Class: Daybreak::Format

Inherits:
Object
  • Object
show all
Defined in:
lib/daybreak/format.rb

Overview

Database format serializer and deserializer. You can create your own implementation of this class and define your own database format!

Constant Summary collapse

MAGIC =

Magic string of the file header

'DAYBREAK'
VERSION =

Database file format version

1
DELETE =

Special value size used for deleted records

(1 << 32) - 1

Instance Method Summary collapse

Instance Method Details

#crc32(s) ⇒ Fixnum (protected)

Compute crc32 of string

Parameters:

  • s (String) —

    a string

Returns:

  • (Fixnum) 


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# File 'lib/daybreak/format.rb', line 59

def crc32(s)
  [Zlib.crc32(s, 0)].pack('N')
end

#dump(record) ⇒ String

Serialize record and return string

Parameters:

  • record (Array) —

    an array with [key, value] or [key] if the record is deleted

Returns:

  • (String) —

    serialized record



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# File 'lib/daybreak/format.rb', line 25

def dump(record)
  data =
    if record.size == 1
      [record[0].bytesize, DELETE].pack('NN') << record[0]
    else
      [record[0].bytesize, record[1].bytesize].pack('NN') << record[0] << record[1]
    end
  data << crc32(data)
end

#header ⇒ String

Return database header as string

Returns:

  • (String) —

    database file header



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# File 'lib/daybreak/format.rb', line 18

def header
  MAGIC + [VERSION].pack('n')
end

#parse(buf) ⇒ Array

Deserialize record from buffer

Parameters:

  • buf (String) —

    the buffer to read from

Returns:

  • (Array) —

    deserialized record [key, value] or [key] if the record is deleted



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# File 'lib/daybreak/format.rb', line 38

def parse(buf)
  key_size, value_size = buf[0, 8].unpack('NN')
  data = buf.slice!(0, 8 + key_size + (value_size == DELETE ? 0 : value_size))
  raise 'CRC mismatch: your data might be corrupted!' unless buf.slice!(0, 4) == crc32(data)
  value_size == DELETE ? [data[8, key_size]] : [data[8, key_size], data[8 + key_size, value_size]]
end

#read_header(input) ⇒ Object

Read database header from input stream

Parameters:

  • input (#read) —

    the input stream

Returns:

  • void



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# File 'lib/daybreak/format.rb', line 10

def read_header(input)
  raise 'Not a Daybreak database' if input.read(MAGIC.bytesize) != MAGIC
  ver = input.read(2).unpack('n').first
  raise "Expected database version #{VERSION}, got #{ver}" if ver != VERSION
end