config: support a configurable, and turn-off-able, pack.window

config/config.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"sort"
+	"strconv"
 
 	format "gopkg.in/src-d/go-git.v4/plumbing/format/config"
 )
@@ -40,6 +41,14 @@ type Config struct {
 		// Worktree is the path to the root of the working tree.
 		Worktree string
 	}
+
+	Pack struct {
+		// Window controls the size of the sliding window for delta
+		// compression.  The default is 10.  A value of 0 turns off
+		// delta compression entirely.
+		Window uint
+	}
+
 	// Remotes list of repository remotes, the key of the map is the name
 	// of the remote, should equal to RemoteConfig.Name.
 	Remotes map[string]*RemoteConfig
@@ -81,10 +90,14 @@ const (
 	remoteSection    = "remote"
 	submoduleSection = "submodule"
 	coreSection      = "core"
+	packSection      = "pack"
 	fetchKey         = "fetch"
 	urlKey           = "url"
 	bareKey          = "bare"
 	worktreeKey      = "worktree"
+	windowKey        = "window"
+
+	defaultPackWindow = uint(10)
 )
 
 // Unmarshal parses a git-config file and stores it.
@@ -98,6 +111,9 @@ func (c *Config) Unmarshal(b []byte) error {
 	}
 
 	c.unmarshalCore()
+	if err := c.unmarshalPack(); err != nil {
+		return err
+	}
 	c.unmarshalSubmodules()
 	return c.unmarshalRemotes()
 }
@@ -111,6 +127,21 @@ func (c *Config) unmarshalCore() {
 	c.Core.Worktree = s.Options.Get(worktreeKey)
 }
 
+func (c *Config) unmarshalPack() error {
+	s := c.Raw.Section(packSection)
+	window := s.Options.Get(windowKey)
+	if window == "" {
+		c.Pack.Window = defaultPackWindow
+	} else {
+		winUint, err := strconv.ParseUint(window, 10, 32)
+		if err != nil {
+			return err
+		}
+		c.Pack.Window = uint(winUint)
+	}
+	return nil
+}
+
 func (c *Config) unmarshalRemotes() error {
 	s := c.Raw.Section(remoteSection)
 	for _, sub := range s.Subsections {
@@ -138,6 +169,7 @@ func (c *Config) unmarshalSubmodules() {
 // Marshal returns Config encoded as a git-config file.
 func (c *Config) Marshal() ([]byte, error) {
 	c.marshalCore()
+	c.marshalPack()
 	c.marshalRemotes()
 	c.marshalSubmodules()
 
@@ -158,6 +190,13 @@ func (c *Config) marshalCore() {
 	}
 }
 
+func (c *Config) marshalPack() {
+	s := c.Raw.Section(packSection)
+	if c.Pack.Window != defaultPackWindow {
+		s.SetOption(windowKey, fmt.Sprintf("%d", c.Pack.Window))
+	}
+}
+
 func (c *Config) marshalRemotes() {
 	s := c.Raw.Section(remoteSection)
 	newSubsections := make(format.Subsections, 0, len(c.Remotes))

config/config_test.go

@@ -10,6 +10,8 @@ func (s *ConfigSuite) TestUnmarshall(c *C) {
 	input := []byte(`[core]
         bare = true
 		worktree = foo
+[pack]
+		window = 20
 [remote "origin"]
         url = [email protected]:mcuadros/go-git.git
         fetch = +refs/heads/*:refs/remotes/origin/*
@@ -33,6 +35,7 @@ func (s *ConfigSuite) TestUnmarshall(c *C) {
 
 	c.Assert(cfg.Core.IsBare, Equals, true)
 	c.Assert(cfg.Core.Worktree, Equals, "foo")
+	c.Assert(cfg.Pack.Window, Equals, uint(20))
 	c.Assert(cfg.Remotes, HasLen, 2)
 	c.Assert(cfg.Remotes["origin"].Name, Equals, "origin")
 	c.Assert(cfg.Remotes["origin"].URLs, DeepEquals, []string{"[email protected]:mcuadros/go-git.git"})
@@ -51,6 +54,8 @@ func (s *ConfigSuite) TestMarshall(c *C) {
 	output := []byte(`[core]
 	bare = true
 	worktree = bar
+[pack]
+	window = 20
 [remote "alt"]
 	url = [email protected]:mcuadros/go-git.git
 	url = [email protected]:src-d/go-git.git
@@ -65,6 +70,7 @@ func (s *ConfigSuite) TestMarshall(c *C) {
 	cfg := NewConfig()
 	cfg.Core.IsBare = true
 	cfg.Core.Worktree = "bar"
+	cfg.Pack.Window = 20
 	cfg.Remotes["origin"] = &RemoteConfig{
 		Name: "origin",
 		URLs: []string{"[email protected]:mcuadros/go-git.git"},
@@ -92,6 +98,8 @@ func (s *ConfigSuite) TestUnmarshallMarshall(c *C) {
 	bare = true
 	worktree = foo
 	custom = ignored
+[pack]
+	window = 20
 [remote "origin"]
 	url = [email protected]:mcuadros/go-git.git
 	fetch = +refs/heads/*:refs/remotes/origin/*

