Trouble with Telnet connection to Linux server about zimodem HOT 14 CLOSED

telnetcap.zip

from zimodem.

Hi. Sorry to hear you are having troubles. First, some information on what the telnet client code does:

1. It keeps garbage characters generated by telnet negotiations from being forwarded to the serial port.

That's it. Oh, it also responds to the TERMTYPE code. But that's it.
So, when the socket is in telnet mode and reads an IAC, it will immediately do a blocking read for the code. Any WILL X or WONT X command it gets, it always responds with DONT X. Any DO or DONT, it just ignores. A Subcode is parsed to see if it is TERMTYPE, and if it is, it responds, but otherwise ignores the subcode.
I'll now go take a look at your capture and see if something stands out.

from zimodem.

So, I looked at the capture, and I see the DO This and DO Thats in the data. There's no response, but given the algorithm I described above, I wouldn't expect any. Does the RFC say that a client must respond to all DO commands, with, WILL or WONT I'm guessing?

from zimodem.

If I am reading this correctly, it does look like the RFC expects at least a confirmation?

From RFC854:

  DO (option code)    253    Indicates the request that the
                             other party perform, or
                             confirmation that you are expecting
                             the other party to perform, the
                             indicated option.

from zimodem.

I'll take a look at the rfc and see if the client MAY respond to that command, or SHALL respond to that command. :) May I ask what sort of server you are trying to connect to? That might tell me a lot.

from zimodem.

Thanks! If I can help is any way at all, please let me know.

I have tried two servers, the trace comes from a Raspberry Pi running Raspbian 8. The other server is a VM running Ubuntu Server 16.04.2 LTS.

Thanks for the quick response tonight!

from zimodem.

Heck, hang around another 30 mins, and I'll probably have a 3.3 for you to try out.

from zimodem.

Haha! I'll be here :-)

from zimodem.

OK, I put 3.3 out there, but won't make it official until it's passed both of our tests.
To force your modem to upgrade to a version that's not official yet (like 3.3), you need to enter this:
AT&U=3.3

from zimodem.

Both platforms are running telnetd (xinetd/in.telnetd) ... the other major option would be inetutils-telnetd from what I'm seeing. Just in case you wanted it more specifically.

from zimodem.

Ah just saw your last reply, sorry. I'll give it a shot and let you know.

from zimodem.

Woooot! That did it. 9600 baud and flow control seems great too.

I'm totally floored by your response to this. THANK YOU, amazing work.

from zimodem.

Hey, you helped me find a crippling bug. You have my thanks as well. I only tested telnet against, wait for it, another telnet server I did that was "roughly inspired" by the RFC.

from zimodem.

I'll let you know if anything else comes up :-)

Thanks again.

from zimodem.