Merge branch 'master' into jc/commit-ammend

35 files changed, 458 insertions, 191 deletions

diff --git a/plumbing/format/commitgraph/encoder.go b/plumbing/format/commitgraph/encoder.go
index d34076f..f61025b 100644
--- a/plumbing/format/commitgraph/encoder.go
+++ b/plumbing/format/commitgraph/encoder.go
@@ -1,11 +1,10 @@
 package commitgraph

 

 import (

-	"crypto/sha1"

-	"hash"

 	"io"

 

 	"github.com/go-git/go-git/v5/plumbing"

+	"github.com/go-git/go-git/v5/plumbing/hash"

 	"github.com/go-git/go-git/v5/utils/binary"

 )

 

@@ -17,7 +16,7 @@ type Encoder struct {
 

 // NewEncoder returns a new stream encoder that writes to w.

 func NewEncoder(w io.Writer) *Encoder {

-	h := sha1.New()

+	h := hash.New(hash.CryptoType)

 	mw := io.MultiWriter(w, h)

 	return &Encoder{mw, h}

 }

@@ -31,7 +30,7 @@ func (e *Encoder) Encode(idx Index) error {
 	hashToIndex, fanout, extraEdgesCount := e.prepare(idx, hashes)

 

 	chunkSignatures := [][]byte{oidFanoutSignature, oidLookupSignature, commitDataSignature}

-	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * 20, uint64(len(hashes)) * 36}

+	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * hash.Size, uint64(len(hashes)) * 36}

 	if extraEdgesCount > 0 {

 		chunkSignatures = append(chunkSignatures, extraEdgeListSignature)

 		chunkSizes = append(chunkSizes, uint64(extraEdgesCount)*4)

@@ -183,6 +182,6 @@ func (e *Encoder) encodeExtraEdges(extraEdges []uint32) (err error) {
 }

 

 func (e *Encoder) encodeChecksum() error {

-	_, err := e.Write(e.hash.Sum(nil)[:20])

+	_, err := e.Write(e.hash.Sum(nil)[:hash.Size])

 	return err

 }

diff --git a/plumbing/format/config/encoder.go b/plumbing/format/config/encoder.go
index 4eac896..de069ae 100644
--- a/plumbing/format/config/encoder.go
+++ b/plumbing/format/config/encoder.go
@@ -11,6 +11,10 @@ type Encoder struct {
 	w io.Writer
 }
 
+var (
+	subsectionReplacer = strings.NewReplacer(`"`, `\"`, `\`, `\\`)
+	valueReplacer = strings.NewReplacer(`"`, `\"`, `\`, `\\`, "\n", `\n`, "\t", `\t`, "\b", `\b`)
+)
 // NewEncoder returns a new encoder that writes to w.
 func NewEncoder(w io.Writer) *Encoder {
 	return &Encoder{w}
@@ -48,8 +52,7 @@ func (e *Encoder) encodeSection(s *Section) error {
 }
 
 func (e *Encoder) encodeSubsection(sectionName string, s *Subsection) error {
-	//TODO: escape
-	if err := e.printf("[%s \"%s\"]\n", sectionName, s.Name); err != nil {
+	if err := e.printf("[%s \"%s\"]\n", sectionName, subsectionReplacer.Replace(s.Name)); err != nil {
 		return err
 	}
 
@@ -58,12 +61,14 @@ func (e *Encoder) encodeSubsection(sectionName string, s *Subsection) error {
 
 func (e *Encoder) encodeOptions(opts Options) error {
 	for _, o := range opts {
-		pattern := "\t%s = %s\n"
-		if strings.Contains(o.Value, "\\") {
-			pattern = "\t%s = %q\n"
+		var value string
+		if strings.ContainsAny(o.Value, "#;\"\t\n\\") || strings.HasPrefix(o.Value, " ") || strings.HasSuffix(o.Value, " ") {
+			value = `"`+valueReplacer.Replace(o.Value)+`"`
+		} else {
+			value = o.Value
 		}
 
-		if err := e.printf(pattern, o.Key, o.Value); err != nil {
+		if err := e.printf("\t%s = %s\n", o.Key, value); err != nil {
 			return err
 		}
 	}
diff --git a/plumbing/format/config/fixtures_test.go b/plumbing/format/config/fixtures_test.go
index f3533df..2fa7840 100644
--- a/plumbing/format/config/fixtures_test.go
+++ b/plumbing/format/config/fixtures_test.go
@@ -43,6 +43,41 @@ var fixtures = []*Fixture{
 		Config: New().AddOption("core", "", "repositoryformatversion", "0"),
 	},
 	{
+		Raw: `[section]
+	option1 = "has # hash"
+	option2 = "has \" quote"
+	option3 = "has \\ backslash"
+	option4 = "has ; semicolon"
+	option5 = "has \n line-feed"
+	option6 = "has \t tab"
+	option7 = "  has leading spaces"
+	option8 = "has trailing spaces  "
+	option9 = has no special characters
+	option10 = has unusual ` + "\x01\x7f\xc8\x80 characters\n",
+		Text: `[section]
+	option1 = "has # hash"
+	option2 = "has \" quote"
+	option3 = "has \\ backslash"
+	option4 = "has ; semicolon"
+	option5 = "has \n line-feed"
+	option6 = "has \t tab"
+	option7 = "  has leading spaces"
+	option8 = "has trailing spaces  "
+	option9 = has no special characters
+	option10 = has unusual ` + "\x01\x7f\xc8\x80 characters\n",
+		Config: New().
+			AddOption("section", "", "option1", `has # hash`).
+			AddOption("section", "", "option2", `has " quote`).
+			AddOption("section", "", "option3", `has \ backslash`).
+			AddOption("section", "", "option4", `has ; semicolon`).
+			AddOption("section", "", "option5", "has \n line-feed").
+			AddOption("section", "", "option6", "has \t tab").
+			AddOption("section", "", "option7", `  has leading spaces`).
+			AddOption("section", "", "option8", `has trailing spaces  `).
+			AddOption("section", "", "option9", `has no special characters`).
+			AddOption("section", "", "option10", "has unusual \x01\x7f\u0200 characters"),
+	},
+	{
 		Raw: `
 			[sect1]
 			opt1 = value1
diff --git a/plumbing/format/config/format.go b/plumbing/format/config/format.go
new file mode 100644
index 0000000..4873ea9
--- /dev/null
+++ b/plumbing/format/config/format.go
@@ -0,0 +1,53 @@
+package config
+
+// RepositoryFormatVersion represents the repository format version,
+// as per defined at:
+//
+//	https://git-scm.com/docs/repository-version
+type RepositoryFormatVersion string
+
+const (
+	// Version_0 is the format defined by the initial version of git,
+	// including but not limited to the format of the repository
+	// directory, the repository configuration file, and the object
+	// and ref storage.
+	//
+	// Specifying the complete behavior of git is beyond the scope
+	// of this document.
+	Version_0 = "0"
+
+	// Version_1 is identical to version 0, with the following exceptions:
+	//
+	//   1. When reading the core.repositoryformatversion variable, a git
+	//		implementation which supports version 1 MUST also read any
+	//		configuration keys found in the extensions section of the
+	//		configuration file.
+	//
+	//	 2. If a version-1 repository specifies any extensions.* keys that
+	//		the running git has not implemented, the operation MUST NOT proceed.
+	//		Similarly, if the value of any known key is not understood by the
+	//		implementation, the operation MUST NOT proceed.
+	//
+	// Note that if no extensions are specified in the config file, then
+	// core.repositoryformatversion SHOULD be set to 0 (setting it to 1 provides
+	// no benefit, and makes the repository incompatible with older
+	// implementations of git).
+	Version_1 = "1"
+
+	// DefaultRepositoryFormatVersion holds the default repository format version.
+	DefaultRepositoryFormatVersion = Version_0
+)
+
+// ObjectFormat defines the object format.
+type ObjectFormat string
+
+const (
+	// SHA1 represents the object format used for SHA1.
+	SHA1 ObjectFormat = "sha1"
+
+	// SHA256 represents the object format used for SHA256.
+	SHA256 ObjectFormat = "sha256"
+
+	// DefaultObjectFormat holds the default object format.
+	DefaultObjectFormat = SHA1
+)
diff --git a/plumbing/format/config/section.go b/plumbing/format/config/section.go
index 07f72f3..4625ac5 100644
--- a/plumbing/format/config/section.go
+++ b/plumbing/format/config/section.go
@@ -103,7 +103,7 @@ func (s *Section) RemoveSubsection(name string) *Section {
 	return s
 }
 
