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libtelnet/telnet-proxy.c

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/*
* Sean Middleditch
* sean@sourcemud.org
*
* The author or authors of this code dedicate any and all copyright interest
* in this code to the public domain. We make this dedication for the benefit
* of the public at large and to the detriment of our heirs and successors. We
* intend this dedication to be an overt act of relinquishment in perpetuity of
* all present and future rights to this code under copyright law.
*/
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <poll.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#ifdef HAVE_ZLIB
#include "zlib.h"
#endif
#include "libtelnet.h"
#ifdef ENABLE_COLOR
# define COLOR_SERVER "\e[35m"
# define COLOR_CLIENT "\e[34m"
# define COLOR_BOLD "\e[1m"
# define COLOR_UNBOLD "\e[22m"
# define COLOR_NORMAL "\e[0m"
#else
# define COLOR_SERVER ""
# define COLOR_CLIENT ""
# define COLOR_BOLD ""
# define COLOR_UNBOLD ""
# define COLOR_NORMAL ""
#endif
struct conn_t {
const char *name;
int sock;
telnet_t telnet;
struct conn_t *remote;
};
static const char *get_cmd(unsigned char cmd) {
static char buffer[4];
switch (cmd) {
case 255: return "IAC";
case 254: return "DONT";
case 253: return "DO";
case 252: return "WONT";
case 251: return "WILL";
case 250: return "SB";
case 249: return "GA";
case 248: return "EL";
case 247: return "EC";
case 246: return "AYT";
case 245: return "AO";
case 244: return "IP";
case 243: return "BREAK";
case 242: return "DM";
case 241: return "NOP";
case 240: return "SE";
case 239: return "EOR";
case 238: return "ABORT";
case 237: return "SUSP";
case 236: return "xEOF";
default:
snprintf(buffer, sizeof(buffer), "%d", (int)cmd);
return buffer;
}
}
static const char *get_opt(unsigned char opt) {
switch (opt) {
case 0: return "BINARY";
case 1: return "ECHO";
case 2: return "RCP";
case 3: return "SGA";
case 4: return "NAMS";
case 5: return "STATUS";
case 6: return "TM";
case 7: return "RCTE";
case 8: return "NAOL";
case 9: return "NAOP";
case 10: return "NAOCRD";
case 11: return "NAOHTS";
case 12: return "NAOHTD";
case 13: return "NAOFFD";
case 14: return "NAOVTS";
case 15: return "NAOVTD";
case 16: return "NAOLFD";
case 17: return "XASCII";
case 18: return "LOGOUT";
case 19: return "BM";
case 20: return "DET";
case 21: return "SUPDUP";
case 22: return "SUPDUPOUTPUT";
case 23: return "SNDLOC";
case 24: return "TTYPE";
case 25: return "EOR";
case 26: return "TUID";
case 27: return "OUTMRK";
case 28: return "TTYLOC";
case 29: return "3270REGIME";
case 30: return "X3PAD";
case 31: return "NAWS";
case 32: return "TSPEED";
case 33: return "LFLOW";
case 34: return "LINEMODE";
case 35: return "XDISPLOC";
case 36: return "ENVIRON";
case 37: return "AUTHENTICATION";
case 38: return "ENCRYPT";
case 39: return "NEW-ENVIRON";
case 70: return "MSSP";
case 85: return "COMPRESS";
case 86: return "COMPRESS2";
case 93: return "ZMP";
case 255: return "EXOPL";
default: return "unknown";
}
}
static void print_buffer(const char *buffer, size_t size) {
size_t i;
for (i = 0; i != size; ++i) {
if (buffer[i] == ' ' || (isprint(buffer[i]) && !isspace(buffer[i])))
printf("%c", (char)buffer[i]);
else if (buffer[i] == '\n')
printf("<" COLOR_BOLD "0x%02X" COLOR_UNBOLD ">\n",
(int)buffer[i]);
else
printf("<" COLOR_BOLD "0x%02X" COLOR_UNBOLD ">", (int)buffer[i]);
}
}
static void _send(int sock, const char *buffer, size_t size) {
int rs;
/* send data */
while (size > 0) {
if ((rs = send(sock, buffer, size, 0)) == -1) {
if (errno != EINTR && errno != ECONNRESET) {
fprintf(stderr, "send() failed: %s\n", strerror(errno));
