Gab Social. All are welcome.

app/lib/ostatus/activity/base.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Base
+  include Redisable
+
+  def initialize(xml, account = nil, **options)
+    @xml     = xml
+    @account = account
+    @options = options
+  end
+
+  def status?
+    [:activity, :note, :comment].include?(type)
+  end
+
+  def verb
+    raw = @xml.at_xpath('./activity:verb', activity: OStatus::TagManager::AS_XMLNS).content
+    OStatus::TagManager::VERBS.key(raw)
+  rescue
+    :post
+  end
+
+  def type
+    raw = @xml.at_xpath('./activity:object-type', activity: OStatus::TagManager::AS_XMLNS).content
+    OStatus::TagManager::TYPES.key(raw)
+  rescue
+    :activity
+  end
+
+  def id
+    @xml.at_xpath('./xmlns:id', xmlns: OStatus::TagManager::XMLNS).content
+  end
+
+  def url
+    link = @xml.xpath('./xmlns:link[@rel="alternate"]', xmlns: OStatus::TagManager::XMLNS).find { |link_candidate| link_candidate['type'] == 'text/html' }
+    link.nil? ? nil : link['href']
+  end
+
+  def activitypub_uri
+    link = @xml.xpath('./xmlns:link[@rel="alternate"]', xmlns: OStatus::TagManager::XMLNS).find { |link_candidate| ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(link_candidate['type']) }
+    link.nil? ? nil : link['href']
+  end
+
+  def activitypub_uri?
+    activitypub_uri.present?
+  end
+
+  private
+
+  def find_status(uri)
+    if OStatus::TagManager.instance.local_id?(uri)
+      local_id = OStatus::TagManager.instance.unique_tag_to_local_id(uri, 'Status')
+      return Status.find_by(id: local_id)
+    elsif ActivityPub::TagManager.instance.local_uri?(uri)
+      local_id = ActivityPub::TagManager.instance.uri_to_local_id(uri)
+      return Status.find_by(id: local_id)
+    end
+
+    Status.find_by(uri: uri)
+  end
+
+  def find_activitypub_status(uri, href)
+    tag_matches = /tag:([^,:]+)[^:]*:objectId=([\d]+)/.match(uri)
+    href_matches = %r{/users/([^/]+)}.match(href)
+
+    unless tag_matches.nil? || href_matches.nil?
+      uri = "https://#{tag_matches[1]}/users/#{href_matches[1]}/statuses/#{tag_matches[2]}"
+      Status.find_by(uri: uri)
+    end
+  end
+end