-// Option return the value for the specified key. Empty string is returned if
+// Option returns the value for the specified key. Empty string is returned if
 // key does not exists.
 func (s *Section) Option(key string) string {
 	return s.Options.Get(key)
diff --git a/plumbing/format/diff/patch.go b/plumbing/format/diff/patch.go
index 39a66a1..c7678b0 100644
--- a/plumbing/format/diff/patch.go
+++ b/plumbing/format/diff/patch.go
@@ -9,7 +9,7 @@ import (
 type Operation int
 
 const (
-	// Equal item represents a equals diff.
+	// Equal item represents an equals diff.
 	Equal Operation = iota
 	// Add item represents an insert diff.
 	Add
@@ -26,15 +26,15 @@ type Patch interface {
 	Message() string
 }
 
-// FilePatch represents the necessary steps to transform one file to another.
+// FilePatch represents the necessary steps to transform one file into another.
 type FilePatch interface {
 	// IsBinary returns true if this patch is representing a binary file.
 	IsBinary() bool
-	// Files returns the from and to Files, with all the necessary metadata to
+	// Files returns the from and to Files, with all the necessary metadata
 	// about them. If the patch creates a new file, "from" will be nil.
 	// If the patch deletes a file, "to" will be nil.
 	Files() (from, to File)
-	// Chunks returns a slice of ordered changes to transform "from" File to
+	// Chunks returns a slice of ordered changes to transform "from" File into
 	// "to" File. If the file is a binary one, Chunks will be empty.
 	Chunks() []Chunk
 }
@@ -49,7 +49,7 @@ type File interface {
 	Path() string
 }
 
-// Chunk represents a portion of a file transformation to another.
+// Chunk represents a portion of a file transformation into another.
 type Chunk interface {
 	// Content contains the portion of the file.
 	Content() string
diff --git a/plumbing/format/gitattributes/attributes.go b/plumbing/format/gitattributes/attributes.go
index 329e667..d36ec1b 100644
--- a/plumbing/format/gitattributes/attributes.go
+++ b/plumbing/format/gitattributes/attributes.go
@@ -3,7 +3,6 @@ package gitattributes
 import (
 	"errors"
 	"io"
-	"io/ioutil"
 	"strings"
 )
 
@@ -89,7 +88,7 @@ func (a attribute) String() string {
 
 // ReadAttributes reads patterns and attributes from the gitattributes format.
 func ReadAttributes(r io.Reader, domain []string, allowMacro bool) (attributes []MatchAttribute, err error) {
-	data, err := ioutil.ReadAll(r)
+	data, err := io.ReadAll(r)
 	if err != nil {
 		return nil, err
 	}
diff --git a/plumbing/format/gitattributes/pattern.go b/plumbing/format/gitattributes/pattern.go
index d961aba..f101f47 100644
--- a/plumbing/format/gitattributes/pattern.go
+++ b/plumbing/format/gitattributes/pattern.go
@@ -52,6 +52,11 @@ func (p *pattern) Match(path []string) bool {
 	var match, doublestar bool
 	var err error
 	for _, part := range path {
+		// path is deeper than pattern
+		if len(pattern) == 0 {
+			return false
+		}
+
 		// skip empty
 		if pattern[0] == "" {
 			pattern = pattern[1:]
diff --git a/plumbing/format/gitattributes/pattern_test.go b/plumbing/format/gitattributes/pattern_test.go
index f95be6e..981d56f 100644
--- a/plumbing/format/gitattributes/pattern_test.go
+++ b/plumbing/format/gitattributes/pattern_test.go
@@ -174,6 +174,12 @@ func (s *PatternSuite) TestGlobMatch_tailingAsterisks_single(c *C) {
 	c.Assert(r, Equals, true)
 }
 
+func (s *PatternSuite) TestGlobMatch_tailingAsterisk_single(c *C) {
+	p := ParsePattern("/*lue/*", nil)
+	r := p.Match([]string{"value", "volcano", "tail"})
+	c.Assert(r, Equals, false)
+}
+
 func (s *PatternSuite) TestGlobMatch_tailingAsterisks_exactMatch(c *C) {
 	p := ParsePattern("/*lue/vol?ano/**", nil)
 	r := p.Match([]string{"value", "volcano"})
diff --git a/plumbing/format/gitignore/dir.go b/plumbing/format/gitignore/dir.go
index 15bc9c7..d8fb30c 100644
--- a/plumbing/format/gitignore/dir.go
+++ b/plumbing/format/gitignore/dir.go
@@ -3,11 +3,12 @@ package gitignore
 import (
 	"bufio"
 	"bytes"
-	"io/ioutil"
+	"io"
 	"os"
 	"strings"
 
 	"github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-git/v5/internal/path_util"
 	"github.com/go-git/go-git/v5/plumbing/format/config"
 	gioutil "github.com/go-git/go-git/v5/utils/ioutil"
 )
@@ -25,6 +26,9 @@ const (
 
 // readIgnoreFile reads a specific git ignore file.
 func readIgnoreFile(fs billy.Filesystem, path []string, ignoreFile string) (ps []Pattern, err error) {
+
+	ignoreFile, _ = path_util.ReplaceTildeWithHome(ignoreFile)
+
 	f, err := fs.Open(fs.Join(append(path, ignoreFile)...))
 	if err == nil {
 		defer f.Close()
@@ -86,7 +90,7 @@ func loadPatterns(fs billy.Filesystem, path string) (ps []Pattern, err error) {
 
 	defer gioutil.CheckClose(f, &err)
 
-	b, err := ioutil.ReadAll(f)
+	b, err := io.ReadAll(f)
 	if err != nil {
 		return
 	}
diff --git a/plumbing/format/gitignore/dir_test.go b/plumbing/format/gitignore/dir_test.go
index facc36d..465c571 100644
--- a/plumbing/format/gitignore/dir_test.go
+++ b/plumbing/format/gitignore/dir_test.go
@@ -2,7 +2,9 @@ package gitignore
 
 import (
 	"os"
+	"os/user"
 	"strconv"
+	"strings"
 
 	"github.com/go-git/go-billy/v5"
 	"github.com/go-git/go-billy/v5/memfs"
@@ -12,6 +14,8 @@ import (
 type MatcherSuite struct {
 	GFS  billy.Filesystem // git repository root
 	RFS  billy.Filesystem // root that contains user home
+	RFSR billy.Filesystem // root that contains user home, but with relative ~/.gitignore_global
+	RFSU billy.Filesystem // root that contains user home, but with relative ~user/.gitignore_global
 	MCFS billy.Filesystem // root that contains user home, but missing ~/.gitconfig
 	MEFS billy.Filesystem // root that contains user home, but missing excludesfile entry
 	MIFS billy.Filesystem // root that contains user home, but missing .gitignore
@@ -63,6 +67,27 @@ func (s *MatcherSuite) SetUpTest(c *C) {
 	err = fs.MkdirAll("vendor/gopkg.in", os.ModePerm)
 	c.Assert(err, IsNil)
 
