Fix data race in eestream (#377)

pkg/eestream/encode.go

@@ -201,19 +201,25 @@ func (er *encodedReader) fillBuffer() {
 // targeted reader buffer
 func (er *encodedReader) copyData(num int, copier <-chan block) {
 	// close the respective buffer channel when this goroutine exits
-	defer func() {
-		if er.eps[num].ch != nil {
-			close(er.eps[num].ch)
-		}
-	}()
+	defer er.closeReaderChannel(num)
 	// process the channel until closed
 	for b := range copier {
 		er.addToReader(b)
 	}
 }
 
+func (er *encodedReader) closeReaderChannel(num int) {
+	// use mutex to avoid data race with checkSlowChannel
+	er.mux.Lock()
+	defer er.mux.Unlock()
+	if !er.eps[num].closed {
+		er.eps[num].closed = true
+		close(er.eps[num].ch)
+	}
+}
+
 func (er *encodedReader) addToReader(b block) {
-	if er.eps[b.i].ch == nil {
+	if er.eps[b.i].closed {
 		// this channel is already closed for slowness - skip it
 		return
 	}
@@ -222,6 +228,7 @@ func (er *encodedReader) addToReader(b block) {
 		timer := time.NewTimer(50 * time.Millisecond)
 		defer timer.Stop()
 		// add the encoded data to the respective reader buffer channel
+
 		select {
 		case er.eps[b.i].ch <- b:
 			return
@@ -241,7 +248,7 @@ func (er *encodedReader) checkSlowChannel(num int) (closed bool) {
 	// check how many buffer channels are already empty
 	ec := 0
 	for i := range er.eps {
-		if er.eps[i].ch != nil && len(er.eps[i].ch) == 0 {
+		if !er.eps[i].closed && len(er.eps[i].ch) == 0 {
 			ec++
 		}
 	}
@@ -250,8 +257,8 @@ func (er *encodedReader) checkSlowChannel(num int) (closed bool) {
 	// canceled
 	closed = ec >= er.rs.MinimumThreshold()
 	if closed {
+		er.eps[num].closed = true
 		close(er.eps[num].ch)
-		er.eps[num].ch = nil
 		er.eps[num].cancel()
 	}
 	return closed
@@ -278,6 +285,7 @@ type encodedPiece struct {
 	cancel context.CancelFunc
 	er     *encodedReader
 	ch     chan block
+	closed bool
 	outbuf []byte
 	err    error
 }