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 != 0)
  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         size_t i;
  49         for (i = 0; block->filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
  50                 // Don't allow too many filters.
  51                 if (i == LZMA_FILTERS_MAX)
  52                         return LZMA_PROG_ERROR;
  53
  54                 uint32_t add;
  55                 return_if_error(lzma_filter_flags_size(&add,
  56                                 block->filters + i));
  57
  58                 size += add;
  59         }
  60
  61         // Pad to a multiple of four bytes.
  62         block->header_size = (size + 3) & ~UINT32_C(3);
  63
  64         // NOTE: We don't verify that the encoded size of the Block stays
  65         // within limits. This is because it is possible that we are called
  66         // with exaggerated Compressed Size (e.g. LZMA_VLI_MAX) to reserve
  67         // space for Block Header, and later called again with lower,
  68         // real values.
  69
  70         return LZMA_OK;
  71 }
  72
  73
  74 extern LZMA_API(lzma_ret)
  75 lzma_block_header_encode(const lzma_block *block, uint8_t *out)
  76 {
  77         // Validate everything but filters.
  78         if (lzma_block_unpadded_size(block) == 0
  79                         || !lzma_vli_is_valid(block->uncompressed_size))
  80                 return LZMA_PROG_ERROR;
  81
  82         // Indicate the size of the buffer _excluding_ the CRC32 field.
  83         const size_t out_size = block->header_size - 4;
  84
  85         // Store the Block Header Size.
  86         out[0] = out_size / 4;
  87
  88         // We write Block Flags in pieces.
  89         out[1] = 0x00;
  90         size_t out_pos = 2;
  91
  92         // Compressed Size
  93         if (block->compressed_size != LZMA_VLI_UNKNOWN) {
  94                 return_if_error(lzma_vli_encode(block->compressed_size, NULL,
  95                                 out, &out_pos, out_size));
  96
  97                 out[1] |= 0x40;
  98         }
  99
 100         // Uncompressed Size
 101         if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
 102                 return_if_error(lzma_vli_encode(block->uncompressed_size, NULL,
 103                                 out, &out_pos, out_size));
 104
 105                 out[1] |= 0x80;
 106         }
 107
 108         // Filter Flags
 109         if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
 110                 return LZMA_PROG_ERROR;
 111
 112         size_t filter_count = 0;
 113         do {
 114                 // There can be a maximum of four filters.
 115                 if (filter_count == LZMA_FILTERS_MAX)
 116                         return LZMA_PROG_ERROR;
 117
 118                 return_if_error(lzma_filter_flags_encode(
 119                                 block->filters + filter_count,
 120                                 out, &out_pos, out_size));
 121
 122         } while (block->filters[++filter_count].id != LZMA_VLI_UNKNOWN);
 123
 124         out[1] |= filter_count - 1;
 125
 126         // Padding
 127         memzero(out + out_pos, out_size - out_pos);
 128
 129         // CRC32
 130         unaligned_write32le(out + out_size, lzma_crc32(out, out_size, 0));
 131
 132         return LZMA_OK;
 133 }