S3: fix quota update after an upload error

S3 uploads are atomic, if the upload fails we have no partial file so we
have to update the user quota only if the upload succeed

sftpd/transfer.go

@@ -44,6 +44,7 @@ type Transfer struct {
 	isFinished     bool
 	minWriteOffset int64
 	expectedSize   int64
+	initialSize    int64
 	lock           *sync.Mutex
 }
 
@@ -163,9 +164,7 @@ func (t *Transfer) Close() error {
 	}
 	metrics.TransferCompleted(t.bytesSent, t.bytesReceived, t.transferType, t.transferError)
 	removeTransfer(t)
-	if t.transferType == transferUpload && (numFiles != 0 || t.bytesReceived > 0) {
-		dataprovider.UpdateUserQuota(dataProvider, t.user, numFiles, t.bytesReceived, false)
-	}
+	t.updateQuota(numFiles)
 	return err
 }
 
@@ -181,6 +180,18 @@ func (t *Transfer) closeIO() error {
 	return err
 }
 
+func (t *Transfer) updateQuota(numFiles int) bool {
+	// S3 uploads are atomic, if there is an error nothing is uploaded
+	if t.file == nil && t.transferError != nil {
+		return false
+	}
+	if t.transferType == transferUpload && (numFiles != 0 || t.bytesReceived > 0) {
+		dataprovider.UpdateUserQuota(dataProvider, t.user, numFiles, t.bytesReceived-t.initialSize, false)
+		return true
+	}
+	return false
+}
+
 func (t *Transfer) checkDownloadSize() {
 	if t.transferType == transferDownload && t.transferError == nil && t.bytesSent < t.expectedSize {
 		t.transferError = fmt.Errorf("incomplete download: %v/%v bytes transferred", t.bytesSent, t.expectedSize)