bugfix: fix dfget panic when link error between output file and tmp f…

…ile.

Signed-off-by: zhouchencheng <zhouchencheng@bilibili.com>

dfget/core/downloader/p2p_downloader/client_stream_writer.go

@@ -164,7 +164,7 @@ func (csw *ClientStreamWriter) writePieceToPipe(p *Piece) error {
 			break
 		}
 
-		_, err := io.Copy(csw.pipeWriter, p.RawContent(csw.cdnSource == apiTypes.CdnSourceSource))
+		_, err := p.WriteTo(csw.pipeWriter, csw.cdnSource == apiTypes.CdnSourceSource)
 		if err != nil {
 			return err
 		}

dfget/core/downloader/p2p_downloader/client_writer.go

@@ -18,7 +18,6 @@ package downloader
 
 import (
 	"context"
-	"io"
 	"math/rand"
 	"os"
 	"time"
@@ -220,6 +219,7 @@ func (cw *ClientWriter) write(piece *Piece) error {
 	}
 
 	if cw.acrossWrite {
+		piece.IncWriter()
 		cw.targetQueue.Put(piece)
 	}
 
@@ -245,7 +245,7 @@ func writePieceToFile(piece *Piece, file *os.File, cdnSource apiTypes.CdnSource)
 	}
 
 	writer := pool.AcquireWriter(file)
-	_, err := io.Copy(writer, piece.RawContent(noWrapper))
+	_, err := piece.WriteTo(writer, noWrapper)
 	pool.ReleaseWriter(writer)
 	writer = nil
 	return err

dfget/core/downloader/p2p_downloader/piece.go

@@ -19,6 +19,9 @@ package downloader
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
+	"io"
+	"sync/atomic"
 
 	apiTypes "github.com/dragonflyoss/Dragonfly/apis/types"
 	"github.com/dragonflyoss/Dragonfly/pkg/constants"
@@ -57,20 +60,32 @@ type Piece struct {
 	// length the length of the content.
 	length int64
 
-	// autoReset automatically reset content after reading.
-	autoReset bool
+	// writerNum record the writer number which will write this piece.
+	writerNum int32
+}
+
+// WriteTo writes piece raw data in content buffer to w.
+// If the piece has wrapper, the piece content will remove the head and tail before writing.
+func (p *Piece) WriteTo(w io.Writer, noWrapper bool) (n int64, err error) {
+	defer p.TryResetContent()
+
+	content := p.RawContent(noWrapper)
+	if content != nil {
+		return content.WriteTo(w)
+	}
+	return 0, fmt.Errorf("piece content length less than 5 bytes")
+}
+
+// IncWriter increase a writer for the piece.
+func (p *Piece) IncWriter() {
+	atomic.AddInt32(&p.writerNum, 1)
 }
 
 // RawContent returns raw contents,
 // If the piece has wrapper, and the piece content will remove the head and tail.
 func (p *Piece) RawContent(noWrapper bool) *bytes.Buffer {
 	contents := p.Content.Bytes()
 	length := len(contents)
-	defer func() {
-		if p.autoReset {
-			p.ResetContent()
-		}
-	}()
 
 	if noWrapper {
 		return bytes.NewBuffer(contents[:])
@@ -97,7 +112,11 @@ func (p *Piece) String() string {
 }
 
 // ResetContent reset contents and returns it back to buffer pool.
-func (p *Piece) ResetContent() {
+func (p *Piece) TryResetContent() {
+	if atomic.AddInt32(&p.writerNum, -1) > 0 {
+		return
+	}
+
 	if p.Content == nil {
 		return
 	}
@@ -118,7 +137,7 @@ func NewPiece(taskID, node, dstCid, pieceRange string, result, status int, cdnSo
 		Result:    result,
 		Status:    status,
 		Content:   nil,
-		autoReset: true,
+		writerNum: 1,
 	}
 }
 
@@ -130,7 +149,7 @@ func NewPieceSimple(taskID string, node string, status int, cdnSource apiTypes.C
 		Status:    status,
 		Result:    constants.ResultInvalid,
 		Content:   nil,
-		autoReset: true,
+		writerNum: 1,
 	}
 }
 
@@ -146,6 +165,6 @@ func NewPieceContent(taskID, node, dstCid, pieceRange string,
 		Status:    status,
 		Content:   contents,
 		length:    int64(contents.Len()),
-		autoReset: true,
+		writerNum: 1,
 	}
 }

dfget/core/downloader/p2p_downloader/piece_test.go

@@ -48,6 +48,37 @@ func (s *PieceTestSuite) TestRawContent(c *check.C) {
 	}
 }
 
+func (s *PieceTestSuite) TestTryResetContent(c *check.C) {
+	piece := &Piece{writerNum: 2, Content: pool.NewBufferString("")}
+	piece.TryResetContent()
+	c.Assert(piece.writerNum, check.Equals, int32(1))
+	c.Assert(piece.Content, check.NotNil)
+
+	piece.TryResetContent()
+	c.Assert(piece.writerNum, check.Equals, int32(0))
+	c.Assert(piece.Content, check.IsNil)
+}
+
+func (s *PieceTestSuite) TestWriteTo(c *check.C) {
+	var cases = []struct {
+		piece     *Piece
+		noWrapper bool
+		expected  *bytes.Buffer
+		hasErr    bool
+	}{
+		{piece: &Piece{Content: pool.NewBufferString("")}, noWrapper: false, expected: &bytes.Buffer{}, hasErr: true},
+		{piece: &Piece{Content: pool.NewBufferString("000010")}, noWrapper: false, expected: bytes.NewBufferString("1"), hasErr: false},
+		{piece: &Piece{Content: pool.NewBufferString("000020")}, noWrapper: true, expected: bytes.NewBufferString("000020"), hasErr: false},
+	}
+
+	for _, v := range cases {
+		result := &bytes.Buffer{}
+		_, err := v.piece.WriteTo(result, v.noWrapper)
+		c.Assert(err != nil, check.Equals, v.hasErr)
+		c.Assert(result, check.DeepEquals, v.expected)
+	}
+}
+
 func (s *PieceTestSuite) TestString(c *check.C) {
 	var cases = []struct {
 		piece    *Piece