Login.cpp

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/*
 * Copyright (C) 2015 Niek Linnenbank
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/utsname.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "Login.h"
 
Login::Login(int argc, char **argv)
    : POSIXApplication(argc, argv)
{
    parser().setDescription("Login program which starts the user shell");
    parser().registerPositional("INPUT", "Input character device for reading standard input");
    parser().registerPositional("OUTPUT", "Output character device for writing standard output");
}
 
Login::~Login()
{
}
 
void Login::printPrompt() const
{
    struct utsname uts;
 
    if (uname(&uts) != -1)
    {
        printf("\r\n%s %s\r\n\r\nlogin: ",
            uts.sysname,
            uts.release
        );
    }
}
 
const char * Login::getUsername() const
{
    static char line[1024];
    Size total = 0;
    
    /* Read a line. */
    while (total < sizeof(line) - 1)
    {
        /* Read a character. */
        read(0, line + total, 1);
 
        /* Process character. */
        switch (line[total])
        {
            case '\r':
            case '\n':
                printf("\r\n");
                line[total] = ZERO;
                return line;
 
            case '\b':
                if (total > 0)
                {
                    total--;
                    printf("\b \b");
                }
                break;
        
            default:
                printf("%c", line[total]);
                total++;
                break;
        }
    }
    line[total] = ZERO;
    return line;
}
 
Login::Result Login::exec()
{
    const char *user;
    const char *sh_argv[] = { "/bin/sh", 0 };
    pid_t pid;
    int status;
 
    // Wait until the I/O files are available (busy loop)
    while (true)
    {
        // Re-open standard I/O
        close(0);
        close(1);
        close(2);
 
        // Stdin
        if (open(arguments().get("INPUT"), O_RDONLY) == -1)
            continue;
 
        // Stdout
        if (open(arguments().get("OUTPUT"), O_RDWR) == -1)
            continue;
 
        // Stderr
        if (open(arguments().get("OUTPUT"), O_RDWR) == -1)
            continue;
 
        // Done
        break;
    }
 
    // Loop forever with a login prompt
    while (true)
    {
        printPrompt();
        user = getUsername();
 
        if (strlen(user) > 0)
        {
            // Start the shell
            if ((pid = forkexec("/bin/sh", sh_argv)) != (pid_t) -1)
            {
                waitpid(pid, &status, 0);
            }
            else
            {
                ERROR("forkexec '" << sh_argv[0] << "' failed: " << strerror(errno));
            }
        }
    }
    return Success;
}