+	err = fs.MkdirAll("multiple/sub/ignores/first", os.ModePerm)
+	c.Assert(err, IsNil)
+	err = fs.MkdirAll("multiple/sub/ignores/second", os.ModePerm)
+	c.Assert(err, IsNil)
+	f, err = fs.Create("multiple/sub/ignores/first/.gitignore")
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("ignore_dir\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+	f, err = fs.Create("multiple/sub/ignores/second/.gitignore")
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("ignore_dir\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+	err = fs.MkdirAll("multiple/sub/ignores/first/ignore_dir", os.ModePerm)
+	c.Assert(err, IsNil)
+	err = fs.MkdirAll("multiple/sub/ignores/second/ignore_dir", os.ModePerm)
+	c.Assert(err, IsNil)
+
 	s.GFS = fs
 
 	// setup root that contains user home
@@ -95,6 +120,64 @@ func (s *MatcherSuite) SetUpTest(c *C) {
 
 	s.RFS = fs
 
+	// root that contains user home, but with relative ~/.gitignore_global
+	fs = memfs.New()
+	err = fs.MkdirAll(home, os.ModePerm)
+	c.Assert(err, IsNil)
+
+	f, err = fs.Create(fs.Join(home, gitconfigFile))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("[core]\n"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("	excludesfile = ~/.gitignore_global" + "\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	f, err = fs.Create(fs.Join(home, ".gitignore_global"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("# IntelliJ\n"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte(".idea/\n"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("*.iml\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	s.RFSR = fs
+
+	// root that contains user home, but with relative ~user/.gitignore_global
+	fs = memfs.New()
+	err = fs.MkdirAll(home, os.ModePerm)
+	c.Assert(err, IsNil)
+
+	f, err = fs.Create(fs.Join(home, gitconfigFile))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("[core]\n"))
+	c.Assert(err, IsNil)
+	currentUser, err := user.Current()
+	c.Assert(err, IsNil)
+	// remove domain for windows
+	username := currentUser.Username[strings.Index(currentUser.Username, "\\")+1:]
+	_, err = f.Write([]byte("	excludesfile = ~" + username + "/.gitignore_global" + "\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	f, err = fs.Create(fs.Join(home, ".gitignore_global"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("# IntelliJ\n"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte(".idea/\n"))
+	c.Assert(err, IsNil)
+	_, err = f.Write([]byte("*.iml\n"))
+	c.Assert(err, IsNil)
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	s.RFSU = fs
+
 	// root that contains user home, but missing ~/.gitconfig
 	fs = memfs.New()
 	err = fs.MkdirAll(home, os.ModePerm)
@@ -183,15 +266,39 @@ func (s *MatcherSuite) SetUpTest(c *C) {
 }
 
 func (s *MatcherSuite) TestDir_ReadPatterns(c *C) {
+	checkPatterns := func(ps []Pattern) {
+		c.Assert(ps, HasLen, 6)
+		m := NewMatcher(ps)
+
+		c.Assert(m.Match([]string{"exclude.crlf"}, true), Equals, true)
+		c.Assert(m.Match([]string{"ignore.crlf"}, true), Equals, true)
+		c.Assert(m.Match([]string{"vendor", "gopkg.in"}, true), Equals, true)
+		c.Assert(m.Match([]string{"vendor", "github.com"}, true), Equals, false)
+		c.Assert(m.Match([]string{"multiple", "sub", "ignores", "first", "ignore_dir"}, true), Equals, true)
+		c.Assert(m.Match([]string{"multiple", "sub", "ignores", "second", "ignore_dir"}, true), Equals, true)
+	}
+
 	ps, err := ReadPatterns(s.GFS, nil)
 	c.Assert(err, IsNil)
-	c.Assert(ps, HasLen, 4)
+	checkPatterns(ps)
 
-	m := NewMatcher(ps)
-	c.Assert(m.Match([]string{"exclude.crlf"}, true), Equals, true)
-	c.Assert(m.Match([]string{"ignore.crlf"}, true), Equals, true)
-	c.Assert(m.Match([]string{"vendor", "gopkg.in"}, true), Equals, true)
-	c.Assert(m.Match([]string{"vendor", "github.com"}, true), Equals, false)
+	// passing an empty slice with capacity to check we don't hit a bug where the extra capacity is reused incorrectly
+	ps, err = ReadPatterns(s.GFS, make([]string, 0, 6))
+	c.Assert(err, IsNil)
+	checkPatterns(ps)
+}
+
+func (s *MatcherSuite) TestDir_ReadRelativeGlobalGitIgnore(c *C) {
+	for _, fs := range []billy.Filesystem{s.RFSR, s.RFSU} {
+		ps, err := LoadGlobalPatterns(fs)
+		c.Assert(err, IsNil)
+		c.Assert(ps, HasLen, 2)
+
+		m := NewMatcher(ps)
+		c.Assert(m.Match([]string{".idea/"}, true), Equals, false)
+		c.Assert(m.Match([]string{"*.iml"}, true), Equals, true)
+		c.Assert(m.Match([]string{"IntelliJ"}, true), Equals, false)
+	}
 }
 
 func (s *MatcherSuite) TestDir_LoadGlobalPatterns(c *C) {
diff --git a/plumbing/format/gitignore/pattern.go b/plumbing/format/gitignore/pattern.go
index 098cb50..450b3cd 100644
--- a/plumbing/format/gitignore/pattern.go
+++ b/plumbing/format/gitignore/pattern.go
@@ -39,6 +39,8 @@ type pattern struct {
 
 // ParsePattern parses a gitignore pattern string into the Pattern structure.
 func ParsePattern(p string, domain []string) Pattern {
+	// storing domain, copy it to ensure it isn't changed externally
+	domain = append([]string(nil), domain...)
 	res := pattern{domain: domain}
 
 	if strings.HasPrefix(p, inclusionPrefix) {
diff --git a/plumbing/format/idxfile/decoder.go b/plumbing/format/idxfile/decoder.go
index 51a3904..9afdce3 100644
--- a/plumbing/format/idxfile/decoder.go
+++ b/plumbing/format/idxfile/decoder.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"io"
 
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/utils/binary"
 )
 
@@ -19,7 +20,7 @@ var (
 
 const (
 	fanout         = 256
-	objectIDLength = 20
+	objectIDLength = hash.Size
 )
 
 // Decoder reads and decodes idx files from an input stream.
diff --git a/plumbing/format/idxfile/decoder_test.go b/plumbing/format/idxfile/decoder_test.go
index 94059cc..2c4a801 100644
--- a/plumbing/format/idxfile/decoder_test.go
+++ b/plumbing/format/idxfile/decoder_test.go
@@ -5,7 +5,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"testing"
 
 	"github.com/go-git/go-git/v5/plumbing"
@@ -119,7 +118,7 @@ ch2xUA==
 
 func BenchmarkDecode(b *testing.B) {
 	f := fixtures.Basic().One()
-	fixture, err := ioutil.ReadAll(f.Idx())
+	fixture, err := io.ReadAll(f.Idx())
 	if err != nil {
 		b.Errorf("unexpected error reading idx file: %s", err)
 	}
diff --git a/plumbing/format/idxfile/encoder.go b/plumbing/format/idxfile/encoder.go
index 26b2e4d..7514737 100644
--- a/plumbing/format/idxfile/encoder.go
+++ b/plumbing/format/idxfile/encoder.go
@@ -1,10 +1,9 @@
 package idxfile
 
 import (
-	"crypto/sha1"
-	"hash"
 	"io"
 
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/utils/binary"
 )
 
