/*

    mtr  --  a network diagnostic tool

    Copyright (C) 2016  Matt Kimball

    This program is free software; you can redistribute it and/or modify

    it under the terms of the GNU General Public License version 2 as

    published by the Free Software Foundation.

    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, write to the Free Software

    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#include "command.h"

#include <errno.h>

#include <fcntl.h>

#include <string.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

/*

    Initialize the command buffer and put the command stream in

    non-blocking mode.

*/

void init_command_buffer(

    struct command_buffer_t *command_buffer,

    int command_stream)

{

    int flags;

    memset(command_buffer, 0, sizeof(struct command_buffer_t));

    command_buffer->command_stream = command_stream;

    /*  Get the current command stream flags  */

    flags = fcntl(command_stream, F_GETFL, 0);

    if (flags == -1) {

        perror("Unexpected command stream error");

        exit(EXIT_FAILURE);

    }

    /*  Set the O_NONBLOCK bit  */

    if (fcntl(command_stream, F_SETFL, flags | O_NONBLOCK)) {

        perror("Unexpected command stream error");

        exit(EXIT_FAILURE);

    }

}

/*  Read currently available data from the command stream  */

int read_commands(

    struct command_buffer_t *buffer)

{

    int space_remaining =

        COMMAND_BUFFER_SIZE - buffer->incoming_read_position - 1;

    char *read_position =

        &buffer->incoming_buffer[buffer->incoming_read_position];

    int read_count;

    int command_stream = buffer->command_stream;

    read_count = read(command_stream, read_position, space_remaining);

    /*  If the command stream has been closed, read will return zero.  */

    if (read_count == 0) {

        errno = EPIPE;

        return -1;

    }

    if (read_count > 0) {

        /*  Account for the newly read data  */

        buffer->incoming_read_position += read_count;

    }

    if (read_count < 0) {

        /*  EAGAIN simply means there is no available data to read  */

        /*  EINTR indicates we received a signal during read  */

        if (errno != EINTR && errno != EAGAIN) {

            perror("Unexpected command buffer read error");

            exit(EXIT_FAILURE);

        }

    }

    return 0;

}