plumbing/format/packfile/delta_selector.go

@@ -9,9 +9,6 @@ import (
 )
 
 const (
-	// How far back in the sorted list to search for deltas.  10 is
-	// the default in command line git.
-	deltaWindowSize = 10
 	// deltas based on deltas, how many steps we can do.
 	// 50 is the default value used in JGit
 	maxDepth = int64(50)
@@ -31,14 +28,24 @@ func newDeltaSelector(s storer.EncodedObjectStorer) *deltaSelector {
 	return &deltaSelector{s}
 }
 
-// ObjectsToPack creates a list of ObjectToPack from the hashes provided,
-// creating deltas if it's suitable, using an specific internal logic
-func (dw *deltaSelector) ObjectsToPack(hashes []plumbing.Hash) ([]*ObjectToPack, error) {
-	otp, err := dw.objectsToPack(hashes)
+// ObjectsToPack creates a list of ObjectToPack from the hashes
+// provided, creating deltas if it's suitable, using an specific
+// internal logic.  `packWindow` specifies the size of the sliding
+// window used to compare objects for delta compression; 0 turns off
+// delta compression entirely.
+func (dw *deltaSelector) ObjectsToPack(
+	hashes []plumbing.Hash,
+	packWindow uint,
+) ([]*ObjectToPack, error) {
+	otp, err := dw.objectsToPack(hashes, packWindow)
 	if err != nil {
 		return nil, err
 	}
 
+	if packWindow == 0 {
+		return otp, nil
+	}
+
 	dw.sort(otp)
 
 	var objectGroups [][]*ObjectToPack
@@ -60,7 +67,7 @@ func (dw *deltaSelector) ObjectsToPack(hashes []plumbing.Hash) ([]*ObjectToPack,
 		objs := objs
 		wg.Add(1)
 		go func() {
-			if walkErr := dw.walk(objs); walkErr != nil {
+			if walkErr := dw.walk(objs, packWindow); walkErr != nil {
 				once.Do(func() {
 					err = walkErr
 				})
@@ -77,10 +84,19 @@ func (dw *deltaSelector) ObjectsToPack(hashes []plumbing.Hash) ([]*ObjectToPack,
 	return otp, nil
 }
 
-func (dw *deltaSelector) objectsToPack(hashes []plumbing.Hash) ([]*ObjectToPack, error) {
+func (dw *deltaSelector) objectsToPack(
+	hashes []plumbing.Hash,
+	packWindow uint,
+) ([]*ObjectToPack, error) {
 	var objectsToPack []*ObjectToPack
 	for _, h := range hashes {
-		o, err := dw.encodedDeltaObject(h)
+		var o plumbing.EncodedObject
+		var err error
+		if packWindow == 0 {
+			o, err = dw.encodedObject(h)
+		} else {
+			o, err = dw.encodedDeltaObject(h)
+		}
 		if err != nil {
 			return nil, err
 		}
@@ -93,6 +109,10 @@ func (dw *deltaSelector) objectsToPack(hashes []plumbing.Hash) ([]*ObjectToPack,
 		objectsToPack = append(objectsToPack, otp)
 	}
 
+	if packWindow == 0 {
+		return objectsToPack, nil
+	}
+
 	if err := dw.fixAndBreakChains(objectsToPack); err != nil {
 		return nil, err
 	}
@@ -201,7 +221,10 @@ func (dw *deltaSelector) sort(objectsToPack []*ObjectToPack) {
 	sort.Sort(byTypeAndSize(objectsToPack))
 }
 
