src/liblzma/common/stream_decoder.c - jrn/xz - Git at Google

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

 #include "stream_decoder.h"
 #include "block_decoder.h"


 struct lzma_coder_s {
 	enum {
 		SEQ_STREAM_HEADER,
 		SEQ_BLOCK_HEADER,
 		SEQ_BLOCK,
 		SEQ_INDEX,
 		SEQ_STREAM_FOOTER,
 		SEQ_STREAM_PADDING,
 	} sequence;

 	/// Block or Metadata decoder. This takes little memory and the same
 	/// data structure can be used to decode every Block Header, so it's
 	/// a good idea to have a separate lzma_next_coder structure for it.
 	lzma_next_coder block_decoder;

 	/// Block options decoded by the Block Header decoder and used by
 	/// the Block decoder.
 	lzma_block block_options;

 	/// Stream Flags from Stream Header
 	lzma_stream_flags stream_flags;

 	/// Index is hashed so that it can be compared to the sizes of Blocks
 	/// with O(1) memory usage.
 	lzma_index_hash *index_hash;

 	/// Memory usage limit
 	uint64_t memlimit;

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

 	/// If true, LZMA_NO_CHECK is returned if the Stream has
 	/// no integrity check.
 	bool tell_no_check;

 	/// If true, LZMA_UNSUPPORTED_CHECK is returned if the Stream has
 	/// an integrity check that isn't supported by this liblzma build.
 	bool tell_unsupported_check;

 	/// If true, LZMA_GET_CHECK is returned after decoding Stream Header.
 	bool tell_any_check;

 	/// If true, we will tell the Block decoder to skip calculating
 	/// and verifying the integrity check.
 	bool ignore_check;

 	/// If true, we will decode concatenated Streams that possibly have
 	/// Stream Padding between or after them. LZMA_STREAM_END is returned
 	/// once the application isn't giving us any new input, and we aren't
 	/// in the middle of a Stream, and possible Stream Padding is a
 	/// multiple of four bytes.
 	bool concatenated;

 	/// When decoding concatenated Streams, this is true as long as we
 	/// are decoding the first Stream. This is needed to avoid misleading
 	/// LZMA_FORMAT_ERROR in case the later Streams don't have valid magic
 	/// bytes.
 	bool first_stream;

 	/// Write position in buffer[] and position in Stream Padding
 	size_t pos;

 	/// Buffer to hold Stream Header, Block Header, and Stream Footer.
 	/// Block Header has biggest maximum size.
 	uint8_t buffer[LZMA_BLOCK_HEADER_SIZE_MAX];
 };


 static lzma_ret
 stream_decoder_reset(lzma_coder *coder, const lzma_allocator *allocator)
 {
 	// Initialize the Index hash used to verify the Index.
 	coder->index_hash = lzma_index_hash_init(coder->index_hash, allocator);
 	if (coder->index_hash == NULL)
 		return LZMA_MEM_ERROR;

 	// Reset the rest of the variables.
 	coder->sequence = SEQ_STREAM_HEADER;
 	coder->pos = 0;

 	return LZMA_OK;
 }


 static lzma_ret
 stream_decode(lzma_coder *coder, const 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)
 {
 	// When decoding the actual Block, it may be able to produce more
 	// output even if we don't give it any new input.
 	while (true)
 	switch (coder->sequence) {
 	case SEQ_STREAM_HEADER: {
 		// Copy the Stream Header to the internal buffer.
 		lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
 				LZMA_STREAM_HEADER_SIZE);

 		// Return if we didn't get the whole Stream Header yet.
 		if (coder->pos < LZMA_STREAM_HEADER_SIZE)
 			return LZMA_OK;

 		coder->pos = 0;

 		// Decode the Stream Header.
 		const lzma_ret ret = lzma_stream_header_decode(
 				&coder->stream_flags, coder->buffer);
 		if (ret != LZMA_OK)
 			return ret == LZMA_FORMAT_ERROR && !coder->first_stream
 					? LZMA_DATA_ERROR : ret;

