Why can't I simulate auto-completion with '\t' in busybox - c

Question

I want to use "yp\t\n\0" to run “ypdomainname” command by exploiting auto-completion in busybox, but it failed. my code and result are below:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <fcntl.h>
#define DEFAULT_BUSYBOX_PATH "/bin/busybox"
#define MAX_BUF 1000
int main()
{
int fd[2];
pid_t pid;
FILE *file;
int status;
if(pipe(fd) < 0){
fprintf(stderr, "pipe error!\n");
return -1;
}
if((pid = fork()) < 0){
fprintf(stderr, "pipe error!\n");
}else if(pid == 0){ //child
close(fd[1]);
int fd_output;
fd_output = open("result", O_CREAT | O_RDWR, 777);
if(fd_output != STDOUT_FILENO){
if(dup2(fd_output, STDOUT_FILENO) != STDOUT_FILENO)
fprintf(stderr, "dup2 error to stdout\n");
}
if(fd[0] != STDIN_FILENO){
if(dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
fprintf(stderr, "dup2 error to stdin\n");
}
execl(DEFAULT_BUSYBOX_PATH, DEFAULT_BUSYBOX_PATH, "ash", NULL);
close(fd[0]);
close(fd_output);
return 0;
}else{ //parent
close(fd[0]);
char buf[MAX_BUF] = "yp";
buf[2] = '\t';
buf[3] = '\n';
buf[4] = '\0';
write(fd[1], buf, strlen(buf));
close(fd[1]);
return 0;
}
}
Result of my code
What makes me confused is that the character is not changed in function lineedit_read_key() in file lineedit.c and it will run the function input_tab() when the character is '\t'.
input_tab will be executed when character is '\t'
Recently, i took some time to learn about terminal to simulate auto-completion, but i still failed. My code is below:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>
#include <signal.h>
#include <pty.h>
#define DEFAULT_BUSYBOX_PATH "/bin/busybox"
#define MAX_BUF 1000
#define BUFFSIZE 512
typedef void Sigfunc(int);
static void sig_term(int);
static volatile sig_atomic_t sigcaught;
ssize_t writen(int fd, const void *ptr, size_t n){
size_t nleft;
ssize_t nwritten;
nleft = n;
while(nleft > 0){
if((nwritten = write(fd, ptr, nleft)) < 0){
if(nleft == n){
return(-1);
}else{
break;
}
}else if(nwritten == 0) {
break;
}
nleft -= nwritten;
ptr += nwritten;
}
return(n - nleft);
}
Sigfunc *signal_intr(int signo, Sigfunc *func){
struct sigaction act;
struct sigaction oact;
act.sa_handler = func;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
#ifdef SA_INTERRUPT
act.sa_flags |= SA_INTERRUPT;
#endif
if (sigaction(signo, &act, &oact) < 0)
return(SIG_ERR);
return(oact.sa_handler);
}
int ptym_open(char *pts_name, int pts_namesz)
{
char ptr[50];
int fdm;
int err;
if((fdm = posix_openpt(O_RDWR)) < 0){
return(-1);
}
if(grantpt(fdm) < 0){
goto errout;
}
if(unlockpt(fdm) < 0){
goto errout;
}
if(ptsname_r(fdm, ptr, 50) != 0){
goto errout;
}
strncpy(pts_name, ptr, pts_namesz);
pts_name[pts_namesz - 1] = '\0';
return(fdm); /* return fd of master */
errout:
err = errno;
close(fdm);
errno = err;
return(-1);
}
int ptys_open(char *pts_name){
int fds;
if((fds = open(pts_name, O_RDWR)) < 0)
return(-1);
return(fds);
}
pid_t pty_fork(int *ptrfdm, char *slave_name, int slave_namesz, const struct termios *slave_termios, const struct winsize *slave_winsize){
int fdm, fds;
pid_t pid;
char pts_name[20];
if((fdm = ptym_open(pts_name, sizeof(pts_name))) < 0){
fprintf(stderr, "can't open master pty: %s, error %d", pts_name, fdm);
