1 files changed, 284 insertions, 0 deletions
diff --git a/storage/filesystem/dotgit/writers.go b/storage/filesystem/dotgit/writers.go
new file mode 100644
index 0000000..93d2d8c
--- /dev/null
+++ b/storage/filesystem/dotgit/writers.go
@@ -0,0 +1,284 @@
+package dotgit
+
+import (
+	"fmt"
+	"io"
+	"sync/atomic"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/objfile"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
+
+	"gopkg.in/src-d/go-billy.v4"
+)
+
+// PackWriter is a io.Writer that generates the packfile index simultaneously,
+// a packfile.Decoder is used with a file reader to read the file being written
+// this operation is synchronized with the write operations.
+// The packfile is written in a temp file, when Close is called this file
+// 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)
+
+	fs       billy.Filesystem
+	fr, fw   billy.File
+	synced   *syncedReader
+	checksum plumbing.Hash
+	parser   *packfile.Parser
+	writer   *idxfile.Writer
+	result   chan error
+}
+
+func newPackWrite(fs billy.Filesystem) (*PackWriter, error) {
+	fw, err := fs.TempFile(fs.Join(objectsPath, packPath), "tmp_pack_")
+	if err != nil {
+		return nil, err
+	}
+
+	fr, err := fs.Open(fw.Name())
+	if err != nil {
+		return nil, err
+	}
+
+	writer := &PackWriter{
+		fs:     fs,
+		fw:     fw,
+		fr:     fr,
+		synced: newSyncedReader(fw, fr),
+		result: make(chan error),
+	}
+
+	go writer.buildIndex()
+	return writer, nil
+}
+
+func (w *PackWriter) buildIndex() {
+	s := packfile.NewScanner(w.synced)
+	w.writer = new(idxfile.Writer)
+	var err error
+	w.parser, err = packfile.NewParser(s, w.writer)
+	if err != nil {
+		w.result <- err
+		return
+	}
+
+	checksum, err := w.parser.Parse()
+	if err != nil {
+		w.result <- err
+		return
+	}
+
+	w.checksum = checksum
+	w.result <- err
+}
+
+// waitBuildIndex waits until buildIndex function finishes, this can terminate
+// with a packfile.ErrEmptyPackfile, this means that nothing was written so we
+// ignore the error
+func (w *PackWriter) waitBuildIndex() error {
+	err := <-w.result
+	if err == packfile.ErrEmptyPackfile {
+		return nil
+	}
+
+	return err
+}
+
+func (w *PackWriter) Write(p []byte) (int, error) {
+	return w.synced.Write(p)
+}
+
+// Close closes all the file descriptors and save the final packfile, if nothing
+// was written, the tempfiles are deleted without writing a packfile.
+func (w *PackWriter) Close() error {
+	defer func() {
+		if w.Notify != nil && w.writer != nil && w.writer.Finished() {
+			w.Notify(w.checksum, w.writer)
+		}
+
+		close(w.result)
+	}()
+
+	if err := w.synced.Close(); err != nil {
+		return err
+	}
+
+	if err := w.waitBuildIndex(); err != nil {
+		return err
+	}
+
+	if err := w.fr.Close(); err != nil {
+		return err
+	}
+
+	if err := w.fw.Close(); err != nil {
+		return err
+	}
+
+	if w.writer == nil || !w.writer.Finished() {
+		return w.clean()
+	}
+
+	return w.save()
+}
+
+func (w *PackWriter) clean() error {
+	return w.fs.Remove(w.fw.Name())
+}
+
+func (w *PackWriter) save() error {
+	base := w.fs.Join(objectsPath, packPath, fmt.Sprintf("pack-%s", w.checksum))
+	idx, err := w.fs.Create(fmt.Sprintf("%s.idx", base))
+	if err != nil {
+		return err
+	}
+
+	if err := w.encodeIdx(idx); err != nil {
+		return err
+	}
+
+	if err := idx.Close(); err != nil {
+		return err
+	}
+
+	return w.fs.Rename(w.fw.Name(), fmt.Sprintf("%s.pack", base))
+}
+
+func (w *PackWriter) encodeIdx(writer io.Writer) error {
+	idx, err := w.writer.Index()
+	if err != nil {
+		return err
+	}
+
+	e := idxfile.NewEncoder(writer)
+	_, err = e.Encode(idx)
+	return err
+}
+
+type syncedReader struct {
+	w io.Writer
+	r io.ReadSeeker
+
+	blocked, done uint32
+	written, read uint64
+	news          chan bool
+}
+
+func newSyncedReader(w io.Writer, r io.ReadSeeker) *syncedReader {
+	return &syncedReader{
+		w:    w,
+		r:    r,
+		news: make(chan bool),
+	}
+}
+
+func (s *syncedReader) Write(p []byte) (n int, err error) {
+	defer func() {
+		written := atomic.AddUint64(&s.written, uint64(n))
+		read := atomic.LoadUint64(&s.read)
+		if written > read {
+			s.wake()
+		}
+	}()
+
+	n, err = s.w.Write(p)
+	return
+}
+
+func (s *syncedReader) Read(p []byte) (n int, err error) {
+	defer func() { atomic.AddUint64(&s.read, uint64(n)) }()
+
+	for {
+		s.sleep()
+		n, err = s.r.Read(p)
+		if err == io.EOF && !s.isDone() && n == 0 {
+			continue
+		}
+
+		break
+	}
+
+	return
+}
+
+func (s *syncedReader) isDone() bool {
+	return atomic.LoadUint32(&s.done) == 1
+}
+
+func (s *syncedReader) isBlocked() bool {
+	return atomic.LoadUint32(&s.blocked) == 1
+}
+
+func (s *syncedReader) wake() {
+	if s.isBlocked() {
+		atomic.StoreUint32(&s.blocked, 0)
+		s.news <- true
+	}
+}
+
+func (s *syncedReader) sleep() {
+	read := atomic.LoadUint64(&s.read)
+	written := atomic.LoadUint64(&s.written)
+	if read >= written {
+		atomic.StoreUint32(&s.blocked, 1)
+		<-s.news
+	}
+
+}
+
+func (s *syncedReader) Seek(offset int64, whence int) (int64, error) {
+	if whence == io.SeekCurrent {
+		return s.r.Seek(offset, whence)
+	}
+
+	p, err := s.r.Seek(offset, whence)
+	atomic.StoreUint64(&s.read, uint64(p))
+
+	return p, err
+}
+
+func (s *syncedReader) Close() error {
+	atomic.StoreUint32(&s.done, 1)
+	close(s.news)
+	return nil
+}
+
+type ObjectWriter struct {
+	objfile.Writer
+	fs billy.Filesystem
+	f  billy.File
+}
+
+func newObjectWriter(fs billy.Filesystem) (*ObjectWriter, error) {
+	f, err := fs.TempFile(fs.Join(objectsPath, packPath), "tmp_obj_")
+	if err != nil {
+		return nil, err
+	}
+
+	return &ObjectWriter{
+		Writer: (*objfile.NewWriter(f)),
+		fs:     fs,
+		f:      f,
+	}, nil
+}
+
+func (w *ObjectWriter) Close() error {
+	if err := w.Writer.Close(); err != nil {
+		return err
+	}
+
+	if err := w.f.Close(); err != nil {
+		return err
+	}
+
+	return w.save()
+}
+
+func (w *ObjectWriter) save() error {
+	hash := w.Hash().String()
+	file := w.fs.Join(objectsPath, hash[0:2], hash[2:40])
+
+	return w.fs.Rename(w.f.Name(), file)
+}