hash_digest

HashDigest

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

Extracted from RemoteTable.

Note plz

• You should use HashDigest.digest3 for new applications. hexdigest and digest2 are legacy.
• 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

• Represent the hash as a URL querystring
• Sort by key
• SHA1 hexdigest

digest2 (deprecated and not recommended)

• Represent the hash as a URL querystring
• Sort by key
• MurmurHash3 V32 (this turned out to have too many collisions)
• 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.

• Stringify keys
• Create an array of strings like "url_encode(key)=url_encode(value)" by going through each key in alphabetical order
• Join the array together with "&"
• 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