@@ -16,7 +15,7 @@ type Encoder struct {
 
 // NewEncoder returns a new stream encoder that writes to w.
 func NewEncoder(w io.Writer) *Encoder {
-	h := sha1.New()
+	h := hash.New(hash.CryptoType)
 	mw := io.MultiWriter(w, h)
 	return &Encoder{mw, h}
 }
@@ -133,10 +132,10 @@ func (e *Encoder) encodeChecksums(idx *MemoryIndex) (int, error) {
 		return 0, err
 	}
 
-	copy(idx.IdxChecksum[:], e.hash.Sum(nil)[:20])
+	copy(idx.IdxChecksum[:], e.hash.Sum(nil)[:hash.Size])
 	if _, err := e.Write(idx.IdxChecksum[:]); err != nil {
 		return 0, err
 	}
 
-	return 40, nil
+	return hash.HexSize, nil
 }
diff --git a/plumbing/format/idxfile/encoder_test.go b/plumbing/format/idxfile/encoder_test.go
index 32b60f9..b8ece83 100644
--- a/plumbing/format/idxfile/encoder_test.go
+++ b/plumbing/format/idxfile/encoder_test.go
@@ -2,7 +2,7 @@ package idxfile_test
 
 import (
 	"bytes"
-	"io/ioutil"
+	"io"
 
 	. "github.com/go-git/go-git/v5/plumbing/format/idxfile"
 
@@ -12,7 +12,7 @@ import (
 
 func (s *IdxfileSuite) TestDecodeEncode(c *C) {
 	fixtures.ByTag("packfile").Test(c, func(f *fixtures.Fixture) {
-		expected, err := ioutil.ReadAll(f.Idx())
+		expected, err := io.ReadAll(f.Idx())
 		c.Assert(err, IsNil)
 
 		idx := new(MemoryIndex)
diff --git a/plumbing/format/idxfile/idxfile.go b/plumbing/format/idxfile/idxfile.go
index 64dd8dc..9237a74 100644
--- a/plumbing/format/idxfile/idxfile.go
+++ b/plumbing/format/idxfile/idxfile.go
@@ -8,6 +8,7 @@ import (
 	encbin "encoding/binary"
 
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 )
 
 const (
@@ -53,8 +54,8 @@ type MemoryIndex struct {
 	Offset32         [][]byte
 	CRC32            [][]byte
 	Offset64         []byte
-	PackfileChecksum [20]byte
-	IdxChecksum      [20]byte
+	PackfileChecksum [hash.Size]byte
+	IdxChecksum      [hash.Size]byte
 
 	offsetHash       map[int64]plumbing.Hash
 	offsetHashIsFull bool
diff --git a/plumbing/format/idxfile/writer.go b/plumbing/format/idxfile/writer.go
index daa1605..c4c21e1 100644
--- a/plumbing/format/idxfile/writer.go
+++ b/plumbing/format/idxfile/writer.go
@@ -84,11 +84,8 @@ func (w *Writer) OnFooter(h plumbing.Hash) error {
 	w.checksum = h
 	w.finished = true
 	_, err := w.createIndex()
-	if err != nil {
-		return err
-	}
 
-	return nil
+	return err
 }
 
 // creatIndex returns a filled MemoryIndex with the information filled by
@@ -139,15 +136,23 @@ func (w *Writer) createIndex() (*MemoryIndex, error) {
 
 		offset := o.Offset
 		if offset > math.MaxInt32 {
-			offset = w.addOffset64(offset)
+			var err error
+			offset, err = w.addOffset64(offset)
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		buf.Truncate(0)
-		binary.WriteUint32(buf, uint32(offset))
+		if err := binary.WriteUint32(buf, uint32(offset)); err != nil {
+			return nil, err
+		}
 		idx.Offset32[bucket] = append(idx.Offset32[bucket], buf.Bytes()...)
 
 		buf.Truncate(0)
-		binary.WriteUint32(buf, o.CRC32)
+		if err := binary.WriteUint32(buf, o.CRC32); err != nil {
+			return nil, err
+		}
 		idx.CRC32[bucket] = append(idx.CRC32[bucket], buf.Bytes()...)
 	}
 
@@ -161,15 +166,17 @@ func (w *Writer) createIndex() (*MemoryIndex, error) {
 	return idx, nil
 }
 
-func (w *Writer) addOffset64(pos uint64) uint64 {
+func (w *Writer) addOffset64(pos uint64) (uint64, error) {
 	buf := new(bytes.Buffer)
-	binary.WriteUint64(buf, pos)
-	w.index.Offset64 = append(w.index.Offset64, buf.Bytes()...)
+	if err := binary.WriteUint64(buf, pos); err != nil {
+		return 0, err
+	}
 
+	w.index.Offset64 = append(w.index.Offset64, buf.Bytes()...)
 	index := uint64(w.offset64 | (1 << 31))
 	w.offset64++
 
-	return index
+	return index, nil
 }
 
 func (o objects) Len() int {
diff --git a/plumbing/format/idxfile/writer_test.go b/plumbing/format/idxfile/writer_test.go
index fba3e42..eaa8605 100644
--- a/plumbing/format/idxfile/writer_test.go
+++ b/plumbing/format/idxfile/writer_test.go
@@ -3,7 +3,7 @@ package idxfile_test
 import (
 	"bytes"
 	"encoding/base64"
-	"io/ioutil"
+	"io"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/format/idxfile"
@@ -34,7 +34,7 @@ func (s *WriterSuite) TestWriter(c *C) {
 	c.Assert(err, IsNil)
 
 	idxFile := f.Idx()
-	expected, err := ioutil.ReadAll(idxFile)
+	expected, err := io.ReadAll(idxFile)
 	c.Assert(err, IsNil)
 	idxFile.Close()
 
@@ -65,7 +65,7 @@ func (s *WriterSuite) TestWriterLarge(c *C) {
 
 	// load fixture index
 	f := bytes.NewBufferString(fixtureLarge4GB)
-	expected, err := ioutil.ReadAll(base64.NewDecoder(base64.StdEncoding, f))
+	expected, err := io.ReadAll(base64.NewDecoder(base64.StdEncoding, f))
 	c.Assert(err, IsNil)
 
 	buf := new(bytes.Buffer)
diff --git a/plumbing/format/index/decoder.go b/plumbing/format/index/decoder.go
index 036b636..6778cf7 100644
--- a/plumbing/format/index/decoder.go
+++ b/plumbing/format/index/decoder.go
@@ -3,15 +3,14 @@ package index
 import (
 	"bufio"
 	"bytes"
-	"crypto/sha1"
 	"errors"
-	"hash"
 	"io"
-	"io/ioutil"
+
 	"strconv"
 	"time"
 
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/utils/binary"
 )
 
@@ -49,7 +48,7 @@ type Decoder struct {
 
 // NewDecoder returns a new decoder that reads from r.
 func NewDecoder(r io.Reader) *Decoder {
-	h := sha1.New()
+	h := hash.New(hash.CryptoType)
 	return &Decoder{
 		r:         io.TeeReader(r, h),
 		hash:      h,
@@ -202,7 +201,7 @@ func (d *Decoder) padEntry(idx *Index, e *Entry, read int) error {
 
 	entrySize := read + len(e.Name)
 	padLen := 8 - entrySize%8
-	_, err := io.CopyN(ioutil.Discard, d.r, int64(padLen))
+	_, err := io.CopyN(io.Discard, d.r, int64(padLen))
 	return err
 }
 
diff --git a/plumbing/format/index/encoder.go b/plumbing/format/index/encoder.go
index 2c94d93..fa2d814 100644
--- a/plumbing/format/index/encoder.go
+++ b/plumbing/format/index/encoder.go
@@ -2,13 +2,12 @@ package index
 
 import (
 	"bytes"
-	"crypto/sha1"
 	"errors"
-	"hash"
 	"io"
 	"sort"
 	"time"
 
