.cacheGet(hash)
+	}
+
+	if !ok {
+		base, err = p.GetByOffset(offset)
+		if err != nil {
+			return err
+		}
+
+		p.cachePut(base)
+	}
+
+	obj.SetType(base.Type())
+	err = ApplyDelta(obj, base, buf.Bytes())
+	p.cachePut(obj)
+
+	return err
+}
+
+func (p *Packfile) cacheGet(h plumbing.Hash) (plumbing.EncodedObject, bool) {
+	if p.deltaBaseCache == nil {
+		return nil, false
+	}
+
+	return p.deltaBaseCache.Get(h)
+}
+
+func (p *Packfile) cachePut(obj plumbing.EncodedObject) {
+	if p.deltaBaseCache == nil {
+		return
+	}
+
+	p.deltaBaseCache.Put(obj)
+}
+
+// GetAll returns an iterator with all encoded objects in the packfile.
+// The iterator returned is not thread-safe, it should be used in the same
+// thread as the Packfile instance.
+func (p *Packfile) GetAll() (storer.EncodedObjectIter, error) {
+	return p.GetByType(plumbing.AnyObject)
+}
+
+// GetByType returns all the objects of the given type.
+func (p *Packfile) GetByType(typ plumbing.ObjectType) (storer.EncodedObjectIter, error) {
+	switch typ {
+	case plumbing.AnyObject,
+		plumbing.BlobObject,
+		plumbing.TreeObject,
+		plumbing.CommitObject,
+		plumbing.TagObject:
+		entries, err := p.Entries()
+		if err != nil {
+			return nil, err
+		}
+
+		return &objectIter{
+			// Easiest way to provide an object decoder is just to pass a Packfile
+			// instance. To not mess with the seeks, it's a new instance with a
+			// different scanner but the same cache and offset to hash map for
+			// reusing as much cache as possible.
+			p:    p,
+			iter: entries,
+			typ:  typ,
+		}, nil
+	default:
+		return nil, plumbing.ErrInvalidType
+	}
+}
+
+// ID returns the ID of the packfile, which is the checksum at the end of it.
+func (p *Packfile) ID() (plumbing.Hash, error) {
+	prev, err := p.file.Seek(-20, io.SeekEnd)
+	if err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	var hash plumbing.Hash
+	if _, err := io.ReadFull(p.file, hash[:]); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	if _, err := p.file.Seek(prev, io.SeekStart); err != nil {
+		return plumbing.ZeroHash, err
+	}
+
+	return hash, nil
+}
+
+// Close the packfile and its resources.
+func (p *Packfile) Close() error {
+	closer, ok := p.file.(io.Closer)
+	if !ok {
+		return nil
+	}
+
+	return closer.Close()
+}
+
+type objectIter struct {
+	p    *Packfile
+	typ  plumbing.ObjectType
+	iter idxfile.EntryIter
+}
+
+func (i *objectIter) Next() (plumbing.EncodedObject, error) {
+	for {
+		e, err := i.iter.Next()
+		if err != nil {
+			return nil, err
+		}
+
+		obj, err := i.p.GetByOffset(int64(e.Offset))
+		if err != nil {
+			return nil, err
+		}
+
+		if i.typ == plumbing.AnyObject || obj.Type() == i.typ {
+			return obj, nil
+		}
+	}
+}
+
+func (i *objectIter) ForEach(f func(plumbing.EncodedObject) error) error {
+	for {
+		o, err := i.Next()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+
+		if err := f(o); err != nil {
+			return err
+		}
+	}
+}
+
+func (i *objectIter) Close() {
+	i.iter.Close()
+}
+
+// isInvalid checks whether an error is an os.PathError with an os.ErrInvalid
+// error inside. It also checks for the windows error, which is different from
+// os.ErrInvalid.
+func isInvalid(err error) bool {
+	pe, ok := err.(*os.PathError)
+	if !ok {
+		return false
+	}
+
+	errstr := pe.Err.Error()
+	return errstr == errInvalidUnix || errstr == errInvalidWindows
+}
+
+// errInvalidWindows is the Windows equivalent to os.ErrInvalid
+const errInvalidWindows = "The parameter is incorrect."
