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 



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# 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 



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# 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 



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# 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 



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# 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