/*
 * The Qubes OS Project, http://www.qubes-os.org
 *
 * Copyright (C) 2010  Rafal Wojtczuk  <rafal@invisiblethingslab.com>
 *
 * 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 2
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 */

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <libvchan.h>
#include "qrexec.h"
#include "libqrexec-utils.h"

/* 
There is buffered data in "buffer" for client and select()
reports that "fd" is writable. Write as much as possible to fd.
*/
int flush_client_data(int fd, struct buffer *buffer)
{
    int ret;
    int len;
    for (;;) {
        len = buffer_len(buffer);
        if (!len) {
            return WRITE_STDIN_OK;
        }
        if (len > MAX_DATA_CHUNK)
            len = MAX_DATA_CHUNK;
        ret = write(fd, buffer_data(buffer), len);
        if (ret == -1) {
            if (errno != EAGAIN) {
                return WRITE_STDIN_ERROR;
            } else
                return WRITE_STDIN_BUFFERED;
        }
        // we previously called buffer_remove(buffer, len)
        // it will be wrong if we change MAX_DATA_CHUNK to something large
        // as pipes writes are atomic only to PIPE_MAX limit 
        buffer_remove(buffer, ret);
    }

}

/*
 * Write "len" bytes from "data" to "fd". If not all written, buffer the rest
 * to "buffer".
 */
int write_stdin(int fd, const char *data, int len, struct buffer *buffer)
{
    int ret;
    int written = 0;

    if (buffer_len(buffer)) {
        buffer_append(buffer, data, len);
        return WRITE_STDIN_BUFFERED;
    }
    while (written < len) {
        ret = write(fd, data + written, len - written);
        if (ret == 0) {
            perror("write_stdin: write returns 0 ???");
            exit(1);
        }
        if (ret == -1) {
            if (errno != EAGAIN)
                return WRITE_STDIN_ERROR;

            buffer_append(buffer, data + written,
                    len - written);

            return WRITE_STDIN_BUFFERED;
        }
        written += ret;
    }
    return WRITE_STDIN_OK;
}

/* 
 * Data feed process has exited, so we need to clear all control structures for 
 * the client. However, if we have buffered data for the client (which is rare btw),
 * fire&forget a separate process to flush them.
 */
int fork_and_flush_stdin(int fd, struct buffer *buffer)
{
    int i;
    if (!buffer_len(buffer))
        return 0;
    switch (fork()) {
        case -1:
            perror("fork");
            exit(1);
        case 0:
            break;
        default:
            return 1;
    }
    for (i = 0; i < MAX_FDS; i++)
        if (i != fd && i != 2)
            close(i);
    set_block(fd);
    write_all(fd, buffer_data(buffer), buffer_len(buffer));
    _exit(0);
}