Make opening a torrent in storage an explicit method

This is storage types where opening can fail, like mmap

client.go

@@ -1949,9 +1949,9 @@ func (cl *Client) AddTorrentSpec(spec *TorrentSpec) (T Torrent, new bool, err er
 		if spec.ChunkSize != 0 {
 			t.chunkSize = pp.Integer(spec.ChunkSize)
 		}
-		t.storage = spec.Storage
-		if t.storage == nil {
-			t.storage = cl.defaultStorage
+		t.storageOpener = spec.Storage
+		if t.storageOpener == nil {
+			t.storageOpener = cl.defaultStorage
 		}
 	}
 	if spec.DisplayName != "" {

client_test.go

@@ -92,7 +92,7 @@ func TestTorrentInitialState(t *testing.T) {
 		return
 	}())
 	tor.chunkSize = 2
-	tor.storage = storage.NewFile(dir)
+	tor.storageOpener = storage.NewFile(dir)
 	// Needed to lock for asynchronous piece verification.
 	tor.cl = new(Client)
 	err := tor.setMetadata(&mi.Info.Info, mi.Info.Bytes)
@@ -464,6 +464,14 @@ func TestMergingTrackersByAddingSpecs(t *testing.T) {
 
 type badStorage struct{}
 
+func (me badStorage) OpenTorrent(*metainfo.InfoEx) (storage.Torrent, error) {
+	return me, nil
+}
+
+func (me badStorage) Close() error {
+	return nil
+}
+
 func (me badStorage) Piece(p metainfo.Piece) storage.Piece {
 	return badStoragePiece{p}
 }

mmap_span/mmap_span.go

@@ -2,6 +2,7 @@ package mmap_span
 
 import (
 	"io"
+	"log"
 
 	"github.com/edsrzf/mmap-go"
 )
@@ -22,10 +23,14 @@ func (me *MMapSpan) Append(mmap mmap.MMap) {
 	me.span = append(me.span, segment{&mmap})
 }
 
-func (me MMapSpan) Close() {
+func (me MMapSpan) Close() error {
 	for _, mMap := range me.span {
-		mMap.(segment).Unmap()
+		err := mMap.(segment).Unmap()
+		if err != nil {
+			log.Print(err)
+		}
 	}
+	return nil
 }
 
 func (me MMapSpan) Size() (ret int64) {

storage/file.go

@@ -21,6 +21,14 @@ func NewFile(baseDir string) I {
 	}
 }
 
+func (me *fileStorage) OpenTorrent(info *metainfo.InfoEx) (Torrent, error) {
+	return fileTorrentStorage{me}, nil
+}
+
+type fileTorrentStorage struct {
+	*fileStorage
+}
+
 func (me *fileStorage) Piece(p metainfo.Piece) Piece {
 	_io := &fileStorageTorrent{
 		p.Info,
@@ -34,6 +42,10 @@ func (me *fileStorage) Piece(p metainfo.Piece) Piece {
 	}
 }
 
+func (me *fileStorage) Close() error {
+	return nil
+}
+
 type fileStoragePiece struct {
 	*fileStorage
 	p metainfo.Piece

storage/file_test.go

@@ -19,7 +19,7 @@ func TestShortFile(t *testing.T) {
 	td, err := ioutil.TempDir("", "")
 	require.NoError(t, err)
 	defer os.RemoveAll(td)
-	data := NewFile(td)
+	s := NewFile(td)
 	info := &metainfo.InfoEx{
 		Info: metainfo.Info{
 			Name:        "a",
@@ -27,12 +27,14 @@ func TestShortFile(t *testing.T) {
 			PieceLength: missinggo.MiB,
 		},
 	}
+	ts, err := s.OpenTorrent(info)
+	assert.NoError(t, err)
 	f, err := os.Create(filepath.Join(td, "a"))
 	err = f.Truncate(1)
 	f.Close()
 	var buf bytes.Buffer
 	p := info.Piece(0)
-	n, err := io.Copy(&buf, io.NewSectionReader(data.Piece(p), 0, p.Length()))
+	n, err := io.Copy(&buf, io.NewSectionReader(ts.Piece(p), 0, p.Length()))
 	assert.EqualValues(t, 1, n)
 	assert.Equal(t, io.ErrUnexpectedEOF, err)
 }

storage/interface.go

@@ -6,11 +6,18 @@ import (
 	"github.com/anacrolix/torrent/metainfo"
 )
 