+
+var errInvalidUnix = os.ErrInvalid.Error()
diff --git a/plumbing/format/packfile/packfile_test.go b/plumbing/format/packfile/packfile_test.go
new file mode 100644
index 0000000..05dc8a7
--- /dev/null
+++ b/plumbing/format/packfile/packfile_test.go
@@ -0,0 +1,279 @@
+package packfile_test
+
+import (
+	"io"
+	"math"
+
+	. "gopkg.in/check.v1"
+	"gopkg.in/src-d/go-billy.v4/osfs"
+	fixtures "gopkg.in/src-d/go-git-fixtures.v3"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+type PackfileSuite struct {
+	fixtures.Suite
+	p   *packfile.Packfile
+	idx *idxfile.MemoryIndex
+	f   *fixtures.Fixture
+}
+
+var _ = Suite(&PackfileSuite{})
+
+func (s *PackfileSuite) TestGet(c *C) {
+	for h := range expectedEntries {
+		obj, err := s.p.Get(h)
+		c.Assert(err, IsNil)
+		c.Assert(obj, Not(IsNil))
+		c.Assert(obj.Hash(), Equals, h)
+	}
+
+	_, err := s.p.Get(plumbing.ZeroHash)
+	c.Assert(err, Equals, plumbing.ErrObjectNotFound)
+}
+
+func (s *PackfileSuite) TestGetByOffset(c *C) {
+	for h, o := range expectedEntries {
+		obj, err := s.p.GetByOffset(o)
+		c.Assert(err, IsNil)
+		c.Assert(obj, Not(IsNil))
+		c.Assert(obj.Hash(), Equals, h)
+	}
+
+	_, err := s.p.GetByOffset(math.MaxInt64)
+	c.Assert(err, Equals, plumbing.ErrObjectNotFound)
+}
+
+func (s *PackfileSuite) TestID(c *C) {
+	id, err := s.p.ID()
+	c.Assert(err, IsNil)
+	c.Assert(id, Equals, s.f.PackfileHash)
+}
+
+func (s *PackfileSuite) TestGetAll(c *C) {
+	iter, err := s.p.GetAll()
+	c.Assert(err, IsNil)
+
+	var objects int
+	for {
+		o, err := iter.Next()
+		if err == io.EOF {
+			break
+		}
+		c.Assert(err, IsNil)
+
+		objects++
+		_, ok := expectedEntries[o.Hash()]
+		c.Assert(ok, Equals, true)
+	}
+
+	c.Assert(objects, Equals, len(expectedEntries))
+}
+
+var expectedEntries = map[plumbing.Hash]int64{
+	plumbing.NewHash("1669dce138d9b841a518c64b10914d88f5e488ea"): 615,
+	plumbing.NewHash("32858aad3c383ed1ff0a0f9bdf231d54a00c9e88"): 1524,
+	plumbing.NewHash("35e85108805c84807bc66a02d91535e1e24b38b9"): 1063,
+	plumbing.NewHash("49c6bb89b17060d7b4deacb7b338fcc6ea2352a9"): 78882,
+	plumbing.NewHash("4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd"): 84688,
+	plumbing.NewHash("586af567d0bb5e771e49bdd9434f5e0fb76d25fa"): 84559,
+	plumbing.NewHash("5a877e6a906a2743ad6e45d99c1793642aaf8eda"): 84479,
+	plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5"): 186,
+	plumbing.NewHash("7e59600739c96546163833214c36459e324bad0a"): 84653,
+	plumbing.NewHash("880cd14280f4b9b6ed3986d6671f907d7cc2a198"): 78050,
+	plumbing.NewHash("8dcef98b1d52143e1e2dbc458ffe38f925786bf2"): 84741,
+	plumbing.NewHash("918c48b83bd081e863dbe1b80f8998f058cd8294"): 286,
+	plumbing.NewHash("9a48f23120e880dfbe41f7c9b7b708e9ee62a492"): 80998,
+	plumbing.NewHash("9dea2395f5403188298c1dabe8bdafe562c491e3"): 84032,
+	plumbing.NewHash("a39771a7651f97faf5c72e08224d857fc35133db"): 84430,
+	plumbing.NewHash("a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69"): 838,
+	plumbing.NewHash("a8d315b2b1c615d43042c3a62402b8a54288cf5c"): 84375,
+	plumbing.NewHash("aa9b383c260e1d05fbbf6b30a02914555e20c725"): 84760,
