perf(ftp): non use `SIZE FTP` command (close #5150)

drivers/ftp/driver.go

@@ -64,7 +64,7 @@ func (d *FTP) Link(ctx context.Context, file model.Obj, args model.LinkArgs) (*m
 		return nil, err
 	}
 
-	r := NewFTPFileReader(d.conn, file.GetPath())
+	r := NewFileReader(d.conn, file.GetPath(), file.GetSize())
 	link := &model.Link{
 		MFile: r,
 	}

drivers/ftp/util.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"os"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/jlaffaye/ftp"
@@ -30,31 +31,32 @@ func (d *FTP) login() error {
 	return nil
 }
 
-// An FTP file reader that implements io.MFile for seeking.
-type FTPFileReader struct {
+// FileReader An FTP file reader that implements io.MFile for seeking.
+type FileReader struct {
 	conn         *ftp.ServerConn
 	resp         *ftp.Response
-	offset       int64
+	offset       atomic.Int64
 	readAtOffset int64
 	mu           sync.Mutex
 	path         string
+	size         int64
 }
 
-func NewFTPFileReader(conn *ftp.ServerConn, path string) *FTPFileReader {
-	return &FTPFileReader{
+func NewFileReader(conn *ftp.ServerConn, path string, size int64) *FileReader {
+	return &FileReader{
 		conn: conn,
 		path: path,
+		size: size,
 	}
 }
 
-func (r *FTPFileReader) Read(buf []byte) (n int, err error) {
-	n, err = r.ReadAt(buf, r.offset)
-	r.mu.Lock()
-	defer r.mu.Unlock()
-	r.offset += int64(n)
+func (r *FileReader) Read(buf []byte) (n int, err error) {
+	n, err = r.ReadAt(buf, r.offset.Load())
+	r.offset.Add(int64(n))
 	return
 }
-func (r *FTPFileReader) ReadAt(buf []byte, off int64) (n int, err error) {
+
+func (r *FileReader) ReadAt(buf []byte, off int64) (n int, err error) {
 	if off < 0 {
 		return -1, os.ErrInvalid
 	}
@@ -80,11 +82,8 @@ func (r *FTPFileReader) ReadAt(buf []byte, off int64) (n int, err error) {
 	return
 }
 
-func (r *FTPFileReader) Seek(offset int64, whence int) (int64, error) {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-
-	oldOffset := r.offset
+func (r *FileReader) Seek(offset int64, whence int) (int64, error) {
+	oldOffset := r.offset.Load()
 	var newOffset int64
 	switch whence {
 	case io.SeekStart:
@@ -92,11 +91,7 @@ func (r *FTPFileReader) Seek(offset int64, whence int) (int64, error) {
 	case io.SeekCurrent:
 		newOffset = oldOffset + offset
 	case io.SeekEnd:
-		size, err := r.conn.FileSize(r.path)
-		if err != nil {
-			return oldOffset, err
-		}
-		newOffset = offset + int64(size)
+		return r.size, nil
 	default:
 		return -1, os.ErrInvalid
 	}
@@ -109,11 +104,11 @@ func (r *FTPFileReader) Seek(offset int64, whence int) (int64, error) {
 		// offset not changed, so return directly
 		return oldOffset, nil
 	}
-	r.offset = newOffset
+	r.offset.Store(newOffset)
 	return newOffset, nil
 }
 
-func (r *FTPFileReader) Close() error {
+func (r *FileReader) Close() error {
 	if r.resp != nil {
 		return r.resp.Close()
 	}