fix: progress data races (#17)

Packfile writers are created and the index gets built in a separate
goroutine. A data race occurred when setting up the progress
collector. I plumbed the progress collector into the `newPackWrite`
funtion outright. That way, the call to `buildIndex` could take
it. Furthermore, using a mutex to serialize reporting for receiving
objects and resolving deltas.

plumbing/format/packfile/parser.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"io"
 	"io/ioutil"
+	"sync"
 
 	"github.com/goabstract/go-git/v5/plumbing"
 	"github.com/goabstract/go-git/v5/plumbing/cache"
@@ -55,6 +56,7 @@ type Parser struct {
 
 	ob []Observer
 
+	m                 sync.Mutex
 	ProgressCollector *progress.Collector
 	objectsSeen       uint32
 	deltasTotal       uint32
@@ -94,7 +96,18 @@ func NewParserWithStorage(
 	}, nil
 }
 
+// UseProgressCollector sets up the parser to use a *progress.Collector
+func (p *Parser) UseProgressCollector(c *progress.Collector) {
+	p.m.Lock()
+	defer p.m.Unlock()
+
+	p.ProgressCollector = c
+}
+
 func (p *Parser) writeDeltaProgress() {
+	p.m.Lock()
+	defer p.m.Unlock()
+
 	if p.ProgressCollector == nil {
 		return
 	}
@@ -103,6 +116,9 @@ func (p *Parser) writeDeltaProgress() {
 }
 
 func (p *Parser) writeObjectProgress() {
+	p.m.Lock()
+	defer p.m.Unlock()
+
 	if p.ProgressCollector == nil {
 		return
 	}

storage/filesystem/dotgit/dotgit.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/go-git/go-billy/v5/osfs"
 	"github.com/goabstract/go-git/v5/plumbing"
+	"github.com/goabstract/go-git/v5/plumbing/progress"
 	"github.com/goabstract/go-git/v5/storage"
 	"github.com/goabstract/go-git/v5/utils/ioutil"
 
@@ -193,9 +194,9 @@ func (d *DotGit) Shallow() (billy.File, error) {
 
 // NewObjectPack return a writer for a new packfile, it saves the packfile to
 // disk and also generates and save the index for the given packfile.
-func (d *DotGit) NewObjectPack() (*PackWriter, error) {
+func (d *DotGit) NewObjectPack(pc *progress.Collector) (*PackWriter, error) {
 	d.cleanPackList()
-	return newPackWrite(d.fs)
+	return newPackWrite(d.fs, pc)
 }
 
 // ObjectPacks returns the list of availables packfiles

storage/filesystem/dotgit/writers.go

@@ -21,8 +21,7 @@ import (
 // is renamed/moved (depends on the Filesystem implementation) to the final
 // location, if the PackWriter is not used, nothing is written
 type PackWriter struct {
-	Notify            func(plumbing.Hash, *idxfile.Writer)
-	ProgressCollector *progress.Collector
+	Notify func(plumbing.Hash, *idxfile.Writer)
 
 	fs       billy.Filesystem
 	fr, fw   billy.File
@@ -33,7 +32,7 @@ type PackWriter struct {
 	result   chan error
 }
 
-func newPackWrite(fs billy.Filesystem) (*PackWriter, error) {
+func newPackWrite(fs billy.Filesystem, pc *progress.Collector) (*PackWriter, error) {
 	fw, err := fs.TempFile(fs.Join(objectsPath, packPath), "tmp_pack_")
 	if err != nil {
 		return nil, err
@@ -52,21 +51,22 @@ func newPackWrite(fs billy.Filesystem) (*PackWriter, error) {
 		result: make(chan error),
 	}
 
-	go writer.buildIndex()
+	go writer.buildIndex(pc)
 	return writer, nil
 }
 
-func (w *PackWriter) buildIndex() {
+func (w *PackWriter) buildIndex(pc *progress.Collector) {
 	s := packfile.NewScanner(w.synced)
 	w.writer = new(idxfile.Writer)
 	var err error
 	w.parser, err = packfile.NewParser(s, w.writer)
-	w.parser.ProgressCollector = w.ProgressCollector
 	if err != nil {
 		w.result <- err
 		return
 	}
 
+	w.parser.UseProgressCollector(pc)
+
 	checksum, err := w.parser.Parse()
 	if err != nil {
 		w.result <- err

storage/filesystem/dotgit/writers_test.go

@@ -30,7 +30,7 @@ func (s *SuiteDotGit) TestNewObjectPack(c *C) {
 	fs := osfs.New(dir)
 	dot := New(fs)
 
-	w, err := dot.NewObjectPack()
+	w, err := dot.NewObjectPack(nil)
 	c.Assert(err, IsNil)
 
 	_, err = io.Copy(w, f.Packfile())
@@ -75,7 +75,7 @@ func (s *SuiteDotGit) TestNewObjectPackUnused(c *C) {
 	fs := osfs.New(dir)
 	dot := New(fs)
 
-	w, err := dot.NewObjectPack()
+	w, err := dot.NewObjectPack(nil)
 	c.Assert(err, IsNil)
 
 	c.Assert(w.Close(), IsNil)
@@ -146,7 +146,7 @@ func (s *SuiteDotGit) TestPackWriterUnusedNotify(c *C) {
 
 	fs := osfs.New(dir)
 
-	w, err := newPackWrite(fs)
+	w, err := newPackWrite(fs, nil)
 	c.Assert(err, IsNil)
 
 	w.Notify = func(h plumbing.Hash, idx *idxfile.Writer) {

storage/filesystem/object.go

@@ -99,13 +99,11 @@ func (s *ObjectStorage) packfileWriter(pc *progress.Collector) (io.WriteCloser,
 		return nil, err
 	}
 
-	w, err := s.dir.NewObjectPack()
+	w, err := s.dir.NewObjectPack(pc)
 	if err != nil {
 		return nil, err
 	}
 
-	w.ProgressCollector = pc
-
 	w.Notify = func(h plumbing.Hash, writer *idxfile.Writer) {
 		index, err := writer.Index()
 		if err == nil {