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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 }