+	plumbing.NewHash("af2d6a6954d532f8ffb47615169c8fdf9d383a1a"): 449,
+	plumbing.NewHash("b029517f6300c2da0f4b651b8642506cd6aaf45d"): 1392,
+	plumbing.NewHash("b8e471f58bcbca63b07bda20e428190409c2db47"): 1230,
+	plumbing.NewHash("c192bd6a24ea1ab01d78686e417c8bdc7c3d197f"): 1713,
+	plumbing.NewHash("c2d30fa8ef288618f65f6eed6e168e0d514886f4"): 84725,
+	plumbing.NewHash("c8f1d8c61f9da76f4cb49fd86322b6e685dba956"): 80725,
+	plumbing.NewHash("cf4aa3b38974fb7d81f367c0830f7d78d65ab86b"): 84608,
+	plumbing.NewHash("d3ff53e0564a9f87d8e84b6e28e5060e517008aa"): 1685,
+	plumbing.NewHash("d5c0f4ab811897cadf03aec358ae60d21f91c50d"): 2351,
+	plumbing.NewHash("dbd3641b371024f44d0e469a9c8f5457b0660de1"): 84115,
+	plumbing.NewHash("e8d3ffab552895c19b9fcf7aa264d277cde33881"): 12,
+	plumbing.NewHash("eba74343e2f15d62adedfd8c883ee0262b5c8021"): 84708,
+	plumbing.NewHash("fb72698cab7617ac416264415f13224dfd7a165e"): 84671,
+}
+
+func (s *PackfileSuite) SetUpTest(c *C) {
+	s.f = fixtures.Basic().One()
+
+	fs := osfs.New("")
+	f, err := fs.Open(s.f.Packfile().Name())
+	c.Assert(err, IsNil)
+
+	s.idx = idxfile.NewMemoryIndex()
+	c.Assert(idxfile.NewDecoder(s.f.Idx()).Decode(s.idx), IsNil)
+
+	s.p = packfile.NewPackfile(s.idx, fs, f)
+}
+
+func (s *PackfileSuite) TearDownTest(c *C) {
+	c.Assert(s.p.Close(), IsNil)
+}
+
+func (s *PackfileSuite) TestDecode(c *C) {
+	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
+		index := getIndexFromIdxFile(f.Idx())
+		fs := osfs.New("")
+		pf, err := fs.Open(f.Packfile().Name())
+		c.Assert(err, IsNil)
+
+		p := packfile.NewPackfile(index, fs, pf)
+		defer p.Close()
+
+		for _, h := range expectedHashes {
+			obj, err := p.Get(plumbing.NewHash(h))
+			c.Assert(err, IsNil)
+			c.Assert(obj.Hash().String(), Equals, h)
+		}
+	})
+}
+
+func (s *PackfileSuite) TestDecodeByTypeRefDelta(c *C) {
+	f := fixtures.Basic().ByTag("ref-delta").One()
+
+	index := getIndexFromIdxFile(f.Idx())
+	fs := osfs.New("")
+	pf, err := fs.Open(f.Packfile().Name())
+	c.Assert(err, IsNil)
+
+	packfile := packfile.NewPackfile(index, fs, pf)
+	defer packfile.Close()
+
+	iter, err := packfile.GetByType(plumbing.CommitObject)
+	c.Assert(err, IsNil)
+
+	var count int
+	for {
+		obj, err := iter.Next()
+		if err == io.EOF {
+			break
+		}
+		count++
+		c.Assert(err, IsNil)
+		c.Assert(obj.Type(), Equals, plumbing.CommitObject)
+	}
+
+	c.Assert(count > 0, Equals, true)
+}
+
+func (s *PackfileSuite) TestDecodeByType(c *C) {
+	ts := []plumbing.ObjectType{
+		plumbing.CommitObject,
+		plumbing.TagObject,
+		plumbing.TreeObject,
+		plumbing.BlobObject,
+	}
+
+	fixtures.Basic().ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
+		for _, t := range ts {
+			index := getIndexFromIdxFile(f.Idx())
+			fs := osfs.New("")
+			pf, err := fs.Open(f.Packfile().Name())
+			c.Assert(err, IsNil)
+
+			packfile := packfile.NewPackfile(index, fs, pf)
+			defer packfile.Close()
+
+			iter, err := packfile.GetByType(t)
+			c.Assert(err, IsNil)
+
+			c.Assert(iter.ForEach(func(obj plumbing.EncodedObject) error {
+				c.Assert(obj.Type(), Equals, t)
