/*
* piaip's simplified implementation of TELNET protocol
*/
#ifdef DEBUG
#define TELOPTS
#define TELCMDS
#endif
#include "bbs.h"
#ifdef DETECT_CLIENT
void UpdateClientCode(unsigned char c); // see mbbsd.c
#endif
unsigned int telnet_handler(unsigned char c) ;
void telnet_init(void);
ssize_t tty_read(unsigned char *buf, size_t max);
enum TELNET_IAC_STATES {
IAC_NONE,
IAC_COMMAND,
IAC_WAIT_OPT,
IAC_WAIT_SE,
IAC_PROCESS_OPT,
IAC_ERROR
};
static unsigned char iac_state = 0; /* as byte to reduce memory */
#define TELNET_IAC_MAXLEN (16)
/* We don't reply to most commands, so this maxlen can be minimal.
* Warning: if you want to support ENV passing or other long commands,
* remember to increase this value. Howver, some poorly implemented
* terminals like xxMan may not follow the protocols and user will hang
* on those terminals when IACs were sent.
*/
void
telnet_init(void)
{
/* We are the boss. We don't respect to client.
* It's client's responsibility to follow us.
* Please write these codes in i-dont-care opt handlers.
*/
const char telnet_init_cmds[] = {
/* retrieve terminal type and throw away.
* why? because without this, clients enter line mode.
*/
IAC, DO, TELOPT_TTYPE,
IAC, SB, TELOPT_TTYPE, TELQUAL_SEND, IAC, SE,
/* i'm a smart term with resize ability. */
IAC, DO, TELOPT_NAWS,
/* i will echo. */
IAC, WILL, TELOPT_ECHO,
/* supress ga. */
IAC, WILL, TELOPT_SGA,
/* 8 bit binary. */
IAC, WILL, TELOPT_BINARY,
IAC, DO, TELOPT_BINARY,
};
raw_connection = 1;
write(0, telnet_init_cmds, sizeof(telnet_init_cmds));
}
/* tty_read
* read from tty, process telnet commands if raw connection.
* return: >0 = length, <=0 means read more, abort/eof is automatically processed.
*/
ssize_t
tty_read(unsigned char *buf, size_t max)
{
ssize_t l = read(0, buf, max);
if(l == 0 || (l < 0 && !(errno == EINTR || errno == EAGAIN)))
abort_bbs(0);
if(!raw_connection)
return l;
/* process buffer */
if (l > 0) {
unsigned char *buf2 = buf;
size_t i = 0, i2 = 0;
/* prescan. because IAC is rare,
* this cost is worthy. */
if (iac_state == IAC_NONE && memchr(buf, IAC, l) == NULL)
return l;
/* we have to look into the buffer. */
for (i = 0; i < l; i++, buf++)
if(telnet_handler(*buf) == 0)
*(buf2++) = *buf;
else
i2 ++;
l = (i2 == l) ? -1L : l - i2;
}
return l;
}
/* input: raw character
* output: telnet command if c was handled, otherwise zero.
*/
unsigned int
telnet_handler(unsigned char c)
{
static unsigned char iac_quote = 0; /* as byte to reduce memory */
static unsigned char iac_opt_req = 0;
static unsigned char iac_buf[TELNET_IAC_MAXLEN];
static unsigned int iac_buflen = 0;
/* we have to quote all IACs. */
if(c == IAC && !iac_quote) {
iac_quote = 1;
return NOP;
}
#ifdef DETECT_CLIENT
/* hash client telnet sequences */
if(cuser.userid[0]==0) {
if(iac_state == IAC_WAIT_SE) {
// skip suboption
} else {
if(iac_quote)
UpdateClientCode(IAC);
UpdateClientCode(c);
}
}
#endif
/* a special case is the top level iac. otherwise, iac is just a quote. */
if (iac_quote) {
if(iac_state == IAC_NONE)
iac_state = IAC_COMMAND;
if(iac_state == IAC_WAIT_SE && c == SE)
iac_state = IAC_PROCESS_OPT;
iac_quote = 0;
}
/* now, let's process commands by state */
switch(iac_state) {
case IAC_NONE:
return 0;
case IAC_COMMAND:
#if 0 // def DEBUG
{
int cx = c; /* to make compiler happy */
write(0, "-", 1);
if(TELCMD_OK(cx))
write(0, TELCMD(c), strlen(TELCMD(c)));
write(0, " ", 1);
}
#endif
iac_state = IAC_NONE; /* by default we restore state. */
switch(c) {
case IAC:
return 0;
/* we don't want to process these. or maybe in future. */
case BREAK: /* break */
