feat: sftp server support (#7643)

* feat: sftp server support

* fix(sftp-server): try fix build failed

* fix: sftp download lack

server/ftp/site.go

@@ -0,0 +1,21 @@
+package ftp
+
+import (
+	"fmt"
+	ftpserver "github.com/KirCute/ftpserverlib-pasvportmap"
+	"strconv"
+)
+
+func HandleSIZE(param string, client ftpserver.ClientDriver) (int, string) {
+	fs, ok := client.(*AferoAdapter)
+	if !ok {
+		return ftpserver.StatusNotLoggedIn, "Unexpected exception (driver is nil)"
+	}
+	size, err := strconv.ParseInt(param, 10, 64)
+	if err != nil {
+		return ftpserver.StatusSyntaxErrorParameters, fmt.Sprintf(
+			"Couldn't parse file size, given: %s, err: %v", param, err)
+	}
+	fs.SetNextFileSize(size)
+	return ftpserver.StatusOK, "Accepted next file size"
+}