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/utils/binary"
 )
 
@@ -29,7 +28,7 @@ type Encoder struct {
 
 // NewEncoder returns a new encoder that writes to w.
 func NewEncoder(w io.Writer) *Encoder {
-	h := sha1.New()
+	h := hash.New(hash.CryptoType)
 	mw := io.MultiWriter(w, h)
 	return &Encoder{mw, h}
 }
diff --git a/plumbing/format/objfile/reader.go b/plumbing/format/objfile/reader.go
index b6b2ca0..d7932f4 100644
--- a/plumbing/format/objfile/reader.go
+++ b/plumbing/format/objfile/reader.go
@@ -1,13 +1,13 @@
 package objfile
 
 import (
-	"compress/zlib"
 	"errors"
 	"io"
 	"strconv"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/format/packfile"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 var (
@@ -20,20 +20,22 @@ var (
 // Reader implements io.ReadCloser. Close should be called when finished with
 // the Reader. Close will not close the underlying io.Reader.
 type Reader struct {
-	multi  io.Reader
-	zlib   io.ReadCloser
-	hasher plumbing.Hasher
+	multi   io.Reader
+	zlib    io.Reader
+	zlibref sync.ZLibReader
+	hasher  plumbing.Hasher
 }
 
 // NewReader returns a new Reader reading from r.
 func NewReader(r io.Reader) (*Reader, error) {
-	zlib, err := zlib.NewReader(r)
+	zlib, err := sync.GetZlibReader(r)
 	if err != nil {
 		return nil, packfile.ErrZLib.AddDetails(err.Error())
 	}
 
 	return &Reader{
-		zlib: zlib,
+		zlib:    zlib.Reader,
+		zlibref: zlib,
 	}, nil
 }
 
@@ -110,5 +112,6 @@ func (r *Reader) Hash() plumbing.Hash {
 // Close releases any resources consumed by the Reader. Calling Close does not
 // close the wrapped io.Reader originally passed to NewReader.
 func (r *Reader) Close() error {
-	return r.zlib.Close()
+	sync.PutZlibReader(r.zlibref)
+	return nil
 }
diff --git a/plumbing/format/objfile/reader_test.go b/plumbing/format/objfile/reader_test.go
index d697d54..5526f7f 100644
--- a/plumbing/format/objfile/reader_test.go
+++ b/plumbing/format/objfile/reader_test.go
@@ -5,7 +5,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 
 	"github.com/go-git/go-git/v5/plumbing"
 
@@ -36,7 +35,7 @@ func testReader(c *C, source io.Reader, hash plumbing.Hash, t plumbing.ObjectTyp
 	c.Assert(typ, Equals, t)
 	c.Assert(content, HasLen, int(size))
 
-	rc, err := ioutil.ReadAll(r)
+	rc, err := io.ReadAll(r)
 	c.Assert(err, IsNil)
 	c.Assert(rc, DeepEquals, content, Commentf("%scontent=%s, expected=%s", base64.StdEncoding.EncodeToString(rc), base64.StdEncoding.EncodeToString(content)))
 
diff --git a/plumbing/format/objfile/writer.go b/plumbing/format/objfile/writer.go
index 2a96a43..0d0f154 100644
--- a/plumbing/format/objfile/writer.go
+++ b/plumbing/format/objfile/writer.go
@@ -7,6 +7,7 @@ import (
 	"strconv"
 
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 var (
@@ -18,9 +19,9 @@ var (
 // not close the underlying io.Writer.
 type Writer struct {
 	raw    io.Writer
-	zlib   io.WriteCloser
 	hasher plumbing.Hasher
 	multi  io.Writer
+	zlib   *zlib.Writer
 
 	closed  bool
 	pending int64 // number of unwritten bytes
@@ -31,9 +32,10 @@ type Writer struct {
 // The returned Writer implements io.WriteCloser. Close should be called when
 // finished with the Writer. Close will not close the underlying io.Writer.
 func NewWriter(w io.Writer) *Writer {
+	zlib := sync.GetZlibWriter(w)
 	return &Writer{
 		raw:  w,
-		zlib: zlib.NewWriter(w),
+		zlib: zlib,
 	}
 }
 
@@ -100,6 +102,7 @@ func (w *Writer) Hash() plumbing.Hash {
 // Calling Close does not close the wrapped io.Writer originally passed to
 // NewWriter.
 func (w *Writer) Close() error {
+	defer sync.PutZlibWriter(w.zlib)
 	if err := w.zlib.Close(); err != nil {
 		return err
 	}
diff --git a/plumbing/format/packfile/common.go b/plumbing/format/packfile/common.go
index df423ad..36c5ef5 100644
--- a/plumbing/format/packfile/common.go
+++ b/plumbing/format/packfile/common.go
@@ -1,10 +1,7 @@
 package packfile
 
 import (
-	"bytes"
-	"compress/zlib"
 	"io"
-	"sync"
 
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/utils/ioutil"
@@ -61,18 +58,3 @@ func WritePackfileToObjectStorage(
 
 	return err
 }
-
-var bufPool = sync.Pool{
-	New: func() interface{} {
-		return bytes.NewBuffer(nil)
-	},
-}
-
-var zlibInitBytes = []byte{0x78, 0x9c, 0x01, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x01}
-
-var zlibReaderPool = sync.Pool{
-	New: func() interface{} {
-		r, _ := zlib.NewReader(bytes.NewReader(zlibInitBytes))
-		return r
-	},
-}
diff --git a/plumbing/format/packfile/delta_test.go b/plumbing/format/packfile/delta_test.go
index 137e485..e8f5ea6 100644
--- a/plumbing/format/packfile/delta_test.go
+++ b/plumbing/format/packfile/delta_test.go
@@ -2,7 +2,7 @@ package packfile
 
 import (
 	"bytes"
-	"io/ioutil"
+	"io"
 	"math/rand"
 
 	"github.com/go-git/go-git/v5/plumbing"
@@ -109,14 +109,14 @@ func (s *DeltaSuite) TestAddDeltaReader(c *C) {
 		targetBuf := genBytes(t.target)
 
 		delta := DiffDelta(baseBuf, targetBuf)
-		deltaRC := ioutil.NopCloser(bytes.NewReader(delta))
+		deltaRC := io.NopCloser(bytes.NewReader(delta))
 
 		c.Log("Executing test case:", t.description)
 
 		resultRC, err := ReaderFromDelta(baseObj, deltaRC)
 		c.Assert(err, IsNil)
 
-		result, err := ioutil.ReadAll(resultRC)
+		result, err := io.ReadAll(resultRC)
 		c.Assert(err, IsNil)
 
 		err = resultRC.Close()
@@ -164,12 +164,12 @@ func (s *DeltaSuite) TestMaxCopySizeDeltaReader(c *C) {
 	targetBuf = append(targetBuf, byte(1))
 
 	delta := DiffDelta(baseBuf, targetBuf)
-	deltaRC := ioutil.NopCloser(bytes.NewReader(delta))
+	deltaRC := io.NopCloser(bytes.NewReader(delta))
 
 	resultRC, err := ReaderFromDelta(baseObj, deltaRC)
 	c.Assert(err, IsNil)
 
-	result, err := ioutil.ReadAll(resultRC)
+	result, err := io.ReadAll(resultRC)
 	c.Assert(err, IsNil)
 
 	err = resultRC.Close()
diff --git a/plumbing/format/packfile/diff_delta.go b/plumbing/format/packfile/diff_delta.go
index 1951b34..2c7a335 100644
--- a/plumbing/format/packfile/diff_delta.go
+++ b/plumbing/format/packfile/diff_delta.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/utils/ioutil"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 // See https://github.com/jelmer/dulwich/blob/master/dulwich/pack.py and
@@ -43,18 +44,16 @@ func getDelta(index *deltaIndex, base, target plumbing.EncodedObject) (o plumbin
 
 	defer ioutil.CheckClose(tr, &err)
 