+				return nil
+			}), IsNil)
+		}
+	})
+}
+
+func (s *PackfileSuite) TestDecodeByTypeConstructor(c *C) {
+	f := fixtures.Basic().ByTag("packfile").One()
+	index := getIndexFromIdxFile(f.Idx())
+	fs := osfs.New("")
+	pf, err := fs.Open(f.Packfile().Name())
+	c.Assert(err, IsNil)
+
+	packfile := packfile.NewPackfile(index, fs, pf)
+	defer packfile.Close()
+
+	_, err = packfile.GetByType(plumbing.OFSDeltaObject)
+	c.Assert(err, Equals, plumbing.ErrInvalidType)
+
+	_, err = packfile.GetByType(plumbing.REFDeltaObject)
+	c.Assert(err, Equals, plumbing.ErrInvalidType)
+
+	_, err = packfile.GetByType(plumbing.InvalidObject)
+	c.Assert(err, Equals, plumbing.ErrInvalidType)
+}
+
+var expectedHashes = []string{
+	"918c48b83bd081e863dbe1b80f8998f058cd8294",
+	"af2d6a6954d532f8ffb47615169c8fdf9d383a1a",
+	"1669dce138d9b841a518c64b10914d88f5e488ea",
+	"a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
+	"b8e471f58bcbca63b07bda20e428190409c2db47",
+	"35e85108805c84807bc66a02d91535e1e24b38b9",
+	"b029517f6300c2da0f4b651b8642506cd6aaf45d",
+	"32858aad3c383ed1ff0a0f9bdf231d54a00c9e88",
+	"d3ff53e0564a9f87d8e84b6e28e5060e517008aa",
+	"c192bd6a24ea1ab01d78686e417c8bdc7c3d197f",
+	"d5c0f4ab811897cadf03aec358ae60d21f91c50d",
+	"49c6bb89b17060d7b4deacb7b338fcc6ea2352a9",
+	"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b",
+	"9dea2395f5403188298c1dabe8bdafe562c491e3",
+	"586af567d0bb5e771e49bdd9434f5e0fb76d25fa",
+	"9a48f23120e880dfbe41f7c9b7b708e9ee62a492",
+	"5a877e6a906a2743ad6e45d99c1793642aaf8eda",
+	"c8f1d8c61f9da76f4cb49fd86322b6e685dba956",
+	"a8d315b2b1c615d43042c3a62402b8a54288cf5c",
+	"a39771a7651f97faf5c72e08224d857fc35133db",
+	"880cd14280f4b9b6ed3986d6671f907d7cc2a198",
+	"fb72698cab7617ac416264415f13224dfd7a165e",
+	"4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd",
+	"eba74343e2f15d62adedfd8c883ee0262b5c8021",
+	"c2d30fa8ef288618f65f6eed6e168e0d514886f4",
+	"8dcef98b1d52143e1e2dbc458ffe38f925786bf2",
+	"aa9b383c260e1d05fbbf6b30a02914555e20c725",
+	"6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+	"dbd3641b371024f44d0e469a9c8f5457b0660de1",
+	"e8d3ffab552895c19b9fcf7aa264d277cde33881",
+	"7e59600739c96546163833214c36459e324bad0a",
+}
+
+func assertObjects(c *C, s storer.EncodedObjectStorer, expects []string) {
+	i, err := s.IterEncodedObjects(plumbing.AnyObject)
+	c.Assert(err, IsNil)
+
+	var count int
+	err = i.ForEach(func(plumbing.EncodedObject) error { count++; return nil })
+	c.Assert(err, IsNil)
+	c.Assert(count, Equals, len(expects))
+
+	for _, exp := range expects {
+		obt, err := s.EncodedObject(plumbing.AnyObject, plumbing.NewHash(exp))
+		c.Assert(err, IsNil)
+		c.Assert(obt.Hash().String(), Equals, exp)
+	}
+}
+
+func getIndexFromIdxFile(r io.Reader) idxfile.Index {
+	idxf := idxfile.NewMemoryIndex()
+	d := idxfile.NewDecoder(r)
+	if err := d.Decode(idxf); err != nil {
+		panic(err)
+	}
+
+	return idxf
+}
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
+}
diff --git a/plumbing/format/packfile/parser_test.go b/plumbing/format/packfile/parser_test.go
new file mode 100644
index 0000000..012a140