-func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
+func (dw *deltaSelector) walk(
+	objectsToPack []*ObjectToPack,
+	packWindow uint,
+) error {
 	indexMap := make(map[plumbing.Hash]*deltaIndex)
 	for i := 0; i < len(objectsToPack); i++ {
 		target := objectsToPack[i]
@@ -218,7 +241,7 @@ func (dw *deltaSelector) walk(objectsToPack []*ObjectToPack) error {
 			continue
 		}
 
-		for j := i - 1; j >= 0 && i-j < deltaWindowSize; j-- {
+		for j := i - 1; j >= 0 && i-j < int(packWindow); j-- {
 			base := objectsToPack[j]
 			// Objects must use only the same type as their delta base.
 			// Since objectsToPack is sorted by type and size, once we find

plumbing/format/packfile/delta_selector_test.go

@@ -146,31 +146,32 @@ func (s *DeltaSelectorSuite) createTestObjects() {
 func (s *DeltaSelectorSuite) TestObjectsToPack(c *C) {
 	// Different type
 	hashes := []plumbing.Hash{s.hashes["base"], s.hashes["treeType"]}
-	otp, err := s.ds.ObjectsToPack(hashes)
+	deltaWindowSize := uint(10)
+	otp, err := s.ds.ObjectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
 	c.Assert(len(otp), Equals, 2)
 	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["base"]])
 	c.Assert(otp[1].Object, Equals, s.store.Objects[s.hashes["treeType"]])
 
 	// Size radically different
 	hashes = []plumbing.Hash{s.hashes["bigBase"], s.hashes["target"]}
-	otp, err = s.ds.ObjectsToPack(hashes)
+	otp, err = s.ds.ObjectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
 	c.Assert(len(otp), Equals, 2)
 	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["bigBase"]])
 	c.Assert(otp[1].Object, Equals, s.store.Objects[s.hashes["target"]])
 
 	// Delta Size Limit with no best delta yet
 	hashes = []plumbing.Hash{s.hashes["smallBase"], s.hashes["smallTarget"]}
-	otp, err = s.ds.ObjectsToPack(hashes)
+	otp, err = s.ds.ObjectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
 	c.Assert(len(otp), Equals, 2)
 	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["smallBase"]])
 	c.Assert(otp[1].Object, Equals, s.store.Objects[s.hashes["smallTarget"]])
 
 	// It will create the delta
 	hashes = []plumbing.Hash{s.hashes["base"], s.hashes["target"]}
-	otp, err = s.ds.ObjectsToPack(hashes)
+	otp, err = s.ds.ObjectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
 	c.Assert(len(otp), Equals, 2)
 	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["target"]])
@@ -185,7 +186,7 @@ func (s *DeltaSelectorSuite) TestObjectsToPack(c *C) {
 		s.hashes["o2"],
 		s.hashes["o3"],
 	}
-	otp, err = s.ds.ObjectsToPack(hashes)
+	otp, err = s.ds.ObjectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
 	c.Assert(len(otp), Equals, 3)
 	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["o1"]])
@@ -201,20 +202,32 @@ func (s *DeltaSelectorSuite) TestObjectsToPack(c *C) {
 	// a delta.
 	hashes = make([]plumbing.Hash, 0, deltaWindowSize+2)
 	hashes = append(hashes, s.hashes["base"])
-	for i := 0; i < deltaWindowSize; i++ {
+	for i := uint(0); i < deltaWindowSize; i++ {
 		hashes = append(hashes, s.hashes["smallTarget"])
 	}
 	hashes = append(hashes, s.hashes["target"])
 
 	// Don't sort so we can easily check the sliding window without
 	// creating a bunch of new objects.
-	otp, err = s.ds.objectsToPack(hashes)
+	otp, err = s.ds.objectsToPack(hashes, deltaWindowSize)
 	c.Assert(err, IsNil)
-	err = s.ds.walk(otp)
+	err = s.ds.walk(otp, deltaWindowSize)
 	c.Assert(err, IsNil)
-	c.Assert(len(otp), Equals, deltaWindowSize+2)
+	c.Assert(len(otp), Equals, int(deltaWindowSize)+2)
 	targetIdx := len(otp) - 1
 	c.Assert(otp[targetIdx].IsDelta(), Equals, false)
+
+	// Check that no deltas are created, and the objects are unsorted,
+	// if compression is off.
+	hashes = []plumbing.Hash{s.hashes["base"], s.hashes["target"]}
+	otp, err = s.ds.ObjectsToPack(hashes, 0)
+	c.Assert(err, IsNil)
+	c.Assert(len(otp), Equals, 2)
+	c.Assert(otp[0].Object, Equals, s.store.Objects[s.hashes["base"]])
+	c.Assert(otp[0].IsDelta(), Equals, false)
+	c.Assert(otp[1].Original, Equals, s.store.Objects[s.hashes["target"]])
+	c.Assert(otp[1].IsDelta(), Equals, false)
+	c.Assert(otp[1].Depth, Equals, 0)
 }
 