 		// If we are decoding concatenated Streams, and the later
 		// Streams have invalid Header Magic Bytes, we give
 		// LZMA_DATA_ERROR instead of LZMA_FORMAT_ERROR.
 		coder->first_stream = false;

 		// Copy the type of the Check so that Block Header and Block
 		// decoders see it.
 		coder->block_options.check = coder->stream_flags.check;

 		// Even if we return LZMA_*_CHECK below, we want
 		// to continue from Block Header decoding.
 		coder->sequence = SEQ_BLOCK_HEADER;

 		// Detect if there's no integrity check or if it is
 		// unsupported if those were requested by the application.
 		if (coder->tell_no_check && coder->stream_flags.check
 				== LZMA_CHECK_NONE)
 			return LZMA_NO_CHECK;

 		if (coder->tell_unsupported_check
 				&& !lzma_check_is_supported(
 					coder->stream_flags.check))
 			return LZMA_UNSUPPORTED_CHECK;

 		if (coder->tell_any_check)
 			return LZMA_GET_CHECK;
 	}

 	// Fall through

 	case SEQ_BLOCK_HEADER: {
 		if (*in_pos >= in_size)
 			return LZMA_OK;

 		if (coder->pos == 0) {
 			// Detect if it's Index.
 			if (in[*in_pos] == 0x00) {
 				coder->sequence = SEQ_INDEX;
 				break;
 			}

 			// Calculate the size of the Block Header. Note that
 			// Block Header decoder wants to see this byte too
 			// so don't advance *in_pos.
 			coder->block_options.header_size
 					= lzma_block_header_size_decode(
 						in[*in_pos]);
 		}

 		// Copy the Block Header to the internal buffer.
 		lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
 				coder->block_options.header_size);

 		// Return if we didn't get the whole Block Header yet.
 		if (coder->pos < coder->block_options.header_size)
 			return LZMA_OK;

 		coder->pos = 0;

 		// Version 1 is needed to support the .ignore_check option.
 		coder->block_options.version = 1;

 		// Set up a buffer to hold the filter chain. Block Header
 		// decoder will initialize all members of this array so
 		// we don't need to do it here.
 		lzma_filter filters[LZMA_FILTERS_MAX + 1];
 		coder->block_options.filters = filters;

 		// Decode the Block Header.
 		return_if_error(lzma_block_header_decode(&coder->block_options,
 				allocator, coder->buffer));

 		// If LZMA_IGNORE_CHECK was used, this flag needs to be set.
 		// It has to be set after lzma_block_header_decode() because
 		// it always resets this to false.
 		coder->block_options.ignore_check = coder->ignore_check;

 		// Check the memory usage limit.
 		const uint64_t memusage = lzma_raw_decoder_memusage(filters);
 		lzma_ret ret;

 		if (memusage == UINT64_MAX) {
 			// One or more unknown Filter IDs.
 			ret = LZMA_OPTIONS_ERROR;
 		} else {
 			// Now we can set coder->memusage since we know that
 			// the filter chain is valid. We don't want
 			// lzma_memusage() to return UINT64_MAX in case of
 			// invalid filter chain.
 			coder->memusage = memusage;

 			if (memusage > coder->memlimit) {
 				// The chain would need too much memory.
 				ret = LZMA_MEMLIMIT_ERROR;
 			} else {
 				// Memory usage is OK.
 				// Initialize the Block decoder.
 				ret = lzma_block_decoder_init(
 						&coder->block_decoder,
 						allocator,
 						&coder->block_options);
 			}
 		}

 		// Free the allocated filter options since they are needed
 		// only to initialize the Block decoder.
 		for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i)
 			lzma_free(filters[i].options, allocator);

 		coder->block_options.filters = NULL;

 		// Check if memory usage calculation and Block enocoder
 		// initialization succeeded.
 		if (ret != LZMA_OK)
 			return ret;

 		coder->sequence = SEQ_BLOCK;
 	}

 	// Fall through

 	case SEQ_BLOCK: {
 		const lzma_ret ret = coder->block_decoder.code(
 				coder->block_decoder.coder, allocator,
 				in, in_pos, in_size, out, out_pos, out_size,
 				action);

 		if (ret != LZMA_STREAM_END)
 			return ret;

