Connection Refused even after adding a new Firewall rule

Question

I am trying to connect to my local UNIX server i made from another remote device. the Server is up and listening to the port i specified. i also added a new firewall rule to open that port but still my client cannot connect. it shows ERROR CONNECTION REFUSED

here is my server code

int main() {
  int fd, i,svclient,rval,msg;
  int clients[10], num_clients;
  fd_set read_set,write_set;
  char buf[100];

  struct sockaddr_in addr;

  if ( (fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
    perror("socket error");
    exit(-1);
  }


  bzero((char *) &addr, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_addr.s_addr = INADDR_ANY;
  addr.sin_port = htons(4001);

  //strncpy(addr.sun_path, socket_path, sizeof(addr.sun_path)-1);
  //strcpy(addr.sun_path, NAME);

  if (bind(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
    perror("bind error");
    exit(-1);
  }
  printf("Bind complet...\n");

  if (listen(fd, 20) == -1) {
    perror("listen error");
    exit(-1);
  }

  num_clients = 0;
  int size = sizeof(fd);

   while (1) {

    int clientfd;
    struct sockaddr_in client_addr;
    int addrlen=sizeof(client_addr);
    FD_ZERO(&read_set);
    FD_SET(fd, &read_set);

    for (i = 0; i < num_clients; i++) { //at first this part will not excute
      FD_SET(clients[i], &read_set);
    }

    select(fd + num_clients + 1, &read_set, NULL, NULL, NULL);


    if (FD_ISSET(fd, &read_set)) {
      if ( (clients[num_clients++] = accept(fd,(struct sockaddr*)&client_addr,&addrlen)) == -1) {
        perror("accept error");
        continue;
      }
      /*printf("incoming message..................... !\n \n");*/
      printf("%s:%d connected\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
    }


    for (i = 0; i < num_clients; i++) {

      if (FD_ISSET(clients[i], &read_set)) {
        msg = read(clients[i], buf, sizeof(buf));
        if(msg > 0){
          buf[msg] = 0;
          int savedclnt = clients[i];
          printf("%s \n \n", buf);

          /*for(int p=0;p<num_clients;p++)
          {
            if( clients[p]!= savedclnt){
              write(clients[p],buf,msg);
            }

          }*/
        }

      }

    }
  }
}

and my client

    int main( )
{   

    struct uci_context *uci;
    uci = uci_init();
    int sockfd;
    int ret;
    struct sockaddr_in dest;
    struct addrinfo hint, *res = NULL;
    struct hostent *host;
    char *hostip;
    char *string;



    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
    {
        puts("Unble to create socket");
        exit(1);
    }

    hostip = ucix_get_option(uci, "pack_mon", "pack_monitoring", "address");
    string = ucix_get_option(uci, "pack_mon", "pack_monitoring", "port");

    bzero(&dest, sizeof(dest));
    dest.sin_family = AF_INET;
    dest.sin_port = htons(atoi(string));

    memset(&hint, '\0', sizeof hint);
    hint.ai_family = PF_UNSPEC;
    hint.ai_flags = AI_NUMERICHOST;

    printf(" %s- %s\n", hostip, string );



    if(isdigit(hostip[0])){
        ret = getaddrinfo(hostip, NULL, &hint, &res);// this is more efficient than inet_addr

        if (ret) {

            exit(1);
        }
    }else if( (host = gethostbyname(hostip)) != 0){

        memcpy((char*)&dest.sin_addr , (char*)host->h_addr , (sizeof dest.sin_addr)+1);

    }else{

        exit(1);
        printf("cannot resolve ip address");
    }  


    if ( connect(sockfd, (struct sockaddr *)&dest, sizeof(dest)) < 0 )
    {

        perror("ERROR Connecting" );
        exit(1);
    }else{

        printf("Port number %s is open.....\n",string);
    }


    char *message;
    message = "help";
    write(sockfd,message,strlen(message));


    close(sockfd);
    freeaddrinfo(res);
    return 0;
}

FIREWALL RULE

sudo iptables -I INPUT -p tcp --dport 4001 -j ACCEPT

Error is :

192.168.10.155- 4001

ERROR Connecting: Connection refused

and this logs are coming from this codes :

printf(" %s- %s\n", hostip, string );

perror("ERROR Connecting");

exit(1);

Answer 1

Your client has no code to specify the IP address it wants to connect to. All the code that could do that has been commented out.

Update: Now your bug is here:

    strncpy((char*)&dest.sin_addr , (char*)host->h_addr , sizeof dest.sin_addr);

The strncpy function is only suitable for C-style strings. You need to use memcpy or something similar. This will only copy part of the IP address if any octet other than its last one (in network byte order) is zero.

Update: Now your bug is here:

    printf("%d\n", connect(sockfd, (struct sockaddr *)&dest, sizeof(dest)) < 0);
    perror("hmmmm" );
    exit(1);

This calls connect, then calls printf and then calls perror. The problem is, the call to printf can modify errno even if it succeeds. Thus your call to perror can print a totally irrelevant error message.