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boredos_mirror/src/kernel/userland/telnet.c
boreddevnl 903d4e0510 basic telnet
2026-03-04 09:54:57 +01:00

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// Copyright (c) 2023-2026 Chris (boreddevnl)
// This software is released under the GNU General Public License v3.0. See LICENSE file for details.
// This header needs to maintain in any file it is present in, as per the GPL license terms.
#include <stdlib.h>
#include <syscall.h>
#include "libc/libui.h"
static int term_cols = 116;
static int term_rows = 41;
#define IAC 255
#define DONT 254
#define DO 253
#define WONT 252
#define WILL 251
#define SB 250 // sub-negotiation begin
#define SE 240 // sub-negotiation end
#define GA 249
#define EL 248
#define EC 247
#define AYT 246
#define AO 245
#define IP 244
#define BRK 243
#define DM 242
#define NOP 241
// Telnet options
#define OPT_ECHO 1
#define OPT_SUPPRESS_GA 3
#define OPT_STATUS 5
#define OPT_TIMING_MARK 6
#define OPT_NAWS 31 // Negotiate About Window Size
#define OPT_NEW_ENVIRON 39
#define OPT_TERMINAL_TYPE 24
// ─── IAC send helpers ────────────────────────────────────────────────────────
static void telnet_send(const uint8_t *data, int len) {
sys_tcp_send(data, len);
}
static void telnet_send_3(uint8_t a, uint8_t b, uint8_t c) {
uint8_t buf[3] = { a, b, c };
telnet_send(buf, 3);
}
// Send NAWS subnegotiation with current terminal dimensions
static void telnet_send_naws(void) {
uint8_t buf[9];
buf[0] = IAC;
buf[1] = SB;
buf[2] = OPT_NAWS;
buf[3] = (uint8_t)((term_cols >> 8) & 0xFF);
buf[4] = (uint8_t)(term_cols & 0xFF);
buf[5] = (uint8_t)((term_rows >> 8) & 0xFF);
buf[6] = (uint8_t)(term_rows & 0xFF);
buf[7] = IAC;
buf[8] = SE;
telnet_send(buf, 9);
}
static void telnet_handle_option(uint8_t cmd, uint8_t opt) {
switch (cmd) {
case DO:
if (opt == OPT_NAWS) {
telnet_send_3(IAC, WILL, OPT_NAWS);
telnet_send_naws();
} else if (opt == OPT_TERMINAL_TYPE) {
telnet_send_3(IAC, WILL, OPT_TERMINAL_TYPE);
} else {
telnet_send_3(IAC, WONT, opt);
}
break;
case DONT:
telnet_send_3(IAC, WONT, opt);
break;
case WILL:
if (opt == OPT_SUPPRESS_GA) {
// Good — accept suppressed GA (most BBS systems do this)
telnet_send_3(IAC, DO, OPT_SUPPRESS_GA);
} else if (opt == OPT_ECHO) {
// Server will echo chars (remote echo) — accept it
telnet_send_3(IAC, DO, OPT_ECHO);
} else {
// Refuse other server offers
telnet_send_3(IAC, DONT, opt);
}
break;
case WONT:
telnet_send_3(IAC, DONT, opt);
break;
default:
break;
}
}
static void telnet_handle_sb_terminal_type(const uint8_t *sb_data, int sb_len) {
if (sb_len < 1 || sb_data[0] != 1) return; // 1 = SEND
uint8_t reply[12];
int i = 0;
reply[i++] = IAC;
reply[i++] = SB;
reply[i++] = OPT_TERMINAL_TYPE;
reply[i++] = 0; // IS
reply[i++] = 'A'; reply[i++] = 'N'; reply[i++] = 'S'; reply[i++] = 'I';
reply[i++] = IAC;
reply[i++] = SE;
telnet_send(reply, i);
}
typedef enum {
TS_DATA = 0,
TS_IAC,
TS_CMD,
TS_OPT,
TS_SB,
TS_SB_IAC
} TelnetParseState;
static TelnetParseState ts_state = TS_DATA;
static uint8_t ts_cmd = 0;
static uint8_t ts_sb_opt = 0;
static uint8_t ts_sb_buf[256];
static int ts_sb_pos = 0;
// Output buffer — accumulate non-IAC bytes to write in bulk
static char out_buf[4096];
static int out_pos = 0;
static void flush_out(void) {
if (out_pos > 0) {
sys_write(1, out_buf, out_pos);
out_pos = 0;
}
}
static void out_char(char c) {
if (out_pos >= (int)(sizeof(out_buf) - 1)) {
flush_out();
}
out_buf[out_pos++] = c;
}
// Process a chunk of raw TCP data from server. Returns false if connection lost.
