liblzma/common/index_encoder.c

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       index_encoder.c
/// \brief      Encodes the Index field
//
//  Author:     Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#include "index_encoder.h"
#include "index.h"
#include "check.h"


typedef struct {
	enum {
		SEQ_INDICATOR,
		SEQ_COUNT,
		SEQ_UNPADDED,
		SEQ_UNCOMPRESSED,
		SEQ_NEXT,
		SEQ_PADDING,
		SEQ_CRC32,
	} sequence;

	/// Index being encoded
	const lzma_index *index;

	/// Iterator for the Index being encoded
	lzma_index_iter iter;

	/// Position in integers
	size_t pos;

	/// CRC32 of the List of Records field
	uint32_t crc32;
} lzma_index_coder;


static lzma_ret
index_encode(void *coder_ptr,
		const lzma_allocator *allocator lzma_attribute((__unused__)),
		const uint8_t *restrict in lzma_attribute((__unused__)),
		size_t *restrict in_pos lzma_attribute((__unused__)),
		size_t in_size lzma_attribute((__unused__)),
		uint8_t *restrict out, size_t *restrict out_pos,
		size_t out_size,
		lzma_action action lzma_attribute((__unused__)))
{
	lzma_index_coder *coder = coder_ptr;

	// Position where to start calculating CRC32. The idea is that we
	// need to call lzma_crc32() only once per call to index_encode().
	const size_t out_start = *out_pos;

	// Return value to use if we return at the end of this function.
	// We use "goto out" to jump out of the while-switch construct
	// instead of returning directly, because that way we don't need
	// to copypaste the lzma_crc32() call to many places.
	lzma_ret ret = LZMA_OK;

	while (*out_pos < out_size)
	switch (coder->sequence) {
	case SEQ_INDICATOR:
		out[*out_pos] = INDEX_INDICATOR;
		++*out_pos;
		coder->sequence = SEQ_COUNT;
		break;

	case SEQ_COUNT: {
		const lzma_vli count = lzma_index_block_count(coder->index);
		ret = lzma_vli_encode(count, &coder->pos,
				out, out_pos, out_size);
		if (ret != LZMA_STREAM_END)
			goto out;

		ret = LZMA_OK;
		coder->pos = 0;
		coder->sequence = SEQ_NEXT;
		break;
	}

	case SEQ_NEXT:
		if (lzma_index_iter_next(
				&coder->iter, LZMA_INDEX_ITER_BLOCK)) {
			// Get the size of the Index Padding field.
			coder->pos = lzma_index_padding_size(coder->index);
			assert(coder->pos <= 3);
			coder->sequence = SEQ_PADDING;
			break;
		}

		coder->sequence = SEQ_UNPADDED;
		FALLTHROUGH;

	case SEQ_UNPADDED:
	case SEQ_UNCOMPRESSED: {
		const lzma_vli size = coder->sequence == SEQ_UNPADDED
				? coder->iter.block.unpadded_size
				: coder->iter.block.uncompressed_size;

		ret = lzma_vli_encode(size, &coder->pos,
				out, out_pos, out_size);
		if (ret != LZMA_STREAM_END)
			goto out;

		ret = LZMA_OK;
		coder->pos = 0;

		// Advance to SEQ_UNCOMPRESSED or SEQ_NEXT.
		++coder->sequence;
		break;
	}

	case SEQ_PADDING:
		if (coder->pos > 0) {
			--coder->pos;
			out[(*out_pos)++] = 0x00;
			break;
		}

		// Finish the CRC32 calculation.
		coder->crc32 = lzma_crc32(out + out_start,
				*out_pos - out_start, coder->crc32);

		coder->sequence = SEQ_CRC32;
		FALLTHROUGH;

	case SEQ_CRC32:
		// We don't use the main loop, because we don't want
		// coder->crc32 to be touched anymore.
		do {
			if (*out_pos == out_size)
				return LZMA_OK;

			out[*out_pos] = (coder->crc32 >> (coder->pos * 8))
					& 0xFF;
			++*out_pos;

		} while (++coder->pos < 4);

		return LZMA_STREAM_END;

	default:
		assert(0);
		return LZMA_PROG_ERROR;
	}

out:
	// Update the CRC32.
	//
	// Avoid null pointer + 0 (undefined behavior) in "out + out_start".
	// In such a case we had no input and thus out_used == 0.
	{
		const size_t out_used = *out_pos - out_start;
		if (out_used > 0)
			coder->crc32 = lzma_crc32(out + out_start,
					out_used, coder->crc32);
	}

	return ret;
}


static void
index_encoder_end(void *coder, const lzma_allocator *allocator)
{
	lzma_free(coder, allocator);
	return;
}


static void
index_encoder_reset(lzma_index_coder *coder, const lzma_index *i)
{
	lzma_index_iter_init(&coder->iter, i);

	coder->sequence = SEQ_INDICATOR;
	coder->index = i;
	coder->pos = 0;
	coder->crc32 = 0;

	return;
}


extern lzma_ret
lzma_index_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
		const lzma_index *i)
{
	lzma_next_coder_init(&lzma_index_encoder_init, next, allocator);

	if (i == NULL)
		return LZMA_PROG_ERROR;

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

		next->code = &index_encode;
		next->end = &index_encoder_end;
	}

	index_encoder_reset(next->coder, i);

	return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_encoder(lzma_stream *strm, const lzma_index *i)
{
	lzma_next_strm_init(lzma_index_encoder_init, strm, i);

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

	return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_buffer_encode(const lzma_index *i,
		uint8_t *out, size_t *out_pos, size_t out_size)
{
	// Validate the arguments.
	if (i == NULL || out == NULL || out_pos == NULL || *out_pos > out_size)
		return LZMA_PROG_ERROR;

	// Don't try to encode if there's not enough output space.
	if (out_size - *out_pos < lzma_index_size(i))
		return LZMA_BUF_ERROR;

	// The Index encoder needs just one small data structure so we can
	// allocate it on stack.
	lzma_index_coder coder;
	index_encoder_reset(&coder, i);

	// Do the actual encoding. This should never fail, but store
	// the original *out_pos just in case.
	const size_t out_start = *out_pos;
	lzma_ret ret = index_encode(&coder, NULL, NULL, NULL, 0,
			out, out_pos, out_size, LZMA_RUN);

	if (ret == LZMA_STREAM_END) {
		ret = LZMA_OK;
	} else {
		// We should never get here, but just in case, restore the
		// output position and set the error accordingly if something
		// goes wrong and debugging isn't enabled.
		assert(0);
		*out_pos = out_start;
		ret = LZMA_PROG_ERROR;
	}

	return ret;
}