All,
Ok...so I know I *should* be able to control a process's stdin and stdout from the parent by creating pipes and then dup'ing them in the child. And, this works with all "normal" programs that I've tried. Unfortunately, I want to intercept the stdin/out of the scp application and it seems scp is actively refusing to allow me to. The code is:
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
int main()
{
char usr[32];
char host[32];
char remote_path[64];
char local_path[64];
int outfd[2];
int infd[2];
/* set usr/host/remote_path/local_path to something meaningful */
/* create pipes for stdin/out to dup in the child */
pipe(outfd); /* Where the parent is going to write to */
pipe(infd); /* From where parent is going to read */
if(!fork())
{
char cmd[1024];
/* child, close stdin/out and use parent pipes instead */
close(STDOUT_FILENO);
close(STDIN_FILENO);
dup2(outfd[0], STDIN_FILENO);
dup2(infd[1], STDOUT_FILENO);
/* close all pipe ends, needed end has been dup'd other end
is not needed */
close(outfd[0]);
close(outfd[1]);
close(infd[0]);
close(infd[1]);
/* execute scp */
sprintf(cmd, "scp %s@%s:%s %s",
usr, host, remote_path, local_path);
return system(cmd);
}
/* parent */
char input[100];
close(outfd[0]); /* These are being used by the child */
close(infd[1]);
input[read(infd[0],input,100)] = 0; /* Read from child's stdout */
printf("%s",input);
/* once I can actually read/write to scp here, I'll have to determine if this is
the password prompt or the "add to host key file" prompt and respond
accordingly. */
close(outfd[1]);
close(infd[0]);
}
I know the code works if I use something other than scp, I can write and read to the pipes all day long and control the process as desired. But, it seems that scp is specifically figuring out what the controlling terminal of the process is and actively refusing to co-operate with my pipes.
I then thought maybe I could try to "disown" the terminal by calling "setsid()" right before invoking scp (and tried it right after the fork). Well, that "works," but then the stupid thing connects to my X server and pops up a box to ask for the password. Of course, preventing scp from asking me anything is the exact reason I want to control the standard in of the process so I can funnel the password in through there.
So...does any one have another idea how I can redirect stdin/stdout for this most difficult process? It seems I'll actually need to "hook into" the terminal directly since scp is "so smart." Indeed, I believe scp may be openning up its own connection to the terminal to get input and send output....
Thanks....
P.S. I know there is a better way to do this, like creating the ssh keys so scp never asks for passwords to begin with. Unfortunately, the environment where I'm trying to use this disallows this. They want us to enter passwords every time and this "stupid" rule is circumventing my ability to automate tasks through scp; of course ftp is also taboo. So...I want this "scp wrapper" to read my local password file and just pass it through so I can get back to my regularly scheduled automation. Otherwise, I'll have to enter the passwords again and again while the scripts run...and that's just...well...pointless.
