Fix compacted JSON-LD possibly causing compatibility issues on forwarding

This commit is contained in:
Claire 2022-02-02 11:55:57 +01:00
parent 9d92e9204f
commit 77cc434f2b
3 changed files with 170 additions and 2 deletions

View file

@ -77,6 +77,78 @@ module JsonLdHelper
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.class == 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, on_behalf_of = nil)
unless id
json = fetch_resource_without_id_validation(uri, on_behalf_of)

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@ -5,13 +5,27 @@ class ActivityPub::ProcessCollectionService < BaseService
def call(body, account, **options)
@account = account
@json = Oj.load(body, mode: :strict)
@json = original_json = Oj.load(body, mode: :strict)
@options = options
@json = compact(@json) if @json['signature'].is_a?(Hash)
begin
@json = compact(@json) if @json['signature'].is_a?(Hash)
rescue JSON::LD::JsonLdError => e
Rails.logger.debug "Error when compacting JSON-LD document for #{value_or_id(@json['actor'])}: #{e.message}"
@json = original_json.without('signature')
end
return if !supported_context? || (different_actor? && verify_account!.nil?) || suspended_actor? || @account.local?
if @json['signature'].present?
# We have verified the signature, but in the compaction step above, might
# have introduced incompatibilities with other servers that do not
# normalize the JSON-LD documents (for instance, previous Mastodon
# versions), so skip redistribution if we can't get a safe document.
patch_for_forwarding!(original_json, @json)
@json.delete('signature') unless safe_for_forwarding?(original_json, @json)
end
case @json['type']
when 'Collection', 'CollectionPage'
process_items @json['items']

View file

@ -89,4 +89,86 @@ describe JsonLdHelper do
expect(fetch_resource_without_id_validation('https://host.test/')).to eq({})
end
end
context 'compaction and forwarding' do
let(:json) do
{
'@context' => [
'https://www.w3.org/ns/activitystreams',
'https://w3id.org/security/v1',
{
'obsolete' => 'http://ostatus.org#',
'convo' => 'obsolete:conversation',
'new' => 'https://obscure-unreleased-test.joinmastodon.org/#',
},
],
'type' => 'Create',
'to' => ['https://www.w3.org/ns/activitystreams#Public'],
'object' => {
'id' => 'https://example.com/status',
'type' => 'Note',
'inReplyTo' => nil,
'convo' => 'https://example.com/conversation',
'tag' => [
{
'type' => 'Mention',
'href' => ['foo'],
}
],
},
'signature' => {
'type' => 'RsaSignature2017',
'created' => '2022-02-02T12:00:00Z',
'creator' => 'https://example.com/actor#main-key',
'signatureValue' => 'some-sig',
},
}
end
describe '#compact' do
it 'properly compacts JSON-LD with alternative context definitions' do
expect(compact(json).dig('object', 'conversation')).to eq 'https://example.com/conversation'
end
it 'compacts single-item arrays' do
expect(compact(json).dig('object', 'tag', 'href')).to eq 'foo'
end
it 'compacts the activistreams Public collection' do
expect(compact(json)['to']).to eq 'as:Public'
end
it 'properly copies signature' do
expect(compact(json)['signature']).to eq json['signature']
end
end
describe 'patch_for_forwarding!' do
it 'properly patches incompatibilities' do
json['object'].delete('convo')
compacted = compact(json)
patch_for_forwarding!(json, compacted)
expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
expect(compacted.dig('object', 'tag', 0, 'href')).to eq ['foo']
expect(safe_for_forwarding?(json, compacted)).to eq true
end
end
describe 'safe_for_forwarding?' do
it 'deems a safe compacting as such' do
json['object'].delete('convo')
compacted = compact(json)
deemed_compatible = patch_for_forwarding!(json, compacted)
expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
expect(safe_for_forwarding?(json, compacted)).to eq true
end
it 'deems an unsafe compacting as such' do
compacted = compact(json)
deemed_compatible = patch_for_forwarding!(json, compacted)
expect(compacted['to']).to eq ['https://www.w3.org/ns/activitystreams#Public']
expect(safe_for_forwarding?(json, compacted)).to eq false
end
end
end
end