 		// Block decoded successfully. Add the new size pair to
 		// the Index hash.
 		return_if_error(lzma_index_hash_append(coder->index_hash,
 				lzma_block_unpadded_size(
 					&coder->block_options),
 				coder->block_options.uncompressed_size));

 		coder->sequence = SEQ_BLOCK_HEADER;
 		break;
 	}

 	case SEQ_INDEX: {
 		// If we don't have any input, don't call
 		// lzma_index_hash_decode() since it would return
 		// LZMA_BUF_ERROR, which we must not do here.
 		if (*in_pos >= in_size)
 			return LZMA_OK;

 		// Decode the Index and compare it to the hash calculated
 		// from the sizes of the Blocks (if any).
 		const lzma_ret ret = lzma_index_hash_decode(coder->index_hash,
 				in, in_pos, in_size);
 		if (ret != LZMA_STREAM_END)
 			return ret;

 		coder->sequence = SEQ_STREAM_FOOTER;
 	}

 	// Fall through

 	case SEQ_STREAM_FOOTER: {
 		// Copy the Stream Footer to the internal buffer.
 		lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
 				LZMA_STREAM_HEADER_SIZE);

 		// Return if we didn't get the whole Stream Footer yet.
 		if (coder->pos < LZMA_STREAM_HEADER_SIZE)
 			return LZMA_OK;

 		coder->pos = 0;

 		// Decode the Stream Footer. The decoder gives
 		// LZMA_FORMAT_ERROR if the magic bytes don't match,
 		// so convert that return code to LZMA_DATA_ERROR.
 		lzma_stream_flags footer_flags;
 		const lzma_ret ret = lzma_stream_footer_decode(
 				&footer_flags, coder->buffer);
 		if (ret != LZMA_OK)
 			return ret == LZMA_FORMAT_ERROR
 					? LZMA_DATA_ERROR : ret;

 		// Check that Index Size stored in the Stream Footer matches
 		// the real size of the Index field.
 		if (lzma_index_hash_size(coder->index_hash)
 				!= footer_flags.backward_size)
 			return LZMA_DATA_ERROR;

 		// Compare that the Stream Flags fields are identical in
 		// both Stream Header and Stream Footer.
 		return_if_error(lzma_stream_flags_compare(
 				&coder->stream_flags, &footer_flags));

 		if (!coder->concatenated)
 			return LZMA_STREAM_END;

 		coder->sequence = SEQ_STREAM_PADDING;
 	}

 	// Fall through

 	case SEQ_STREAM_PADDING:
 		assert(coder->concatenated);

 		// Skip over possible Stream Padding.
 		while (true) {
 			if (*in_pos >= in_size) {
 				// Unless LZMA_FINISH was used, we cannot
 				// know if there's more input coming later.
 				if (action != LZMA_FINISH)
 					return LZMA_OK;

 				// Stream Padding must be a multiple of
 				// four bytes.
 				return coder->pos == 0
 						? LZMA_STREAM_END
 						: LZMA_DATA_ERROR;
 			}

 			// If the byte is not zero, it probably indicates
 			// beginning of a new Stream (or the file is corrupt).
 			if (in[*in_pos] != 0x00)
 				break;

 			++*in_pos;
 			coder->pos = (coder->pos + 1) & 3;
 		}

 		// Stream Padding must be a multiple of four bytes (empty
 		// Stream Padding is OK).
 		if (coder->pos != 0) {
 			++*in_pos;
 			return LZMA_DATA_ERROR;
 		}

