app/helpers/jsonld_helper.rb
# frozen_string_literal: true
module JsonLdHelper
include ContextHelper
def equals_or_includes?(haystack, needle)
haystack.is_a?(Array) ? haystack.include?(needle) : haystack == needle
end
def equals_or_includes_any?(haystack, needles)
needles.any? { |needle| equals_or_includes?(haystack, needle) }
end
def first_of_value(value)
value.is_a?(Array) ? value.first : value
end
def uri_from_bearcap(str)
if str&.start_with?('bear:')
Addressable::URI.parse(str).query_values['u']
else
str
end
end
# The url attribute can be a string, an array of strings, or an array of objects.
# The objects could include a mimeType. Not-included mimeType means it's text/html.
def url_to_href(value, preferred_type = nil)
single_value = if value.is_a?(Array) && !value.first.is_a?(String)
value.find { |link| preferred_type.nil? || ((link['mimeType'].presence || 'text/html') == preferred_type) }
elsif value.is_a?(Array)
value.first
else
value
end
if single_value.nil? || single_value.is_a?(String)
single_value
else
single_value['href']
end
end
def as_array(value)
if value.nil?
[]
elsif value.is_a?(Array)
value
else
[value]
end
end
def value_or_id(value)
value.is_a?(String) || value.nil? ? value : value['id']
end
def supported_context?(json)
!json.nil? && equals_or_includes?(json['@context'], ActivityPub::TagManager::CONTEXT)
end
def unsupported_uri_scheme?(uri)
uri.nil? || !uri.start_with?('http://', 'https://')
end
def non_matching_uri_hosts?(base_url, comparison_url)
return true if unsupported_uri_scheme?(comparison_url)
needle = Addressable::URI.parse(comparison_url).host
haystack = Addressable::URI.parse(base_url).host
!haystack.casecmp(needle).zero?
end
def canonicalize(json)
graph = RDF::Graph.new << JSON::LD::API.toRdf(json, documentLoader: method(:load_jsonld_context))
graph.dump(:normalize)
end
def compact(json)
compacted = JSON::LD::API.compact(json.without('signature'), full_context, documentLoader: method(:load_jsonld_context))
compacted['signature'] = json['signature']
compacted
end
# Patches a JSON-LD document to avoid compatibility issues on redistribution
#
# Since compacting a JSON-LD document against Mastodon's built-in vocabulary
# means other extension namespaces will be expanded, malformed JSON-LD
# attributes lost, and some values “unexpectedly” compacted this method
# patches the following likely sources of incompatibility:
# - 'https://www.w3.org/ns/activitystreams#Public' being compacted to
# 'as:Public' (for instance, pre-3.4.0 Mastodon does not understand
# 'as:Public')
# - single-item arrays being compacted to the item itself (`[foo]` being
# compacted to `foo`)
#
# It is not always possible for `patch_for_forwarding!` to produce a document
# deemed safe for forwarding. Use `safe_for_forwarding?` to check the status
# of the output document.
#
# @param original [Hash] The original JSON-LD document used as reference
# @param compacted [Hash] The compacted JSON-LD document to be patched
# @return [void]
def patch_for_forwarding!(original, compacted)
original.without('@context', 'signature').each do |key, value|
next if value.nil? || !compacted.key?(key)
compacted_value = compacted[key]
if value.is_a?(Hash) && compacted_value.is_a?(Hash)
patch_for_forwarding!(value, compacted_value)
elsif value.is_a?(Array)
compacted_value = [compacted_value] unless compacted_value.is_a?(Array)
return if value.size != compacted_value.size
compacted[key] = value.zip(compacted_value).map do |v, vc|
if v.is_a?(Hash) && vc.is_a?(Hash)
patch_for_forwarding!(v, vc)
vc
elsif v == 'https://www.w3.org/ns/activitystreams#Public' && vc == 'as:Public'
v
else
vc
end
end
elsif value == 'https://www.w3.org/ns/activitystreams#Public' && compacted_value == 'as:Public'
compacted[key] = value
end
end
end
# Tests whether a JSON-LD compaction is deemed safe for redistribution,
# that is, if it doesn't change its meaning to consumers that do not actually
# handle JSON-LD, but rely on values being serialized in a certain way.
#
# See `patch_for_forwarding!` for details.
#
# @param original [Hash] The original JSON-LD document used as reference
# @param compacted [Hash] The compacted JSON-LD document to be patched
# @return [Boolean] Whether the patched document is deemed safe
def safe_for_forwarding?(original, compacted)
original.without('@context', 'signature').all? do |key, value|
compacted_value = compacted[key]
return false unless value.instance_of?(compacted_value.class)
if value.is_a?(Hash)
safe_for_forwarding?(value, compacted_value)
elsif value.is_a?(Array)
value.zip(compacted_value).all? do |v, vc|
v.is_a?(Hash) ? (vc.is_a?(Hash) && safe_for_forwarding?(v, vc)) : v == vc
end
else
value == compacted_value
end
end
end
def fetch_resource(uri, id_is_known, on_behalf_of = nil, request_options: {})
unless id_is_known
json = fetch_resource_without_id_validation(uri, on_behalf_of)
return if !json.is_a?(Hash) || unsupported_uri_scheme?(json['id'])
uri = json['id']
end
json = fetch_resource_without_id_validation(uri, on_behalf_of, request_options: request_options)
json.present? && json['id'] == uri ? json : nil
end
def fetch_resource_without_id_validation(uri, on_behalf_of = nil, raise_on_temporary_error = false, request_options: {})
on_behalf_of ||= Account.representative
build_request(uri, on_behalf_of, options: request_options).perform do |response|
raise Mastodon::UnexpectedResponseError, response unless response_successful?(response) || response_error_unsalvageable?(response) || !raise_on_temporary_error
body_to_json(response.body_with_limit) if response.code == 200 && valid_activitypub_content_type?(response)
end
end
def valid_activitypub_content_type?(response)
return true if response.mime_type == 'application/activity+json'
# When the mime type is `application/ld+json`, we need to check the profile,
# but `http.rb` does not parse it for us.
return false unless response.mime_type == 'application/ld+json'
response.headers[HTTP::Headers::CONTENT_TYPE]&.split(';')&.map(&:strip)&.any? do |str|
str.start_with?('profile="') && str[9...-1].split.include?('https://www.w3.org/ns/activitystreams')
end
end
def body_to_json(body, compare_id: nil)
json = body.is_a?(String) ? Oj.load(body, mode: :strict) : body
return if compare_id.present? && json['id'] != compare_id
json
rescue Oj::ParseError
nil
end
def response_successful?(response)
(200...300).cover?(response.code)
end
def response_error_unsalvageable?(response)
response.code == 501 || ((400...500).cover?(response.code) && ![401, 408, 429].include?(response.code))
end
def build_request(uri, on_behalf_of = nil, options: {})
Request.new(:get, uri, **options).tap do |request|
request.on_behalf_of(on_behalf_of) if on_behalf_of
request.add_headers('Accept' => 'application/activity+json, application/ld+json')
end
end
def load_jsonld_context(url, _options = {}, &block)
json = Rails.cache.fetch("jsonld:context:#{url}", expires_in: 30.days, raw: true) do
request = Request.new(:get, url)
request.add_headers('Accept' => 'application/ld+json')
request.perform do |res|
raise JSON::LD::JsonLdError::LoadingDocumentFailed unless res.code == 200 && res.mime_type == 'application/ld+json'
res.body_with_limit
end
end
doc = JSON::LD::API::RemoteDocument.new(json, documentUrl: url)
block ? yield(doc) : doc
end
end