Module: Familia::Features::ExternalIdentifier

Defined in:
lib/familia/features/external_identifier.rb

Overview

Familia::Features::ExternalIdentifier

Defined Under Namespace

Modules: ClassMethods Classes: ExternalIdentifierError, ExternalIdentifierFieldType

Instance Method Summary collapse

Instance Method Details

#derive_external_identifier ⇒ String?

Derives a deterministic, public-facing external identifier from the object’s internal objid.

This method uses the objid’s high-quality randomness to seed a pseudorandom number generator (PRNG). The PRNG then acts as a complex, deterministic function to produce a new identifier that has no discernible mathematical correlation to the objid. This is a security measure to prevent leaking information (like timestamps from UUIDv7) from the internal identifier to the public one.

The resulting identifier is always deterministic: the same objid will always produce the same extid, which is crucial for lookups.

Returns:

  • (String, nil) —

    A prefixed, base36-encoded external identifier, or nil if the objid is not present.

Raises:



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# File 'lib/familia/features/external_identifier.rb', line 180

def derive_external_identifier
  raise ExternalIdentifierError, 'Missing objid field' unless respond_to?(:objid)

  current_objid = objid
  return nil if current_objid.nil? || current_objid.to_s.empty?

  # Validate objid provenance for security guarantees
  validate_objid_provenance!

  # Normalize the objid to a consistent hex representation first.
  normalized_hex = normalize_objid_to_hex(current_objid)

  # Use the objid's randomness to create a deterministic, yet secure,
  # external identifier. We do not use SecureRandom here because the output
  # must be deterministic.
  #
  # The process is as follows:
  # 1. The objid (a high-entropy value) is hashed to create a uniform seed.
  # 2. The seed initializes a standard PRNG (Random.new).
  # 3. The PRNG acts as a deterministic function to generate a sequence of
  #    bytes that appears random, obscuring the original objid.

  # 1. Create a high-quality, uniform seed from the objid's entropy.
  seed = Digest::SHA256.digest(normalized_hex)

  # 2. Initialize a PRNG with the seed. The same seed will always produce
  #    the same sequence of "random" numbers.
  prng = Random.new(seed.unpack1('Q>'))

  # 3. Generate 16 bytes (128 bits) of deterministic output.
  random_bytes = prng.bytes(16)

  # Encode as a base36 string for a compact, URL-safe identifier.
  # 128 bits is approximately 25 characters in base36.
  external_part = random_bytes.unpack1('H*').to_i(16).to_s(36).rjust(25, '0')

  # Get prefix from feature options, default to "ext"
  options = self.class.feature_options(:external_identifier)
  prefix = options[:prefix] || 'ext'

  "#{prefix}_#{external_part}"
end

#destroy! ⇒ Object 



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# File 'lib/familia/features/external_identifier.rb', line 239

def destroy!
  # Clean up extid mapping when object is destroyed
  current_extid = instance_variable_get(:@extid)
  self.class.extid_lookup.remove_field(current_extid) if current_extid

  super if defined?(super)
end

#external_identifier ⇒ String

Full-length alias for extid for clarity when needed

Returns:

  • (String) —

    The external identifier



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# File 'lib/familia/features/external_identifier.rb', line 227

def external_identifier
  extid
end

#external_identifier=(value) ⇒ Object

Full-length alias setter for extid

Parameters:

  • value (String) —

    The external identifier to set



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# File 'lib/familia/features/external_identifier.rb', line 235

def external_identifier=(value)
  self.extid = value
end