Conference atlant::terminals

3247.0. "Trying to write a Telnet client" by METALX::SWANSON (Victim of Changes) Thu Feb 06 1997 13:12

    Hi,  I hope this is the right conference to ask this in.
    At first it might sound like this belongs in a programming notesfile,
    but bear with me.  :')
    
    I am trying to write a Telnet client as an excercise in Visual C++
    programming.
    
    I've got it so that I can connect up to a remote host and receive
    text from the host and print it out etc.  But I can't get past the
    "Username:" prompt.  (I'm testing to a VMS system).
    
    At first I tried sending one byte at a time to the remote host.  Each
    key that the user pressed would get sent out the windows socket to
    the remote host.  When trying to type a username at the "Username"
    prompt, the remote host would echo back the character I typed, and
    then do a CR/LF, blow past the "password" prompt, and say "User
    Authorization failure" and ask me for a username again!
    
    Then I tried buffering the chars until a CR, and then send the whole
    line to the remote host.  (I had to convert the DOS CR to a LF before
    sending).  This allowed me to type a full username in (although I
    wouldn't see what was being typed because the remote host wasn't
    getting any data to echo back until I pressed CR), but once I entered
    the line, I saw the username get echoed back by the host, but instead
    of getting a "password" prompt next, I got some unprintable chars, and
    that's it.  Everything else I typed would get echoed back after I
    entered the line, and then several unprintable chars.  I suspect that
    there's some special code sequence thats happening before the
    "Password:" prompt is sent, that has to do with blanking out the
    password as it's typed.  But since I'm not interpreting any escape
    sequences yet in my program, I don't understand why the remote host
    is acting so "different" when it goes to send the "password" prompt.
    SHouldn't I see all chars sent from the remote host if I'm printing
    all printable characters?  What's happening at the password prompt
    that would cause me to stop receiving printable characters from the
    remote host?
    
    Does anyone know?
    
    -Ken
    

    One more question:
    
    I'm going by an example program that someone has started and said
    they didn't have time to finish, so they posted it to the Web for
    anyone who's interested to hack up.
    
    In one section of the example program, it responds to the ASCII
    code 255 being sent from the remote host.  If a 255 is received, 
    followed by a 253, and a third byte, then it sends 255  252 <3rd byte>
    back to the host.
    
    Does anyone know what the purpose of that is?  The code wasn't
    commented.  I put the same functionality into my program, but it didn't
    help the problem described in .0
    
    I looked at an ASCII table, but instead of having a character or
    abbreviation for that code, the box in the table was greyed out!
    
    Any help is appreciated.
    
    -Ken
    

Nevermind on .0, I found the problem.

If someone could answer .1 though, that would be helpful!

Ken

If you don't have the telnet RFP yet, you should get it.  There's lots
of stuff that can be sent *other* than printable characters, like whole
conversations regarding terminal type and stuff like that.

I wrote telnet for vtstar.  If you send me email, I can give you a copy
of our source module.

/Eric