ttynvt: Enable disabling telnet processing

Similar to suggestion by Jo Luxer:
"Make applications work, which expect a tty but the remote end is just a
network port."
https://gitlab.com/lars-thrane-as/ttynvt/-/merge_requests/9

src/telnet.h

@@ -21,7 +21,7 @@ typedef struct {
 
     unsigned int    bytes_rx;   /* Rx byte count */
     unsigned int    off_rx;     /* Rx buffer offset */
-    unsigned char   mode_telnet;        /* Telnet mode */
+    signed char     mode_telnet;        /* Telnet mode */
     unsigned char   mode_rfc2217;       /* RFC-2217 mode */
     unsigned char   telnet_ack[256];    /* telnet option ack counter */
 } tn_ctx_t;
@@ -29,7 +29,7 @@ typedef struct {
 extern tn_ctx_t *telnet_ctx_init(void *cctx, srv_tx_f * ftx, srv_rx_f * frx,
                                  srv_ms_f * fss);
 
-extern int      telnet_open(tn_ctx_t * tcc);
+extern int      telnet_open(tn_ctx_t * tcc, int mode);
 
 extern int      telnet_rx(tn_ctx_t * tcc, char *buf, int *plen);
 extern int      telnet_tx(tn_ctx_t * tcc, const char *buf, int len);
@@ -44,6 +44,10 @@ extern void     telnet_rfc2217_cfg(tn_ctx_t * tcc, int cmd,
                                    const void *val, int nd);
 extern void     telnet_rfc2217_ctl(tn_ctx_t * tcc, unsigned int val);
 
+/* Telnet mode */
+#define TN_MODE_RAW         0   /* Telnet processing off */
+#define TN_MODE_TELNET      1   /* Telnet mode */
+
 /*RFC2217 modem state*/
 #define TNS_STATE_DCD    0x80
 #define TNS_STATE_RI     0x40

src/telnet_basic.c

@@ -128,6 +128,10 @@ int telnet_rx(tn_ctx_t * tcc, char *buf, int *plen)
     int             np, nd;
     int             b1, b2;
 
+    /* Skip telnet processing entirely in raw mode */
+    if (tcc->mode_telnet < 0)
+        return 0;
+
     len = *plen;
     tcc->bytes_rx += len;
 
@@ -236,7 +240,7 @@ int telnet_tx(tn_ctx_t * tcc, const char *buf, int len)
 
     for (s = buf, rem = len; rem > 0; s = p)
     {
-        if (tcc->mode_telnet)
+        if (tcc->mode_telnet > 0)
             p = memchr(s, TNC_FF_IAC, rem);
         else
             p = NULL;
@@ -259,12 +263,18 @@ int telnet_tx(tn_ctx_t * tcc, const char *buf, int len)
     return 0;
 }
 
-int telnet_open(tn_ctx_t * tcc)
+int telnet_open(tn_ctx_t * tcc, int mode)
 {
     time_t          t = time(NULL);;
     char            buf[3];
     int             res;
 
+    if (mode == TN_MODE_RAW)
+    {
+        tcc->mode_telnet = -1;  /* Raw mode - no telnet processing */
+        return 0;
+    }
+
     buf[0] = TNC_FF_IAC;
     buf[1] = TNC_FB_WILL;
     buf[2] = TNO_CPCO;

src/ttynvt.c

@@ -44,6 +44,7 @@ static struct ttynvt_param {
     unsigned int    quiet;
     unsigned int    debug;
     int             logstd;
+    int             raw;        /* No telnet processing */
     const char     *close_delay;
     /* Derived */
     unsigned int    close_delay_us;
@@ -467,12 +468,14 @@ static void ttynvt_open(fuse_req_t req, struct fuse_file_info *info)
     tty->fds[FD_SLAVE].fd = fd;
     tty->fds[FD_SLAVE].events = POLLIN;
 
-    res = telnet_open(tty->tn);
+    res =
+        telnet_open(tty->tn, ttynvt_param.raw ? TN_MODE_RAW : TN_MODE_TELNET);
     if (res < 0)
     {
         errno = EPROTO;
         goto open_err;
     }
+
     if ((res = pthread_mutex_init(&tty->tty_lock, NULL) < 0) ||
         (res = pthread_mutex_init(&tty->poll_lock, NULL) < 0) ||
         (res = pthread_create(&tty->ptid_poll, NULL, &_read_net, tty)))
@@ -1140,6 +1143,7 @@ static const struct fuse_opt ttynvt_opts[] = {
     TTYNET_OPT("-n %s", dev_name, 0),
     TTYNET_OPT("--name=%s", dev_name, 0),
     TTYNET_OPT("-q", quiet, 1),
+    TTYNET_OPT("-r", raw, 1),
     TTYNET_OPT("-s %s", close_delay, 0),
     TTYNET_OPT("-S %s", server, 0),
     TTYNET_OPT("--server=%s", server, 0),
@@ -1160,6 +1164,7 @@ static void print_help(void)
             "\t-n name, --name=name (default: ttyNVT0)\n"
             "\t\tDevice will be created in /dev/$name.\n"
             "\t-q\t\tBe quiet (suppress informational messages)\n"
+            "\t-r\t\tDisable telnet processing\n"
             "\t-s delay \t\tDelay at close in ms (use u suffix for us)\n"
             "\t-S server, --server=host:port\n");
 }