toys/other/netcat.c

/* netcat.c - Forward stdin/stdout to a file or network connection.
 *
 * Copyright 2007 Rob Landley <rob@landley.net>
 *
 * TODO: udp, ipv6, genericize for telnet/microcom/tail-f

USE_NETCAT(OLDTOY(nc, netcat, TOYFLAG_USR|TOYFLAG_BIN))
USE_NETCAT(NEWTOY(netcat, USE_NETCAT_LISTEN("^tlL")"w#p#s:q#f:", TOYFLAG_BIN))

config NETCAT
  bool "netcat"
  default y
  help
    usage: netcat [-u] [-wpq #] [-s addr] {IPADDR PORTNUM|-f FILENAME}

    -f	use FILENAME (ala /dev/ttyS0) instead of network
    -p	local port number
    -q	SECONDS quit this many seconds after EOF on stdin.
    -s	local ipv4 address
    -w	SECONDS timeout for connection

    Use "stty 115200 -F /dev/ttyS0 && stty raw -echo -ctlecho" with
    netcat -f to connect to a serial port.

config NETCAT_LISTEN
  bool "netcat server options (-let)"
  default y
  depends on NETCAT
  help
    usage: netcat [-t] [-lL COMMAND...]

    -t	allocate tty (must come before -l or -L)
    -l	listen for one incoming connection.
    -L	listen for multiple incoming connections (server mode).

    The command line after -l or -L is executed to handle each incoming
    connection. If none, the connection is forwarded to stdin/stdout.

    For a quick-and-dirty server, try something like:
    netcat -s 127.0.0.1 -p 1234 -tL /bin/bash -l
*/

#define FOR_netcat
#include "toys.h"

GLOBALS(
  char *filename;        // -f read from filename instead of network
  long quit_delay;       // -q Exit after EOF from stdin after # seconds.
  char *source_address;  // -s Bind to a specific source address.
  long port;             // -p Bind to a specific source port.
  long wait;             // -w Wait # seconds for a connection.
)

static void timeout(int signum)
{
  if (TT.wait) error_exit("Timeout");
  // This should be xexit() but would need siglongjmp()...
  exit(0);
}

static void set_alarm(int seconds)
{
  xsignal(SIGALRM, seconds ? timeout : SIG_DFL);
  alarm(seconds);
}

// Translate x.x.x.x numeric IPv4 address, or else DNS lookup an IPv4 name.
static void lookup_name(char *name, uint32_t *result)
{
  struct hostent *hostbyname;

  hostbyname = gethostbyname(name); // getaddrinfo
  if (!hostbyname) error_exit("no host '%s'", name);
  *result = *(uint32_t *)*hostbyname->h_addr_list;
}

// Worry about a fancy lookup later.
static void lookup_port(char *str, uint16_t *port)
{
  *port = SWAP_BE16(atoi(str));
}

void netcat_main(void)
{
  int sockfd=-1, pollcount=2;
  struct pollfd pollfds[2];

  memset(pollfds, 0, 2*sizeof(struct pollfd));
  pollfds[0].events = pollfds[1].events = POLLIN;
  set_alarm(TT.wait);

  // The argument parsing logic can't make "<2" conditional on other
  // arguments like -f and -l, so we do it by hand here.
  if (toys.optflags&FLAG_f) {
    if (toys.optc) toys.exithelp++;
  } else if (!(toys.optflags&(FLAG_l|FLAG_L)) && toys.optc!=2) toys.exithelp++;

  if (toys.exithelp) error_exit("Argument count wrong");

  if (TT.filename) pollfds[0].fd = xopen(TT.filename, O_RDWR);
  else {
    int temp;
    struct sockaddr_in address;

    // Setup socket
    sockfd = xsocket(AF_INET, SOCK_STREAM, 0);
    fcntl(sockfd, F_SETFD, FD_CLOEXEC);
    temp = 1;
    setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &temp, sizeof(temp));
    memset(&address, 0, sizeof(address));
    address.sin_family = AF_INET;
    if (TT.source_address || TT.port) {
      address.sin_port = SWAP_BE16(TT.port);
      if (TT.source_address)
        lookup_name(TT.source_address, (uint32_t *)&address.sin_addr);
      if (bind(sockfd, (struct sockaddr *)&address, sizeof(address)))
        perror_exit("bind");
    }

    // Dial out

    if (!CFG_NETCAT_LISTEN || !(toys.optflags&(FLAG_L|FLAG_l))) {
      // Figure out where to dial out to.
      lookup_name(*toys.optargs, (uint32_t *)&address.sin_addr);
      lookup_port(toys.optargs[1], &address.sin_port);
      temp = connect(sockfd, (struct sockaddr *)&address, sizeof(address));
      if (temp<0) perror_exit("connect");
      pollfds[0].fd = sockfd;

    // Listen for incoming connections

    } else {
      socklen_t len = sizeof(address);

      if (listen(sockfd, 5)) error_exit("listen");
      if (!TT.port) {
        getsockname(sockfd, (struct sockaddr *)&address, &len);
        printf("%d\n", SWAP_BE16(address.sin_port));
        fflush(stdout);
      }
      // Do we need to return immediately because -l has arguments?

      if ((toys.optflags & FLAG_l) && toys.optc) {
        if (xfork()) goto cleanup;
        close(0);
        close(1);
        close(2);
      }

      for (;;) {
        pid_t child = 0;

        // For -l, call accept from the _new_ process.

        pollfds[0].fd = accept(sockfd, (struct sockaddr *)&address, &len);
        if (pollfds[0].fd<0) perror_exit("accept");

        // Do we need a tty?

        if (toys.optflags&FLAG_t)
          child = forkpty(&(pollfds[1].fd), NULL, NULL, NULL);

        // Do we need to fork and/or redirect for exec?

        else {
          if (toys.optflags&FLAG_L) child = fork();
          if (!child && toys.optc) {
            int fd = pollfds[0].fd;

            dup2(fd, 0);
            dup2(fd, 1);
            if (toys.optflags&FLAG_L) dup2(fd, 2);
            if (fd>2) close(fd);
          }
        }

        if (child<0) error_msg("Fork failed\n");
        if (child<1) break;
        close(pollfds[0].fd);
      }
    }
  }

  // We have a connection.  Disarm timeout.
  // (Does not play well with -L, but what _should_ that do?)
  set_alarm(0);

  if (CFG_NETCAT_LISTEN && (toys.optflags&(FLAG_L|FLAG_l) && toys.optc))
    xexec(toys.optargs);

  // Poll loop copying stdin->socket and socket->stdout.
  for (;;) {
    int i;

    if (0>poll(pollfds, pollcount, -1)) perror_exit("poll");

    for (i=0; i<pollcount; i++) {
      if (pollfds[i].revents & POLLIN) {
        int len = read(pollfds[i].fd, toybuf, sizeof(toybuf));
        if (len<1) goto dohupnow;
        xwrite(i ? pollfds[0].fd : 1, toybuf, len);
      } else if (pollfds[i].revents & POLLHUP) {
dohupnow:
        // Close half-connection.  This is needed for things like
        // "echo GET / | netcat landley.net 80"
        if (i) {
          shutdown(pollfds[0].fd, SHUT_WR);
          pollcount--;
          set_alarm(TT.quit_delay);
        } else goto cleanup;
      }
    }
  }
cleanup:
  if (CFG_TOYBOX_FREE) {
    close(pollfds[0].fd);
    close(sockfd);
  }
}