xiph.h

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/*****************************************************************************
 * xiph.h: Xiph helpers
 *****************************************************************************
 * Copyright (C) 2010 Laurent Aimar
 * $Id: dc1df97582868f20aafc38d67e08691edad235d9 $
 *
 * Authors: Laurent Aimar <fenrir _AT_ videolan _DOT_ org>
 *
 * 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 <assert.h>
#define XIPH_MAX_HEADER_COUNT (256)

static inline int xiph_SplitHeaders(unsigned packet_size[], void *packet[], unsigned *packet_count,
                                    unsigned extra_size, const void *extra)
{
    const uint8_t *current = (const uint8_t*)extra;
    const uint8_t *end = &current[extra_size];
    if (extra_size < 1)
        return VLC_EGENERIC;

    /* Parse the packet count and their sizes */
    const unsigned count = 1 + *current++;
    if (packet_count)
        *packet_count = count;
    unsigned size = 0;
    for (unsigned i = 0; i < count - 1; i++) {
        packet_size[i] = 0;
        for (;;) {
            if (current >= end)
                return VLC_EGENERIC;
            packet_size[i] += *current;
            if (*current++ != 255)
                break;
        }
        size += packet_size[i];
    }
    if (end - current < size)
        return VLC_EGENERIC;
    packet_size[count - 1] = end - current - size;

    /* Copy the payloads */
    for (unsigned i = 0; i < count; i++) {
        packet[i] = malloc(packet_size[i]);
        if (!packet[i]) {
            for (unsigned j = 0; j < i; j++)
                free(packet[j]);
            return VLC_ENOMEM;
        }
        if (packet_size[i] > 0) {
            memcpy(packet[i], current, packet_size[i]);
            current += packet_size[i];
        }
    }
    return VLC_SUCCESS;
}

static inline int xiph_PackHeaders(int *extra_size, void **extra,
                                   unsigned packet_size[], void *packet[], unsigned packet_count )
{
    if (packet_count <= 0 || packet_count > XIPH_MAX_HEADER_COUNT)
        return VLC_EGENERIC;

    /* Compute the size needed for the whole extra data */
    unsigned payload_size = 0;
    unsigned header_size = 1;
    for (unsigned i = 0; i < packet_count; i++) {
        payload_size += packet_size[i];
        if (i < packet_count - 1)
            header_size += 1 + packet_size[i] / 255;
    }

    /* */
    *extra_size = header_size + payload_size;
    *extra = malloc(*extra_size);
    if (*extra == NULL)
        return VLC_ENOMEM;

    /* Write the header */
    uint8_t *current = (uint8_t*)*extra;
    *current++ = packet_count - 1;
    for (unsigned i = 0; i < packet_count - 1; i++) {
        unsigned t = packet_size[i];
        for (;;) {
            if (t >= 255) {
                *current++ = 255;
                t -= 255;
            } else {
                *current++ = t;
                break;
            }
        }
    }

    /* Copy the payloads */
    for (unsigned i = 0; i < packet_count; i++) {
        if (packet_size[i] > 0) {
            memcpy(current, packet[i], packet_size[i]);
            current += packet_size[i];
        }
    }
    assert(current == (uint8_t*)*extra + *extra_size);
    return VLC_SUCCESS;
}

static inline int xiph_AppendHeaders(int *extra_size, void **extra,
                                     unsigned size, const void *data)
{
    unsigned packet_size[XIPH_MAX_HEADER_COUNT];
    void *packet[XIPH_MAX_HEADER_COUNT];
    unsigned count;
    if (*extra_size > 0 && *extra) {
        if (xiph_SplitHeaders(packet_size, packet, &count, *extra_size, *extra))
            return VLC_EGENERIC;
    } else {
        count = 0;
    }
    if (count >= XIPH_MAX_HEADER_COUNT)
        return VLC_EGENERIC;

    free(*extra);

    packet_size[count] = size;
    packet[count]      = (void*)data;
    if (xiph_PackHeaders(extra_size, extra, packet_size, packet, count + 1)) {
        *extra_size = 0;
        *extra      = NULL;
    }
    for (unsigned i = 0; i < count; i++)
        free(packet[i]);

    if (*extra_size <= 0)
        return VLC_EGENERIC;
    return VLC_SUCCESS;
}