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;

}