ptproxy.c

#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pty.h>
#include <sys/select.h>

static void copy(int from, int to) {
  char buf[4096];
  ssize_t size;

  size = read(from, &buf, sizeof(buf));
  switch (size) {
    case -1:
      perror("read");
      exit(1);

    case 0:
      exit(0);

    default:
      write(to, &buf, size);
  }
}

int main(int argc, char *argv[]) {
  if (argc < 2) { exit(1); }

  int amaster;
  pid_t pid = forkpty(&amaster, NULL, NULL, NULL);
  if (pid < 0) { perror("forkpty"); exit(1); }

  if (!pid) {
    execvp(argv[1], &argv[1]);
    perror("execv");
    exit(1);
  }

  while (1) {
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(STDIN_FILENO, &fds);
    FD_SET(amaster, &fds);

    int ret = select(amaster+1, &fds, NULL, NULL, NULL);
    if (ret < 0) { perror("select"); exit(1); }

    if (ret > 0) {
      if (FD_ISSET(STDIN_FILENO, &fds)) copy(STDIN_FILENO, amaster);
      if (FD_ISSET(amaster, &fds)) copy(amaster, STDOUT_FILENO);
    }
  }
}