Refactor StartBackup to Support Custom Backup Handlers (#849)

* Refactor StartBackup to Support Custom Backup Handlers

* fix: TestStartBackupEndInGivenTime test failure

* Refactor StartBackupToFile to create backup directory before initiating backup

* fix: Add error handling for w.Close()

* style：Rename filename to binlogFilename for clarity in StartBackup

* docs: Simplify the comments of the StartBackup method

* refactor: Rename the StartBackup method to StartBackupWithHandler so that the StartBackup method retains its original behavior

replication/backup.go

@@ -14,6 +14,25 @@ import (
 // StartBackup: Like mysqlbinlog remote raw backup
 // Backup remote binlog from position (filename, offset) and write in backupDir
 func (b *BinlogSyncer) StartBackup(backupDir string, p Position, timeout time.Duration) error {
+	err := os.MkdirAll(backupDir, 0755)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	return b.StartBackupWithHandler(p, timeout, func(filename string) (io.WriteCloser, error) {
+		return os.OpenFile(path.Join(backupDir, filename), os.O_CREATE|os.O_WRONLY, 0644)
+	})
+}
+
+// StartBackupWithHandler starts the backup process for the binary log using the specified position and handler.
+// The process will continue until the timeout is reached or an error occurs.
+//
+// Parameters:
+//   - p: The starting position in the binlog from which to begin the backup.
+//   - timeout: The maximum duration to wait for new binlog events before stopping the backup process.
+//     If set to 0, a default very long timeout (30 days) is used instead.
+//   - handler: A function that takes a binlog filename and returns an WriteCloser for writing raw events to.
+func (b *BinlogSyncer) StartBackupWithHandler(p Position, timeout time.Duration,
+	handler func(binlogFilename string) (io.WriteCloser, error)) (retErr error) {
 	if timeout == 0 {
 		// a very long timeout here
 		timeout = 30 * 3600 * 24 * time.Second
@@ -22,10 +41,6 @@ func (b *BinlogSyncer) StartBackup(backupDir string, p Position, timeout time.Du
 	// Force use raw mode
 	b.parser.SetRawMode(true)
 
-	if err := os.MkdirAll(backupDir, 0755); err != nil {
-		return errors.Trace(err)
-	}
-
 	s, err := b.StartSync(p)
 	if err != nil {
 		return errors.Trace(err)
@@ -34,10 +49,14 @@ func (b *BinlogSyncer) StartBackup(backupDir string, p Position, timeout time.Du
 	var filename string
 	var offset uint32
 
-	var f *os.File
+	var w io.WriteCloser
 	defer func() {
-		if f != nil {
-			f.Close()
+		var closeErr error
+		if w != nil {
+			closeErr = w.Close()
+		}
+		if retErr == nil {
+			retErr = closeErr
 		}
 	}()
 
@@ -67,26 +86,29 @@ func (b *BinlogSyncer) StartBackup(backupDir string, p Position, timeout time.Du
 		} else if e.Header.EventType == FORMAT_DESCRIPTION_EVENT {
 			// FormateDescriptionEvent is the first event in binlog, we will close old one and create a new
 
-			if f != nil {
-				f.Close()
+			if w != nil {
+				if err = w.Close(); err != nil {
+					w = nil
+					return errors.Trace(err)
+				}
 			}
 
 			if len(filename) == 0 {
 				return errors.Errorf("empty binlog filename for FormateDescriptionEvent")
 			}
 
-			f, err = os.OpenFile(path.Join(backupDir, filename), os.O_CREATE|os.O_WRONLY, 0644)
+			w, err = handler(filename)
 			if err != nil {
 				return errors.Trace(err)
 			}
 
 			// write binlog header fe'bin'
-			if _, err = f.Write(BinLogFileHeader); err != nil {
+			if _, err = w.Write(BinLogFileHeader); err != nil {
 				return errors.Trace(err)
 			}
 		}
 
-		if n, err := f.Write(e.RawData); err != nil {
+		if n, err := w.Write(e.RawData); err != nil {
 			return errors.Trace(err)
 		} else if n != len(e.RawData) {
 			return errors.Trace(io.ErrShortWrite)