accounting: enable accounting without passing through the stream #2252

This is in preparation for multithreaded downloads

fs/accounting/accounting.go

@@ -154,21 +154,23 @@ func (acc *Account) averageLoop() {
 	}
 }
 
-// read bytes from the io.Reader passed in and account them
+// Check the read is valid
-func (acc *Account) read(in io.Reader, p []byte) (n int, err error) {
+func (acc *Account) checkRead() (err error) {
 	acc.statmu.Lock()
 	if acc.max >= 0 && Stats.GetBytes() >= acc.max {
 		acc.statmu.Unlock()
-		return 0, ErrorMaxTransferLimitReached
+		return ErrorMaxTransferLimitReached
 	}
 	// Set start time.
 	if acc.start.IsZero() {
 		acc.start = time.Now()
 	}
 	acc.statmu.Unlock()
+	return nil
+}
 
-	n, err = in.Read(p)
+// Account the read and limit bandwidth
-
+func (acc *Account) accountRead(n int) {
 	// Update Stats
 	acc.statmu.Lock()
 	acc.lpBytes += n
@@ -178,7 +180,16 @@ func (acc *Account) read(in io.Reader, p []byte) (n int, err error) {
 	Stats.Bytes(int64(n))
 
 	limitBandwidth(n)
-	return
+}
+
+// read bytes from the io.Reader passed in and account them
+func (acc *Account) read(in io.Reader, p []byte) (n int, err error) {
+	err = acc.checkRead()
+	if err == nil {
+		n, err = in.Read(p)
+		acc.accountRead(n)
+	}
+	return n, err
 }
 
 // Read bytes from the object - see io.Reader
@@ -188,6 +199,17 @@ func (acc *Account) Read(p []byte) (n int, err error) {
 	return acc.read(acc.in, p)
 }
 
+// AccountRead account having read n bytes
+func (acc *Account) AccountRead(n int) (err error) {
+	acc.mu.Lock()
+	defer acc.mu.Unlock()
+	err = acc.checkRead()
+	if err == nil {
+		acc.accountRead(n)
+	}
+	return err
+}
+
 // Close the object
 func (acc *Account) Close() error {
 	acc.mu.Lock()
@@ -198,6 +220,9 @@ func (acc *Account) Close() error {
 	acc.closed = true
 	close(acc.exit)
 	Stats.inProgress.clear(acc.name)
+	if acc.close == nil {
+		return nil
+	}
 	return acc.close.Close()
 }