module Sprockets::DigestUtils

def integrity_uri(digest, content_type = nil)

Returns a String or nil if hash algorithm is incompatible.

will block the loading of the asset.
be accurate if provided. Otherwise, subresource integrity
content_type - The content-type the asset will be served with. This *must*
digest - The String byte digest of the asset content.

attribute of an asset tag as per the subresource integrity specification.
Internal: Generate a "named information" URI for use in the `integrity` 
def integrity_uri(digest, content_type = nil)
  case digest
  when Digest::Base
    digest_class = digest.class
    digest = digest.digest
  when String
    digest_class = DIGEST_SIZES[digest.bytesize]
  else
    raise TypeError, "unknown digest: #{digest.inspect}"
  end
  if hash_name = NI_HASH_ALGORITHMS[digest_class]
    uri = "ni:///#{hash_name};#{pack_urlsafe_base64digest(digest)}"
    uri << "?ct=#{content_type}" if content_type
    uri
  end
end