The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       stream_flags_decoder.c
/// \brief      Decodes Stream Header and Stream Footer from .xz files
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "stream_flags_common.h"


static bool
stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
{
    // Reserved bits must be unset.
    if (in[0] != 0x00 || (in[1] & 0xF0))
        return true;

    options->version = 0;
    options->check = in[1] & 0x0F;

    return false;
}


extern LZMA_API(lzma_ret)
lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
{
    // Magic
    if (memcmp(in, lzma_header_magic, sizeof(lzma_header_magic)) != 0)
        return LZMA_FORMAT_ERROR;

    // Verify the CRC32 so we can distinguish between corrupt
    // and unsupported files.
    const uint32_t crc = lzma_crc32(in + sizeof(lzma_header_magic),
            LZMA_STREAM_FLAGS_SIZE, 0);
    if (crc != unaligned_read32le(in + sizeof(lzma_header_magic)
            + LZMA_STREAM_FLAGS_SIZE))
        return LZMA_DATA_ERROR;

    // Stream Flags
    if (stream_flags_decode(options, in + sizeof(lzma_header_magic)))
        return LZMA_OPTIONS_ERROR;

    // Set Backward Size to indicate unknown value. That way
    // lzma_stream_flags_compare() can be used to compare Stream Header
    // and Stream Footer while keeping it useful also for comparing
    // two Stream Footers.
    options->backward_size = LZMA_VLI_UNKNOWN;

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_stream_footer_decode(lzma_stream_flags *options, const uint8_t *in)
{
    // Magic
    if (memcmp(in + sizeof(uint32_t) * 2 + LZMA_STREAM_FLAGS_SIZE,
            lzma_footer_magic, sizeof(lzma_footer_magic)) != 0)
        return LZMA_FORMAT_ERROR;

    // CRC32
    const uint32_t crc = lzma_crc32(in + sizeof(uint32_t),
            sizeof(uint32_t) + LZMA_STREAM_FLAGS_SIZE, 0);
    if (crc != unaligned_read32le(in))
        return LZMA_DATA_ERROR;

    // Stream Flags
    if (stream_flags_decode(options, in + sizeof(uint32_t) * 2))
        return LZMA_OPTIONS_ERROR;

    // Backward Size
    options->backward_size = unaligned_read32le(in + sizeof(uint32_t));
    options->backward_size = (options->backward_size + 1) * 4;

    return LZMA_OK;
}