openssh unix dev - Jan 2001 - Detection of identical file doesn't work for localhost:

Hi,

I had to notice that scp is able to detect if a file is copied to itself
if you use "scp foo /path/to/foo" or "scp foo .". If you
type in "scp
foo localhost:/path/to/foo" it will still overwrite the old version of
foo. Is it possible to change this behaviour of scp? 

I only had a quick glance at scp.c and I'm also not a C coder, only
learning C right now, so please give me some hints if I'm wrong. You use
the function "colon" in 984 to check if you should to a remote copy or
a
local copy. I think it would be possible to add a check to it to see if
the name of the remote host will be localhost and then also use the
function "tolocal" for doing a local copy instead of calling
"toremote".
What do you guys think? Would you please add this feature?

Ciao
     Christian

P.S.: Would somebody please change s/debain/debian/ in the ChangeLog to
fix my email-address? Thanks
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 242 bytes
Desc: not available
Url :
http://lists.mindrot.org/pipermail/openssh-unix-dev/attachments/20010130/d87d034d/attachment.bin

Hi,

On Tue, Jan 30, 2001 at 08:27:49AM +0100, Christian Kurz
wrote:
> I had to notice that scp is able to detect if a file is copied to itself
> if you use "scp foo /path/to/foo" or "scp foo .". If
you type in "scp
> foo localhost:/path/to/foo" it will still overwrite the old version of
> foo. Is it possible to change this behaviour of scp? 
> 
> I only had a quick glance at scp.c and I'm also not a C coder, only
> learning C right now, so please give me some hints if I'm wrong. You
use
> the function "colon" in 984 to check if you should to a remote
copy or a
> local copy. I think it would be possible to add a check to it to see if
> the name of the remote host will be localhost and then also use the
> function "tolocal" for doing a local copy instead of calling
"toremote".
> What do you guys think? Would you please add this feature?
I don't think it's reasonable.  If a user want to shoot into his own
foot,
he will always be able to do this.

If you trap "localhost", people will use 127.0.0.1, or the real name
of
the machine, or one of its ethernet IP addresses, etc.

(Why on earth would anybody do an "scp localhost:..." in the first
place?)

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at
greenie.muc.de
fax: +49-89-35655025                        gert.doering at
physik.tu-muenchen.de

On Tue, 30 Jan 2001, Christian Kurz wrote:
> Hi,
> 
> I had to notice that scp is able to detect if a file is copied to itself
> if you use "scp foo /path/to/foo" or "scp foo .". If
you type in "scp
> foo localhost:/path/to/foo" it will still overwrite the old version of
> foo. Is it possible to change this behaviour of scp? 
> 
> I only had a quick glance at scp.c and I'm also not a C coder, only
> learning C right now, so please give me some hints if I'm wrong. You
use
> the function "colon" in 984 to check if you should to a remote
copy or a
> local copy. I think it would be possible to add a check to it to see if
> the name of the remote host will be localhost and then also use the
> function "tolocal" for doing a local copy instead of calling
"toremote".
> What do you guys think? Would you please add this feature?
This has come up before, IIRC we decided not to put such a check in
because there are so many ways to refer to the local host 
(localhost, hostname(s), ip addresses, etc) that such a check would 
cover a small range of the cases.

OTOH a patch to make scp write to a temp file and then rename it as the
final step may make more sense and achieve a better result.
> P.S.: Would somebody please change s/debain/debian/ in the ChangeLog to
> fix my email-address? Thanks
Done.

-d

-- 
| ``We've all heard that a million monkeys banging on | Damien Miller -
| a million typewriters will eventually reproduce the | <djm at
mindrot.org>
| works of Shakespeare. Now, thanks to the Internet, / 
| we know this is not true.'' - Robert Wilensky UCB /
http://www.mindrot.org

> I had to notice that scp is able to detect if a file is copied to itself
> if you use "scp foo /path/to/foo" or "scp foo .". If
you type in "scp
> foo localhost:/path/to/foo" it will still overwrite the old version of
> foo. Is it possible to change this behaviour of scp? 
how could 'scp' tell that it's really the identical file?

>>(Why on earth would anybody do an "scp localhost:..." in the
first place?)
>
>Why? Well, one reason would be to copy from a chroot()ed environment
>back to the real host, of course... Probably not, but it is possible.
>There is no guarentee that localhost:/some/directory is in the same
>filesystem as /some/directory on the current machine as viewed by
>the currently running scp program.
But if that is the case then the reported problem doesn't occur because
the source and destination are different.

A check like this is likely to do more harm than good, just to fix one
or two edge cases where the user did something strange and didn't like
what they got.



--
Darren J Moffat