plumbing/idxfile: object iterators returns entries in offset order

In the latest change the order was changed from offset order in
packfiles to hash order. This makes reading all the objects not as
efficient as before. It also created problems when the previous order
was expected.

Also added EntriesByOffset to indexes.

Signed-off-by: Javi Fontan <jfontan@gmail.com>

Author: jfontan

plumbing/format/idxfile/idxfile.go

@@ -3,6 +3,7 @@ package idxfile
 import (
 	"bytes"
 	"io"
+	"sort"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/utils/binary"
@@ -34,6 +35,9 @@ type Index interface {
 	Count() (int64, error)
 	// Entries returns an iterator to retrieve all index entries.
 	Entries() (EntryIter, error)
+	// EntriesByOffset returns an iterator to retrieve all index entries ordered
+	// by offset.
+	EntriesByOffset() (EntryIter, error)
 }
 
 // MemoryIndex is the in memory representation of an idx file.
@@ -215,6 +219,36 @@ func (idx *MemoryIndex) Entries() (EntryIter, error) {
 	return &idxfileEntryIter{idx, 0, 0, 0}, nil
 }
 
+// EntriesByOffset implements the Index interface.
+func (idx *MemoryIndex) EntriesByOffset() (EntryIter, error) {
+	count, err := idx.Count()
+	if err != nil {
+		return nil, err
+	}
+
+	iter := &idxfileEntryOffsetIter{
+		entries: make(entriesByOffset, count),
+	}
+
+	entries, err := idx.Entries()
+	if err != nil {
+		return nil, err
+	}
+
+	for pos := 0; int64(pos) < count; pos++ {
+		entry, err := entries.Next()
+		if err != nil {
+			return nil, err
+		}
+
+		iter.entries[pos] = entry
+	}
+
+	sort.Sort(iter.entries)
+
+	return iter, nil
+}
+
 // EntryIter is an iterator that will return the entries in a packfile index.
 type EntryIter interface {
 	// Next returns the next entry in the packfile index.
@@ -276,3 +310,38 @@ type Entry struct {
 	CRC32  uint32
 	Offset uint64
 }
+
+type idxfileEntryOffsetIter struct {
+	entries entriesByOffset
+	pos     int
+}
+
+func (i *idxfileEntryOffsetIter) Next() (*Entry, error) {
+	if i.pos >= len(i.entries) {
+		return nil, io.EOF
+	}
+
+	entry := i.entries[i.pos]
+	i.pos++
+
+	return entry, nil
+}
+
+func (i *idxfileEntryOffsetIter) Close() error {
+	i.pos = len(i.entries) + 1
+	return nil
+}
+
+type entriesByOffset []*Entry
+
+func (o entriesByOffset) Len() int {
+	return len(o)
+}
+
+func (o entriesByOffset) Less(i int, j int) bool {
+	return o[i].Offset < o[j].Offset
+}
+
+func (o entriesByOffset) Swap(i int, j int) {
+	o[i], o[j] = o[j], o[i]
+}

plumbing/format/idxfile/idxfile_test.go

@@ -115,6 +115,21 @@ func (s *IndexSuite) TestFindHash(c *C) {
 	}
 }
 
+func (s *IndexSuite) TestEntriesByOffset(c *C) {
+	idx, err := fixtureIndex()
+	c.Assert(err, IsNil)
+
+	entries, err := idx.EntriesByOffset()
+	c.Assert(err, IsNil)
+
+	for _, pos := range fixtureOffsets {
+		e, err := entries.Next()
+		c.Assert(err, IsNil)
+
+		c.Assert(e.Offset, Equals, uint64(pos))
+	}
+}
+
 var fixtureHashes = []plumbing.Hash{
 	plumbing.NewHash("303953e5aa461c203a324821bc1717f9b4fff895"),
 	plumbing.NewHash("5296768e3d9f661387ccbff18c4dea6c997fd78c"),

plumbing/format/packfile/packfile.go

@@ -394,7 +394,7 @@ func (p *Packfile) GetByType(typ plumbing.ObjectType) (storer.EncodedObjectIter,
 		plumbing.TreeObject,
 		plumbing.CommitObject,
 		plumbing.TagObject:
-		entries, err := p.Entries()
+		entries, err := p.EntriesByOffset()
 		if err != nil {
 			return nil, err
 		}