app/lib/ostatus/activity/creation.rb

@@ -0,0 +1,219 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Creation < OStatus::Activity::Base
+  def perform
+    if redis.exists("delete_upon_arrival:#{@account.id}:#{id}")
+      Rails.logger.debug "Delete for status #{id} was queued, ignoring"
+      return [nil, false]
+    end
+
+    return [nil, false] if @account.suspended? || invalid_origin?
+
+    RedisLock.acquire(lock_options) do |lock|
+      if lock.acquired?
+        # Return early if status already exists in db
+        @status = find_status(id)
+        return [@status, false] unless @status.nil?
+        @status = process_status
+      else
+        raise GabSocial::RaceConditionError
+      end
+    end
+
+    [@status, true]
+  end
+
+  def process_status
+    Rails.logger.debug "Creating remote status #{id}"
+    cached_reblog = reblog
+    status = nil
+
+    # Skip if the reblogged status is not public
+    return if cached_reblog && !(cached_reblog.public_visibility? || cached_reblog.unlisted_visibility?)
+
+    media_attachments = save_media.take(4)
+
+    ApplicationRecord.transaction do
+      status = Status.create!(
+        uri: id,
+        url: url,
+        account: @account,
+        reblog: cached_reblog,
+        text: content,
+        spoiler_text: content_warning,
+        created_at: published,
+        override_timestamps: @options[:override_timestamps],
+        reply: thread?,
+        language: content_language,
+        visibility: visibility_scope,
+        conversation: find_or_create_conversation,
+        thread: thread? ? find_status(thread.first) || find_activitypub_status(thread.first, thread.second) : nil,
+        media_attachment_ids: media_attachments.map(&:id),
+        sensitive: sensitive?
+      )
+
+      save_mentions(status)
+      save_hashtags(status)
+      save_emojis(status)
+    end
+
+    if thread? && status.thread.nil? && Request.valid_url?(thread.second)
+      Rails.logger.debug "Trying to attach #{status.id} (#{id}) to #{thread.first}"
+      ThreadResolveWorker.perform_async(status.id, thread.second)
+    end
+
+    Rails.logger.debug "Queuing remote status #{status.id} (#{id}) for distribution"
+
+    LinkCrawlWorker.perform_async(status.id) unless status.spoiler_text?
+
+    # Only continue if the status is supposed to have arrived in real-time.
+    # Note that if @options[:override_timestamps] isn't set, the status
+    # may have a lower snowflake id than other existing statuses, potentially
+    # "hiding" it from paginated API calls
+    return status unless @options[:override_timestamps] || status.within_realtime_window?
+
+    DistributionWorker.perform_async(status.id)
+
+    status
+  end
+
+  def content
+    @xml.at_xpath('./xmlns:content', xmlns: OStatus::TagManager::XMLNS).content
+  end
+
+  def content_language
+    @xml.at_xpath('./xmlns:content', xmlns: OStatus::TagManager::XMLNS)['xml:lang']&.presence || 'en'
+  end
+
+  def content_warning
+    @xml.at_xpath('./xmlns:summary', xmlns: OStatus::TagManager::XMLNS)&.content || ''
+  end
+
+  def visibility_scope
+    @xml.at_xpath('./gabsocial:scope', gabsocial: OStatus::TagManager::GABSCL_XMLNS)&.content&.to_sym || :public
+  end
+
+  def published
+    @xml.at_xpath('./xmlns:published', xmlns: OStatus::TagManager::XMLNS).content
+  end
+
+  def thread?
+    !@xml.at_xpath('./thr:in-reply-to', thr: OStatus::TagManager::THR_XMLNS).nil?
+  end
+
+  def thread
+    thr = @xml.at_xpath('./thr:in-reply-to', thr: OStatus::TagManager::THR_XMLNS)
+    [thr['ref'], thr['href']]
+  end
+
+  private
+
+  def sensitive?
+    # OStatus-specific convention (not standard)
+    @xml.xpath('./xmlns:category', xmlns: OStatus::TagManager::XMLNS).any? { |category| category['term'] == 'nsfw' }
+  end
+
+  def find_or_create_conversation
+    uri = @xml.at_xpath('./ostatus:conversation', ostatus: OStatus::TagManager::OS_XMLNS)&.attribute('ref')&.content
+    return if uri.nil?
+
+    if OStatus::TagManager.instance.local_id?(uri)
+      local_id = OStatus::TagManager.instance.unique_tag_to_local_id(uri, 'Conversation')
+      return Conversation.find_by(id: local_id)
+    end
+
+    Conversation.find_by(uri: uri) || Conversation.create!(uri: uri)
+  end
+
+  def save_mentions(parent)
+    processed_account_ids = []
+
+    @xml.xpath('./xmlns:link[@rel="mentioned"]', xmlns: OStatus::TagManager::XMLNS).each do |link|
+      next if [OStatus::TagManager::TYPES[:group], OStatus::TagManager::TYPES[:collection]].include? link['ostatus:object-type']
+
+      mentioned_account = account_from_href(link['href'])
+
+      next if mentioned_account.nil? || processed_account_ids.include?(mentioned_account.id)
+
+      mentioned_account.mentions.where(status: parent).first_or_create(status: parent)
+
+      # So we can skip duplicate mentions
+      processed_account_ids << mentioned_account.id
+    end
+  end
+
+  def save_hashtags(parent)
+    tags = @xml.xpath('./xmlns:category', xmlns: OStatus::TagManager::XMLNS).map { |category| category['term'] }.select(&:present?)
+    ProcessHashtagsService.new.call(parent, tags)
+  end
+
+  def save_media
+    do_not_download = DomainBlock.find_by(domain: @account.domain)&.reject_media?
+    media_attachments = []
+
+    @xml.xpath('./xmlns:link[@rel="enclosure"]', xmlns: OStatus::TagManager::XMLNS).each do |link|
+      next unless link['href']
+
+      media = MediaAttachment.where(status: nil, remote_url: link['href']).first_or_initialize(account: @account, status: nil, remote_url: link['href'])
+      parsed_url = Addressable::URI.parse(link['href']).normalize
+
+      next if !%w(http https).include?(parsed_url.scheme) || parsed_url.host.empty?
+
+      media.save
+      media_attachments << media
+
+      next if do_not_download
+
+      begin
+        media.file_remote_url = link['href']
+        media.save!
+      rescue ActiveRecord::RecordInvalid
+        next
+      end
+    end
+
+    media_attachments
+  end
+
+  def save_emojis(parent)
+    do_not_download = DomainBlock.find_by(domain: parent.account.domain)&.reject_media?
+
+    return if do_not_download
+
+    @xml.xpath('./xmlns:link[@rel="emoji"]', xmlns: OStatus::TagManager::XMLNS).each do |link|
+      next unless link['href'] && link['name']
+
+      shortcode = link['name'].delete(':')
+      emoji     = CustomEmoji.find_by(shortcode: shortcode, domain: parent.account.domain)
+
+      next unless emoji.nil?
+
+      emoji = CustomEmoji.new(shortcode: shortcode, domain: parent.account.domain)
+      emoji.image_remote_url = link['href']
+      emoji.save
+    end
+  end
+
+  def account_from_href(href)
+    url = Addressable::URI.parse(href).normalize
+
+    if TagManager.instance.web_domain?(url.host)
+      Account.find_local(url.path.gsub('/users/', ''))
+    else
+      Account.where(uri: href).or(Account.where(url: href)).first || FetchRemoteAccountService.new.call(href)
+    end
+  end
+
+  def invalid_origin?
+    return false unless id.start_with?('http') # Legacy IDs cannot be checked
+
+    needle = Addressable::URI.parse(id).normalized_host
+
+    !(needle.casecmp(@account.domain).zero? ||
+      needle.casecmp(Addressable::URI.parse(@account.remote_url.presence || @account.uri).normalized_host).zero?)
+  end
+
+  def lock_options
+    { redis: Redis.current, key: "create:#{id}" }
+  end
+end

