[ftpext] End byte of transfer in FTP

[Tatsuhiro Tsujikawa <[e-mail]>]

Hi,

In FTP, user can set start byte of transfer by REST command.
But it seems it lacks the feature to set end byte of transfer, like
HTTP's Range request.
Does it really lack this feature? Are there any ftp server/client support this?

Issuing ABOR command is workaround but sometimes it does not stop immediately
and unused bytes are transfered.
Another possible workaround is that just closing data connection and
wait for reply
from control connection(I've not tested this yet).

A example of utilization this feature is Metalink download.
In Metalink, it contains several URIs for one file. So we can download it from
several sources. From each server, client downloads non-overlapping segment.
For example, when downloading 1 file using 2 FTP servers.
We can use REST command for second half of the download and it downloads given
 point to the end of file. This is fine. The control connection can be reused.
For the first half of the download, since we cannot set end byte, we
have to close connection
entirely after first half of file is downloaded. The control
connection cannot be reused this time.
We can use ABOR, but it has drawback as I mentioned earlier.

Best regards,

Tatsuhiro Tsujikawa