Fix compacted JSON-LD possibly causing compatibility issues on forwarding
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3 changed files with 170 additions and 2 deletions
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@ -77,6 +77,78 @@ module JsonLdHelper
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compacted
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end
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# Patches a JSON-LD document to avoid compatibility issues on redistribution
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#
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# Since compacting a JSON-LD document against Mastodon's built-in vocabulary
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# means other extension namespaces will be expanded, malformed JSON-LD
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# attributes lost, and some values “unexpectedly” compacted this method
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# patches the following likely sources of incompatibility:
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# - 'https://www.w3.org/ns/activitystreams#Public' being compacted to
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# 'as:Public' (for instance, pre-3.4.0 Mastodon does not understand
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# 'as:Public')
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# - single-item arrays being compacted to the item itself (`[foo]` being
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# compacted to `foo`)
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#
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# It is not always possible for `patch_for_forwarding!` to produce a document
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# deemed safe for forwarding. Use `safe_for_forwarding?` to check the status
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# of the output document.
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#
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# @param original [Hash] The original JSON-LD document used as reference
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# @param compacted [Hash] The compacted JSON-LD document to be patched
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# @return [void]
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def patch_for_forwarding!(original, compacted)
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original.without('@context', 'signature').each do |key, value|
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next if value.nil? || !compacted.key?(key)
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compacted_value = compacted[key]
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if value.is_a?(Hash) && compacted_value.is_a?(Hash)
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patch_for_forwarding!(value, compacted_value)
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elsif value.is_a?(Array)
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compacted_value = [compacted_value] unless compacted_value.is_a?(Array)
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return if value.size != compacted_value.size
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compacted[key] = value.zip(compacted_value).map do |v, vc|
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if v.is_a?(Hash) && vc.is_a?(Hash)
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patch_for_forwarding!(v, vc)
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vc
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elsif v == 'https://www.w3.org/ns/activitystreams#Public' && vc == 'as:Public'
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v
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else
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vc
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end
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end
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elsif value == 'https://www.w3.org/ns/activitystreams#Public' && compacted_value == 'as:Public'
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compacted[key] = value
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end
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end
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end
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# Tests whether a JSON-LD compaction is deemed safe for redistribution,
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# that is, if it doesn't change its meaning to consumers that do not actually
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# handle JSON-LD, but rely on values being serialized in a certain way.
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#
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# See `patch_for_forwarding!` for details.
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#
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# @param original [Hash] The original JSON-LD document used as reference
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# @param compacted [Hash] The compacted JSON-LD document to be patched
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# @return [Boolean] Whether the patched document is deemed safe
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def safe_for_forwarding?(original, compacted)
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original.without('@context', 'signature').all? do |key, value|
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compacted_value = compacted[key]
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return false unless value.class == compacted_value.class
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if value.is_a?(Hash)
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safe_for_forwarding?(value, compacted_value)
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elsif value.is_a?(Array)
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value.zip(compacted_value).all? do |v, vc|
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v.is_a?(Hash) ? (vc.is_a?(Hash) && safe_for_forwarding?(v, vc)) : v == vc
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end
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else
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value == compacted_value
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end
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end
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end
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def fetch_resource(uri, id, on_behalf_of = nil)
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unless id
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json = fetch_resource_without_id_validation(uri, on_behalf_of)
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@ -5,13 +5,27 @@ class ActivityPub::ProcessCollectionService < BaseService
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def call(body, account, **options)
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@account = account
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@json = Oj.load(body, mode: :strict)
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@json = original_json = Oj.load(body, mode: :strict)
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@options = options
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begin
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@json = compact(@json) if @json['signature'].is_a?(Hash)
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rescue JSON::LD::JsonLdError => e
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Rails.logger.debug "Error when compacting JSON-LD document for #{value_or_id(@json['actor'])}: #{e.message}"
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@json = original_json.without('signature')
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end
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return if !supported_context? || (different_actor? && verify_account!.nil?) || suspended_actor? || @account.local?
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if @json['signature'].present?
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# We have verified the signature, but in the compaction step above, might
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# have introduced incompatibilities with other servers that do not
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# normalize the JSON-LD documents (for instance, previous Mastodon
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# versions), so skip redistribution if we can't get a safe document.
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patch_for_forwarding!(original_json, @json)
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@json.delete('signature') unless safe_for_forwarding?(original_json, @json)
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end
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case @json['type']
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when 'Collection', 'CollectionPage'
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process_items @json['items']
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@ -89,4 +89,86 @@ describe JsonLdHelper do
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expect(fetch_resource_without_id_validation('https://host.test/')).to eq({})
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end
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end
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context 'compaction and forwarding' do
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let(:json) do
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{
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'@context' => [
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'https://www.w3.org/ns/activitystreams',
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'https://w3id.org/security/v1',
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{
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'obsolete' => 'http://ostatus.org#',
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'convo' => 'obsolete:conversation',
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'new' => 'https://obscure-unreleased-test.joinmastodon.org/#',
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},
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],
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'type' => 'Create',
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'to' => ['https://www.w3.org/ns/activitystreams#Public'],
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'object' => {
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'id' => 'https://example.com/status',
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'type' => 'Note',
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'inReplyTo' => nil,
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'convo' => 'https://example.com/conversation',
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'tag' => [
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{
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'type' => 'Mention',
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'href' => ['foo'],
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}
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],
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},
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'signature' => {
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'type' => 'RsaSignature2017',
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'created' => '2022-02-02T12:00:00Z',
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'creator' => 'https://example.com/actor#main-key',
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'signatureValue' => 'some-sig',
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},
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}
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end
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describe '#compact' do
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it 'properly compacts JSON-LD with alternative context definitions' do
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expect(compact(json).dig('object', 'conversation')).to eq 'https://example.com/conversation'
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end
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it 'compacts single-item arrays' do
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expect(compact(json).dig('object', 'tag', 'href')).to eq 'foo'
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end
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it 'compacts the activistreams Public collection' do
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expect(compact(json)['to']).to eq 'as:Public'
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end
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it 'properly copies signature' do
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expect(compact(json)['signature']).to eq json['signature']
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end
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end
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describe 'patch_for_forwarding!' do
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it 'properly patches incompatibilities' do
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json['object'].delete('convo')
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compacted = compact(json)
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patch_for_forwarding!(json, compacted)
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expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
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expect(compacted.dig('object', 'tag', 0, 'href')).to eq ['foo']
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expect(safe_for_forwarding?(json, compacted)).to eq true
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end
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end
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describe 'safe_for_forwarding?' do
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it 'deems a safe compacting as such' do
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json['object'].delete('convo')
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compacted = compact(json)
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deemed_compatible = patch_for_forwarding!(json, compacted)
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expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
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expect(safe_for_forwarding?(json, compacted)).to eq true
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end
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it 'deems an unsafe compacting as such' do
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compacted = compact(json)
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deemed_compatible = patch_for_forwarding!(json, compacted)
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expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
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expect(safe_for_forwarding?(json, compacted)).to eq false
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end
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end
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end
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end
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