 		// Prepare to decode the next Stream.
 		return_if_error(stream_decoder_reset(coder, allocator));
 		break;

 	default:
 		assert(0);
 		return LZMA_PROG_ERROR;
 	}

 	// Never reached
 }


 static void
 stream_decoder_end(lzma_coder *coder, const lzma_allocator *allocator)
 {
 	lzma_next_end(&coder->block_decoder, allocator);
 	lzma_index_hash_end(coder->index_hash, allocator);
 	lzma_free(coder, allocator);
 	return;
 }


 static lzma_check
 stream_decoder_get_check(const lzma_coder *coder)
 {
 	return coder->stream_flags.check;
 }


 static lzma_ret
 stream_decoder_memconfig(lzma_coder *coder, uint64_t *memusage,
 		uint64_t *old_memlimit, uint64_t new_memlimit)
 {
 	*memusage = coder->memusage;
 	*old_memlimit = coder->memlimit;

 	if (new_memlimit != 0) {
 		if (new_memlimit < coder->memusage)
 			return LZMA_MEMLIMIT_ERROR;

 		coder->memlimit = new_memlimit;
 	}

 	return LZMA_OK;
 }


 extern lzma_ret
 lzma_stream_decoder_init(
 		lzma_next_coder *next, const lzma_allocator *allocator,
 		uint64_t memlimit, uint32_t flags)
 {
 	lzma_next_coder_init(&lzma_stream_decoder_init, next, allocator);

 	if (memlimit == 0)
 		return LZMA_PROG_ERROR;

 	if (flags & ~LZMA_SUPPORTED_FLAGS)
 		return LZMA_OPTIONS_ERROR;

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

 		next->code = &stream_decode;
 		next->end = &stream_decoder_end;
 		next->get_check = &stream_decoder_get_check;
 		next->memconfig = &stream_decoder_memconfig;

 		next->coder->block_decoder = LZMA_NEXT_CODER_INIT;
 		next->coder->index_hash = NULL;
 	}

 	next->coder->memlimit = memlimit;
 	next->coder->memusage = LZMA_MEMUSAGE_BASE;
 	next->coder->tell_no_check = (flags & LZMA_TELL_NO_CHECK) != 0;
 	next->coder->tell_unsupported_check
 			= (flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;
 	next->coder->tell_any_check = (flags & LZMA_TELL_ANY_CHECK) != 0;
 	next->coder->ignore_check = (flags & LZMA_IGNORE_CHECK) != 0;
 	next->coder->concatenated = (flags & LZMA_CONCATENATED) != 0;
 	next->coder->first_stream = true;

 	return stream_decoder_reset(next->coder, allocator);
 }


 extern LZMA_API(lzma_ret)
 lzma_stream_decoder(lzma_stream *strm, uint64_t memlimit, uint32_t flags)
 {
 	lzma_next_strm_init(lzma_stream_decoder_init, strm, memlimit, flags);

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

 	return LZMA_OK;
 }
	///////////////////////////////////////////////////////////////////////////////
	//
	/// \file stream_decoder.c
	/// \brief Decodes .xz Streams
	//
	// Author: Lasse Collin
	//
	// This file has been put into the public domain.
	// You can do whatever you want with this file.
	//
	///////////////////////////////////////////////////////////////////////////////

	#include "stream_decoder.h"
	#include "block_decoder.h"


	struct lzma_coder_s {
	enum {
	SEQ_STREAM_HEADER,
	SEQ_BLOCK_HEADER,
	SEQ_BLOCK,
	SEQ_INDEX,
	SEQ_STREAM_FOOTER,
	SEQ_STREAM_PADDING,
	} sequence;

	/// Block or Metadata decoder. This takes little memory and the same
	/// data structure can be used to decode every Block Header, so it's
	/// a good idea to have a separate lzma_next_coder structure for it.
	lzma_next_coder block_decoder;

	/// Block options decoded by the Block Header decoder and used by
	/// the Block decoder.
	lzma_block block_options;

	/// Stream Flags from Stream Header
	lzma_stream_flags stream_flags;

	/// Index is hashed so that it can be compared to the sizes of Blocks
	/// with O(1) memory usage.
	lzma_index_hash *index_hash;

	/// Memory usage limit
	uint64_t memlimit;

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

	/// If true, LZMA_NO_CHECK is returned if the Stream has
	/// no integrity check.
	bool tell_no_check;

	/// If true, LZMA_UNSUPPORTED_CHECK is returned if the Stream has
	/// an integrity check that isn't supported by this liblzma build.
	bool tell_unsupported_check;

	/// If true, LZMA_GET_CHECK is returned after decoding Stream Header.
	bool tell_any_check;

