c++ - telnet LINEMODE suboption TRAPSIG does not work -

i want telnet client pass interrupts/signals normal ascii values in message server.

i send following telnet command server client in code.

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iac sb linemode trapsig 0 iac se

sprintf(msg, "%c%c%c%c%c%c%c", 255 /*iac*/, 250 /*sb*/, 34 /*linemode*/,  2 /*trapsig*/, 0 /*mask*/, 255 /*iac*/, 240 /*se*/); 

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but on pressing ctrl+c on telnet prompt, client still pass telnet commands rather ascii values.

message received server: iac ip iac 6 (timing mark)

instead of "iac ip" want receive ctrl+c (3).

any idea how can make client send across ascii values rather telnet commands while server receives whole line telnet client not character character.

any highly appreciated!

it appears way negotiate linemode not correct.

you cannot send iac sb out of blue option hasn't been negotiated first will or do or hasn't been replied positively do or will, respectively.

for line mode in particular, according rfc 1184, server side should ever initiate iac do linemode (not will).

it wait client reply either iac will linemode or iac wont linemode. in latter case, there's nothing can do, client isn't willing support line mode @ point in time , subsequently sending sub-negotiation pointless (a conforming client ignore it).

if client answered request iac will linemode, means further sub-negotiation of line mode take place, it initiated client, not (the server).

that means should wait client send send iac sb linemode iac se , in reaction should request mode , forwardmask suboptions.

in particular, want request edit turned on in client, that's actual mode client sends complete lines, , more importantly want request trapsig turned off in client, trapping signals means client intercepts key presses in question , translates them telnet commands (such iac ip), don't want. is:

iac sb linemode mode 1 iac se

(1 means edit on , trapsig off.)

and want negotiate forwardmask bits associated control characters wish receive set, otherwise receive characters when client sends completed line or not @ all.

for ctrl-c (ascii 3) minimum forward mask request be:

iac sb linemode do forwardmask 16 iac se

(the 16 decimal. note bits counted starting msb, not lsb, can confusing if you're not aware of it.)

then have wait client acknowledge both mode forward mask. client required honor server's request edit , trapsig settings if agreed negotiate line mode @ (however, no guarantee pass special key presses on you), free refuse forward mask.

in end, if want client negotiate desired options you, need make sure stick protocol close possible. suggest @ least read , understand sample communication in section 5.10 of rfc.