src/liblzma/common/block_header_encoder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       block_header_encoder.c
   4 /// \brief      Encodes Block Header for .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 "common.h"
  14 #include "check.h"
  15
  16
  17 extern LZMA_API(lzma_ret)
  18 lzma_block_header_size(lzma_block *block)
  19 {
  20         if (block->version > 1)
  21                 return LZMA_OPTIONS_ERROR;
  22
  23         // Block Header Size + Block Flags + CRC32.
  24         uint32_t size = 1 + 1 + 4;
  25
  26         // Compressed Size
  27         if (block->compressed_size != LZMA_VLI_UNKNOWN) {
  28                 const uint32_t add = lzma_vli_size(block->compressed_size);
  29                 if (add == 0 || block->compressed_size == 0)
  30                         return LZMA_PROG_ERROR;
  31
  32                 size += add;
  33         }
  34
  35         // Uncompressed Size
  36         if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
  37                 const uint32_t add = lzma_vli_size(block->uncompressed_size);
  38                 if (add == 0)
  39                         return LZMA_PROG_ERROR;
  40
  41                 size += add;
  42         }
  43
  44         // List of Filter Flags
  45         if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
  46                 return LZMA_PROG_ERROR;
  47
  48         for (size_t i = 0; block->filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
  49                 // Don't allow too many filters.
  50                 if (i == LZMA_FILTERS_MAX)
  51                         return LZMA_PROG_ERROR;
  52
  53                 uint32_t add;
  54                 return_if_error(lzma_filter_flags_size(&add,
  55                                 block->filters + i));
  56
  57                 size += add;
  58         }
  59
  60         // Pad to a multiple of four bytes.
  61         block->header_size = (size + 3) & ~UINT32_C(3);
  62
  63         // NOTE: We don't verify that the encoded size of the Block stays
  64         // within limits. This is because it is possible that we are called
  65         // with exaggerated Compressed Size (e.g. LZMA_VLI_MAX) to reserve
  66         // space for Block Header, and later called again with lower,
  67         // real values.
  68
  69         return LZMA_OK;
  70 }
  71
  72
  73 extern LZMA_API(lzma_ret)
  74 lzma_block_header_encode(const lzma_block *block, uint8_t *out)
  75 {
  76         // Validate everything but filters.
  77         if (lzma_block_unpadded_size(block) == 0
  78                         || !lzma_vli_is_valid(block->uncompressed_size))
  79                 return LZMA_PROG_ERROR;
  80
  81         // Indicate the size of the buffer _excluding_ the CRC32 field.
  82         const size_t out_size = block->header_size - 4;
  83
  84         // Store the Block Header Size.
  85         out[0] = out_size / 4;
  86
  87         // We write Block Flags in pieces.
  88         out[1] = 0x00;
  89         size_t out_pos = 2;
  90
  91         // Compressed Size
  92         if (block->compressed_size != LZMA_VLI_UNKNOWN) {
  93                 return_if_error(lzma_vli_encode(block->compressed_size, NULL,
  94                                 out, &out_pos, out_size));
  95
  96                 out[1] |= 0x40;
  97         }
  98
  99         // Uncompressed Size
 100         if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
 101                 return_if_error(lzma_vli_encode(block->uncompressed_size, NULL,
 102                                 out, &out_pos, out_size));
 103
 104                 out[1] |= 0x80;
 105         }
 106
 107         // Filter Flags
 108         if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
 109                 return LZMA_PROG_ERROR;
 110
 111         size_t filter_count = 0;
 112         do {
 113                 // There can be a maximum of four filters.
 114                 if (filter_count == LZMA_FILTERS_MAX)
 115                         return LZMA_PROG_ERROR;
 116
 117                 return_if_error(lzma_filter_flags_encode(
 118                                 block->filters + filter_count,
 119                                 out, &out_pos, out_size));
 120
 121         } while (block->filters[++filter_count].id != LZMA_VLI_UNKNOWN);
 122
 123         out[1] |= filter_count - 1;
 124
 125         // Padding
 126         memzero(out + out_pos, out_size - out_pos);
 127
 128         // CRC32
 129         write32le(out + out_size, lzma_crc32(out, out_size, 0));
 130
 131         return LZMA_OK;
 132 }