CoCalc provides the best real-time collaborative environment for Jupyter Notebooks, LaTeX documents, and SageMath, scalable from individual users to large groups and classes!

1
# -*- coding => binary -*-
2

3
require 'json'
4
require 'fileutils'
5

6
#
7
# This class provides a thread-friendly hash file store in JSON format
8
#
9
module Rex
10
class JSONHashFile
11

12
  attr_accessor :path
13

14
  def initialize(path)
15
    self.path = path
16
    @lock = Mutex.new
17
    @hash = {}
18
    @last = 0
19
  end
20

21
  def [](k)
22
    synced_update
23
    @hash[k]
24
  end
25

26
  def []=(k,v)
27
    synced_update do
28
      @hash[k] = v
29
    end
30
  end
31

32
  def keys
33
    synced_update
34
    @hash.keys
35
  end
36

37
  def delete(k)
38
    synced_update do
39
      @hash.delete(k)
40
    end
41
  end
42

43
  def clear
44
    synced_update do
45
      @hash.clear
46
    end
47
  end
48

49
private
50

51
  # Save the file, but prevent thread & process contention
52
  def synced_update(&block)
53
    @lock.synchronize do
54
      ::FileUtils.mkdir_p(::File.dirname(path))
55
      ::File.open(path, ::File::RDWR|::File::CREAT) do |fd|
56
        fd.flock(::File::LOCK_EX)
57

58
        # Reload and merge if the file has changed recently
59
        if fd.stat.mtime.to_f > @last
60
          parse_data(fd.read).merge(@hash).each_pair do |k,v|
61
            @hash[k] = v
62
          end
63
        end
64

65
        res = nil
66

67
        # Update the file on disk if new data is written
68
        if block_given?
69
          res = block.call
70
          fd.rewind
71
          fd.write(JSON.pretty_generate(@hash))
72
          fd.sync
73
          fd.truncate(fd.pos)
74
        end
75

76
        @last = fd.stat.mtime.to_f
77

78
        res
79
      end
80
    end
81
  end
82

83
  def parse_data(data)
84
    return {} if data.to_s.strip.length == 0
85
    begin
86
      JSON.parse(data)
87
    rescue JSON::ParserError => e
88
      elog("JSONHashFile at #{path} was corrupt", error: e)
89
      {}
90
    end
91
  end
92

93
end
94
end
95

96