The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       block_header_decoder.c
/// \brief      Decodes Block Header 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 "common.h"
#include "check.h"


static void
free_properties(lzma_block *block, lzma_allocator *allocator)
{
    // Free allocated filter options. The last array member is not
    // touched after the initialization in the beginning of
    // lzma_block_header_decode(), so we don't need to touch that here.
    for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i) {
        lzma_free(block->filters[i].options, allocator);
        block->filters[i].id = LZMA_VLI_UNKNOWN;
        block->filters[i].options = NULL;
    }

    return;
}


extern LZMA_API(lzma_ret)
lzma_block_header_decode(lzma_block *block,
        lzma_allocator *allocator, const uint8_t *in)
{
    // NOTE: We consider the header to be corrupt not only when the
    // CRC32 doesn't match, but also when variable-length integers
    // are invalid or over 63 bits, or if the header is too small
    // to contain the claimed information.

    // Initialize the filter options array. This way the caller can
    // safely free() the options even if an error occurs in this function.
    for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) {
        block->filters[i].id = LZMA_VLI_UNKNOWN;
        block->filters[i].options = NULL;
    }

    // Always zero for now.
    block->version = 0;

    // Validate Block Header Size and Check type. The caller must have
    // already set these, so it is a programming error if this test fails.
    if (lzma_block_header_size_decode(in[0]) != block->header_size
            || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX)
        return LZMA_PROG_ERROR;

    // Exclude the CRC32 field.
    const size_t in_size = block->header_size - 4;

    // Verify CRC32
    if (lzma_crc32(in, in_size, 0) != unaligned_read32le(in + in_size))
        return LZMA_DATA_ERROR;

    // Check for unsupported flags.
    if (in[1] & 0x3C)
        return LZMA_OPTIONS_ERROR;

    // Start after the Block Header Size and Block Flags fields.
    size_t in_pos = 2;

    // Compressed Size
    if (in[1] & 0x40) {
        return_if_error(lzma_vli_decode(&block->compressed_size,
                NULL, in, &in_pos, in_size));

        // Validate Compressed Size. This checks that it isn't zero
        // and that the total size of the Block is a valid VLI.
        if (lzma_block_unpadded_size(block) == 0)
            return LZMA_DATA_ERROR;
    } else {
        block->compressed_size = LZMA_VLI_UNKNOWN;
    }

    // Uncompressed Size
    if (in[1] & 0x80)
        return_if_error(lzma_vli_decode(&block->uncompressed_size,
                NULL, in, &in_pos, in_size));
    else
        block->uncompressed_size = LZMA_VLI_UNKNOWN;

    // Filter Flags
    const size_t filter_count = (in[1] & 3) + 1;
    for (size_t i = 0; i < filter_count; ++i) {
        const lzma_ret ret = lzma_filter_flags_decode(
                &block->filters[i], allocator,
                in, &in_pos, in_size);
        if (ret != LZMA_OK) {
            free_properties(block, allocator);
            return ret;
        }
    }

    // Padding
    while (in_pos < in_size) {
        if (in[in_pos++] != 0x00) {
            free_properties(block, allocator);

            // Possibly some new field present so use
            // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
            return LZMA_OPTIONS_ERROR;
        }
    }

    return LZMA_OK;
}