Class: Aws::TreeHash

Inherits:
Object
  • Object
show all
Defined in:
lib/aws-sdk-core/tree_hash.rb

Overview

Used for computing a tree hash SHA256 checksum of an object.

tree_hash = TreeHash.new
tree_hash.update(file.read(1024 * 1024)) until file.eof?
tree_hash.digest

Limitations and Notes

There are two main limitations to be aware of when using TreeHash:

  • TreeHash is not thread safe. Use multiple TreeHash objects to concurrently compute a tree hash of a large object. Join their hashes at the end into a single TreeHash and then call #digest

    TreeHash.new(tree_hashes.map(&:hashes).flatten)

  • You must call #update with 1MB chunks of data. Only the final chunk may be smaller than 1MB.

If you have a large object/file, and you would like to compute the chunks concurrently, you must break the original file/data into sections that are evenly divisible by 1MB. Each section of data requires a seperate TreeHash object to compute hashes. Once all sections of data are complete, you can rejoin their #hashes in sequential order into a single TreeHash, then call #digest on the final tree hash.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(hashes = []) ⇒ TreeHash

Returns a new instance of TreeHash.



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# File 'lib/aws-sdk-core/tree_hash.rb', line 33

def initialize(hashes = [])
  @digest = OpenSSL::Digest.new('sha256')
  @hashes = hashes
end

Instance Attribute Details

#hashes ⇒ Array<String>

Returns The built up list of hashes. Each hash is a sha255 digest of a 1MB chunk.

Returns:

  • (Array<String>) —

    The built up list of hashes. Each hash is a sha255 digest of a 1MB chunk.



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# File 'lib/aws-sdk-core/tree_hash.rb', line 40

def hashes
  @hashes
end

Instance Method Details

#digest ⇒ Object 



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# File 'lib/aws-sdk-core/tree_hash.rb', line 50

def digest
  hashes = @hashes
  digest = OpenSSL::Digest.new('sha256')
  until hashes.count == 1
    hashes = hashes.each_slice(2).map do |h1,h2|
      digest.reset
      if h2
        digest.update(h1)
        digest.update(h2)
        digest.digest
      else
        h1
      end
    end
  end
  hashes.first.bytes.map{|x| x.to_i.to_s(16).rjust(2, '0')}.join('')
end

#update(chunk) ⇒ String

Returns the computed SHA256 digest of the chunk.

Parameters:

  • chunk (String)

Returns:

  • (String) —

    Returns the computed SHA256 digest of the chunk.



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# File 'lib/aws-sdk-core/tree_hash.rb', line 44

def update(chunk)
  @hashes << @digest.update(chunk).digest
  @digest.reset
  @hashes.last
end