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libtelnet
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libtelnet/telnet-proxy.c

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9.6 KiB
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 <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"
struct conn_t {
const char *name;
int sock;
struct libtelnet_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(unsigned char *buffer, unsigned int size) {
unsigned int 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("<\e[1m0x%02X\e[22m>\n", (int)buffer[i]);
else
printf("<\e[1m0x%02X\e[22m>", (int)buffer[i]);
}
}
static void _data_cb(struct libtelnet_t *telnet, unsigned char *buffer,
unsigned int size, void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s DATA: ", conn->name);
print_buffer(buffer, size);
printf("\e[0m\n");
libtelnet_send_data(&conn->remote->telnet, buffer, size,
conn->remote);
}
static void _send_cb(struct libtelnet_t *telnet, unsigned char *buffer,
unsigned int size, void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
int rs;
/* DONT SPAM
printf("%s SEND: ", conn->name);
print_buffer(buffer, size);
printf("\e[0m\n");
*/
/* send data */
while (size > 0) {
if ((rs = send(conn->sock, buffer, size, 0)) == -1) {
fprintf(stderr, "send() failed: %s\n", strerror(errno));
exit(1);
} 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 _command_cb(struct libtelnet_t *telnet, unsigned char cmd,
void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s IAC %s\e[0m\n", conn->name, get_cmd(cmd));
libtelnet_send_command(&conn->remote->telnet, cmd, conn->remote);
}
static void _negotiate_cb(struct libtelnet_t *telnet, unsigned char cmd,
unsigned char opt, void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s IAC %s %d (%s)\e[0m\n", conn->name, get_cmd(cmd),
(int)opt, get_opt(opt));
libtelnet_send_negotiate(&conn->remote->telnet, cmd, opt,
conn->remote);
}
static void _subnegotiation_cb(struct libtelnet_t *telnet,
unsigned char type, unsigned char *buffer, unsigned int size,
void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s SUB %d (%s)", conn->name, (int)type, get_opt(type));
if (size > 0) {
printf(" [%u]: ", size);
print_buffer(buffer, size);
}
printf("\e[0m\n");
libtelnet_send_subnegotiation(&conn->remote->telnet, type, buffer, size,
conn->remote);
}
static void _compress_cb(struct libtelnet_t *telnet, char enabled,
void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s COMPRESSION %s\e[0m\n", conn->name, enabled ? "ON" : "OFF");
}
static void _error_cb(struct libtelnet_t *telnet, enum libtelnet_error_t error,
const char *msg, void *user_data) {
struct conn_t *conn = (struct conn_t*)user_data;
printf("%s ERROR: %s\e[0m\n", conn->name, msg);
exit(1);
}
int main(int argc, char **argv) {
unsigned char buffer[512];
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 libtelnet_cb_t cb_table;
/* check usage */
if (argc != 4) {
fprintf(stderr, "Usage:\n ./telnet-proxy <remote ip> <remote port> "
"<local port>\n");
return 1;
}
/* 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(strtol(argv[3], 0, 10));
if (bind(listen_sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
fprintf(stderr, "bind() failed: %s\n", strerror(errno));
return 1;
}
/* wait for client */
if (listen(listen_sock, 5) == -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;
}
/* stop listening now that we have a client */
close(listen_sock);
/* create server socket */
if ((server.sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
fprintf(stderr, "socket() failed: %s\n", strerror(errno));
return 1;
}
/* connect to server */
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;
}
memset(&addr, 0, sizeof(addr));
if (inet_pton(AF_INET, argv[1], &addr.sin_addr) != 1) {
fprintf(stderr, "inet_pton() failed: %s\n", strerror(errno));
return 1;
}
addr.sin_family = AF_INET;
addr.sin_port = htons(strtol(argv[2], 0, 10));
if (connect(server.sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
fprintf(stderr, "server() failed: %s\n", strerror(errno));
return 1;
}
/* initialize connection structs */
server.name = "\e[35mSERVER";
server.remote = &client;
client.name = "\e[34mCLIENT";
client.remote = &server;
/* initialize libtelnet callback table */
memset(&cb_table, 0, sizeof(cb_table));
cb_table.data = _data_cb;
cb_table.send = _send_cb;
cb_table.command = _command_cb;
cb_table.negotiate = _negotiate_cb;
cb_table.subnegotiation = _subnegotiation_cb;
cb_table.compress = _compress_cb;
cb_table.error = _error_cb;
/* initialize telnet boxes
* NOTE: we set the server connect to the CLIENT mode because we
* are acting as a client of the server; likewise, we set the
* client connection to SERVER mode becauser we are acting as a
* server to the client. */
libtelnet_init(&server.telnet, &cb_table, LIBTELNET_MODE_CLIENT);
libtelnet_init(&client.telnet, &cb_table, LIBTELNET_MODE_SERVER);
/* 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) {
libtelnet_push(&server.telnet, buffer, rs, (void*)&server);
} else if (rs == 0) {
printf("%s DISCONNECTED\e[0m\n", server.name);
break;
} else {
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) {
libtelnet_push(&client.telnet, buffer, rs, (void*)&client);
} else if (rs == 0) {
printf("%s DISCONNECTED\e[0m\n", client.name);
break;
} else {
fprintf(stderr, "recv(client) failed: %s\n", strerror(errno));
exit(1);
}
}
}
/* clean up */
libtelnet_free(&server.telnet);
libtelnet_free(&client.telnet);
close(server.sock);
close(client.sock);
return 0;
}
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