C execvp /bin/sh - interact programatically (dup2 stdin/stdout, etc) - c

Question

I'm using the following code to create a child process. The idea is to filter (more generally speaking execute an arbitrary function on) stdin and stdout of the child.
For one shots this example should work, but for an interactive shell there are things missing to work. The question is basically: Is this the right way to achieve what I want? What am I missing? (e.g. I tried to catch all signals (execept STOP and KILL) and relay them to the child, but it didnt really help much)
I'm eager to understand the issue so I'd be glad for any help and insight on that matter
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
/* since pipes are unidirectional, we need two pipes.
one for data to flow from parent's stdout to child's
stdin and the other for child's stdout to flow to
parent's stdin */
#define NUM_PIPES 2
#define PARENT_WRITE_PIPE 0
#define PARENT_READ_PIPE 1
int pipes[NUM_PIPES][2];
/* always in a pipe[], pipe[0] is for read and
pipe[1] is for write */
#define READ_FD 0
#define WRITE_FD 1
#define PARENT_FROM_CHILD_FD ( pipes[PARENT_READ_PIPE][READ_FD] )
#define PARENT_TO_CHILD_FD ( pipes[PARENT_WRITE_PIPE][WRITE_FD] )
#define CHILD_FROM_PARENT_FD ( pipes[PARENT_WRITE_PIPE][READ_FD] )
#define CHILD_TO_PARENT_FD ( pipes[PARENT_READ_PIPE][WRITE_FD] )
pid_t pid;
void filterStream( char* buffer, int count){
printf("filter\n");
}
int main () {
// pipes for parent to write and read
pipe(pipes[PARENT_READ_PIPE]);
pipe(pipes[PARENT_WRITE_PIPE]);
if ((pid = fork()) < 0) {
exit(1);
}
if (pid==0){
/*child*/
char *argv[]={ "sh","-i",0};
dup2(CHILD_FROM_PARENT_FD, STDIN_FILENO);
dup2(CHILD_TO_PARENT_FD, STDOUT_FILENO);
//edit
close(CHILD_FROM_PARENT_FD);
close(CHILD_TO_PARENT_FD);
close(PARENT_FROM_CHILD_FD);
close(PARENT_TO_CHILD_FD);
execvp(argv[0], argv);
} else {
/*parent*/
char buffer[8192];
int count;
int buflen=sizeof(buffer)-1;
/* close fds not required by parent */
close(CHILD_FROM_PARENT_FD);
close(CHILD_TO_PARENT_FD);
while(1){
// read stdin
while((count = read(STDIN_FILENO, buffer, buflen))>0){
filterStream(buffer,count);
buffer[count] = 0;
write(PARENT_TO_CHILD_FD,buffer,count);
if (count<buflen){
break;
}
}
if (count<0){
printf("IOERR: %d\n",errno);
}
// Read from child’s stdout
while((count = read(PARENT_FROM_CHILD_FD, buffer, buflen))>0){
filterStream(buffer,count);
buffer[count] = 0;
write(STDOUT_FILENO,buffer,count);
if (count<buflen){
break;
}
}
if (count<0){
printf("IOERR2: %d\n",errno);
}
}
}
}
Problem 1:
After the first command no further commands are executed: Is this just a redirection problem from parent to child or is it deeper?
./a.out
sh-5.1$ touch test
filter
touch test
sh-5.1$ exit
# hangs
^C
sh-5.1$ exit
# hangs...
Problem 2: on some commands the shell just backgrounds: Who backgrounds it exactly?
./a.out
sh-5.1$ whoami
filter
whoami
filter
currentuser
[1] + 238242 suspended (tty input) ./a.out