static int telnet_process(const uint8_t *data, int len) {
for (int i = 0; i < len; i++) {
uint8_t b = data[i];
switch (ts_state) {
case TS_DATA:
if (b == IAC) {
ts_state = TS_IAC;
} else {
// Pass directly to display
out_char((char)b);
}
break;
case TS_IAC:
switch (b) {
case IAC:
// Escaped IAC — literal 0xFF
out_char((char)0xFF);
ts_state = TS_DATA;
break;
case DO: case DONT: case WILL: case WONT:
ts_cmd = b;
ts_state = TS_OPT;
break;
case SB:
ts_sb_pos = 0;
ts_state = TS_CMD;
break;
case GA: case NOP: case DM: case BRK: case IP:
case AO: case AYT: case EC: case EL:
ts_state = TS_DATA;
break;
default:
ts_state = TS_DATA;
break;
}
break;
case TS_CMD:
ts_sb_opt = b;
ts_sb_pos = 0;
ts_state = TS_SB;
break;
case TS_OPT:
flush_out();
telnet_handle_option(ts_cmd, b);
ts_state = TS_DATA;
break;
case TS_SB:
if (b == IAC) {
ts_state = TS_SB_IAC;
} else {
if (ts_sb_pos < (int)sizeof(ts_sb_buf) - 1) {
ts_sb_buf[ts_sb_pos++] = b;
}
}
break;
case TS_SB_IAC:
if (b == SE) {
flush_out();
if (ts_sb_opt == OPT_TERMINAL_TYPE) {
telnet_handle_sb_terminal_type(ts_sb_buf, ts_sb_pos);
}
ts_state = TS_DATA;
} else if (b == IAC) {
if (ts_sb_pos < (int)sizeof(ts_sb_buf) - 1) {
ts_sb_buf[ts_sb_pos++] = IAC;
}
ts_state = TS_SB;
} else {
ts_state = TS_DATA;
}
break;
}
}
flush_out();
return 1;
}
static int map_key(char c, uint8_t *key_out) {
if (c == 29) {
// Ctrl+]
return -1;
}
if (c == 17) {
// UP arrow
key_out[0] = 0x1b; key_out[1] = '['; key_out[2] = 'A';
return 3;
}
if (c == 18) {
// DOWN arrow
key_out[0] = 0x1b; key_out[1] = '['; key_out[2] = 'B';
return 3;
}
if (c == 20) {
// RIGHT arrow
key_out[0] = 0x1b; key_out[1] = '['; key_out[2] = 'C';
return 3;
}
if (c == 19) {
// LEFT arrow
key_out[0] = 0x1b; key_out[1] = '['; key_out[2] = 'D';
return 3;
}
if (c == '\n') {
// Enter
key_out[0] = '\r'; key_out[1] = '\n';
return 2;
}
if (c == '\b') {
// Backspace
key_out[0] = '\x7f';
return 1;
}
// Normal printable character
key_out[0] = (uint8_t)c;
return 1;
}
static int my_atoi(const char *s) {
int v = 0;
while (*s >= '0' && *s <= '9') { v = v*10 + (*s - '0'); s++; }
return v;
}
static int parse_ip(const char *s, net_ipv4_address_t *ip) {
int part = 0, val = 0;
while (*s) {
if (*s >= '0' && *s <= '9') {
val = val*10 + (*s - '0');
if (val > 255) return -1;
} else if (*s == '.') {
if (part > 3) return -1;
ip->bytes[part++] = (uint8_t)val;
val = 0;
} else {
return -1;
}
s++;
}
if (part != 3) return -1;
ip->bytes[3] = (uint8_t)val;
return 0;
}
int main(int argc, char **argv) {
if (argc < 2) {
printf("Usage: telnet <host> [port]\n");
printf(" Connect to a Telnet BBS or server.\n");
printf(" Default port: 23\n");
printf(" Press Ctrl+] to disconnect.\n");
return 1;
}
const char *host = argv[1];
int port = (argc >= 3) ? my_atoi(argv[2]) : 23;
if (port <= 0 || port > 65535) port = 23;
if (!sys_network_is_initialized()) {
printf("Initializing network...\n");
sys_network_init();
}
if (!sys_network_has_ip()) {
printf("Acquiring DHCP...\n");
if (sys_network_dhcp_acquire() != 0) {
printf("DHCP failed.\n");
return 1;
}
}
net_ipv4_address_t ip;
if (parse_ip(host, &ip) != 0) {
printf("Resolving %s...\n", host);
if (sys_dns_lookup(host, &ip) != 0) {
printf("Failed to resolve: %s\n", host);
return 1;
}
}
printf("Connecting to %s:%d...\n", host, port);
if (sys_tcp_connect(&ip, (uint16_t)port) != 0) {
printf("Connection failed.\n");
return 1;
}
printf("Connected. Press Ctrl+] to disconnect.\n\n");
sys_system(41, 1, 0, 0, 0); // SYSTEM_CMD_SET_RAW_MODE = 1
uint8_t recv_buf[4096];
int total = 0;
int idle_count = 0;
int connected = 1;
while (connected) {
gui_event_t ev;
while (ui_get_event(0, &ev)) { // win=0 for console proc
if (ev.type == GUI_EVENT_KEY) {
uint8_t key_data[16];
int key_len = map_key((char)ev.arg1, key_data);
if (key_len < 0) {
connected = 0;
break;
}
telnet_send(key_data, key_len);
}
}
if (!connected) break;
int len = sys_tcp_recv(recv_buf, sizeof(recv_buf) - 1);
if (len < 0) {
printf("\r\n[Connection error]\r\n");
connected = 0;
break;
}
if (len == 0) {
idle_count++;
// Don't timeout too fast if we are just waiting for user input
if (idle_count > 10000000) {
printf("\r\n[Connection timed out]\r\n");
connected = 0;
break;
}
// Brief spin
for (volatile int d = 0; d < 100; d++);
continue;
}
idle_count = 0;
total += len;
if (total > 10000000) {
printf("\r\n[Data limit reached]\r\n");
connected = 0;
break;
}
if (!telnet_process(recv_buf, len)) {
connected = 0;
}
}
// Disable raw mode before exiting
sys_system(41, 0, 0, 0, 0);
sys_tcp_close();
printf("\r\n[Telnet session ended]\r\n");
return 0;
}
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