SCP in SFTP mode

[Dmitry Belyavskiy]

Hello,

When we use scp in sftp mode to copy folder to the machines with the "old"
version of ssh, we get the following error:
======
$ scp -vvv -r test/ touser at machine:/home/touser
...
debug1: Sending subsystem: sftp
...
debug2: subsystem request accepted on channel 0
debug2: Remote version: 3
debug2: Server supports extension "posix-rename at openssh.com" revision 1
debug2: Server supports extension "statvfs at openssh.com" revision 2
debug2: Server supports extension "fstatvfs at openssh.com" revision 2
debug2: Server supports extension "hardlink at openssh.com" revision 1
debug2: Server supports extension "fsync at openssh.com" revision 1
debug2: Server supports extension "lsetstat at openssh.com" revision 1
debug3: Sent message fd 6 T:17 I:1
debug3: Recevied stat reply T:105 I:1 F:0x000f M:40700
debug3: source_sftp: copying local test to remote /home/touser/test
debug3: Sent message fd 6 T:16 I:2
Couldn't canonicalize: No such file or directory


*Unable to canonicalize path "/home/touser/test"failed to upload directory
test to /home/touser/test*debug2: channel 0: read<=0 rfd 4 len 0
debug2: channel 0: read failed
debug2: chan_shutdown_read: channel 0: (i0 o0 sock -1 wfd 4 efd 6 [write])
debug2: channel 0: input open -> drain
debug2: channel 0: ibuf empty
debug2: channel 0: send eof
========

If I understand correctly, the failure is caused by the lack of the "
expand-path at openssh.com"
extension to sftp protocol in old releases and (lack of) processing it on
the server side.

For the recent version self-compatibility it was fixed in
https://github.com/openssh/openssh-portable/commit/ac7c9ec894ed0825d04ef69c55babb49bab1d32e

Is a similar fix feasible to reach better backward compatibility?

Many thanks in advance!

-- 
Dmitry Belyavskiy