a sha1 based key/value in the filesystem store.

gistfile1.rb

require 'digest/sha1'

class Sha1File
  attr_reader :path

  def initialize(sha1, base)
    @base = base
    @path = sha1_path sha1, base
    @dir = File.dirname @path
  end

  # If a block is given, then we yield the file opened for writing. Otherwise
  # we write the value parameter into the file.
  def write(value=nil)
    Dir.mkdir @base unless File.directory? @base
    Dir.mkdir @dir unless File.directory? @dir

    File.open(@path, 'wb') do |f|
      block_given? ? yield(f) : f << value
    end
  end

  def read
    File.open(@path, 'r').read if file_exists?
  end

  def delete
    value = read
    if file_exists?
      File.delete @path
      Dir.unlink @dir if dir_empty?
    end
    return value
  end

  def self.clear(base)
    dir_glob = File.join base, '??'
    file_glob = File.join dir_glob, '*'

    Dir.glob(file_glob).each{|f| File.unlink f}
    Dir.glob(dir_glob).each{|d| Dir.unlink d}
  end

  private

  def dir_empty?
    !Dir.foreach(@dir){|e| break true unless /^.\.?$/ =~ e}
  end

  def file_exists?
    File.file?(@path)
  end

  def sha1_path(sha1, base)
    File.join base, sha1[0..1], sha1[2..-1]
  end
end

# The sha1 of the key is calculated and the value is stored under that sha1
class KeyValueStore
  def initialize(options={})
    @base = options[:base] || 'key_value_store'
  end

  def [](key)
    Sha1File.new(sha1(key), @base).read
  end

  def path(key)
    Sha1File.new(sha1(key), @base).path
  end

  def []=(key, value)
    Sha1File.new(sha1(key), @base).write value
  end

  def delete(key)
    Sha1File.new(sha1(key), @base).delete
  end

  def clear
    Sha1File.clear @base
  end

  private

  def sha1(key)
    Digest::SHA1.hexdigest key
  end
end

# The sha1 of the value is calculated and the value is stored under that sha1
class ObjectStore
  def initialize(options={})
    @base = options[:base] || 'key_value_store'
  end

  def store(value)
    sha1 = Digest::SHA1.hexdigest value
    Sha1File.new(sha1, @base).write value
    return sha1
  end

  def retrieve(sha1, with_data_validation=nil)
    value = Sha1File.new(sha1, @base).read
    if with_data_validation
      sha1_validation = Digest::SHA1.hexdigest value
      if sha1 != sha1_validation
        raise StandardError, "The object with sha1 #{sha1} is invalid. The data on the filesystem has sha1 #{sha1_validation}."
      end
    end
    return value
  end

  def delete(sha1)
    Sha1File.new(sha1, @base).delete
  end

  def clear
    Sha1File.clear @base
  end
end

if $0 == __FILE__
s = KeyValueStore.new :base => 'temp/sha'
s['hay'] = 'is for horses'
s['you'] = 'are my hero'

p s['hay']
p s['you']
p s['uhoh']

s.delete('hay')
s.delete('uhoh')

s.clear

o = ObjectStore.new :base => 'temp/obj'
sha1_a = o.store 'Ob la di Ob la Da'
sha1_b = o.store 'Life goes on... ra!'
p o.retrieve(sha1_a, true)

#o.delete sha1_a
#o.clear
end