Send the local GPS NMEA stream to a remote UDP server

/* DESC: This script sends the local GPS NMEA stream to a remote UDP server
 * (including device identity).
 * In addition, a Telit module is used to provide the GPRMC frame from the
 * GNSS data block using a regular expression.
 * Copyright (C) 2013-2025 NetModule AG, Switzerland
 */

###############################################################################
DEBUG=flase;      # Enable debugging with true or disable with false
DEBUGALL=flase;   # Enable debugging with true or disable with false
###############################################################################

release_point = 0;

void usage()
{
    nb_syslog("usage: gps-broadcast.are <server> <port>");
    printf("No server IP address or port was entered <server> <port>\n");
    exit(1);
}

if (argc < 2) {
    usage();
}

SERVER = trim((string) argv[1]);
PORT = (int) argv[2];

int gpsd_request (int fd)
{
    nb_syslog("Requesting NMEA stream");

    if (send(fd, "R\n") != 2) {
        nb_syslog("ERROR: cannot send to gpsd");
        return -1;
    }

    return 0;
}

int gpsd_init ()
{
    /* connect to gpsd */
    fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (fd < 0) {
        nb_syslog("ERROR: unable to open socket to gpsd");
        return -1;
    }

    if (connect(fd, "127.0.0.1", 2947) < 0){
        nb_syslog("ERROR: unable to connect to gpsd");
        close(fd);
        return -1;
    }

    if (gpsd_request(fd) != 0) {
        close(fd);
        return -1;
    }

    return fd;
}

void gpsd_uninit (int fd)
{
    if (fd >= 0) {
        close(fd);
    }
}

int server_init ()
{
    /* open UDP server socket */
    fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (fd < 0) {
        nb_syslog("ERROR: unable to open server socket");
        return -1;
    } else {
        return fd;
    }
}

void server_uninit (int fd)
{
    if (fd >= 0) {
        close(fd);
    }
}


int gpsd_process (int gpsd, int server)
{
    /* process NMEA stream */
    nb_syslog("Processing NMEA data");
    while(1) {
        /* wait for client socket data  */
        rv = select(gpsd, 3);
        if (rv == -1) {
            nb_syslog("ERROR: select failed");
            return -1;
        } else if (rv == 0) {
            /* nb_syslog("nothing received"); */
            continue;
        }
        data = recv(gpsd);
        if(DEBUG || DEBUGALL)printf("The raw data frames from the GNSS module:\n%s\n",data);
        status = nb_status("wwan");
        info = struct_get(status, "MOBILE1_MODULE_INFO");
        info = right(info,strlen(info)-14);
        len = strlen(info);
        temp = len - 6;
        info = left(info,strlen(info)-temp);
        if(DEBUGALL)printf("Querying the modem module in the router: %s\n", info);
        if (info == "Telit "){
          if(DEBUGALL)printf("A Telit module was installed!\n\n");
          len = strlen(data);
          if (len > 200){
            if(DEBUG || DEBUGALL)printf("The GNSS data block is larger than 200 bytes: %s bytes\n",len);
            data_gprmc = pcre_compile("\\$GPRMC.*\\r\\n?", 0);
            m = pcre_exec( data_gprmc, data, 0);
            len = strlen(m[0]);
            if(DEBUGALL)printf("Check whether the GPRMC frame is present in the GNSS data block: %s bytes\n",len);
            if (len != 0){
               if(DEBUG || DEBUGALL)printf("The data block is searched for the GPRMC frame using a regex rule:\n%s\n", m[0]);
              release_point = 1;
              } else {
                  if(DEBUGALL)printf("The GPRMC frame does not contain GNSS data blocks: %s bytes\n",len);
                }
          }
        }
        if (strlen(data) == 0) {
            nb_syslog("ERROR: no NMEA data");
            return -1;
        }

        status = nb_status("system");
        serial = struct_get(status, "SERIAL_NUMBER");
        sentence = strcat("PNMID,", serial);
        sentenceLength = strlen(sentence);
        sentenceArray = explode(sentence);

        checksum = 0;
        for (i = 0; i < sentenceLength; i++) {
            currentChar = ord(sentenceArray[i]);
            checksum ^= currentChar;
        }

        checksum = sprintf("%02X",checksum);
        nmsentence = strcat("$", sentence , "*", checksum ,"\r\n");
        if (release_point == 0){
          data = strcat(data, nmsentence);
          if(DEBUG || DEBUGALL)printf("The GNSS frame has been extended with the serial number from the router:\n%s\n",data);
        }
        if (release_point == 1){
          if(DEBUG || DEBUGALL)printf("Approval for the GPRMC frame: %s\n",release_point);
          m = strcat(m[0], nmsentence);
          if(DEBUG || DEBUGALL)printf("The GPRMC frame has been extended with the serial number from the router:\n%s\n",m);
          release_point = 0;
          data = m;
        }
        len = strlen(data);
        if (len <= 0) continue;
        sent = sendto(server, data, SERVER, PORT);
        if(DEBUG || DEBUGALL)printf("This GNSS data frame is sent: %s bytes\n\n\n",sent);
        if (sent != len) {
            nb_syslog("ERROR: unable to send to %s:%d", SERVER, PORT);
            return -1;
        }
    }

    return 0;
}

/* main */

while (1) {
    nb_syslog("Initializing connection to gpsd");
    gpsd = gpsd_init();
    server = server_init();

    if (gpsd >= 0 && server >= 0) {
        gpsd_process(gpsd, server);
    }

    server_uninit(server);
    gpsd_uninit(gpsd);
    sleep(5);
}
exit(0);