Subj : Solved issue with SyncTerm after up/download on my BBS
To   : AKAcastor
From : Digital Man
Date : Wed Apr 17 2024 01:39 pm

  Re: Solved issue with SyncTerm after up/download on my BBS
  By: AKAcastor to Digital Man on Wed Apr 17 2024 12:55 pm

 >  DM> If ASCII (non-binary-tx) mode is negotiated succesfully
 >  DM> when SyncTERM first connects to telnet server, then it
 >  DM> should be free to return to ASCII mode later.
 >
 > ASCII mode was never negotiated successfully, the session was in binary mode
 > from the beginning.

ASCII mode is the default, so if there's no mention of "BINARY TX" in either direction during initial conneciton, then ASCII mode was successfully negotiated. As I recall, SyncTERM doesn't initate any explicit Telnet commands regarding BINARY TX upon initial connection, so unless the Telnet server does (e.g. sends "DONT BINARY TX"), then SyncTERM is correct in assuming ASCII mode.

 > SyncTerm is incorrectly 'returning' to ASCII mode after
 > file transfers.

SyncTERM *attempts* to return to ASCII mode, but the server can definitely NAK the messages (as you've discovered).

If the Telnet server explicitly requested the client to be in BINARY TX mode during initial connection, then I suppose it could be considered "incorrect" for SyncTERM to want to *return* to a mode it wasn't already in. But I'm not clear that's the case since I didn't see a log of telnet commands sent and received from the start of the connection.

 > I don't think I see a pressing need for my system to support ASCII mode
 > telnet as I expect any client should support binary mode.  (maybe there's
 > some edge cases in niche implementations or a benefit of ASCII mode that I
 > am missing?)

I guess you'll find out. :-)

 >  DM> It just sounds like there's a bug in the DOSBOX-X
 >  DM> terminal server with tracking the remote and/or local
 >  DM> "BINARY TX" state and that needs to be fixed rather
 >  DM> than just blindly rejecting requests to exit binary
 >  DM> transmission mode.
 >
 >  DM> Maybe you would have had better luck with DOSBOX-
 >  DM> staging instead of of DOSBOX-X?
 >
 > I agree there is likely a bug hiding in the telnet emulation, I may dig
 > deeper for it yet.  In the meantime, convincing SyncTerm to stop switching
 > to ASCII modes removes the issue from my system.
 >
 > Telnet emulation in DOSBox-Staging is broken also.  I don't know if it has
 > the same behaviour with ASCII vs binary mode but it has other telnet
 > protocol bugs, like sending binary data from DOSBox does not escape the IAC
 > bytes.  (due to this binary transfers work when DOSBox is receiving, but not
 > when sending)
 >
 > I haven't ruled out DOSBox-Staging in the long term, but DOSBox-X has been
 > working well for me and I have already been patching it to suit my needs
 > (mostly a bit of cleanup/hackjobs in softmodem.cpp).  Eventually I hope to
 > get the softmodem code cleaned up enough to submit to the github project.

k, cool. I might play with connecting to your BBS and see what I find wrt its telnet server and comment further.... or not. :-)
-- 
                                            digital man (rob)

Synchronet/BBS Terminology Definition #90:
XON = Transmit On (ASCII 17, Ctrl-Q)
Norco, CA WX: 79.5øF, 29.0% humidity, 6 mph W wind, 0.00 inches rain/24hrs

.