app/lib/ostatus/activity/deletion.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Deletion < OStatus::Activity::Base
+  def perform
+    Rails.logger.debug "Deleting remote status #{id}"
+
+    status   = Status.find_by(uri: id, account: @account)
+    status ||= Status.find_by(uri: activitypub_uri, account: @account) if activitypub_uri?
+
+    if status.nil?
+      redis.setex("delete_upon_arrival:#{@account.id}:#{id}", 6 * 3_600, id)
+    else
+      RemoveStatusService.new.call(status)
+    end
+  end
+end

app/lib/ostatus/activity/general.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::General < OStatus::Activity::Base
+  def specialize
+    special_class&.new(@xml, @account, @options)
+  end
+
+  private
+
+  def special_class
+    case verb
+    when :post
+      OStatus::Activity::Post
+    when :share
+      OStatus::Activity::Share
+    when :delete
+      OStatus::Activity::Deletion
+    end
+  end
+end

app/lib/ostatus/activity/post.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Post < OStatus::Activity::Creation
+  def perform
+    status, just_created = super
+
+    if just_created
+      status.mentions.includes(:account).each do |mention|
+        mentioned_account = mention.account
+        next unless mentioned_account.local?
+        NotifyService.new.call(mentioned_account, mention)
+      end
+    end
+
+    status
+  end
+
+  private
+
+  def reblog
+    nil
+  end
+end

app/lib/ostatus/activity/remote.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Remote < OStatus::Activity::Base
+  def perform
+    if activitypub_uri?
+      find_status(activitypub_uri) || FetchRemoteStatusService.new.call(url)
+    else
+      find_status(id) || FetchRemoteStatusService.new.call(url)
+    end
+  end
+end

app/lib/ostatus/activity/share.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+class OStatus::Activity::Share < OStatus::Activity::Creation
+  def perform
+    return if reblog.nil?
+
+    status, just_created = super
+    NotifyService.new.call(reblog.account, status) if reblog.account.local? && just_created
+    status
+  end
+
+  def object
+    @xml.at_xpath('.//activity:object', activity: OStatus::TagManager::AS_XMLNS)
+  end
+
+  private
+
+  def reblog
+    return @reblog if defined? @reblog
+
+    original_status = OStatus::Activity::Remote.new(object).perform
+    return if original_status.nil?
+
+    @reblog = original_status.reblog? ? original_status.reblog : original_status
+  end
+end