exit(1);
} else {
return;
}
} else if (rs == 0) {
fprintf(stderr, "send() unexpectedly returned 0\n");
exit(1);
}
/* update pointer and size to see if we've got more to send */
buffer += rs;
size -= rs;
}
}
static void _event_handler(telnet_t *telnet, telnet_event_t *ev,
void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
switch (ev->type) {
/* data received */
case TELNET_EV_DATA:
printf("%s DATA: ", conn->name);
print_buffer(ev->buffer, ev->size);
printf(COLOR_NORMAL "\n");
telnet_send(&conn->remote->telnet, ev->buffer, ev->size);
break;
/* data must be sent */
case TELNET_EV_SEND:
/* DONT SPAM
printf("%s SEND: ", conn->name);
print_buffer(ev->buffer, ev->size);
printf(COLOR_BOLD "\n");
*/
_send(conn->sock, ev->buffer, ev->size);
break;
/* IAC command */
case TELNET_EV_IAC:
printf("%s IAC %s" COLOR_NORMAL "\n", conn->name,
get_cmd(ev->command));
telnet_iac(&conn->remote->telnet, ev->command);
break;
/* negotiation, WILL */
case TELNET_EV_WILL:
printf("%s IAC WILL %d (%s)" COLOR_NORMAL "\n", conn->name,
(int)ev->telopt, get_opt(ev->telopt));
telnet_negotiate(&conn->remote->telnet, TELNET_WILL,
ev->telopt);
break;
/* negotiation, WONT */
case TELNET_EV_WONT:
printf("%s IAC WONT %d (%s)" COLOR_NORMAL "\n", conn->name,
(int)ev->telopt, get_opt(ev->telopt));
telnet_negotiate(&conn->remote->telnet, TELNET_WONT,
ev->telopt);
break;
/* negotiation, DO */
case TELNET_EV_DO:
printf("%s IAC DO %d (%s)" COLOR_NORMAL "\n", conn->name,
(int)ev->telopt, get_opt(ev->telopt));
telnet_negotiate(&conn->remote->telnet, TELNET_DO,
ev->telopt);
break;
case TELNET_EV_DONT:
printf("%s IAC DONT %d (%s)" COLOR_NORMAL "\n", conn->name,
(int)ev->telopt, get_opt(ev->telopt));
telnet_negotiate(&conn->remote->telnet, TELNET_DONT,
ev->telopt);
break;
/* subnegotiation */
case TELNET_EV_SUBNEGOTIATION:
if (ev->telopt == TELNET_TELOPT_ZMP) {
if (ev->argc != 0) {
size_t i;
printf("%s ZMP [%zi params]", conn->name, ev->argc);
for (i = 0; i != ev->argc; ++i) {
printf(" \"");
print_buffer(ev->argv[i], strlen(ev->argv[i]));
printf("\"");
}
printf(COLOR_NORMAL "\n");
} else {
printf("%s ZMP (malformed!) [%zi bytes]",
conn->name, ev->size);
print_buffer(ev->buffer, ev->size);
printf(COLOR_NORMAL "\n");
}
} else if (ev->telopt == TELNET_TELOPT_TTYPE ||
ev->telopt == TELNET_TELOPT_ENVIRON ||
ev->telopt == TELNET_TELOPT_NEW_ENVIRON ||
ev->telopt == TELNET_TELOPT_MSSP) {
size_t i;
printf("%s %s [%zi parts]", conn->name, get_opt(ev->telopt),
ev->argc);
for (i = 0; i != ev->argc; ++i) {
printf(" \"");
print_buffer(ev->argv[i], strlen(ev->argv[i] + 1) + 1);
printf("\"");
}
printf(COLOR_NORMAL "\n");
} else {
printf("%s SUB %d (%s)", conn->name, (int)ev->telopt,
get_opt(ev->telopt));
if (ev->size > 0) {
printf(" [%zi bytes]: ", ev->size);
print_buffer(ev->buffer, ev->size);
}
printf(COLOR_NORMAL "\n");
}
/* forward */
telnet_subnegotiation(&conn->remote->telnet, ev->telopt,
ev->buffer, ev->size);
break;
/* compression notification */
case TELNET_EV_COMPRESS:
printf("%s COMPRESSION %s" COLOR_NORMAL "\n", conn->name,
ev->command ? "ON" : "OFF");
break;
/* warning */
case TELNET_EV_WARNING:
printf("%s WARNING: %s" COLOR_NORMAL "\n", conn->name, ev->buffer);
break;
/* error */
case TELNET_EV_ERROR:
printf("%s ERROR: %s" COLOR_NORMAL "\n", conn->name, ev->buffer);
exit(1);
}
}
int main(int argc, char **argv) {
char buffer[512];
short listen_port;
int listen_sock;
int rs;
struct sockaddr_in addr;
socklen_t addrlen;
struct pollfd pfd[2];
struct conn_t server;
struct conn_t client;
struct addrinfo *ai;
struct addrinfo hints;
/* check usage */
if (argc != 4) {
fprintf(stderr, "Usage:\n ./telnet-proxy <remote ip> <remote port> "
