Question

trying to write primitive test. Program must startup tcp-server, receive connection and redirect received data to forked program. Here is the code:

#include "TcpServer.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <termios.h>
#include <stropts.h>
#include <sys/ioctl.h>

//test
#include <pty.h>

int main() {

    if (setsid() < 1) {
        perror("cannot setsid()");
        return 1;
    }

    TcpServer tcp_server;
    int client;
    char buf[1024];

    int master, slave;
    char * slave_name;


    bzero(buf, sizeof(buf));

    tcp_server.setPort(1025);
    int server = tcp_server.startup();
    client = accept(server, NULL, NULL);

    fprintf(stderr, "forking...\n");
    pid_t pid = forkpty(&master, NULL, NULL, NULL);


    if (pid == 0) {
        setsid();


        fprintf(stderr, "slave pty is opened\n");

        fprintf(stdout, "hello, client!\n");

        char * cmd[] = {"upper.py", NULL};

        fprintf(stderr, "slave: start to login\n");
        int res = execvp("upper.py", cmd);
        if (res < 0) {
            fprintf(stderr, "trouble while running exec - '%s'\n", strerror(errno));
            return 1;
        }
        fprintf(stderr, "slave: quit\n");
        return 0;
    } else if (pid < 0) {
        perror("cannot fork off process");
        return 1;
    }

    fd_set in;
    int max_fd, n;

    struct termios ot, t;
    tcgetattr(master, &ot);
    t = ot;
    t.c_lflag &= ~(ICANON | ISIG | ECHO | ECHOCTL | ECHOE | ECHOK | ECHOKE | ECHONL | ECHOPRT );
    t.c_iflag |= IGNBRK;
    t.c_cc[VMIN] = 1;
    t.c_cc[VTIME] = 0;
    tcsetattr(master, TCSANOW, &t);

    while (1) {
        FD_ZERO(&in);

        max_fd = (master > max_fd) ? master : max_fd;
        FD_SET(master, &in);

        max_fd = (client > max_fd) ? client : max_fd;
        FD_SET(client, &in);

        fprintf(stderr, "select starts\n");
        if (select(max_fd + 1, &in, NULL, NULL, NULL) < 0) {
            fprintf(stderr, "select returned incorrectly\n");
            if (errno == EINTR) 
                continue;

            perror("error while select");
            return 1;
        }

        if (FD_ISSET(client, &in)) {
            fprintf(stderr, "client is set\n");
            n = recv(client, buf, sizeof(buf), 0);

            if (n < 0) {
                fprintf(stderr, "error while receiving data from client '%s'\n", strerror(errno));
                return 1;
            }

            if (n <= sizeof(buf)) {
                buf[n] = 0;
            }

            fprintf(stderr, "received from client: '%s'\n", buf);

            n = write(master, buf, n);
            tcflush(master, TCIOFLUSH);
        }

        if (FD_ISSET(master, &in)) {
            fprintf(stderr, "master is set ");

            n = read(master, buf, sizeof(buf));

            if (n < 0) {
                fprintf(stderr, ": %s - ", strerror(errno));
                return 1;
            }
            if (n <= sizeof(buf)) 
                buf[n] = 0;
            fprintf(stderr, "sending data - '%s'\n", buf);
            n = send(client, buf, n, 0);
        }

    }

    return 0;
}

program’s output:

[milo@milo telnetd]$ sudo ./server 
forking...
select starts
master is set sending data - 'slave pty is opened
hello, client!
slave: start to login
'
select starts
master is set sending data - 'input string: '
select starts
client is set
received from client: 'hello'
select starts

The trouble in short: server sucessfully receives data from tcp-client, writes it to master pty, but slave-end don’t receive it. I’ve seen a lot of examples, but cannot see error. Please suggest me…

UPD I’ve tried to int len = read(STDIN_FILENO, buf, sizeof(buf)); instead of execvp and it works fine! I think I have to send some kind of controlling symbol like enter… Any thoughts?

Answer 1

Yahoo! I’ve solved this problem! The mistake was (as i said earlier in UPD) in absence of \n symbol in input! otherside-program waits input until endline symbol is came!