The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       block_decoder.c
/// \brief      Decodes .xz Blocks
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "block_decoder.h"
#include "filter_decoder.h"
#include "check.h"


struct lzma_coder_s {
    enum {
        SEQ_CODE,
        SEQ_PADDING,
        SEQ_CHECK,
    } sequence;

    /// The filters in the chain; initialized with lzma_raw_decoder_init().
    lzma_next_coder next;

    /// Decoding options; we also write Compressed Size and Uncompressed
    /// Size back to this structure when the decoding has been finished.
    lzma_block *block;

    /// Compressed Size calculated while decoding
    lzma_vli compressed_size;

    /// Uncompressed Size calculated while decoding
    lzma_vli uncompressed_size;

    /// Maximum allowed Compressed Size; this takes into account the
    /// size of the Block Header and Check fields when Compressed Size
    /// is unknown.
    lzma_vli compressed_limit;

    /// Position when reading the Check field
    size_t check_pos;

    /// Check of the uncompressed data
    lzma_check_state check;
};


static inline bool
update_size(lzma_vli *size, lzma_vli add, lzma_vli limit)
{
    if (limit > LZMA_VLI_MAX)
        limit = LZMA_VLI_MAX;

    if (limit < *size || limit - *size < add)
        return true;

    *size += add;

    return false;
}


static inline bool
is_size_valid(lzma_vli size, lzma_vli reference)
{
    return reference == LZMA_VLI_UNKNOWN || reference == size;
}


static lzma_ret
block_decode(lzma_coder *coder, lzma_allocator *allocator,
        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)
{
    switch (coder->sequence) {
    case SEQ_CODE: {
        const size_t in_start = *in_pos;
        const size_t out_start = *out_pos;

        const lzma_ret ret = coder->next.code(coder->next.coder,
                allocator, in, in_pos, in_size,
                out, out_pos, out_size, action);

        const size_t in_used = *in_pos - in_start;
        const size_t out_used = *out_pos - out_start;

        // NOTE: We compare to compressed_limit here, which prevents
        // the total size of the Block growing past LZMA_VLI_MAX.
        if (update_size(&coder->compressed_size, in_used,
                    coder->compressed_limit)
                || update_size(&coder->uncompressed_size,
                    out_used,
                    coder->block->uncompressed_size))
            return LZMA_DATA_ERROR;

        lzma_check_update(&coder->check, coder->block->check,
                out + out_start, out_used);

        if (ret != LZMA_STREAM_END)
            return ret;

        // Compressed and Uncompressed Sizes are now at their final
        // values. Verify that they match the values given to us.
        if (!is_size_valid(coder->compressed_size,
                    coder->block->compressed_size)
                || !is_size_valid(coder->uncompressed_size,
                    coder->block->uncompressed_size))
            return LZMA_DATA_ERROR;

        // Copy the values into coder->block. The caller
        // may use this information to construct Index.
        coder->block->compressed_size = coder->compressed_size;
        coder->block->uncompressed_size = coder->uncompressed_size;

        coder->sequence = SEQ_PADDING;
    }

    // Fall through

    case SEQ_PADDING:
        // Compressed Data is padded to a multiple of four bytes.
        while (coder->compressed_size & 3) {
            if (*in_pos >= in_size)
                return LZMA_OK;

            // We use compressed_size here just get the Padding
            // right. The actual Compressed Size was stored to
            // coder->block already, and won't be modified by
            // us anymore.
            ++coder->compressed_size;

            if (in[(*in_pos)++] != 0x00)
                return LZMA_DATA_ERROR;
        }

        if (coder->block->check == LZMA_CHECK_NONE)
            return LZMA_STREAM_END;

        lzma_check_finish(&coder->check, coder->block->check);
        coder->sequence = SEQ_CHECK;

    // Fall through

    case SEQ_CHECK: {
        const size_t check_size = lzma_check_size(coder->block->check);
        lzma_bufcpy(in, in_pos, in_size, coder->block->raw_check,
                &coder->check_pos, check_size);
        if (coder->check_pos < check_size)
            return LZMA_OK;

        // Validate the Check only if we support it.
        // coder->check.buffer may be uninitialized
        // when the Check ID is not supported.
        if (lzma_check_is_supported(coder->block->check)
                && memcmp(coder->block->raw_check,
                    coder->check.buffer.u8,
                    check_size) != 0)
            return LZMA_DATA_ERROR;

        return LZMA_STREAM_END;
    }
    }

    return LZMA_PROG_ERROR;
}


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


extern lzma_ret
lzma_block_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
        lzma_block *block)
{
    lzma_next_coder_init(&lzma_block_decoder_init, next, allocator);

    // Validate the options. lzma_block_unpadded_size() does that for us
    // except for Uncompressed Size and filters. Filters are validated
    // by the raw decoder.
    if (lzma_block_unpadded_size(block) == 0
            || !lzma_vli_is_valid(block->uncompressed_size))
        return LZMA_PROG_ERROR;

    // Allocate and initialize *next->coder if needed.
    if (next->coder == NULL) {
        next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
        if (next->coder == NULL)
            return LZMA_MEM_ERROR;

        next->code = &block_decode;
        next->end = &block_decoder_end;
        next->coder->next = LZMA_NEXT_CODER_INIT;
    }

    // Basic initializations
    next->coder->sequence = SEQ_CODE;
    next->coder->block = block;
    next->coder->compressed_size = 0;
    next->coder->uncompressed_size = 0;

    // If Compressed Size is not known, we calculate the maximum allowed
    // value so that encoded size of the Block (including Block Padding)
    // is still a valid VLI and a multiple of four.
    next->coder->compressed_limit
            = block->compressed_size == LZMA_VLI_UNKNOWN
                ? (LZMA_VLI_MAX & ~LZMA_VLI_C(3))
                    - block->header_size
                    - lzma_check_size(block->check)
                : block->compressed_size;

    // Initialize the check. It's caller's problem if the Check ID is not
    // supported, and the Block decoder cannot verify the Check field.
    // Caller can test lzma_check_is_supported(block->check).
    next->coder->check_pos = 0;
    lzma_check_init(&next->coder->check, block->check);

    // Initialize the filter chain.
    return lzma_raw_decoder_init(&next->coder->next, allocator,
            block->filters);
}


extern LZMA_API(lzma_ret)
lzma_block_decoder(lzma_stream *strm, lzma_block *block)
{
    lzma_next_strm_init(lzma_block_decoder_init, strm, block);

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

    return LZMA_OK;
}