external/public-domain/xz/dist/src/liblzma/common/stream_flags_decoder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       stream_flags_decoder.c
   4 /// \brief      Decodes Stream Header and Stream Footer from .xz files
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "stream_flags_common.h"
  14
  15
  16 static bool
  17 stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
  18 {
  19         // Reserved bits must be unset.
  20         if (in[0] != 0x00 || (in[1] & 0xF0))
  21                 return true;
  22
  23         options->version = 0;
  24         options->check = in[1] & 0x0F;
  25
  26         return false;
  27 }
  28
  29
  30 extern LZMA_API(lzma_ret)
  31 lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
  32 {
  33         // Magic
  34         if (memcmp(in, lzma_header_magic, sizeof(lzma_header_magic)) != 0)
  35                 return LZMA_FORMAT_ERROR;
  36
  37         // Verify the CRC32 so we can distinguish between corrupt
  38         // and unsupported files.
  39         const uint32_t crc = lzma_crc32(in + sizeof(lzma_header_magic),
  40                         LZMA_STREAM_FLAGS_SIZE, 0);
  41         if (crc != unaligned_read32le(in + sizeof(lzma_header_magic)
  42                         + LZMA_STREAM_FLAGS_SIZE))
  43                 return LZMA_DATA_ERROR;
  44
  45         // Stream Flags
  46         if (stream_flags_decode(options, in + sizeof(lzma_header_magic)))
  47                 return LZMA_OPTIONS_ERROR;
  48
  49         // Set Backward Size to indicate unknown value. That way
  50         // lzma_stream_flags_compare() can be used to compare Stream Header
  51         // and Stream Footer while keeping it useful also for comparing
  52         // two Stream Footers.
  53         options->backward_size = LZMA_VLI_UNKNOWN;
  54
  55         return LZMA_OK;
  56 }
  57
  58
  59 extern LZMA_API(lzma_ret)
  60 lzma_stream_footer_decode(lzma_stream_flags *options, const uint8_t *in)
  61 {
  62         // Magic
  63         if (memcmp(in + sizeof(uint32_t) * 2 + LZMA_STREAM_FLAGS_SIZE,
  64                         lzma_footer_magic, sizeof(lzma_footer_magic)) != 0)
  65                 return LZMA_FORMAT_ERROR;
  66
  67         // CRC32
  68         const uint32_t crc = lzma_crc32(in + sizeof(uint32_t),
  69                         sizeof(uint32_t) + LZMA_STREAM_FLAGS_SIZE, 0);
  70         if (crc != unaligned_read32le(in))
  71                 return LZMA_DATA_ERROR;
  72
  73         // Stream Flags
  74         if (stream_flags_decode(options, in + sizeof(uint32_t) * 2))
  75                 return LZMA_OPTIONS_ERROR;
  76
  77         // Backward Size
  78         options->backward_size = unaligned_read32le(in + sizeof(uint32_t));
  79         options->backward_size = (options->backward_size + 1) * 4;
  80
  81         return LZMA_OK;
  82 }