case ABORT: /* Abort process */
case SUSP: /* Suspend process */
case AO: /* abort output--but let prog finish */
case IP: /* interrupt process--permanently */
case EOR: /* end of record (transparent mode) */
case DM: /* data mark--for connect. cleaning */
case xEOF: /* End of file: EOF is already used... */
return NOP;
case NOP: /* nop */
return NOP;
/* we should process these, but maybe in future. */
case GA: /* you may reverse the line */
case EL: /* erase the current line */
case EC: /* erase the current character */
return NOP;
/* good */
case AYT: /* are you there */
{
const char *alive = "I'm still alive, loading: ";
char buf[STRLEN];
/* respond as fast as we can */
write(0, alive, strlen(alive));
cpuload(buf);
write(0, buf, strlen(buf));
write(0, "\r\n", 2);
}
return NOP;
case DONT: /* you are not to use option */
case DO: /* please, you use option */
case WONT: /* I won't use option */
case WILL: /* I will use option */
iac_opt_req = c;
iac_state = IAC_WAIT_OPT;
return NOP;
case SB: /* interpret as subnegotiation */
iac_state = IAC_WAIT_SE;
iac_buflen = 0;
return NOP;
case SE: /* end sub negotiation */
default:
return NOP;
}
return 1;
case IAC_WAIT_OPT:
#if 0 // def DEBUG
write(0, "-", 1);
if(TELOPT_OK(c))
write(0, TELOPT(c), strlen(TELOPT(c)));
write(0, " ", 1);
#endif
iac_state = IAC_NONE;
/*
* According to RFC, there're some tricky steps to prevent loop.
* However because we have a poor term which does not allow
* most abilities, let's be a strong boss here.
*
* Although my old imeplementation worked, it's even better to follow this:
* http://www.tcpipguide.com/free/t_TelnetOptionsandOptionNegotiation-3.htm
*/
switch(c) {
/* i-dont-care: i don't care about what client is.
* these should be clamed in init and
* client must follow me. */
case TELOPT_TTYPE: /* termtype or line. */
case TELOPT_NAWS: /* resize terminal */
case TELOPT_SGA: /* supress GA */
case TELOPT_ECHO: /* echo */
case TELOPT_BINARY: /* we are CJK. */
break;
/* i-dont-agree: i don't understand/agree these.
* according to RFC, saying NO stopped further
* requests so there'll not be endless loop. */
case TELOPT_RCP: /* prepare to reconnect */
default:
if (iac_opt_req == WILL || iac_opt_req == DO)
{
/* unknown option, reply with won't */
unsigned char cmd[3] = { IAC, DONT, 0 };
if(iac_opt_req == DO) cmd[1] = WONT;
cmd[2] = c;
write(0, cmd, sizeof(cmd));
}
break;
}
return 1;
case IAC_WAIT_SE:
iac_buf[iac_buflen++] = c;
/* no need to convert state because previous quoting will do. */
if(iac_buflen == TELNET_IAC_MAXLEN) {
/* may be broken protocol?
* whether finished or not, break for safety
* or user may be frozen.
*/
iac_state = IAC_NONE;
return 0;
}
return 1;
case IAC_PROCESS_OPT:
iac_state = IAC_NONE;
#if 0 // def DEBUG
write(0, "-", 1);
if(TELOPT_OK(iac_buf[0]))
write(0, TELOPT(iac_buf[0]), strlen(TELOPT(iac_buf[0])));
write(0, " ", 1);
#endif
switch(iac_buf[0]) {
/* resize terminal */
case TELOPT_NAWS:
{
int w = (iac_buf[1] << 8) + (iac_buf[2]);
int h = (iac_buf[3] << 8) + (iac_buf[4]);
term_resize(w, h);
#ifdef DETECT_CLIENT
if(cuser.userid[0]==0) {
UpdateClientCode(iac_buf[0]);
if(w==80 && h==24)
UpdateClientCode(1);
else if(w==80)
UpdateClientCode(2);
else if(h==24)
UpdateClientCode(3);
else
UpdateClientCode(4);
UpdateClientCode(IAC);
UpdateClientCode(SE);
}
#endif
}
break;
default:
#ifdef DETECT_CLIENT
if(cuser.userid[0]==0) {
int i;
for(i=0;i<iac_buflen;i++)
UpdateClientCode(iac_buf[i]);
UpdateClientCode(IAC);
UpdateClientCode(SE);
}
#endif
break;
}
return 1;
}
return 1; /* never reached */
}
// vim: sw=4
