modem.c in git
MODEM(1) FreeBSD General Commands Manual MODEM(1)
NAME
modem – fixed baud rate wrapper
SYNOPSIS
modem command ...
DESCRIPTION
modem runs the command in a new PTY with a fixed baud rate of 19.2 kbps.
BUGS
Window size changes are not propagated to the child PTY.
FreeBSD 12.0-RELEASE-p10 July 8, 2019 FreeBSD 12.0-RELEASE-p10
#include <err.h>
#include <poll.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <termios.h>
#include <unistd.h>
#if defined __FreeBSD__
#include <libutil.h>
#elif defined __linux__
#include <pty.h>
#else
#include <util.h>
#endif
typedef unsigned uint;
typedef unsigned char byte;
static const uint BaudRate = 19200;
static struct termios saveTerm;
static void restoreTerm(void) {
tcsetattr(STDIN_FILENO, TCSADRAIN, &saveTerm);
}
int main(int argc, char *argv[]) {
int error;
if (argc < 2) return EX_USAGE;
error = tcgetattr(STDIN_FILENO, &saveTerm);
if (error) err(EX_IOERR, "tcgetattr");
atexit(restoreTerm);
struct termios raw = saveTerm;
cfmakeraw(&raw);
error = tcsetattr(STDIN_FILENO, TCSADRAIN, &raw);
if (error) err(EX_IOERR, "tcsetattr");
struct winsize window;
error = ioctl(STDIN_FILENO, TIOCGWINSZ, &window);
if (error) err(EX_IOERR, "TIOCGWINSZ");
int pty;
pid_t pid = forkpty(&pty, NULL, NULL, &window);
if (pid < 0) err(EX_OSERR, "forkpty");
if (!pid) {
execvp(argv[1], &argv[1]);
err(EX_NOINPUT, "%s", argv[1]);
}
byte c;
struct pollfd fds[2] = {
{ .events = POLLIN, .fd = STDIN_FILENO },
{ .events = POLLIN, .fd = pty },
};
while (usleep(8 * 1000000 / BaudRate), 0 < poll(fds, 2, -1)) {
if (fds[0].revents) {
ssize_t size = read(STDIN_FILENO, &c, 1);
if (size < 0) err(EX_IOERR, "read(%d)", STDIN_FILENO);
size = write(pty, &c, 1);
if (size < 0) err(EX_IOERR, "write(%d)", pty);
}
if (fds[1].revents) {
ssize_t size = read(pty, &c, 1);
if (size < 0) err(EX_IOERR, "read(%d)", pty);
size = write(STDOUT_FILENO, &c, 1);
if (size < 0) err(EX_IOERR, "write(%d)", STDOUT_FILENO);
}
int status;
pid_t dead = waitpid(pid, &status, WNOHANG);
if (dead < 0) err(EX_OSERR, "waitpid");
if (dead) return WIFEXITED(status) ? WEXITSTATUS(status) : EX_SOFTWARE;
}
err(EX_IOERR, "poll");
}