The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       alone_decoder.c
/// \brief      Decoder for LZMA_Alone files
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "alone_decoder.h"
#include "lzma_decoder.h"
#include "lz_decoder.h"


struct lzma_coder_s {
    lzma_next_coder next;

    enum {
        SEQ_PROPERTIES,
        SEQ_DICTIONARY_SIZE,
        SEQ_UNCOMPRESSED_SIZE,
        SEQ_CODER_INIT,
        SEQ_CODE,
    } sequence;

    /// Position in the header fields
    size_t pos;

    /// Uncompressed size decoded from the header
    lzma_vli uncompressed_size;

    /// Memory usage limit
    uint64_t memlimit;

    /// Amount of memory actually needed (only an estimate)
    uint64_t memusage;

    /// Options decoded from the header needed to initialize
    /// the LZMA decoder
    lzma_options_lzma options;
};


static lzma_ret
alone_decode(lzma_coder *coder,
        lzma_allocator *allocator lzma_attribute((unused)),
        const uint8_t *restrict in, size_t *restrict in_pos,
        size_t in_size, uint8_t *restrict out,
        size_t *restrict out_pos, size_t out_size,
        lzma_action action)
{
    while (*out_pos < out_size
            && (coder->sequence == SEQ_CODE || *in_pos < in_size))
    switch (coder->sequence) {
    case SEQ_PROPERTIES:
        if (lzma_lzma_lclppb_decode(&coder->options, in[*in_pos]))
            return LZMA_FORMAT_ERROR;

        coder->sequence = SEQ_DICTIONARY_SIZE;
        ++*in_pos;
        break;

    case SEQ_DICTIONARY_SIZE:
        coder->options.dict_size
                |= (size_t)(in[*in_pos]) << (coder->pos * 8);

        if (++coder->pos == 4) {
            if (coder->options.dict_size != UINT32_MAX) {
                // A hack to ditch tons of false positives:
                // We allow only dictionary sizes that are
                // 2^n or 2^n + 2^(n-1). LZMA_Alone created
                // only files with 2^n, but accepts any
                // dictionary size. If someone complains, this
                // will be reconsidered.
                uint32_t d = coder->options.dict_size - 1;
                d |= d >> 2;
                d |= d >> 3;
                d |= d >> 4;
                d |= d >> 8;
                d |= d >> 16;
                ++d;

                if (d != coder->options.dict_size)
                    return LZMA_FORMAT_ERROR;
            }

            coder->pos = 0;
            coder->sequence = SEQ_UNCOMPRESSED_SIZE;
        }

        ++*in_pos;
        break;

    case SEQ_UNCOMPRESSED_SIZE:
        coder->uncompressed_size
                |= (lzma_vli)(in[*in_pos]) << (coder->pos * 8);
        ++*in_pos;
        if (++coder->pos < 8)
            break;

        // Another hack to ditch false positives: Assume that
        // if the uncompressed size is known, it must be less
        // than 256 GiB. Again, if someone complains, this
        // will be reconsidered.
        if (coder->uncompressed_size != LZMA_VLI_UNKNOWN
                && coder->uncompressed_size
                    >= (LZMA_VLI_C(1) << 38))
            return LZMA_FORMAT_ERROR;

        // Calculate the memory usage so that it is ready
        // for SEQ_CODER_INIT.
        coder->memusage = lzma_lzma_decoder_memusage(&coder->options)
                + LZMA_MEMUSAGE_BASE;

        coder->pos = 0;
        coder->sequence = SEQ_CODER_INIT;

    // Fall through

    case SEQ_CODER_INIT: {
        if (coder->memusage > coder->memlimit)
            return LZMA_MEMLIMIT_ERROR;

        lzma_filter_info filters[2] = {
            {
                .init = &lzma_lzma_decoder_init,
                .options = &coder->options,
            }, {
                .init = NULL,
            }
        };

        const lzma_ret ret = lzma_next_filter_init(&coder->next,
                allocator, filters);
        if (ret != LZMA_OK)
            return ret;

        // Use a hack to set the uncompressed size.
        lzma_lz_decoder_uncompressed(coder->next.coder,
                coder->uncompressed_size);

        coder->sequence = SEQ_CODE;
        break;
    }

    case SEQ_CODE: {
        return coder->next.code(coder->next.coder,
                allocator, in, in_pos, in_size,
                out, out_pos, out_size, action);
    }

    default:
        return LZMA_PROG_ERROR;
    }

    return LZMA_OK;
}


static void
alone_decoder_end(lzma_coder *coder, lzma_allocator *allocator)
{
    lzma_next_end(&coder->next, allocator);
    lzma_free(coder, allocator);
    return;
}


static lzma_ret
alone_decoder_memconfig(lzma_coder *coder, uint64_t *memusage,
        uint64_t *old_memlimit, uint64_t new_memlimit)
{
    if (new_memlimit != 0 && new_memlimit < coder->memusage)
        return LZMA_MEMLIMIT_ERROR;

    *memusage = coder->memusage;
    *old_memlimit = coder->memlimit;
    coder->memlimit = new_memlimit;

    return LZMA_OK;
}


extern lzma_ret
lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
        uint64_t memlimit)
{
    lzma_next_coder_init(&lzma_alone_decoder_init, next, allocator);

    if (memlimit == 0)
        return LZMA_PROG_ERROR;

    if (next->coder == NULL) {
        next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
        if (next->coder == NULL)
            return LZMA_MEM_ERROR;

        next->code = &alone_decode;
        next->end = &alone_decoder_end;
        next->memconfig = &alone_decoder_memconfig;
        next->coder->next = LZMA_NEXT_CODER_INIT;
    }

    next->coder->sequence = SEQ_PROPERTIES;
    next->coder->pos = 0;
    next->coder->options.dict_size = 0;
    next->coder->options.preset_dict = NULL;
    next->coder->options.preset_dict_size = 0;
    next->coder->uncompressed_size = 0;
    next->coder->memlimit = memlimit;
    next->coder->memusage = LZMA_MEMUSAGE_BASE;

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_alone_decoder(lzma_stream *strm, uint64_t memlimit)
{
    lzma_next_strm_init(lzma_alone_decoder_init, strm, memlimit);

    strm->internal->supported_actions[LZMA_RUN] = true;
    strm->internal->supported_actions[LZMA_FINISH] = true;

    return LZMA_OK;
}