-	bb := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(bb)
-	bb.Reset()
+	bb := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(bb)
 
 	_, err = bb.ReadFrom(br)
 	if err != nil {
 		return nil, err
 	}
 
-	tb := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(tb)
-	tb.Reset()
+	tb := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(tb)
 
 	_, err = tb.ReadFrom(tr)
 	if err != nil {
@@ -80,9 +79,8 @@ func DiffDelta(src, tgt []byte) []byte {
 }
 
 func diffDelta(index *deltaIndex, src []byte, tgt []byte) []byte {
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
-	buf.Reset()
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
 	buf.Write(deltaEncodeSize(len(src)))
 	buf.Write(deltaEncodeSize(len(tgt)))
 
@@ -90,9 +88,8 @@ func diffDelta(index *deltaIndex, src []byte, tgt []byte) []byte {
 		index.init(src)
 	}
 
-	ibuf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(ibuf)
-	ibuf.Reset()
+	ibuf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(ibuf)
 	for i := 0; i < len(tgt); i++ {
 		offset, l := index.findMatch(src, tgt, i)
 
diff --git a/plumbing/format/packfile/encoder.go b/plumbing/format/packfile/encoder.go
index 5501f88..804f5a8 100644
--- a/plumbing/format/packfile/encoder.go
+++ b/plumbing/format/packfile/encoder.go
@@ -2,11 +2,11 @@ package packfile
 
 import (
 	"compress/zlib"
-	"crypto/sha1"
 	"fmt"
 	"io"
 
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/utils/binary"
 	"github.com/go-git/go-git/v5/utils/ioutil"
@@ -28,7 +28,7 @@ type Encoder struct {
 // OFSDeltaObject. To use Reference deltas, set useRefDeltas to true.
 func NewEncoder(w io.Writer, s storer.EncodedObjectStorer, useRefDeltas bool) *Encoder {
 	h := plumbing.Hasher{
-		Hash: sha1.New(),
+		Hash: hash.New(hash.CryptoType),
 	}
 	mw := io.MultiWriter(w, h)
 	ow := newOffsetWriter(mw)
@@ -131,11 +131,7 @@ func (e *Encoder) entry(o *ObjectToPack) (err error) {
 	defer ioutil.CheckClose(or, &err)
 
 	_, err = io.Copy(e.zw, or)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return err
 }
 
 func (e *Encoder) writeBaseIfDelta(o *ObjectToPack) error {
diff --git a/plumbing/format/packfile/encoder_test.go b/plumbing/format/packfile/encoder_test.go
index c9d49c3..6719f37 100644
--- a/plumbing/format/packfile/encoder_test.go
+++ b/plumbing/format/packfile/encoder_test.go
@@ -3,10 +3,10 @@ package packfile
 import (
 	"bytes"
 	"io"
-	stdioutil "io/ioutil"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/format/idxfile"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 	"github.com/go-git/go-git/v5/storage/memory"
 
 	"github.com/go-git/go-billy/v5/memfs"
@@ -30,10 +30,10 @@ func (s *EncoderSuite) SetUpTest(c *C) {
 }
 
 func (s *EncoderSuite) TestCorrectPackHeader(c *C) {
-	hash, err := s.enc.Encode([]plumbing.Hash{}, 10)
+	h, err := s.enc.Encode([]plumbing.Hash{}, 10)
 	c.Assert(err, IsNil)
 
-	hb := [20]byte(hash)
+	hb := [hash.Size]byte(h)
 
 	// PACK + VERSION + OBJECTS + HASH
 	expectedResult := []byte{'P', 'A', 'C', 'K', 0, 0, 0, 2, 0, 0, 0, 0}
@@ -51,7 +51,7 @@ func (s *EncoderSuite) TestCorrectPackWithOneEmptyObject(c *C) {
 	_, err := s.store.SetEncodedObject(o)
 	c.Assert(err, IsNil)
 
-	hash, err := s.enc.Encode([]plumbing.Hash{o.Hash()}, 10)
+	h, err := s.enc.Encode([]plumbing.Hash{o.Hash()}, 10)
 	c.Assert(err, IsNil)
 
 	// PACK + VERSION(2) + OBJECT NUMBER(1)
@@ -64,7 +64,7 @@ func (s *EncoderSuite) TestCorrectPackWithOneEmptyObject(c *C) {
 		[]byte{120, 156, 1, 0, 0, 255, 255, 0, 0, 0, 1}...)
 
 	// + HASH
-	hb := [20]byte(hash)
+	hb := [hash.Size]byte(h)
 	expectedResult = append(expectedResult, hb[:]...)
 
 	result := s.buf.Bytes()
@@ -277,13 +277,13 @@ func objectsEqual(c *C, o1, o2 plumbing.EncodedObject) {
 	r1, err := o1.Reader()
 	c.Assert(err, IsNil)
 
-	b1, err := stdioutil.ReadAll(r1)
+	b1, err := io.ReadAll(r1)
 	c.Assert(err, IsNil)
 
 	r2, err := o2.Reader()
 	c.Assert(err, IsNil)
 
-	b2, err := stdioutil.ReadAll(r2)
+	b2, err := io.ReadAll(r2)
 	c.Assert(err, IsNil)
 
 	c.Assert(bytes.Compare(b1, b2), Equals, 0)
diff --git a/plumbing/format/packfile/packfile.go b/plumbing/format/packfile/packfile.go
index 8dd6041..6852702 100644
--- a/plumbing/format/packfile/packfile.go
+++ b/plumbing/format/packfile/packfile.go
@@ -2,7 +2,6 @@ package packfile
 
 import (
 	"bytes"
-	"compress/zlib"
 	"fmt"
 	"io"
 	"os"
@@ -13,6 +12,7 @@ import (
 	"github.com/go-git/go-git/v5/plumbing/format/idxfile"
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/utils/ioutil"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 var (
@@ -138,9 +138,8 @@ func (p *Packfile) getObjectSize(h *ObjectHeader) (int64, error) {
 	case plumbing.CommitObject, plumbing.TreeObject, plumbing.BlobObject, plumbing.TagObject:
 		return h.Length, nil
 	case plumbing.REFDeltaObject, plumbing.OFSDeltaObject:
-		buf := bufPool.Get().(*bytes.Buffer)
-		defer bufPool.Put(buf)
-		buf.Reset()
+		buf := sync.GetBytesBuffer()
+		defer sync.PutBytesBuffer(buf)
 
 		if _, _, err := p.s.NextObject(buf); err != nil {
 			return 0, err
@@ -227,9 +226,9 @@ func (p *Packfile) getNextObject(h *ObjectHeader, hash plumbing.Hash) (plumbing.
 		// For delta objects we read the delta data and apply the small object
 		// optimization only if the expanded version of the object still meets
 		// the small object threshold condition.
-		buf := bufPool.Get().(*bytes.Buffer)
-		defer bufPool.Put(buf)
-		buf.Reset()
+		buf := sync.GetBytesBuffer()
+		defer sync.PutBytesBuffer(buf)
+
 		if _, _, err := p.s.NextObject(buf); err != nil {
 			return nil, err
 		}
@@ -290,14 +289,13 @@ func (p *Packfile) getObjectContent(offset int64) (io.ReadCloser, error) {
 
 func asyncReader(p *Packfile) (io.ReadCloser, error) {
 	reader := ioutil.NewReaderUsingReaderAt(p.file, p.s.r.offset)
-	zr := zlibReaderPool.Get().(io.ReadCloser)
-
-	if err := zr.(zlib.Resetter).Reset(reader, nil); err != nil {
+	zr, err := sync.GetZlibReader(reader)
+	if err != nil {
 		return nil, fmt.Errorf("zlib reset error: %s", err)
 	}
 