-// Represents data storage for a Torrent.
+// Represents data storage for an unspecified torrent.
 type I interface {
-	Piece(metainfo.Piece) Piece
+	OpenTorrent(info *metainfo.InfoEx) (Torrent, error)
 }
 
+// Data storage bound to a torrent.
+type Torrent interface {
+	Piece(metainfo.Piece) Piece
+	Close() error
+}
+
+// Interacts with torrent piece data.
 type Piece interface {
 	// Should return io.EOF only at end of torrent. Short reads due to missing
 	// data should return io.ErrUnexpectedEOF.
@@ -23,20 +30,3 @@ type Piece interface {
 	// Returns true if the piece is complete.
 	GetIsComplete() bool
 }
-
-// type PieceStorage interface {
-// 	ReadAt(metainfo.Piece, []byte, int64) (int, error)
-// 	WriteAt(metainfo.Piece, []byte, int64) (int, error)
-// 	MarkComplete(metainfo.Piece) error
-// 	GetIsComplete(metainfo.Piece) bool
-// }
-
-// type wrappedPieceStorage struct {
-// 	ps PieceStorage
-// }
-
-// func WrapPieceStorage(ps PieceStorage) I {
-// 	return wrappedPieceStorage{ps}
-// }
-
-// func (me wrappedPieceStorage) Piece(metainfo.Piece)

storage/mmap.go

@@ -14,9 +14,7 @@ import (
 )
 
 type mmapStorage struct {
-	baseDir   string
-	spans     map[metainfo.InfoHash]mmap_span.MMapSpan
-	completed map[metainfo.InfoHash]bool
+	baseDir string
 }
 
 func NewMMap(baseDir string) I {
@@ -25,36 +23,35 @@ func NewMMap(baseDir string) I {
 	}
 }
 
-func (me *mmapStorage) lazySpan(info *metainfo.InfoEx) error {
-	if me.spans == nil {
-		me.spans = make(map[metainfo.InfoHash]mmap_span.MMapSpan)
-	}
-	if _, ok := me.spans[*info.Hash]; ok {
-		return nil
-	}
+func (me *mmapStorage) OpenTorrent(info *metainfo.InfoEx) (t Torrent, err error) {
 	span, err := MMapTorrent(&info.Info, me.baseDir)
-	if err != nil {
-		return err
+	t = &mmapTorrentStorage{
+		span: span,
 	}
-	me.spans[*info.Hash] = span
-	return nil
+	return
 }
 
-func (me *mmapStorage) Piece(p metainfo.Piece) Piece {
-	err := me.lazySpan(p.Info)
-	if err != nil {
-		panic(err)
-	}
+type mmapTorrentStorage struct {
+	span      mmap_span.MMapSpan
+	completed map[metainfo.InfoHash]bool
+}
+
+func (me *mmapTorrentStorage) Piece(p metainfo.Piece) Piece {
 	return mmapStoragePiece{
 		storage:  me,
 		p:        p,
-		ReaderAt: io.NewSectionReader(me.spans[*p.Info.Hash], p.Offset(), p.Length()),
-		WriterAt: missinggo.NewSectionWriter(me.spans[*p.Info.Hash], p.Offset(), p.Length()),
+		ReaderAt: io.NewSectionReader(me.span, p.Offset(), p.Length()),
+		WriterAt: missinggo.NewSectionWriter(me.span, p.Offset(), p.Length()),
 	}
 }
 
+func (me *mmapTorrentStorage) Close() error {
+	me.span.Close()
+	return nil
+}
+
 type mmapStoragePiece struct {
-	storage *mmapStorage
+	storage *mmapTorrentStorage
 	p       metainfo.Piece
 	io.ReaderAt
 	io.WriterAt

torrent.go

@@ -54,7 +54,8 @@ type torrent struct {
 	// get this from the info dict.
 	length int64
 
-	storage storage.I
+	storageOpener storage.I
+	storage       storage.Torrent
 
 	// The info dict. Nil if we don't have it (yet).
 	Info *metainfo.InfoEx
@@ -230,6 +231,10 @@ func (t *torrent) setMetadata(md *metainfo.Info, infoBytes []byte) (err error) {
 		Bytes: infoBytes,
 		Hash:  &t.InfoHash,
 	}
+	t.storage, err = t.storageOpener.OpenTorrent(t.Info)
+	if err != nil {
+		return
+	}
 	t.length = 0
 	for _, f := range t.Info.UpvertedFiles() {
 		t.length += f.Length