SSH communication using pipes and read() write() - c

Question

I'm recently writing a piece of code to access an external server using SSH and then communicating with interactive shell-like application to which I'm directly connecting through it.
I'm using embedded Linux with only basic libraries available, with no possibility to use any additional software nor library. Also, I have to do it via C/C++ code inside the application. So I've decided to use pipes and read(), write() system calls, and I would rather stick to that.
I've written some code to better understand and test the concept. But it doesn't work as expected. I've used a snippet from here. It seems to work fine, but then the loop in main behaves not as expected
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
static bool
start_subprocess(char *const command[], int *pid, int *infd, int *outfd)
{
int p1[2], p2[2];
if (!pid || !infd || !outfd)
return false;
if (pipe(p1) == -1)
goto err_pipe1;
if (pipe(p2) == -1)
goto err_pipe2;
if ((*pid = fork()) == -1)
goto err_fork;
if (*pid) {
/* Parent process. */
*infd = p1[1];
*outfd = p2[0];
close(p1[0]);
close(p2[1]);
return true;
} else {
/* Child process. */
dup2(p1[0], STDIN_FILENO);
dup2(p2[1], STDOUT_FILENO);
close(p1[0]);
close(p1[1]);
close(p2[0]);
close(p2[1]);
execvp(*command, command);
/* Error occured. */
fprintf(stderr, "error running %s: %s", *command, strerror(errno));
abort();
}
err_fork:
close(p2[1]);
close(p2[0]);
err_pipe2:
close(p1[1]);
close(p1[0]);
err_pipe1:
return false;
}
int main() {
char *cmd[4];
cmd[0] = "/usr/bin/ssh";
cmd[1] = "-tt";
cmd[2] = "user#localhost";
cmd[3] = NULL;
char buf[65535];
char msg[65535];
int pid, infd, outfd;
start_subprocess(cmd, &pid, &infd, &outfd);
printf ("Started app %s as %d\n\n", *cmd, pid);
while(1) {
read(outfd, buf, 65535);
printf(">>> %s\n", buf);
printf("<<< ");
scanf("%s", msg);
if(strcmp(msg, "exit") == 0) break;
write(infd, msg, strlen(msg));
}
return 0;
}
I've experimeted with various SSH -t settings and it seems to somehow work with -tt option enabled (As I understand it forces pseudoterminal), without it I'm getting
Pseudo-terminal will not be allocated because stdin is not a terminal.
So I assume -tt is correct here. But the beheviour is strange. I wanted to connect through SSH, then issue ls command and see the output, which should be similar to normal SSH :
user#xubuntuLTS ~/dev/cpp/pipes$ ssh localhost
>>>> WELCOME TO SSH SERVER <<<<
Last login: Thu Jan 3 22:34:35 2019 from 127.0.0.1
user#xubuntuLTS ~$ ls
Desktop dev Documents Downloads Music Pictures Public Templates TEST_FILE Videos
user#xubuntuLTS ~$
But insted, my application works like this:
user#xubuntuLTS ~/dev/cpp/pipes$ ./a.out
Started app /usr/bin/ssh as 18393
>>>> WELCOME TO SSH SERVER <<<<
>>> Last login: Thu Jan 3 22:35:28 2019 from 127.0.0.1
<<< ls
>>> user#xubuntuLTS ~$
<<<
ls
>>> ls0;user#xubuntuLTS: ~user#xubuntuLTS ~$
<<< ls
>>> ls0;user#xubuntuLTS: ~user#xubuntuLTS ~$
Can you hint me what is wrong in my code? I want to read exactly the same output as I see during "normal" SSH session from terminal, possibly having "appending" output during each read() call, so I can easily perform some automated task with this type of interactive communication. Please note that using standard terminal here is just an example, in the real world solution I'm connecting to some kind of command line interface program directly by logging through SSH, without actual access to shell.
I'm pretty sure that there is something wrong with correct usage of write() and read() here, but I'm not an expert in that matter.