"<local port>\n");
return 1;
}
/* parse listening port */
listen_port = strtol(argv[3], 0, 10);
/* loop forever, until user kills process */
for (;;) {
/* create listening socket */
if ((listen_sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
fprintf(stderr, "socket() failed: %s\n", strerror(errno));
return 1;
}
/* reuse address option */
rs = 1;
setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, &rs, sizeof(rs));
/* bind to listening addr/port */
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(listen_port);
if (bind(listen_sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
fprintf(stderr, "bind() failed: %s\n", strerror(errno));
return 1;
}
printf("LISTENING ON PORT %d\n", listen_port);
/* wait for client */
if (listen(listen_sock, 1) == -1) {
fprintf(stderr, "listen() failed: %s\n", strerror(errno));
return 1;
}
addrlen = sizeof(addr);
if ((client.sock = accept(listen_sock, (struct sockaddr *)&addr,
&addrlen)) == -1) {
fprintf(stderr, "accept() failed: %s\n", strerror(errno));
return 1;
}
printf("CLIENT CONNECTION RECEIVED\n");
/* stop listening now that we have a client */
close(listen_sock);
/* look up server host */
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if ((rs = getaddrinfo(argv[1], argv[2], &hints, &ai)) != 0) {
fprintf(stderr, "getaddrinfo() failed for %s: %s\n", argv[1],
gai_strerror(rs));
return 1;
}
/* create server socket */
if ((server.sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
fprintf(stderr, "socket() failed: %s\n", strerror(errno));
return 1;
}
/* bind server socket */
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
if (bind(server.sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
fprintf(stderr, "bind() failed: %s\n", strerror(errno));
return 1;
}
/* connect */
if (connect(server.sock, ai->ai_addr, ai->ai_addrlen) == -1) {
fprintf(stderr, "server() failed: %s\n", strerror(errno));
return 1;
}
/* free address lookup info */
freeaddrinfo(ai);
printf("SERVER CONNECTION ESTABLISHED\n");
/* initialize connection structs */
server.name = COLOR_SERVER "SERVER";
server.remote = &client;
client.name = COLOR_CLIENT "CLIENT";
client.remote = &server;
/* initialize telnet boxes */
telnet_init(&server.telnet, 0, _event_handler, TELNET_FLAG_PROXY,
&server);
telnet_init(&client.telnet, 0, _event_handler, TELNET_FLAG_PROXY,
&client);
/* initialize poll descriptors */
memset(pfd, 0, sizeof(pfd));
pfd[0].fd = server.sock;
pfd[0].events = POLLIN;
pfd[1].fd = client.sock;
pfd[1].events = POLLIN;
/* loop while both connections are open */
while (poll(pfd, 2, -1) != -1) {
/* read from server */
if (pfd[0].revents & POLLIN) {
if ((rs = recv(server.sock, buffer, sizeof(buffer), 0)) > 0) {
telnet_recv(&server.telnet, buffer, rs);
} else if (rs == 0) {
printf("%s DISCONNECTED" COLOR_NORMAL "\n", server.name);
break;
} else {
if (errno != EINTR && errno != ECONNRESET) {
fprintf(stderr, "recv(server) failed: %s\n",
strerror(errno));
exit(1);
}
}
}
/* read from client */
if (pfd[1].revents & POLLIN) {
if ((rs = recv(client.sock, buffer, sizeof(buffer), 0)) > 0) {
telnet_recv(&client.telnet, buffer, rs);
} else if (rs == 0) {
printf("%s DISCONNECTED" COLOR_NORMAL "\n", client.name);
break;
} else {
if (errno != EINTR && errno != ECONNRESET) {
fprintf(stderr, "recv(server) failed: %s\n",
strerror(errno));
exit(1);
}
}
}
}
/* clean up */
telnet_free(&server.telnet);
telnet_free(&client.telnet);
close(server.sock);
close(client.sock);
/* all done */
printf("BOTH CONNECTIONS CLOSED\n");
}
/* not that we can reach this, but GCC will cry if it's not here */
return 0;
}
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