--- /dev/null
+++ b/plumbing/format/packfile/parser_test.go
@@ -0,0 +1,195 @@
+package packfile_test
+
+import (
+	"testing"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
+
+	. "gopkg.in/check.v1"
+	"gopkg.in/src-d/go-git-fixtures.v3"
+)
+
+type ParserSuite struct {
+	fixtures.Suite
+}
+
+var _ = Suite(&ParserSuite{})
+
+func (s *ParserSuite) TestParserHashes(c *C) {
+	f := fixtures.Basic().One()
+	scanner := packfile.NewScanner(f.Packfile())
+
+	obs := new(testObserver)
+	parser, err := packfile.NewParser(scanner, obs)
+	c.Assert(err, IsNil)
+
+	ch, err := parser.Parse()
+	c.Assert(err, IsNil)
+
+	checksum := "a3fed42da1e8189a077c0e6846c040dcf73fc9dd"
+	c.Assert(ch.String(), Equals, checksum)
+
+	c.Assert(obs.checksum, Equals, checksum)
+	c.Assert(int(obs.count), Equals, int(31))
+
+	commit := plumbing.CommitObject
+	blob := plumbing.BlobObject
+	tree := plumbing.TreeObject
+
+	objs := []observerObject{
+		{"e8d3ffab552895c19b9fcf7aa264d277cde33881", commit, 254, 12, 0xaa07ba4b},
+		{"6ecf0ef2c2dffb796033e5a02219af86ec6584e5", commit, 245, 186, 0xf706df58},
+		{"918c48b83bd081e863dbe1b80f8998f058cd8294", commit, 242, 286, 0x12438846},
+		{"af2d6a6954d532f8ffb47615169c8fdf9d383a1a", commit, 242, 449, 0x2905a38c},
+		{"1669dce138d9b841a518c64b10914d88f5e488ea", commit, 333, 615, 0xd9429436},
+		{"a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69", commit, 332, 838, 0xbecfde4e},
+		{"35e85108805c84807bc66a02d91535e1e24b38b9", commit, 244, 1063, 0x780e4b3e},
+		{"b8e471f58bcbca63b07bda20e428190409c2db47", commit, 243, 1230, 0xdc18344f},
+		{"b029517f6300c2da0f4b651b8642506cd6aaf45d", commit, 187, 1392, 0xcf4e4280},
+		{"32858aad3c383ed1ff0a0f9bdf231d54a00c9e88", blob, 189, 1524, 0x1f08118a},
+		{"d3ff53e0564a9f87d8e84b6e28e5060e517008aa", blob, 18, 1685, 0xafded7b8},
+		{"c192bd6a24ea1ab01d78686e417c8bdc7c3d197f", blob, 1072, 1713, 0xcc1428ed},
+		{"d5c0f4ab811897cadf03aec358ae60d21f91c50d", blob, 76110, 2351, 0x1631d22f},
+		{"880cd14280f4b9b6ed3986d6671f907d7cc2a198", blob, 2780, 78050, 0xbfff5850},
+		{"49c6bb89b17060d7b4deacb7b338fcc6ea2352a9", blob, 217848, 78882, 0xd108e1d8},
+		{"c8f1d8c61f9da76f4cb49fd86322b6e685dba956", blob, 706, 80725, 0x8e97ba25},
+		{"9a48f23120e880dfbe41f7c9b7b708e9ee62a492", blob, 11488, 80998, 0x7316ff70},
+		{"9dea2395f5403188298c1dabe8bdafe562c491e3", blob, 78, 84032, 0xdb4fce56},
+		{"dbd3641b371024f44d0e469a9c8f5457b0660de1", tree, 272, 84115, 0x901cce2c},
+		{"a8d315b2b1c615d43042c3a62402b8a54288cf5c", tree, 271, 84375, 0xec4552b0},
+		{"a39771a7651f97faf5c72e08224d857fc35133db", tree, 38, 84430, 0x847905bf},
+		{"5a877e6a906a2743ad6e45d99c1793642aaf8eda", tree, 75, 84479, 0x3689459a},
+		{"586af567d0bb5e771e49bdd9434f5e0fb76d25fa", tree, 38, 84559, 0xe67af94a},
+		{"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b", tree, 34, 84608, 0xc2314a2e},
+		{"7e59600739c96546163833214c36459e324bad0a", blob, 9, 84653, 0xcd987848},
+		{"fb72698cab7617ac416264415f13224dfd7a165e", tree, 238, 84671, 0x8a853a6d},
+		{"4d081c50e250fa32ea8b1313cf8bb7c2ad7627fd", tree, 179, 84688, 0x70c6518},
