Module: RubySMB::Compression::LZNT1

Defined in:
lib/ruby_smb/compression/lznt1.rb

Class Method Summary collapse

Class Method Details

.compress(buf, chunk_size: 0x1000) ⇒ Object



4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
# File 'lib/ruby_smb/compression/lznt1.rb', line 4

def self.compress(buf, chunk_size: 0x1000)
  out = ''
  until buf.empty?
    chunk = buf[0...chunk_size]
    compressed = compress_chunk(chunk)
    # chunk is compressed
    if compressed.length < chunk.length
      out << [0xb000 | (compressed.length - 1)].pack('v')
      out << compressed
    else
      out << [0x3000 | (chunk.length - 1)].pack('v')
      out << chunk
    end
    buf = buf[chunk_size..-1]
    break if buf.nil?
  end

  out
end

.compress_chunk(chunk) ⇒ Object



24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
# File 'lib/ruby_smb/compression/lznt1.rb', line 24

def self.compress_chunk(chunk)
  blob = chunk
  out = ''
  pow2 = 0x10
  l_mask3 = 0x1002
  o_shift = 12
  until blob.empty?
    bits = 0
    tmp = ''
    i = -1
    loop do
      i += 1
      bits >>= 1
      while pow2 < (chunk.length - blob.length)
        pow2 <<= 1
        l_mask3 = (l_mask3 >> 1) + 1
        o_shift -= 1
      end

      max_len = [blob.length, l_mask3].min
      offset, length = find(chunk[0...(chunk.length - blob.length)], blob, max_len)

      # try to find more compressed pattern
      _offset2, length2 = find(chunk[0...chunk.length - blob.length + 1], blob[1..-1], max_len)

      length = 0 if length < length2

      if length > 0
        symbol = ((offset - 1) << o_shift) | (length - 3)
        tmp << [symbol].pack('v')
        # set the highest bit
        bits |= 0x80
        blob = blob[length..-1]
      else
        tmp += blob[0]
        blob = blob[1..-1]
      end

      break if blob.empty? || i == 7
    end

    out << [bits >> (7 - i)].pack('C')
    out << tmp
  end

  out
end

.decompress(buf, length_check: true) ⇒ Object



72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
# File 'lib/ruby_smb/compression/lznt1.rb', line 72

def self.decompress(buf, length_check: true)
  out = ''
  until buf.empty?
    header = buf.unpack1('v')
    length = (header & 0xfff) + 1
    raise EncodingError, 'invalid chunk length' if length_check && length > (buf.length - 2)

    chunk = buf[2...length + 2]
    out << if header & 0x8000 == 0
             chunk
           else
             decompress_chunk(chunk)
           end
    buf = buf[length + 2..-1]
  end

  out
end

.decompress_chunk(chunk) ⇒ Object



91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
# File 'lib/ruby_smb/compression/lznt1.rb', line 91

def self.decompress_chunk(chunk)
  out = ''
  until chunk.empty?
    flags = chunk[0].unpack1('C')
    chunk = chunk[1..-1]
    8.times do |i|
      if (flags >> i & 1) == 0
        out << chunk[0]
        chunk = chunk[1..-1]
      else
        flag = chunk.unpack1('v')
        pos = out.length - 1
        l_mask = 0xfff
        o_shift = 12
        while pos >= 0x10
          l_mask >>= 1
          o_shift -= 1
          pos >>= 1
        end

        length = (flag & l_mask) + 3
        offset = (flag >> o_shift) + 1

        if length >= offset
          out_offset = out[-offset..-1]
          tmp = out_offset * (0xfff / out_offset.length + 1)
          out << tmp[0...length]
        else
          out << out[-offset..-offset + length - 1]
        end
        chunk = chunk[2..-1]
      end
      break if chunk.empty?
    end
  end

  out
end