	/// If true, we will tell the Block decoder to skip calculating
	/// and verifying the integrity check.
	bool ignore_check;

	/// If true, we will decode concatenated Streams that possibly have
	/// Stream Padding between or after them. LZMA_STREAM_END is returned
	/// once the application isn't giving us any new input, and we aren't
	/// in the middle of a Stream, and possible Stream Padding is a
	/// multiple of four bytes.
	bool concatenated;

	/// When decoding concatenated Streams, this is true as long as we
	/// are decoding the first Stream. This is needed to avoid misleading
	/// LZMA_FORMAT_ERROR in case the later Streams don't have valid magic
	/// bytes.
	bool first_stream;

	/// Write position in buffer[] and position in Stream Padding
	size_t pos;

	/// Buffer to hold Stream Header, Block Header, and Stream Footer.
	/// Block Header has biggest maximum size.
	uint8_t buffer[LZMA_BLOCK_HEADER_SIZE_MAX];
	};


	static lzma_ret
	stream_decoder_reset(lzma_coder coder, const lzma_allocator allocator)
	{
	// Initialize the Index hash used to verify the Index.
	coder->index_hash = lzma_index_hash_init(coder->index_hash, allocator);
	if (coder->index_hash == NULL)
	return LZMA_MEM_ERROR;

	// Reset the rest of the variables.
	coder->sequence = SEQ_STREAM_HEADER;
	coder->pos = 0;

	return LZMA_OK;
	}


	static lzma_ret
	stream_decode(lzma_coder coder, const 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)
	{
	// When decoding the actual Block, it may be able to produce more
	// output even if we don't give it any new input.
	while (true)
	switch (coder->sequence) {
	case SEQ_STREAM_HEADER: {
	// Copy the Stream Header to the internal buffer.
	lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
	LZMA_STREAM_HEADER_SIZE);

	// Return if we didn't get the whole Stream Header yet.
	if (coder->pos < LZMA_STREAM_HEADER_SIZE)
	return LZMA_OK;

	coder->pos = 0;

	// Decode the Stream Header.
	const lzma_ret ret = lzma_stream_header_decode(
	&coder->stream_flags, coder->buffer);
	if (ret != LZMA_OK)
	return ret == LZMA_FORMAT_ERROR && !coder->first_stream
	? LZMA_DATA_ERROR : ret;

	// If we are decoding concatenated Streams, and the later
	// Streams have invalid Header Magic Bytes, we give
	// LZMA_DATA_ERROR instead of LZMA_FORMAT_ERROR.
	coder->first_stream = false;

	// Copy the type of the Check so that Block Header and Block
	// decoders see it.
	coder->block_options.check = coder->stream_flags.check;

	// Even if we return LZMA_*_CHECK below, we want
	// to continue from Block Header decoding.
	coder->sequence = SEQ_BLOCK_HEADER;

	// Detect if there's no integrity check or if it is
	// unsupported if those were requested by the application.
	if (coder->tell_no_check && coder->stream_flags.check
	== LZMA_CHECK_NONE)
	return LZMA_NO_CHECK;

	if (coder->tell_unsupported_check
	&& !lzma_check_is_supported(
	coder->stream_flags.check))
	return LZMA_UNSUPPORTED_CHECK;

	if (coder->tell_any_check)
	return LZMA_GET_CHECK;
	}

	// Fall through

	case SEQ_BLOCK_HEADER: {
	if (*in_pos >= in_size)
	return LZMA_OK;

	if (coder->pos == 0) {
	// Detect if it's Index.
	if (in[*in_pos] == 0x00) {
	coder->sequence = SEQ_INDEX;
	break;
	}

	// Calculate the size of the Block Header. Note that
	// Block Header decoder wants to see this byte too
	// so don't advance *in_pos.
	coder->block_options.header_size
	= lzma_block_header_size_decode(
	in[*in_pos]);
	}

	// Copy the Block Header to the internal buffer.
	lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
	coder->block_options.header_size);

	// Return if we didn't get the whole Block Header yet.
	if (coder->pos < coder->block_options.header_size)
	return LZMA_OK;

	coder->pos = 0;