+		{"eba74343e2f15d62adedfd8c883ee0262b5c8021", tree, 148, 84708, 0x4f4108e2},
+		{"c2d30fa8ef288618f65f6eed6e168e0d514886f4", tree, 110, 84725, 0xd6fe09e9},
+		{"8dcef98b1d52143e1e2dbc458ffe38f925786bf2", tree, 111, 84741, 0xf07a2804},
+		{"aa9b383c260e1d05fbbf6b30a02914555e20c725", tree, 73, 84760, 0x1d75d6be},
+	}
+
+	c.Assert(obs.objects, DeepEquals, objs)
+}
+
+type observerObject struct {
+	hash   string
+	otype  plumbing.ObjectType
+	size   int64
+	offset int64
+	crc    uint32
+}
+
+type testObserver struct {
+	count    uint32
+	checksum string
+	objects  []observerObject
+	pos      map[int64]int
+}
+
+func (t *testObserver) OnHeader(count uint32) error {
+	t.count = count
+	t.pos = make(map[int64]int, count)
+	return nil
+}
+
+func (t *testObserver) OnInflatedObjectHeader(otype plumbing.ObjectType, objSize int64, pos int64) error {
+	o := t.get(pos)
+	o.otype = otype
+	o.size = objSize
+	o.offset = pos
+
+	t.put(pos, o)
+
+	return nil
+}
+
+func (t *testObserver) OnInflatedObjectContent(h plumbing.Hash, pos int64, crc uint32, _ []byte) error {
+	o := t.get(pos)
+	o.hash = h.String()
+	o.crc = crc
+
+	t.put(pos, o)
+
+	return nil
+}
+
+func (t *testObserver) OnFooter(h plumbing.Hash) error {
+	t.checksum = h.String()
+	return nil
+}
+
+func (t *testObserver) get(pos int64) observerObject {
+	i, ok := t.pos[pos]
+	if ok {
+		return t.objects[i]
+	}
+
+	return observerObject{}
+}
+
+func (t *testObserver) put(pos int64, o observerObject) {
+	i, ok := t.pos[pos]
+	if ok {
+		t.objects[i] = o
+		return
+	}
+
+	t.pos[pos] = len(t.objects)
+	t.objects = append(t.objects, o)
+}
+
+func BenchmarkParse(b *testing.B) {
+	if err := fixtures.Init(); err != nil {
+		b.Fatal(err)
+	}
+
+	defer func() {
+		if err := fixtures.Clean(); err != nil {
+			b.Fatal(err)
+		}
+	}()
+
+	for _, f := range fixtures.ByTag("packfile") {
+		b.Run(f.URL, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				parser, err := packfile.NewParser(packfile.NewScanner(f.Packfile()))
+				if err != nil {
+					b.Fatal(err)
+				}
+
+				_, err = parser.Parse()
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+func BenchmarkParseBasic(b *testing.B) {
+	if err := fixtures.Init(); err != nil {
+		b.Fatal(err)
+	}
+
+	defer func() {
+		if err := fixtures.Clean(); err != nil {
+			b.Fatal(err)
+		}
+	}()
+
+	f := fixtures.Basic().One()
+	for i := 0; i < b.N; i++ {
+		parser, err := packfile.NewParser(packfile.NewScanner(f.Packfile()))
+		if err != nil {
+			b.Fatal(err)
+		}
+
+		_, err = parser.Parse()
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
diff --git a/plumbing/format/packfile/patch_delta.go b/plumbing/format/packfile/patch_delta.go
index c604851..a972f1c 100644
--- a/plumbing/format/packfile/patch_delta.go
+++ b/plumbing/format/packfile/patch_delta.go
@@ -63,8 +63,8 @@ func PatchDelta(src, delta []byte) ([]byte, error) {
 	targetSz, delta := decodeLEB128(delta)
 	remainingTargetSz := targetSz
 
-	var dest []byte
 	var cmd byte
+	dest := make([]byte, 0, targetSz)
 	for {
 		if len(delta) == 0 {
 			return nil, ErrInvalidDelta