1 /* telnet.c - Telnet client.
2 *
3 * Copyright 2012 Madhur Verma <[email protected]>
4 * Copyright 2013 Kyungwan Han <[email protected]>
5 * Modified by Ashwini Kumar <[email protected]>
6 *
7 * Not in SUSv4.
8
9 USE_TELNET(NEWTOY(telnet, "<1>2", TOYFLAG_BIN))
10
11 config TELNET
12 bool "telnet"
13 default n
14 help
15 usage: telnet HOST [PORT]
16
17 Connect to telnet server.
18 */
19
20 #define FOR_telnet
21 #include "toys.h"
22 #include <arpa/telnet.h>
23
GLOBALS(int sock;char buf[2048];struct termios old_term;struct termios raw_term;uint8_t mode;int echo,sga;int state,request;)24 GLOBALS(
25 int sock;
26 char buf[2048]; // Half sizeof(toybuf) allows a buffer full of IACs.
27 struct termios old_term;
28 struct termios raw_term;
29 uint8_t mode;
30 int echo, sga;
31 int state, request;
32 )
33
34 #define NORMAL 0
35 #define SAW_IAC 1
36 #define SAW_WWDD 2
37 #define SAW_SB 3
38 #define SAW_SB_TTYPE 4
39 #define WANT_IAC 5
40 #define WANT_SE 6
41 #define SAW_CR 10
42
43 #define CM_TRY 0
44 #define CM_ON 1
45 #define CM_OFF 2
46
47 static void raw(int raw)
48 {
49 tcsetattr(0, TCSADRAIN, raw ? &TT.raw_term : &TT.old_term);
50 }
51
slc(int line)52 static void slc(int line)
53 {
54 TT.mode = line ? CM_OFF : CM_ON;
55 xprintf("Entering %s mode\r\nEscape character is '^%c'.\r\n",
56 line ? "line" : "character", line ? 'C' : ']');
57 raw(!line);
58 }
59
set_mode(void)60 static void set_mode(void)
61 {
62 if (TT.echo) {
63 if (TT.mode == CM_TRY) slc(0);
64 } else if (TT.mode != CM_OFF) slc(1);
65 }
66
handle_esc(void)67 static void handle_esc(void)
68 {
69 char input;
70
71 if (toys.signal) raw(1);
72
73 // This matches busybox telnet, not BSD telnet.
74 xputsn("\r\n"
75 "Console escape. Commands are:\r\n"
76 "\r\n"
77 " l go to line mode\r\n"
78 " c go to character mode\r\n"
79 " z suspend telnet\r\n"
80 " e exit telnet\r\n"
81 "\r\n"
82 "telnet> ");
83 // In particular, the boxes only read a single character, not a line.
84 if (read(0, &input, 1) <= 0 || input == 4 || input == 'e') {
85 xprintf("Connection closed.\r\n");
86 xexit();
87 }
88
89 if (input == 'l') {
90 if (!toys.signal) {
91 TT.mode = CM_TRY;
92 TT.echo = TT.sga = 0;
93 set_mode();
94 dprintf(TT.sock,"%c%c%c%c%c%c",IAC,DONT,TELOPT_ECHO,IAC,DONT,TELOPT_SGA);
95 goto ret;
96 }
97 } else if (input == 'c') {
98 if (toys.signal) {
99 TT.mode = CM_TRY;
100 TT.echo = TT.sga = 1;
101 set_mode();
102 dprintf(TT.sock,"%c%c%c%c%c%c",IAC,DO,TELOPT_ECHO,IAC,DO,TELOPT_SGA);
103 goto ret;
104 }
105 } else if (input == 'z') {
106 raw(0);
107 kill(0, SIGTSTP);
108 raw(1);
109 }
110
111 xprintf("telnet %s %s\r\n", toys.optargs[0], toys.optargs[1] ?: "23");
112 if (toys.signal) raw(0);
113
114 ret:
115 toys.signal = 0;
116 }
117
118 // Handle WILL WONT DO DONT requests from the server.
handle_wwdd(char opt)119 static void handle_wwdd(char opt)
120 {
121 if (opt == TELOPT_ECHO) {
122 if (TT.request == DO) dprintf(TT.sock, "%c%c%c", IAC, WONT, TELOPT_ECHO);
123 if (TT.request == DONT) return;
124 if (TT.echo) {
125 if (TT.request == WILL) return;
126 } else if (TT.request == WONT) return;
127 if (TT.mode != CM_OFF) TT.echo ^= 1;
128 dprintf(TT.sock, "%c%c%c", IAC, TT.echo ? DO : DONT, TELOPT_ECHO);
129 set_mode();
130 } else if (opt == TELOPT_SGA) { // Suppress Go Ahead
131 if (TT.sga) {
132 if (TT.request == WILL) return;
133 } else if (TT.request == WONT) return;
134 TT.sga ^= 1;
135 dprintf(TT.sock, "%c%c%c", IAC, TT.sga ? DO : DONT, TELOPT_SGA);
136 } else if (opt == TELOPT_TTYPE) { // Terminal TYPE
137 dprintf(TT.sock, "%c%c%c", IAC, WILL, TELOPT_TTYPE);
138 } else if (opt == TELOPT_NAWS) { // Negotiate About Window Size
139 unsigned cols = 80, rows = 24;
140
141 terminal_size(&cols, &rows);
142 dprintf(TT.sock, "%c%c%c%c%c%c%c%c%c%c%c%c", IAC, WILL, TELOPT_NAWS,
143 IAC, SB, TELOPT_NAWS, cols>>8, cols, rows>>8, rows,
144 IAC, SE);
145 } else {
146 // Say "no" to anything we don't understand.
