// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////

//

/// \file       alone_decoder.c

/// \brief      Decoder for LZMA_Alone files

//

//  Author:     Lasse Collin

//

///////////////////////////////////////////////////////////////////////////////

#include "alone_decoder.h"

#include "lzma_decoder.h"

#include "lz_decoder.h"

typedef struct {

  lzma_next_coder next;

  enum {

    SEQ_PROPERTIES,

    SEQ_DICTIONARY_SIZE,

    SEQ_UNCOMPRESSED_SIZE,

    SEQ_CODER_INIT,

    SEQ_CODE,

  } sequence;

  /// If true, reject files that are unlikely to be .lzma files.

  /// If false, more non-.lzma files get accepted and will give

  /// LZMA_DATA_ERROR either immediately or after a few output bytes.

  bool picky;

  /// Position in the header fields

  size_t pos;

  /// Uncompressed size decoded from the header

  lzma_vli uncompressed_size;

  /// Memory usage limit

  uint64_t memlimit;

  /// Amount of memory actually needed (only an estimate)

  uint64_t memusage;

  /// Options decoded from the header needed to initialize

  /// the LZMA decoder

  lzma_options_lzma options;

} lzma_alone_coder;

static lzma_ret

alone_decode(void *coder_ptr, 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)

{

  lzma_alone_coder *coder = coder_ptr;

  while (*out_pos < out_size

      && (coder->sequence == SEQ_CODE || *in_pos < in_size))

  switch (coder->sequence) {

  case SEQ_PROPERTIES:

    if (lzma_lzma_lclppb_decode(&coder->options, in[*in_pos]))

      return LZMA_FORMAT_ERROR;

    coder->sequence = SEQ_DICTIONARY_SIZE;

    ++*in_pos;

    break;

  case SEQ_DICTIONARY_SIZE:

    coder->options.dict_size

        |= (size_t)(in[*in_pos]) << (coder->pos * 8);

    if (++coder->pos == 4) {

      if (coder->picky && coder->options.dict_size

          != UINT32_MAX) {

        // A hack to ditch tons of false positives:

        // We allow only dictionary sizes that are

        // 2^n or 2^n + 2^(n-1). LZMA_Alone created

        // only files with 2^n, but accepts any

        // dictionary size.

        uint32_t d = coder->options.dict_size - 1;

        d |= d >> 2;

        d |= d >> 3;

        d |= d >> 4;

        d |= d >> 8;

        d |= d >> 16;

        ++d;

        if (d != coder->options.dict_size)

          return LZMA_FORMAT_ERROR;

      }

      coder->pos = 0;

      coder->sequence = SEQ_UNCOMPRESSED_SIZE;

    }

    ++*in_pos;

    break;

  case SEQ_UNCOMPRESSED_SIZE:

    coder->uncompressed_size

        |= (lzma_vli)(in[*in_pos]) << (coder->pos * 8);

    ++*in_pos;

    if (++coder->pos < 8)

      break;

    // Another hack to ditch false positives: Assume that

    // if the uncompressed size is known, it must be less

    // than 256 GiB.

    //

    // FIXME? Without picky we allow > LZMA_VLI_MAX which doesn't

    // really matter in this specific situation (> LZMA_VLI_MAX is

    // safe in the LZMA decoder) but it's somewhat weird still.

    if (coder->picky

        && coder->uncompressed_size != LZMA_VLI_UNKNOWN

        && coder->uncompressed_size

          >= (LZMA_VLI_C(1) << 38))

      return LZMA_FORMAT_ERROR;

    // Use LZMA_FILTER_LZMA1EXT features to specify the

    // uncompressed size and that the end marker is allowed

    // even when the uncompressed size is known. Both .lzma

    // header and LZMA1EXT use UINT64_MAX indicate that size

    // is unknown.

    coder->options.ext_flags = LZMA_LZMA1EXT_ALLOW_EOPM;

    lzma_set_ext_size(coder->options, coder->uncompressed_size);

    // Calculate the memory usage so that it is ready

    // for SEQ_CODER_INIT. We know that lc/lp/pb are valid

    // so we can use the _nocheck variant.

    coder->memusage

      = lzma_lzma_decoder_memusage_nocheck(&coder->options)

        + LZMA_MEMUSAGE_BASE;

    coder->pos = 0;

    coder->sequence = SEQ_CODER_INIT;

    FALLTHROUGH;

  case SEQ_CODER_INIT: {

    if (coder->memusage > coder->memlimit)

      return LZMA_MEMLIMIT_ERROR;

    lzma_filter_info filters[2] = {

      {

        .id = LZMA_FILTER_LZMA1EXT,

        .init = &lzma_lzma_decoder_init,

        .options = &coder->options,

      }, {

        .init = NULL,

      }

    };

    const lzma_ret ret = lzma_next_filter_init(&coder->next,

        allocator, filters);

    if (ret != LZMA_OK) {

      lzma_next_end(&coder->next, allocator);

      return ret;

    }

    coder->sequence = SEQ_CODE;

    break;

  }

  case SEQ_CODE: {

    return coder->next.code(coder->next.coder,

        allocator, in, in_pos, in_size,

        out, out_pos, out_size, action);

  }

  default:

    return LZMA_PROG_ERROR;

  }

  return LZMA_OK;

}

static void

alone_decoder_end(void *coder_ptr, const lzma_allocator *allocator)

{

  lzma_alone_coder *coder = coder_ptr;

  lzma_next_end(&coder->next, allocator);

  lzma_free(coder, allocator);

  return;

}

static lzma_ret

alone_decoder_memconfig(void *coder_ptr, uint64_t *memusage,

    uint64_t *old_memlimit, uint64_t new_memlimit)

{

  lzma_alone_coder *coder = coder_ptr;

  *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_alone_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,

    uint64_t memlimit, bool picky)

{

  lzma_next_coder_init(&lzma_alone_decoder_init, next, allocator);

  lzma_alone_coder *coder = next->coder;

  if (coder == NULL) {

    coder = lzma_alloc(sizeof(lzma_alone_coder), allocator);

    if (coder == NULL)

      return LZMA_MEM_ERROR;

    next->coder = coder;

    next->code = &alone_decode;

    next->end = &alone_decoder_end;

    next->memconfig = &alone_decoder_memconfig;

    coder->next = LZMA_NEXT_CODER_INIT;

  }

  coder->sequence = SEQ_PROPERTIES;

  coder->picky = picky;

  coder->pos = 0;

  coder->options.dict_size = 0;

  coder->options.preset_dict = NULL;

  coder->options.preset_dict_size = 0;

  coder->uncompressed_size = 0;

  coder->memlimit = my_max(1, memlimit);

  coder->memusage = LZMA_MEMUSAGE_BASE;

  return LZMA_OK;

}

extern LZMA_API(lzma_ret)

lzma_alone_decoder(lzma_stream *strm, uint64_t memlimit)

{

  lzma_next_strm_init(lzma_alone_decoder_init, strm, memlimit, false);

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

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

  return LZMA_OK;

}