HashDigest

Generates non-cryptographic digests of Hashes (and Arrays) indifferent to key type (string or symbol) and ordering.

Extracted from RemoteTable.

Note plz

  1. You should use HashDigest.digest3 for new applications. hexdigest and digest2 are legacy.
  2. digest2 is CASE SENSITIVE and has relatively high level of collisions - not recommended.

Example

Indifferent to key type

>> HashDigest.digest3(:a => 1)
=> "86eda770a6060824b090dd4df091e3bd4121279c"
>> HashDigest.digest3('a' => 1)
=> "86eda770a6060824b090dd4df091e3bd4121279c"

Indifferent to key order

>> HashDigest.digest3(:a => 1, 'b' => 2)
=> "d53cf64e768f4ef09c806bbe12258c78211b2690"
>> HashDigest.digest3(:b => 2, 'a' => 1)
=> "d53cf64e768f4ef09c806bbe12258c78211b2690"

Speed

If you're not on JRuby, having EscapeUtils in your Gemfile will make things much faster.

Algorithm

digest3

  1. Represent the hash as a URL querystring
  2. Sort by key
  3. SHA1 hexdigest

digest2 (deprecated and not recommended)

  1. Represent the hash as a URL querystring
  2. Sort by key
  3. MurmurHash3 V32 (this turned out to have too many collisions)
  4. Convert to base 36 to save space

Note: non-cryptographic and variable length. CASE SENSITIVE.

hexdigest (deprecated)

Basically represent the hash as a URL querystring, ordered by key, and MD5 that.

  1. Stringify keys
  2. Create an array of strings like "url_encode(key)=url_encode(value)" by going through each key in alphabetical order
  3. Join the array together with "&"
  4. MD5 hexdigest the joined string

To digest an array, just pretend it's a hash with keys like 1, 2, 3, etc.

Potential issues

  • Meant for flat hashes, e.g. { :a => 1, :b => 2 } and not { :x => { :y => :z } }

Copyright

Copyright 2013 Seamus Abshere