Extension to the Digest module of the ruby standard library to support marshalling
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Extension to the Digest module of the ruby standard library to support marshalling

With this gem you can accumulatively compute the digest of a byte sequence over several executions by storing the marshalled digest object in a database:

class FakeDatabase
  attr_accessor :value
@db = FakeDatabase.new

def update_digest(part)
  marshalled_digest = Marshal::load(@db.value) # Fetch the last digest from database
  marshalled_digest << part # Compute digest incrementally
  @db.value = Marshal::dump(marshalled_digest) # Store updated digest in database

## parts_array is provided; for example as a series of files
## generated with the command split on a larger file.
@db.value = Marshal::dump(Digest::MD5.new) #An initial value
parts_array.each do |part|
  # Assume this method is invoked in a new process each time, and
  # the only thing they share is the database (faked in the example with @db)
Marshal::load(@db.value).hexdigest.should == Digest::MD5.hexdigest(parts_array.inject("", :+))

The plan is to have this feature to be included in the ruby standard library.

Known issues

Currently the marshalled values are specific to the underlying native library used to compute the digest values. That means that if you are using a ruby that is compiled with linkage to OpenSSL as the underlying md5 library, then the marshalled values (in the database) cannot be used with a ruby version compiled with linkage to rubys native md5 implementation. So take care of that when you consider upgrading your ruby version.

Contributing to digest_extensions

  • Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet

  • Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it

  • Fork the project

  • Start a feature/bugfix branch

  • Commit and push until you are happy with your contribution

  • Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.

  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.


Copyright © 2011-2012 Jarl Friis. See LICENSE.txt for further details.