// SPDX-License-Identifier: 0BSD

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

//

/// \file       stream_decoder.c

/// \brief      Decodes .xz Streams

//

//  Author:     Lasse Collin

//

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

#include "stream_decoder.h"

#include "block_decoder.h"

#include "index.h"

typedef struct {

  enum {

    SEQ_STREAM_HEADER,

    SEQ_BLOCK_HEADER,

    SEQ_BLOCK_INIT,

    SEQ_BLOCK_RUN,

    SEQ_INDEX,

    SEQ_STREAM_FOOTER,

    SEQ_STREAM_PADDING,

  } sequence;

  /// Block decoder

  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 (LZMA_FINISH),

  /// 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];

} lzma_stream_coder;

static lzma_ret

stream_decoder_reset(lzma_stream_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(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_stream_coder *coder = coder_ptr;

  // 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;

    FALLTHROUGH;

  }

  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] == INDEX_INDICATOR) {

        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;

    coder->sequence = SEQ_BLOCK_INIT;

    FALLTHROUGH;

  }

  case SEQ_BLOCK_INIT: {

    // Checking memusage and doing the initialization needs

    // its own sequence point because we need to be able to

    // retry if we return LZMA_MEMLIMIT_ERROR.

    // 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.

    lzma_filters_free(filters, allocator);

    coder->block_options.filters = NULL;

    // Check if memory usage calculation and Block decoder

    // initialization succeeded.

    if (ret != LZMA_OK)

      return ret;

    coder->sequence = SEQ_BLOCK_RUN;

    FALLTHROUGH;

  }

  case SEQ_BLOCK_RUN: {

    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;

    FALLTHROUGH;

  }

  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;

    FALLTHROUGH;

  }

  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(void *coder_ptr, const lzma_allocator *allocator)

{

  lzma_stream_coder *coder = coder_ptr;

  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 void *coder_ptr)

{

  const lzma_stream_coder *coder = coder_ptr;

  return coder->stream_flags.check;

}

static lzma_ret

stream_decoder_memconfig(void *coder_ptr, uint64_t *memusage,

    uint64_t *old_memlimit, uint64_t new_memlimit)

{

  lzma_stream_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_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 (flags & ~LZMA_SUPPORTED_FLAGS)

    return LZMA_OPTIONS_ERROR;

  lzma_stream_coder *coder = next->coder;

  if (coder == NULL) {

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

    if (coder == NULL)

      return LZMA_MEM_ERROR;

    next->coder = coder;

    next->code = &stream_decode;

    next->end = &stream_decoder_end;

    next->get_check = &stream_decoder_get_check;

    next->memconfig = &stream_decoder_memconfig;

    coder->block_decoder = LZMA_NEXT_CODER_INIT;

    coder->index_hash = NULL;

  }

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

  coder->memusage = LZMA_MEMUSAGE_BASE;

  coder->tell_no_check = (flags & LZMA_TELL_NO_CHECK) != 0;

  coder->tell_unsupported_check

      = (flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;

  coder->tell_any_check = (flags & LZMA_TELL_ANY_CHECK) != 0;

  coder->ignore_check = (flags & LZMA_IGNORE_CHECK) != 0;

  coder->concatenated = (flags & LZMA_CONCATENATED) != 0;

  coder->first_stream = true;

  return stream_decoder_reset(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;

}