}
if(slave_name != NULL) {
strncpy(slave_name, pts_name, slave_namesz);
slave_name[slave_namesz - 1] = '\0';
}
if((pid = fork()) < 0) {
return(-1);
}else if (pid == 0) { /* child */
if(setsid() < 0){
fprintf(stderr, "setsid error");
}
if((fds = ptys_open(pts_name)) < 0){
fprintf(stderr, "can't open slave pty");
}
close(fdm);
if(slave_termios != NULL) {
if (tcsetattr(fds, TCSANOW, slave_termios) < 0)
fprintf(stderr, "tcsetattr error on slave pty");
}
if(slave_winsize != NULL) {
if (ioctl(fds, TIOCSWINSZ, slave_winsize) < 0)
fprintf(stderr, "TIOCSWINSZ error on slave pty");
}
if(dup2(fds, STDIN_FILENO) != STDIN_FILENO){
fprintf(stderr, "dup2 error to stdin");
}
if(dup2(fds, STDOUT_FILENO) != STDOUT_FILENO){
fprintf(stderr, "dup2 error to stdout");
}
if(dup2(fds, STDERR_FILENO) != STDERR_FILENO){
fprintf(stderr, "dup2 error to stderr");
}
if(fds != STDIN_FILENO && fds != STDOUT_FILENO && fds != STDERR_FILENO){
close(fds);
}
return(0);
} else { /* parent */
*ptrfdm = fdm;
return(pid);
}
}
void loop(int ptym, int ignoreeof)
{
pid_t child;
int nread;
char buf[BUFFSIZE];
if((child = fork()) < 0) {
fprintf(stderr, "fork error");
}else if(child == 0) {
/*for ( ; ; ){
if((nread = read(STDIN_FILENO, buf, BUFFSIZE)) < 0){
fprintf(stderr, "read error from stdin");
}else if(nread == 0){
break;
}
if(writen(ptym, buf, nread) != nread)
fprintf(stderr, "writen error to master pty");
}*/
char *temp_buf = "yp\t\n";
if(writen(ptym, temp_buf, strlen(temp_buf)) != strlen(temp_buf)){
fprintf(stderr, "writen error to master pty");
}
if(ignoreeof == 0){
kill(getppid(), SIGTERM);
}
exit(0);
}
if (signal_intr(SIGTERM, sig_term) == SIG_ERR)
fprintf(stderr, "signal_intr error for SIGTERM");
for( ; ; ){
if ((nread = read(ptym, buf, BUFFSIZE)) <= 0){
}
//printf("nread = %d\n", nread);
if (writen(STDOUT_FILENO, buf, nread) != nread){
fprintf(stderr, "writen error to stdout");
}
}
if (sigcaught == 0){
printf("sigcaught == 0 and kill child\n");
kill(child, SIGTERM);
}
}
static void sig_term(int signo)
{
sigcaught = 1;
}
int main(int argc, char *argv[]){
int fd[2];
pid_t pid;
FILE *file;
int status;
int fdm;
int ignoreeof;
char slave_name[40];
struct termios orig_termios;
struct winsize size;
pid = pty_fork(&fdm, slave_name, sizeof(slave_name), &orig_termios, &size);
if(pid < 0){
fprintf(stderr, "fork error!\n");
}else if(pid == 0){ //child
if(execl(DEFAULT_BUSYBOX_PATH, DEFAULT_BUSYBOX_PATH, "ash", NULL) < 0){
fprintf(stderr, "can't execute: %s", DEFAULT_BUSYBOX_PATH);
}
/*if(execvp(argv[1], &argv[1]) < 0){
fprintf(stderr, "can't execute: %s", argv[1]);
}*/
}
loop(fdm, ignoreeof);
}
like the result of my first try, the result is: ash: yp: not found.

Answer 1

Your code fails because a pipe is not a terminal. Many programs will use isatty(3) and alike to detect if the standard input is connected to a terminal and adjust their behaviour depending on the result.
What you can do is to open a pseudo terminal pair using openpty(3) and run the command with the slave duplicated to its standard input, output and error descriptors, and using the master to communicate with it. Unfortunately I have no time right now writing a full solution as it is rather intricate; I've done it ever in Python and it was tricky even there.