Help me drive Zmodem over ssh with expect

Question

There's a nifty little tool called zssh that makes it easy to use the lszrz utilities to transfer files using zmodem over an existing ssh connection. It's surprisingly convenient...but it seems like I ought to be able to accomplish the same thing using expect. I've gotten this far...

#!/usr/bin/expect -f

spawn ssh $argv
set ssh_spawn_id $spawn_id
send_user "ssh is: $ssh_spawn_id\n"

interact -o "\030B0000" {
    send_user "\nStarting zmodem receive.\n"

    spawn rz -v
    set rz_spawn_id $spawn_id
    send_user "rz is: $rz_spawn_id\n"

    while {1} {
        expect {
            eof break

            -i $rz_spawn_id -re .+ {
                send -raw -i $ssh_spawn_id $expect_out(buffer)
            }
            -i $ssh_spawn_id -re .+ {
                send -raw -i $rz_spawn_id $expect_out(buffer)
            }
        }
    }

    send_user "\nFinished zmodem receive.\n"
    set spawn_id $ssh_spawn_id
}

This start up rz after seeing a ZRQINIT frame, and it apparently connects rz to the ssh session, but it doesn't work. rz says:

Retry 0: Bad CRCe.**B0100000023be50
Retry 0: Bad CRC**B0600000023d984
Retry 0: Bad CRC**B0600000023d984

...and so forth.

Is there a way to make this work? Thanks!

I'm curious, if you're already using ssh, why not file transfer with scp? — glenn jackman, Feb 16 '11 at 18:13
Mostly (a) I'm just interested in trying to understand expect better, and (b) using scp requires a second connection, which may or may not be easy (for example, if there multiple hops in between my desktop and the remote system, being able to transfer files over the *existing* channel is tremendously convenient). — larsks, Feb 16 '11 at 19:02
Hi Iarsks, have you solved this problem yet? I'd appreciate if you share any progress. — Shawyeok, Apr 13 '20 at 16:02

Lari Hotari · Answer 1 · 2016-02-01T15:36:58.923

4

I've found that using -e / --escape (escape all control characters) option on sender side helps with some problems initiating the zmodem connection.

for example:

sending file:

sz -e somefile.ext

receiving file:

rz -e

This is handy for transfering files over IPMI sol (serial-over-lan) link.

There is iterm2-zmodem on OSX and Konsole on Linux with Zmodem integration.

edited Feb 01 '16 at 15:36

answered Mar 10 '14 at 12:15

Lari Hotari

5,190
1
36
43

score 2 · Accepted Answer · answered Feb 16 '11 at 21:00

using exp_internal 1 while debugging is extremely useful. You're able to view how expect is matching the incoming text.
I wonder if the terminal is getting in the way. Before spawning rz, try stty raw. Then after send_user "Finished..." do stty -raw.

You can use exp_continue instead of a while loop:

spawn rz -v
set rz_spawn_id $spawn_id
send_user "rz is: $rz_spawn_id\n"

expect {
    -i $rz_spawn_id -re .+ {
        send -raw -i $ssh_spawn_id $expect_out(buffer)
        exp_continue
    }
    -i $ssh_spawn_id -re .+ {
        send -raw -i $rz_spawn_id $expect_out(buffer)
        exp_continue
    }
    eof
}

This doesn't have anything to do with the problem, just a matter of style.

Thanks for the suggestions. I believe that when using `interact`, everything is operating in `raw` mode by default...in any case, I added the explicit calls to `stty` and that doesn't seem to have changed the behavior. Setting `exp_internal 1` certainly provides some additional diagnostics; I'll have to look at them more closely to see if I can tell exactly what's going on. — larsks, Feb 16 '11 at 21:15

Help me drive Zmodem over ssh with expect

2 Answers2