-	return ioutil.NewReadCloserWithCloser(zr, func() error {
-		zlibReaderPool.Put(zr)
+	return ioutil.NewReadCloserWithCloser(zr.Reader, func() error {
+		sync.PutZlibReader(zr)
 		return nil
 	}), nil
 
@@ -373,9 +371,9 @@ func (p *Packfile) fillRegularObjectContent(obj plumbing.EncodedObject) (err err
 }
 
 func (p *Packfile) fillREFDeltaObjectContent(obj plumbing.EncodedObject, ref plumbing.Hash) error {
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
-	buf.Reset()
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
+
 	_, _, err := p.s.NextObject(buf)
 	if err != nil {
 		return err
@@ -417,9 +415,9 @@ func (p *Packfile) fillREFDeltaObjectContentWithBuffer(obj plumbing.EncodedObjec
 }
 
 func (p *Packfile) fillOFSDeltaObjectContent(obj plumbing.EncodedObject, offset int64) error {
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
-	buf.Reset()
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
+
 	_, _, err := p.s.NextObject(buf)
 	if err != nil {
 		return err
diff --git a/plumbing/format/packfile/parser.go b/plumbing/format/packfile/parser.go
index ee5c289..edbc0e7 100644
--- a/plumbing/format/packfile/parser.go
+++ b/plumbing/format/packfile/parser.go
@@ -4,12 +4,12 @@ import (
 	"bytes"
 	"errors"
 	"io"
-	stdioutil "io/ioutil"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/cache"
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/utils/ioutil"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 var (
@@ -175,7 +175,8 @@ func (p *Parser) init() error {
 }
 
 func (p *Parser) indexObjects() error {
-	buf := new(bytes.Buffer)
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
 
 	for i := uint32(0); i < p.count; i++ {
 		buf.Reset()
@@ -219,6 +220,7 @@ func (p *Parser) indexObjects() error {
 			ota = newBaseObject(oh.Offset, oh.Length, t)
 		}
 
+		buf.Grow(int(oh.Length))
 		_, crc, err := p.scanner.NextObject(buf)
 		if err != nil {
 			return err
@@ -234,6 +236,15 @@ func (p *Parser) indexObjects() error {
 				return err
 			}
 
+			// Move children of placeholder parent into actual parent, in case this
+			// was a non-external delta reference.
+			if placeholder, ok := p.oiByHash[sha1]; ok {
+				ota.Children = placeholder.Children
+				for _, c := range ota.Children {
+					c.Parent = ota
+				}
+			}
+
 			ota.SHA1 = sha1
 			p.oiByHash[ota.SHA1] = ota
 		}
@@ -264,7 +275,9 @@ func (p *Parser) indexObjects() error {
 }
 
 func (p *Parser) resolveDeltas() error {
-	buf := &bytes.Buffer{}
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
+
 	for _, obj := range p.oi {
 		buf.Reset()
 		err := p.get(obj, buf)
@@ -283,9 +296,10 @@ func (p *Parser) resolveDeltas() error {
 
 		if !obj.IsDelta() && len(obj.Children) > 0 {
 			for _, child := range obj.Children {
-				if err := p.resolveObject(stdioutil.Discard, child, content); err != nil {
+				if err := p.resolveObject(io.Discard, child, content); err != nil {
 					return err
 				}
+				p.resolveExternalRef(child)
 			}
 
 			// Remove the delta from the cache.
@@ -298,6 +312,16 @@ func (p *Parser) resolveDeltas() error {
 	return nil
 }
 
+func (p *Parser) resolveExternalRef(o *objectInfo) {
+	if ref, ok := p.oiByHash[o.SHA1]; ok && ref.ExternalRef {
+		p.oiByHash[o.SHA1] = o
+		o.Children = ref.Children
+		for _, c := range o.Children {
+			c.Parent = o
+		}
+	}
+}
+
 func (p *Parser) get(o *objectInfo, buf *bytes.Buffer) (err error) {
 	if !o.ExternalRef { // skip cache check for placeholder parents
 		b, ok := p.cache.Get(o.Offset)
@@ -335,9 +359,8 @@ func (p *Parser) get(o *objectInfo, buf *bytes.Buffer) (err error) {
 	}
 
 	if o.DiskType.IsDelta() {
-		b := bufPool.Get().(*bytes.Buffer)
-		defer bufPool.Put(b)
-		b.Reset()
+		b := sync.GetBytesBuffer()
+		defer sync.PutBytesBuffer(b)
 		err := p.get(o.Parent, b)
 		if err != nil {
 			return err
@@ -371,9 +394,8 @@ func (p *Parser) resolveObject(
 	if !o.DiskType.IsDelta() {
 		return nil
 	}
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
-	buf.Reset()
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
 	err := p.readData(buf, o)
 	if err != nil {
 		return err
diff --git a/plumbing/format/packfile/parser_test.go b/plumbing/format/packfile/parser_test.go
index b0b4af8..b8d080f 100644
--- a/plumbing/format/packfile/parser_test.go
+++ b/plumbing/format/packfile/parser_test.go
@@ -10,8 +10,10 @@ import (
 	fixtures "github.com/go-git/go-git-fixtures/v4"
 	"github.com/go-git/go-git/v5"
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/cache"
 	"github.com/go-git/go-git/v5/plumbing/format/packfile"
 	"github.com/go-git/go-git/v5/plumbing/storer"
+	"github.com/go-git/go-git/v5/storage/filesystem"
 	. "gopkg.in/check.v1"
 )
 
@@ -132,6 +134,32 @@ func (s *ParserSuite) TestThinPack(c *C) {
 
 }
 
+func (s *ParserSuite) TestResolveExternalRefsInThinPack(c *C) {
+	extRefsThinPack := fixtures.ByTag("codecommit").One()
+
+	scanner := packfile.NewScanner(extRefsThinPack.Packfile())
+
+	obs := new(testObserver)
+	parser, err := packfile.NewParser(scanner, obs)
+	c.Assert(err, IsNil)
+
+	_, err = parser.Parse()
+	c.Assert(err, IsNil)
+}
+
+func (s *ParserSuite) TestResolveExternalRefs(c *C) {
+	extRefsThinPack := fixtures.ByTag("delta-before-base").One()
+
+	scanner := packfile.NewScanner(extRefsThinPack.Packfile())
+
+	obs := new(testObserver)
+	parser, err := packfile.NewParser(scanner, obs)
+	c.Assert(err, IsNil)
+
+	_, err = parser.Parse()
+	c.Assert(err, IsNil)
+}
+
 type observerObject struct {
 	hash   string
 	otype  plumbing.ObjectType
@@ -235,3 +263,29 @@ func BenchmarkParseBasic(b *testing.B) {
 		}
 	}
 }
+
+func BenchmarkParser(b *testing.B) {
+	f := fixtures.Basic().One()
+	defer fixtures.Clean()
+
+	b.ResetTimer()
+	for n := 0; n < b.N; n++ {
+		b.StopTimer()
+		scanner := packfile.NewScanner(f.Packfile())
+		fs := osfs.New(os.TempDir())
+		storage := filesystem.NewStorage(fs, cache.NewObjectLRUDefault())
+
+		parser, err := packfile.NewParserWithStorage(scanner, storage)
+		if err != nil {
+			b.Error(err)
+		}
+
+		b.StartTimer()
+		_, err = parser.Parse()
+
+		b.StopTimer()
+		if err != nil {
+			b.Error(err)
+		}
+	}
+}
diff --git a/plumbing/format/packfile/patch_delta.go b/plumbing/format/packfile/patch_delta.go
index 17da11e..f00562d 100644
--- a/plumbing/format/packfile/patch_delta.go
+++ b/plumbing/format/packfile/patch_delta.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/utils/ioutil"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 // See https://github.com/git/git/blob/49fa3dc76179e04b0833542fa52d0f287a4955ac/delta.h
@@ -34,18 +35,16 @@ func ApplyDelta(target, base plumbing.EncodedObject, delta []byte) (err error) {
 
 	defer ioutil.CheckClose(w, &err)
 