	// Version 1 is needed to support the .ignore_check option.
	coder->block_options.version = 1;

	// Set up a buffer to hold the filter chain. Block Header
	// decoder will initialize all members of this array so
	// we don't need to do it here.
	lzma_filter filters[LZMA_FILTERS_MAX + 1];
	coder->block_options.filters = filters;

	// Decode the Block Header.
	return_if_error(lzma_block_header_decode(&coder->block_options,
	allocator, coder->buffer));

	// If LZMA_IGNORE_CHECK was used, this flag needs to be set.
	// It has to be set after lzma_block_header_decode() because
	// it always resets this to false.
	coder->block_options.ignore_check = coder->ignore_check;

	// Check the memory usage limit.
	const uint64_t memusage = lzma_raw_decoder_memusage(filters);
	lzma_ret ret;

	if (memusage == UINT64_MAX) {
	// One or more unknown Filter IDs.
	ret = LZMA_OPTIONS_ERROR;
	} else {
	// Now we can set coder->memusage since we know that
	// the filter chain is valid. We don't want
	// lzma_memusage() to return UINT64_MAX in case of
	// invalid filter chain.
	coder->memusage = memusage;

	if (memusage > coder->memlimit) {
	// The chain would need too much memory.
	ret = LZMA_MEMLIMIT_ERROR;
	} else {
	// Memory usage is OK.
	// Initialize the Block decoder.
	ret = lzma_block_decoder_init(
	&coder->block_decoder,
	allocator,
	&coder->block_options);
	}
	}

	// Free the allocated filter options since they are needed
	// only to initialize the Block decoder.
	for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i)
	lzma_free(filters[i].options, allocator);

	coder->block_options.filters = NULL;

	// Check if memory usage calculation and Block enocoder
	// initialization succeeded.
	if (ret != LZMA_OK)
	return ret;

	coder->sequence = SEQ_BLOCK;
	}

	// Fall through

	case SEQ_BLOCK: {
	const lzma_ret ret = coder->block_decoder.code(
	coder->block_decoder.coder, allocator,
	in, in_pos, in_size, out, out_pos, out_size,
	action);

	if (ret != LZMA_STREAM_END)
	return ret;

	// Block decoded successfully. Add the new size pair to
	// the Index hash.
	return_if_error(lzma_index_hash_append(coder->index_hash,
	lzma_block_unpadded_size(
	&coder->block_options),
	coder->block_options.uncompressed_size));

	coder->sequence = SEQ_BLOCK_HEADER;
	break;
	}

	case SEQ_INDEX: {
	// If we don't have any input, don't call
	// lzma_index_hash_decode() since it would return
	// LZMA_BUF_ERROR, which we must not do here.
	if (*in_pos >= in_size)
	return LZMA_OK;

	// Decode the Index and compare it to the hash calculated
	// from the sizes of the Blocks (if any).
	const lzma_ret ret = lzma_index_hash_decode(coder->index_hash,
	in, in_pos, in_size);
	if (ret != LZMA_STREAM_END)
	return ret;

	coder->sequence = SEQ_STREAM_FOOTER;
	}

	// Fall through

	case SEQ_STREAM_FOOTER: {
	// Copy the Stream Footer to the internal buffer.
	lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
	LZMA_STREAM_HEADER_SIZE);

	// Return if we didn't get the whole Stream Footer yet.
	if (coder->pos < LZMA_STREAM_HEADER_SIZE)
	return LZMA_OK;

	coder->pos = 0;

	// Decode the Stream Footer. The decoder gives
	// LZMA_FORMAT_ERROR if the magic bytes don't match,
	// so convert that return code to LZMA_DATA_ERROR.
	lzma_stream_flags footer_flags;
	const lzma_ret ret = lzma_stream_footer_decode(
	&footer_flags, coder->buffer);
	if (ret != LZMA_OK)
	return ret == LZMA_FORMAT_ERROR
	? LZMA_DATA_ERROR : ret;

	// Check that Index Size stored in the Stream Footer matches
	// the real size of the Index field.
	if (lzma_index_hash_size(coder->index_hash)
	!= footer_flags.backward_size)
	return LZMA_DATA_ERROR;