147 dprintf(TT.sock, "%c%c%c", IAC, (TT.request == WILL) ? DONT : WONT, opt);
148 }
149 }
150
handle_server_output(int n)151 static void handle_server_output(int n)
152 {
153 char *p = TT.buf, *end = TT.buf + n, ch;
154 int i = 0;
155
156 // Possibilities:
157 //
158 // 1. Regular character
159 // 2. IAC [WILL|WONT|DO|DONT] option
160 // 3. IAC SB option arg... IAC SE
161 //
162 // The only subnegotiation we support is IAC SB TTYPE SEND IAC SE, so we just
163 // hard-code that into our state machine rather than having a more general
164 // "collect the subnegotation into a buffer and handle it after we've seen
165 // the IAC SE at the end". It's 2021, so we're unlikely to need more.
166
167 while (p < end) {
168 ch = *p++;
169 if (TT.state == SAW_IAC) {
170 if (ch >= WILL && ch <= DONT) {
171 TT.state = SAW_WWDD;
172 TT.request = ch;
173 } else if (ch == SB) {
174 TT.state = SAW_SB;
175 } else {
176 TT.state = NORMAL;
177 }
178 } else if (TT.state == SAW_WWDD) {
179 handle_wwdd(ch);
180 TT.state = NORMAL;
181 } else if (TT.state == SAW_SB) {
182 if (ch == TELOPT_TTYPE) TT.state = SAW_SB_TTYPE;
183 else TT.state = WANT_IAC;
184 } else if (TT.state == SAW_SB_TTYPE) {
185 if (ch == TELQUAL_SEND) {
186 dprintf(TT.sock, "%c%c%c%c%s%c%c", IAC, SB, TELOPT_TTYPE, TELQUAL_IS,
187 getenv("TERM") ?: "NVT", IAC, SE);
188 }
189 TT.state = WANT_IAC;
190 } else if (TT.state == WANT_IAC) {
191 if (ch == IAC) TT.state = WANT_SE;
192 } else if (TT.state == WANT_SE) {
193 if (ch == SE) TT.state = NORMAL;
194 } else if (ch == IAC) {
195 TT.state = SAW_IAC;
196 } else {
197 if (TT.state == SAW_CR && ch == '\0') {
198 // CR NUL -> CR
199 } else toybuf[i++] = ch;
200 if (ch == '\r') TT.state = SAW_CR;
201 TT.state = NORMAL;
202 }
203 }
204 if (i) xwrite(0, toybuf, i);
205 }
206
handle_user_input(int n)207 static void handle_user_input(int n)
208 {
209 char *p = TT.buf, ch;
210 int i = 0;
211
212 while (n--) {
213 ch = *p++;
214 if (ch == 0x1d) {
215 handle_esc();
216 return;
217 }
218 toybuf[i++] = ch;
219 if (ch == IAC) toybuf[i++] = IAC; // IAC -> IAC IAC
220 else if (ch == '\r') toybuf[i++] = '\n'; // CR -> CR LF
221 else if (ch == '\n') { // LF -> CR LF
222 toybuf[i-1] = '\r';
223 toybuf[i++] = '\n';
224 }
225 }
226 if (i) xwrite(TT.sock, toybuf, i);
227 }
228
reset_terminal(void)229 static void reset_terminal(void)
230 {
231 raw(0);
232 }
233
telnet_main(void)234 void telnet_main(void)
235 {
236 struct pollfd pfds[2];
237 int n = 1;
238
239 tcgetattr(0, &TT.old_term);
240 TT.raw_term = TT.old_term;
241 cfmakeraw(&TT.raw_term);
242
243 TT.sock = xconnectany(xgetaddrinfo(*toys.optargs, toys.optargs[1] ?: "23", 0,
244 SOCK_STREAM, IPPROTO_TCP, 0));
245 xsetsockopt(TT.sock, SOL_SOCKET, SO_KEEPALIVE, &n, sizeof(n));
246
247 xprintf("Connected to %s.\r\n", *toys.optargs);
248
249 sigatexit(reset_terminal);
250 signal(SIGINT, generic_signal);
251
252 pfds[0].fd = 0;
253 pfds[0].events = POLLIN;
254 pfds[1].fd = TT.sock;
255 pfds[1].events = POLLIN;
256 for (;;) {
257 if (poll(pfds, 2, -1) < 0) {
258 if (toys.signal) handle_esc();
259 else perror_exit("poll");
260 }
261 if (pfds[0].revents) {
262 if ((n = read(0, TT.buf, sizeof(TT.buf))) <= 0) xexit();
263 handle_user_input(n);
264 }
265 if (pfds[1].revents) {
266 if ((n = read(TT.sock, TT.buf, sizeof(TT.buf))) <= 0)
267 error_exit("Connection closed by foreign host\r");
268 handle_server_output(n);
269 }
270 }
271 }
272