Creating an md5 hash of a number, string, array, or hash in Ruby

user_246624 0
Viewed 49729

I need to create a signature string for a variable in Ruby, where the variable can be a number, a string, a hash, or an array. The hash values and array elements can also be any of these types.

This string will be used to compare the values in a database (Mongo, in this case).

My first thought was to create an MD5 hash of a JSON encoded value, like so: (body is the variable referred to above)

def createsig(body)    
  Digest::MD5.hexdigest(JSON.generate(body))
end

This nearly works, but JSON.generate does not encode the keys of a hash in the same order each time, so createsig({:a=>'a',:b=>'b'}) does not always equal createsig({:b=>'b',:a=>'a'}).

What is the best way to create a signature string to fit this need?

Note: For the detail oriented among us, I know that you can't JSON.generate() a number or a string. In these cases, I would just call MD5.hexdigest() directly.

digest md5 ruby
6 Answers

Here's my solution. I walk the data structure and build up a list of pieces that get joined into a single string. In order to ensure that the class types seen affect the hash, I inject a single unicode character that encodes basic type information along the way. (For example, we want ["1", "2", "3"].objsum != [1,2,3].objsum)

I did this as a refinement on Object, it's easily ported to a monkey patch. To use it just require the file and run "using ObjSum".

module ObjSum
  refine Object do
    def objsum
      parts = []
      queue = [self]

      while queue.size > 0
        item = queue.shift

        if item.kind_of?(Hash)
          parts << "\\000"
          item.keys.sort.each do |k| 
            queue << k
            queue << item[k]
          end
        elsif item.kind_of?(Set)
          parts << "\\001"
          item.to_a.sort.each { |i| queue << i }
        elsif item.kind_of?(Enumerable)
          parts << "\\002"
          item.each { |i| queue << i }
        elsif item.kind_of?(Fixnum)
          parts << "\\003"
          parts << item.to_s
        elsif item.kind_of?(Float)
          parts << "\\004"
          parts << item.to_s
        else
          parts << item.to_s
        end
      end

      Digest::MD5.hexdigest(parts.join)
    end
  end
end
user_2879930
Admin1
Related