	// Compare that the Stream Flags fields are identical in
	// both Stream Header and Stream Footer.
	return_if_error(lzma_stream_flags_compare(
	&coder->stream_flags, &footer_flags));

	if (!coder->concatenated)
	return LZMA_STREAM_END;

	coder->sequence = SEQ_STREAM_PADDING;
	}

	// Fall through

	case SEQ_STREAM_PADDING:
	assert(coder->concatenated);

	// Skip over possible Stream Padding.
	while (true) {
	if (*in_pos >= in_size) {
	// Unless LZMA_FINISH was used, we cannot
	// know if there's more input coming later.
	if (action != LZMA_FINISH)
	return LZMA_OK;

	// Stream Padding must be a multiple of
	// four bytes.
	return coder->pos == 0
	? LZMA_STREAM_END
	: LZMA_DATA_ERROR;
	}

	// If the byte is not zero, it probably indicates
	// beginning of a new Stream (or the file is corrupt).
	if (in[*in_pos] != 0x00)
	break;

	++*in_pos;
	coder->pos = (coder->pos + 1) & 3;
	}

	// Stream Padding must be a multiple of four bytes (empty
	// Stream Padding is OK).
	if (coder->pos != 0) {
	++*in_pos;
	return LZMA_DATA_ERROR;
	}

	// Prepare to decode the next Stream.
	return_if_error(stream_decoder_reset(coder, allocator));
	break;

	default:
	assert(0);
	return LZMA_PROG_ERROR;
	}

	// Never reached
	}


	static void
	stream_decoder_end(lzma_coder coder, const lzma_allocator allocator)
	{
	lzma_next_end(&coder->block_decoder, allocator);
	lzma_index_hash_end(coder->index_hash, allocator);
	lzma_free(coder, allocator);
	return;
	}


	static lzma_check
	stream_decoder_get_check(const lzma_coder *coder)
	{
	return coder->stream_flags.check;
	}


	static lzma_ret
	stream_decoder_memconfig(lzma_coder coder, uint64_t memusage,
	uint64_t *old_memlimit, uint64_t new_memlimit)
	{
	*memusage = coder->memusage;
	*old_memlimit = coder->memlimit;

	if (new_memlimit != 0) {
	if (new_memlimit < coder->memusage)
	return LZMA_MEMLIMIT_ERROR;

	coder->memlimit = new_memlimit;
	}

	return LZMA_OK;
	}


	extern lzma_ret
	lzma_stream_decoder_init(
	lzma_next_coder next, const lzma_allocator allocator,
	uint64_t memlimit, uint32_t flags)
	{
	lzma_next_coder_init(&lzma_stream_decoder_init, next, allocator);

	if (memlimit == 0)
	return LZMA_PROG_ERROR;

	if (flags & ~LZMA_SUPPORTED_FLAGS)
	return LZMA_OPTIONS_ERROR;

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

	next->code = &stream_decode;
	next->end = &stream_decoder_end;
	next->get_check = &stream_decoder_get_check;
	next->memconfig = &stream_decoder_memconfig;

	next->coder->block_decoder = LZMA_NEXT_CODER_INIT;
	next->coder->index_hash = NULL;
	}

	next->coder->memlimit = memlimit;
	next->coder->memusage = LZMA_MEMUSAGE_BASE;
	next->coder->tell_no_check = (flags & LZMA_TELL_NO_CHECK) != 0;
	next->coder->tell_unsupported_check
	= (flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;
	next->coder->tell_any_check = (flags & LZMA_TELL_ANY_CHECK) != 0;
	next->coder->ignore_check = (flags & LZMA_IGNORE_CHECK) != 0;
	next->coder->concatenated = (flags & LZMA_CONCATENATED) != 0;
	next->coder->first_stream = true;

	return stream_decoder_reset(next->coder, allocator);
	}


	extern LZMA_API(lzma_ret)
	lzma_stream_decoder(lzma_stream *strm, uint64_t memlimit, uint32_t flags)
	{
	lzma_next_strm_init(lzma_stream_decoder_init, strm, memlimit, flags);

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

	return LZMA_OK;
	}