 func (s *DeltaSelectorSuite) TestMaxDepth(c *C) {

plumbing/format/packfile/encoder.go

@@ -14,10 +14,10 @@ import (
 // Encoder gets the data from the storage and write it into the writer in PACK
 // format
 type Encoder struct {
-	selector     *deltaSelector
-	w            *offsetWriter
-	zw           *zlib.Writer
-	hasher       plumbing.Hasher
+	selector *deltaSelector
+	w        *offsetWriter
+	zw       *zlib.Writer
+	hasher   plumbing.Hasher
 	// offsets is a map of object hashes to corresponding offsets in the packfile.
 	// It is used to determine offset of the base of a delta when a OFS_DELTA is
 	// used.
@@ -45,10 +45,15 @@ func NewEncoder(w io.Writer, s storer.EncodedObjectStorer, useRefDeltas bool) *E
 	}
 }
 
-// Encode creates a packfile containing all the objects referenced in hashes
-// and writes it to the writer in the Encoder.
-func (e *Encoder) Encode(hashes []plumbing.Hash) (plumbing.Hash, error) {
-	objects, err := e.selector.ObjectsToPack(hashes)
+// Encode creates a packfile containing all the objects referenced in
+// hashes and writes it to the writer in the Encoder.  `packWindow`
+// specifies the size of the sliding window used to compare objects
+// for delta compression; 0 turns off delta compression entirely.
+func (e *Encoder) Encode(
+	hashes []plumbing.Hash,
+	packWindow uint,
+) (plumbing.Hash, error) {
+	objects, err := e.selector.ObjectsToPack(hashes, packWindow)
 	if err != nil {
 		return plumbing.ZeroHash, err
 	}
@@ -137,7 +142,7 @@ func (e *Encoder) writeOfsDeltaHeader(deltaOffset int64, base plumbing.Hash) err
 
 	// for OFS_DELTA, offset of the base is interpreted as negative offset
 	// relative to the type-byte of the header of the ofs-delta entry.
-	relativeOffset := deltaOffset-baseOffset
+	relativeOffset := deltaOffset - baseOffset
 	if relativeOffset <= 0 {
 		return fmt.Errorf("bad offset for OFS_DELTA entry: %d", relativeOffset)
 	}

plumbing/format/packfile/encoder_advanced_test.go

@@ -27,12 +27,23 @@ func (s *EncoderAdvancedSuite) TestEncodeDecode(c *C) {
 	fixs.Test(c, func(f *fixtures.Fixture) {
 		storage, err := filesystem.NewStorage(f.DotGit())
 		c.Assert(err, IsNil)
-		s.testEncodeDecode(c, storage)
+		s.testEncodeDecode(c, storage, 10)
 	})
 
 }
 
-func (s *EncoderAdvancedSuite) testEncodeDecode(c *C, storage storer.Storer) {
+func (s *EncoderAdvancedSuite) TestEncodeDecodeNoDeltaCompression(c *C) {
+	fixs := fixtures.Basic().ByTag("packfile").ByTag(".git")
+	fixs = append(fixs, fixtures.ByURL("https://github.com/src-d/go-git.git").
+		ByTag("packfile").ByTag(".git").One())
+	fixs.Test(c, func(f *fixtures.Fixture) {
+		storage, err := filesystem.NewStorage(f.DotGit())
+		c.Assert(err, IsNil)
+		s.testEncodeDecode(c, storage, 0)
+	})
+}
+
+func (s *EncoderAdvancedSuite) testEncodeDecode(c *C, storage storer.Storer, packWindow uint) {
 
 	objIter, err := storage.IterEncodedObjects(plumbing.AnyObject)
 	c.Assert(err, IsNil)
@@ -57,7 +68,7 @@ func (s *EncoderAdvancedSuite) testEncodeDecode(c *C, storage storer.Storer) {
 
 	buf := bytes.NewBuffer(nil)
 	enc := NewEncoder(buf, storage, false)
-	_, err = enc.Encode(hashes)
+	_, err = enc.Encode(hashes, packWindow)
 	c.Assert(err, IsNil)
 
 	scanner := NewScanner(buf)