text: ///////////////////////////////////////////////////////////////////////////////
  //
  /// \file       auto_decoder.c
  /// \brief      Autodetect between .xz Stream and .lzma (LZMA_Alone) formats
  //
  //  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 "alone_decoder.h"
  
  
  struct lzma_coder_s {
  	/// Stream decoder or LZMA_Alone decoder
  	lzma_next_coder next;
  
  	uint64_t memlimit;
  	uint32_t flags;
  
  	enum {
  		SEQ_INIT,
  		SEQ_CODE,
  		SEQ_FINISH,
  	} sequence;
  };
  
  
  static lzma_ret
  auto_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_INIT:
  		if (*in_pos >= in_size)
  			return LZMA_OK;
  
  		// Update the sequence now, because we want to continue from
  		// SEQ_CODE even if we return some LZMA_*_CHECK.
  		coder->sequence = SEQ_CODE;
  
  		// Detect the file format. For now this is simple, since if
  		// it doesn't start with 0xFD (the first magic byte of the
  		// new format), it has to be LZMA_Alone, or something that
  		// we don't support at all.
  		if (in[*in_pos] == 0xFD) {
  			return_if_error(lzma_stream_decoder_init(
  					&coder->next, allocator,
  					coder->memlimit, coder->flags));
  		} else {
  			return_if_error(lzma_alone_decoder_init(&coder->next,
  					allocator, coder->memlimit, true));
  
  			// If the application wants to know about missing
  			// integrity check or about the check in general, we
  			// need to handle it here, because LZMA_Alone decoder
  			// doesn't accept any flags.
  			if (coder->flags & LZMA_TELL_NO_CHECK)
  				return LZMA_NO_CHECK;
  
  			if (coder->flags & LZMA_TELL_ANY_CHECK)
  				return LZMA_GET_CHECK;
  		}
  
  	// Fall through
  
  	case SEQ_CODE: {
  		const lzma_ret ret = coder->next.code(
  				coder->next.coder, allocator,
  				in, in_pos, in_size,
  				out, out_pos, out_size, action);
  		if (ret != LZMA_STREAM_END
  				|| (coder->flags & LZMA_CONCATENATED) == 0)
  			return ret;
  
  		coder->sequence = SEQ_FINISH;
  	}
  
  	// Fall through
  
  	case SEQ_FINISH:
  		// When LZMA_DECODE_CONCATENATED was used and we were decoding
  		// LZMA_Alone file, we need to check check that there is no
  		// trailing garbage and wait for LZMA_FINISH.
  		if (*in_pos < in_size)
  			return LZMA_DATA_ERROR;
  
  		return action == LZMA_FINISH ? LZMA_STREAM_END : LZMA_OK;
  
  	default:
  		assert(0);
  		return LZMA_PROG_ERROR;
  	}
  }
  
  
  static void
  auto_decoder_end(lzma_coder *coder, lzma_allocator *allocator)
  {
  	lzma_next_end(&coder->next, allocator);
  	lzma_free(coder, allocator);
  	return;
  }
  
  
  static lzma_check
  auto_decoder_get_check(const lzma_coder *coder)
  {
  	// It is LZMA_Alone if get_check is NULL.
  	return coder->next.get_check == NULL ? LZMA_CHECK_NONE
  			: coder->next.get_check(coder->next.coder);
  }
  
  
  static lzma_ret
  auto_decoder_memconfig(lzma_coder *coder, uint64_t *memusage,
  		uint64_t *old_memlimit, uint64_t new_memlimit)
  {
  	lzma_ret ret;
  
  	if (coder->next.memconfig != NULL) {
  		ret = coder->next.memconfig(coder->next.coder,
  				memusage, old_memlimit, new_memlimit);
  		assert(*old_memlimit == coder->memlimit);
  	} else {
  		// No coder is configured yet. Use the base value as
  		// the current memory usage.
  		*memusage = LZMA_MEMUSAGE_BASE;
  		*old_memlimit = coder->memlimit;
  		ret = LZMA_OK;
  	}
  
  	if (ret == LZMA_OK && new_memlimit != 0)
  		coder->memlimit = new_memlimit;
  
  	return ret;
  }
  
  
  static lzma_ret
  auto_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
  		uint64_t memlimit, uint32_t flags)
  {
  	lzma_next_coder_init(&auto_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 = &auto_decode;
  		next->end = &auto_decoder_end;
  		next->get_check = &auto_decoder_get_check;
  		next->memconfig = &auto_decoder_memconfig;
  		next->coder->next = LZMA_NEXT_CODER_INIT;
  	}
  
  	next->coder->memlimit = memlimit;
  	next->coder->flags = flags;
  	next->coder->sequence = SEQ_INIT;
  
  	return LZMA_OK;
  }
  
  
  extern LZMA_API(lzma_ret)
  lzma_auto_decoder(lzma_stream *strm, uint64_t memlimit, uint32_t flags)
  {
  	lzma_next_strm_init(auto_decoder_init, strm, memlimit, flags);
  
  	strm->internal->supported_actions[LZMA_RUN] = true;
  	strm->internal->supported_actions[LZMA_FINISH] = true;
  
  	return LZMA_OK;
  }
  