accounting: fix file handle leak on errors - fixes #3547

In 53a1a0e3ef we introduced a problem where if there was an
error on the file being transferred then the file was re-opened and
the old one wasn't closed.

This was partially fixed in bfbddab46b however this didn't
address the case of the old file being closed.

This is now fixed by
- marking the file as open again in UpdateReader
- moving the stopping the accounting machinery to a new method Done

fs/accounting/accounting.go

@@ -124,6 +124,7 @@ func (acc *Account) UpdateReader(in io.ReadCloser) {
 	acc.in = in
 	acc.close = in
 	acc.origIn = in
+	acc.closed = false
 	if acc.withBuf {
 		acc.WithBuffer()
 	}
@@ -243,14 +244,20 @@ func (acc *Account) Close() error {
 		return nil
 	}
 	acc.closed = true
-	close(acc.exit)
-	acc.stats.inProgress.clear(acc.name)
 	if acc.close == nil {
 		return nil
 	}
 	return acc.close.Close()
 }
 
+// Done with accounting - must be called to free accounting goroutine
+func (acc *Account) Done() {
+	acc.mu.Lock()
+	defer acc.mu.Unlock()
+	close(acc.exit)
+	acc.stats.inProgress.clear(acc.name)
+}
+
 // progress returns bytes read as well as the size.
 // Size can be <= 0 if the size is unknown.
 func (acc *Account) progress() (bytes, size int64) {

fs/accounting/accounting_test.go

@@ -32,6 +32,8 @@ func TestNewAccountSizeName(t *testing.T) {
 	assert.Equal(t, acc, stats.inProgress.get("test"))
 	err := acc.Close()
 	assert.NoError(t, err)
+	assert.Equal(t, acc, stats.inProgress.get("test"))
+	acc.Done()
 	assert.Nil(t, stats.inProgress.get("test"))
 }
 
@@ -55,18 +57,31 @@ func TestAccountWithBuffer(t *testing.T) {
 }
 
 func TestAccountGetUpdateReader(t *testing.T) {
+	test := func(doClose bool) func(t *testing.T) {
+		return func(t *testing.T) {
 			in := ioutil.NopCloser(bytes.NewBuffer([]byte{1}))
 			stats := NewStats()
 			acc := newAccountSizeName(stats, in, 1, "test")
 
 			assert.Equal(t, in, acc.GetReader())
+			assert.Equal(t, acc, stats.inProgress.get("test"))
+
+			if doClose {
+				// close the account before swapping it out
+				require.NoError(t, acc.Close())
+			}
 
 			in2 := ioutil.NopCloser(bytes.NewBuffer([]byte{1}))
 			acc.UpdateReader(in2)
 
 			assert.Equal(t, in2, acc.GetReader())
+			assert.Equal(t, acc, stats.inProgress.get("test"))
 
 			assert.NoError(t, acc.Close())
+		}
+	}
+	t.Run("NoClose", test(false))
+	t.Run("Close", test(true))
 }
 
 func TestAccountRead(t *testing.T) {

fs/accounting/transfer.go

@@ -96,9 +96,12 @@ func (tr *Transfer) Done(err error) {
 	tr.mu.RUnlock()
 
 	if acc != nil {
+		// Close the file if it is still open
 		if err := acc.Close(); err != nil {
 			fs.LogLevelPrintf(fs.Config.StatsLogLevel, nil, "can't close account: %+v\n", err)
 		}
+		// Signal done with accounting
+		acc.Done()
 	}
 
 	tr.mu.Lock()