Send string from c to psuedo-terminal to mimic serial device

Question

I'm currently trying to manually feed data into GPSD. To do this I have a script that currently outputs the data (its just a JSON string) to stdout, then use socat to make a sort of fake serial device. However, I don't want to use another process, so essentially I want to integrate the creation, linking, and continuous writing to a pty from that c code. Here's what I currently have, its just some test code to write a string to pty. But when I cat into the device while its running nothing shows up.'

#include <sys/stat.h>
#include <fcntl.h>
#define _XOPEN_SOURCE 600
#include <termios.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#define MAX_SNAME 1000  
int posix_openpt(int flags){
    return open("/dev/ptmx", flags);
}

int ptyMasterOpen(char *slaveName, size_t snLen){
    int masterFd, savedErrno;
    char *p;

    masterFd = posix_openpt(O_RDWR | O_NOCTTY);         /* Open pty master */
    if (masterFd == -1)
        return -1;

    if (grantpt(masterFd) == -1) {              /* Grant access to slave pty */
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    if (unlockpt(masterFd) == -1) {             /* Unlock slave pty */
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    p = ptsname(masterFd);                      /* Get slave pty name */
    if (p == NULL) {
        savedErrno = errno;
        close(masterFd);                        /* Might change 'errno' */
        errno = savedErrno;
        return -1;
    }

    if (strlen(p) < snLen) {
        strncpy(slaveName, p, snLen);
    } else {                    /* Return an error if buffer too small */
        close(masterFd);
        errno = EOVERFLOW;
        return -1;
    }

    return masterFd;
}

int main(int argc, char **argv) {
    int flags = O_RDWR | O_NOCTTY | O_NDELAY;
    char slavename[MAX_SNAME];

    ptyMasterOpen(slavename, 900);
    printf("%s", slavename);
    int fd = open(slavename,flags);
    char msg[] = "hello there......General Kenobi
";
    for(;;){
        write(fd, msg, sizeof(msg));
    }
    close(fd);

    
}       

     

question from:https://stackoverflow.com/questions/65924465/send-string-from-c-to-psuedo-terminal-to-mimic-serial-device

Answer 1

Waitting for answers