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

Question

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

Answer 1

If you could only get a string representation of body and not have the Ruby 1.8 hash come back with different orders from one time to the other, you could reliably hash that string representation. Let's get our hands dirty with some monkey patches:

require 'digest/md5'

class Object
  def md5key
    to_s
  end
end

class Array
  def md5key
    map(&:md5key).join
  end
end

class Hash
  def md5key
    sort.map(&:md5key).join
  end
end

Now any object (of the types mentioned in the question) respond to md5key by returning a reliable key to use for creating a checksum, so:

def createsig(o)
  Digest::MD5.hexdigest(o.md5key)
end

Example:

body = [
  {
    'bar' => [
      345,
      "baz",
    ],
    'qux' => 7,
  },
  "foo",
  123,
]
p body.md5key        # => "bar345bazqux7foo123"
p createsig(body)    # => "3a92036374de88118faf19483fe2572e"

Note: This hash representation does not encode the structure, only the concatenation of the values. Therefore ["a", "b", "c"] will hash the same as ["abc"].