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
-	buf.Reset()
+	buf := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(buf)
 	_, err = buf.ReadFrom(r)
 	if err != nil {
 		return err
 	}
 	src := buf.Bytes()
 
-	dst := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(dst)
-	dst.Reset()
+	dst := sync.GetBytesBuffer()
+	defer sync.PutBytesBuffer(dst)
 	err = patchDelta(dst, src, delta)
 	if err != nil {
 		return err
@@ -53,9 +52,9 @@ func ApplyDelta(target, base plumbing.EncodedObject, delta []byte) (err error) {
 
 	target.SetSize(int64(dst.Len()))
 
-	b := byteSlicePool.Get().([]byte)
-	_, err = io.CopyBuffer(w, dst, b)
-	byteSlicePool.Put(b)
+	b := sync.GetByteSlice()
+	_, err = io.CopyBuffer(w, dst, *b)
+	sync.PutByteSlice(b)
 	return err
 }
 
diff --git a/plumbing/format/packfile/scanner.go b/plumbing/format/packfile/scanner.go
index 5d9e8fb..730343e 100644
--- a/plumbing/format/packfile/scanner.go
+++ b/plumbing/format/packfile/scanner.go
@@ -3,17 +3,15 @@ package packfile
 import (
 	"bufio"
 	"bytes"
-	"compress/zlib"
 	"fmt"
 	"hash"
 	"hash/crc32"
 	"io"
-	stdioutil "io/ioutil"
-	"sync"
 
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/utils/binary"
 	"github.com/go-git/go-git/v5/utils/ioutil"
+	"github.com/go-git/go-git/v5/utils/sync"
 )
 
 var (
@@ -114,7 +112,7 @@ func (s *Scanner) Header() (version, objects uint32, err error) {
 	return
 }
 
-// readSignature reads an returns the signature field in the packfile.
+// readSignature reads a returns the signature field in the packfile.
 func (s *Scanner) readSignature() ([]byte, error) {
 	var sig = make([]byte, 4)
 	if _, err := io.ReadFull(s.r, sig); err != nil {
@@ -243,7 +241,7 @@ func (s *Scanner) discardObjectIfNeeded() error {
 	}
 
 	h := s.pendingObject
-	n, _, err := s.NextObject(stdioutil.Discard)
+	n, _, err := s.NextObject(io.Discard)
 	if err != nil {
 		return err
 	}
@@ -323,14 +321,14 @@ func (s *Scanner) NextObject(w io.Writer) (written int64, crc32 uint32, err erro
 // ReadObject returns a reader for the object content and an error
 func (s *Scanner) ReadObject() (io.ReadCloser, error) {
 	s.pendingObject = nil
-	zr := zlibReaderPool.Get().(io.ReadCloser)
+	zr, err := sync.GetZlibReader(s.r)
 
-	if err := zr.(zlib.Resetter).Reset(s.r, nil); err != nil {
+	if err != nil {
 		return nil, fmt.Errorf("zlib reset error: %s", err)
 	}
 
-	return ioutil.NewReadCloserWithCloser(zr, func() error {
-		zlibReaderPool.Put(zr)
+	return ioutil.NewReadCloserWithCloser(zr.Reader, func() error {
+		sync.PutZlibReader(zr)
 		return nil
 	}), nil
 }
@@ -338,26 +336,20 @@ func (s *Scanner) ReadObject() (io.ReadCloser, error) {
 // ReadRegularObject reads and write a non-deltified object
 // from it zlib stream in an object entry in the packfile.
 func (s *Scanner) copyObject(w io.Writer) (n int64, err error) {
-	zr := zlibReaderPool.Get().(io.ReadCloser)
-	defer zlibReaderPool.Put(zr)
+	zr, err := sync.GetZlibReader(s.r)
+	defer sync.PutZlibReader(zr)
 
-	if err = zr.(zlib.Resetter).Reset(s.r, nil); err != nil {
+	if err != nil {
 		return 0, fmt.Errorf("zlib reset error: %s", err)
 	}
 
-	defer ioutil.CheckClose(zr, &err)
-	buf := byteSlicePool.Get().([]byte)
-	n, err = io.CopyBuffer(w, zr, buf)
-	byteSlicePool.Put(buf)
+	defer ioutil.CheckClose(zr.Reader, &err)
+	buf := sync.GetByteSlice()
+	n, err = io.CopyBuffer(w, zr.Reader, *buf)
+	sync.PutByteSlice(buf)
 	return
 }
 
-var byteSlicePool = sync.Pool{
-	New: func() interface{} {
-		return make([]byte, 32*1024)
-	},
-}
-
 // SeekFromStart sets a new offset from start, returns the old position before
 // the change.
 func (s *Scanner) SeekFromStart(offset int64) (previous int64, err error) {
@@ -387,9 +379,10 @@ func (s *Scanner) Checksum() (plumbing.Hash, error) {
 
 // Close reads the reader until io.EOF
 func (s *Scanner) Close() error {
-	buf := byteSlicePool.Get().([]byte)
-	_, err := io.CopyBuffer(stdioutil.Discard, s.r, buf)
-	byteSlicePool.Put(buf)
+	buf := sync.GetByteSlice()
+	_, err := io.CopyBuffer(io.Discard, s.r, *buf)
+	sync.PutByteSlice(buf)
+
 	return err
 }
 
@@ -399,13 +392,13 @@ func (s *Scanner) Flush() error {
 }
 
 // scannerReader has the following characteristics:
-// - Provides an io.SeekReader impl for bufio.Reader, when the underlying
-//   reader supports it.
-// - Keeps track of the current read position, for when the underlying reader
-//   isn't an io.SeekReader, but we still want to know the current offset.
-// - Writes to the hash writer what it reads, with the aid of a smaller buffer.
-//   The buffer helps avoid a performance penality for performing small writes
-//   to the crc32 hash writer.
+//   - Provides an io.SeekReader impl for bufio.Reader, when the underlying
+//     reader supports it.
+//   - Keeps track of the current read position, for when the underlying reader
+//     isn't an io.SeekReader, but we still want to know the current offset.
+//   - Writes to the hash writer what it reads, with the aid of a smaller buffer.
+//     The buffer helps avoid a performance penalty for performing small writes
+//     to the crc32 hash writer.
 type scannerReader struct {
 	reader io.Reader
 	crc    io.Writer
diff --git a/plumbing/format/packfile/scanner_test.go b/plumbing/format/packfile/scanner_test.go
index 892a27c..9dcc359 100644
--- a/plumbing/format/packfile/scanner_test.go
+++ b/plumbing/format/packfile/scanner_test.go
@@ -6,6 +6,7 @@ import (
 
 	fixtures "github.com/go-git/go-git-fixtures/v4"
 	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/hash"
 
 	. "gopkg.in/check.v1"
 )
@@ -71,7 +72,7 @@ func (s *ScannerSuite) testNextObjectHeader(c *C, tag string,
 
 	n, err := p.Checksum()
 	c.Assert(err, IsNil)
-	c.Assert(n, HasLen, 20)
+	c.Assert(n, HasLen, hash.Size)
 }
 
 func (s *ScannerSuite) TestNextObjectHeaderWithOutReadObject(c *C) {