3 files changed, 42 insertions, 2 deletions
diff --git a/formats/idxfile/encoder.go b/formats/idxfile/encoder.go
index e9b0338..0fe9ae6 100644
--- a/formats/idxfile/encoder.go
+++ b/formats/idxfile/encoder.go
@@ -3,8 +3,12 @@ package idxfile
 import (
 	"crypto/sha1"
 	"encoding/binary"
+	"fmt"
 	"hash"
 	"io"
+	"sort"
+
+	"gopkg.in/src-d/go-git.v4/core"
 )
 
 // An Encoder writes idx files to an output stream.
@@ -22,6 +26,8 @@ func NewEncoder(w io.Writer) *Encoder {
 
 // Encode writes the idx in an idx file format to the stream of the encoder.
 func (e *Encoder) Encode(idx *Idxfile) (int, error) {
+	idx.Entries.Sort()
+
 	flow := []func(*Idxfile) (int, error){
 		e.encodeHeader,
 		e.encodeFanout,
@@ -65,16 +71,24 @@ func (e *Encoder) encodeFanout(idx *Idxfile) (int, error) {
 }
 
 func (e *Encoder) encodeHashes(idx *Idxfile) (int, error) {
+	repet := make(map[core.Hash]int, 0)
+
 	sz := 0
 	for _, ent := range idx.Entries {
 		i, err := e.Write(ent.Hash[:])
 		sz += i
 
+		repet[ent.Hash]++
 		if err != nil {
 			return sz, err
 		}
 	}
 
+	for h, c := range repet {
+		if c > 1 {
+			fmt.Println(h, c)
+		}
+	}
 	return sz, nil
 }
 
@@ -122,3 +136,10 @@ func (e *Encoder) encodeChecksums(idx *Idxfile) (int, error) {
 func (e *Encoder) writeInt32(value uint32) error {
 	return binary.Write(e, binary.BigEndian, value)
 }
+
+type EntryList []Entry
+
+func (p EntryList) Len() int           { return len(p) }
+func (p EntryList) Less(i, j int) bool { return p[i].Hash.String() < p[j].Hash.String() }
+func (p EntryList) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p EntryList) Sort()              { sort.Sort(p) }
diff --git a/formats/idxfile/encoder_test.go b/formats/idxfile/encoder_test.go
index 11ecaee..380b8e8 100644
--- a/formats/idxfile/encoder_test.go
+++ b/formats/idxfile/encoder_test.go
@@ -5,6 +5,7 @@ import (
 	"io/ioutil"
 
 	. "gopkg.in/check.v1"
+	"gopkg.in/src-d/go-git.v4/core"
 	"gopkg.in/src-d/go-git.v4/fixtures"
 )
 
@@ -13,7 +14,25 @@ func (s *IdxfileSuite) SetUpSuite(c *C) {
 }
 
 func (s *IdxfileSuite) TestEncode(c *C) {
-	fixtures.All().Test(c, func(f *fixtures.Fixture) {
+	expected := &Idxfile{}
+	expected.Add(core.NewHash("4bfc730165c370df4a012afbb45ba3f9c332c0d4"), 82, 82)
+	expected.Add(core.NewHash("8fa2238efdae08d83c12ee176fae65ff7c99af46"), 42, 42)
+
+	buf := bytes.NewBuffer(nil)
+	e := NewEncoder(buf)
+	_, err := e.Encode(expected)
+	c.Assert(err, IsNil)
+
+	idx := &Idxfile{}
+	d := NewDecoder(buf)
+	err = d.Decode(idx)
+	c.Assert(err, IsNil)
+
+	c.Assert(idx.Entries, DeepEquals, expected.Entries)
+}
+
+func (s *IdxfileSuite) TestDecodeEncode(c *C) {
+	fixtures.ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
 		expected, err := ioutil.ReadAll(f.Idx())
 		c.Assert(err, IsNil)
 
diff --git a/formats/idxfile/idxfile.go b/formats/idxfile/idxfile.go
index 65b58b5..8549d3f 100644
--- a/formats/idxfile/idxfile.go
+++ b/formats/idxfile/idxfile.go
@@ -16,7 +16,7 @@ type Idxfile struct {
 	Version          uint32
 	Fanout           [255]uint32
 	ObjectCount      uint32
-	Entries          []Entry
+	Entries          EntryList
 	PackfileChecksum [20]byte
 	IdxChecksum      [20]byte
 }