app/lib/ostatus/atom_serializer.rb

@@ -0,0 +1,378 @@
+# frozen_string_literal: true
+
+class OStatus::AtomSerializer
+  include RoutingHelper
+  include ActionView::Helpers::SanitizeHelper
+
+  class << self
+    def render(element)
+      document = Ox::Document.new(version: '1.0')
+      document << element
+      ('<?xml version="1.0"?>' + Ox.dump(element, effort: :tolerant)).force_encoding('UTF-8')
+    end
+  end
+
+  def author(account)
+    author = Ox::Element.new('author')
+
+    uri = OStatus::TagManager.instance.uri_for(account)
+
+    append_element(author, 'id', uri)
+    append_element(author, 'activity:object-type', OStatus::TagManager::TYPES[:person])
+    append_element(author, 'uri', uri)
+    append_element(author, 'name', account.username)
+    append_element(author, 'email', account.local? ? account.local_username_and_domain : account.acct)
+    append_element(author, 'summary', Formatter.instance.simplified_format(account).to_str, type: :html) if account.note?
+    append_element(author, 'link', nil, rel: :alternate, type: 'text/html', href: ::TagManager.instance.url_for(account))
+    append_element(author, 'link', nil, rel: :avatar, type: account.avatar_content_type, 'media:width': 120, 'media:height': 120, href: full_asset_url(account.avatar.url(:original))) if account.avatar?
+    append_element(author, 'link', nil, rel: :header, type: account.header_content_type, 'media:width': 700, 'media:height': 335, href: full_asset_url(account.header.url(:original))) if account.header?
+    account.emojis.each do |emoji|
+      append_element(author, 'link', nil, rel: :emoji, href: full_asset_url(emoji.image.url), name: emoji.shortcode)
+    end
+    append_element(author, 'poco:preferredUsername', account.username)
+    append_element(author, 'poco:displayName', account.display_name) if account.display_name?
+    append_element(author, 'poco:note', account.local? ? account.note : strip_tags(account.note)) if account.note?
+    append_element(author, 'gabsocial:scope', account.locked? ? :private : :public)
+
+    author
+  end
+
+  def feed(account, stream_entries)
+    feed = Ox::Element.new('feed')
+
+    add_namespaces(feed)
+
+    append_element(feed, 'id', account_url(account, format: 'atom'))
+    append_element(feed, 'title', account.display_name.presence || account.username)
+    append_element(feed, 'subtitle', account.note)
+    append_element(feed, 'updated', account.updated_at.iso8601)
+    append_element(feed, 'logo', full_asset_url(account.avatar.url(:original)))
+
+    feed << author(account)
+
+    append_element(feed, 'link', nil, rel: :alternate, type: 'text/html', href: ::TagManager.instance.url_for(account))
+    append_element(feed, 'link', nil, rel: :self, type: 'application/atom+xml', href: account_url(account, format: 'atom'))
+    append_element(feed, 'link', nil, rel: :next, type: 'application/atom+xml', href: account_url(account, format: 'atom', max_id: stream_entries.last.id)) if stream_entries.size == 20
+    append_element(feed, 'link', nil, rel: :hub, href: api_push_url)
+    append_element(feed, 'link', nil, rel: :salmon, href: api_salmon_url(account.id))
+
+    stream_entries.each do |stream_entry|
+      feed << entry(stream_entry)
+    end
+
+    feed
+  end
+
+  def entry(stream_entry, root = false)
+    entry = Ox::Element.new('entry')
+
+    add_namespaces(entry) if root
+
+    append_element(entry, 'id', OStatus::TagManager.instance.uri_for(stream_entry.status))
+    append_element(entry, 'published', stream_entry.created_at.iso8601)
+    append_element(entry, 'updated', stream_entry.updated_at.iso8601)
+    append_element(entry, 'title', stream_entry&.status&.title || "#{stream_entry.account.acct} deleted status")
+
+    entry << author(stream_entry.account) if root
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[stream_entry.object_type])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[stream_entry.verb])
+
+    entry << object(stream_entry.target) if stream_entry.targeted?
+
+    if stream_entry.status.nil?
+      append_element(entry, 'content', 'Deleted status')
+    elsif stream_entry.status.destroyed?
+      append_element(entry, 'content', 'Deleted status')
+      append_element(entry, 'link', nil, rel: :alternate, type: 'application/activity+json', href: ActivityPub::TagManager.instance.uri_for(stream_entry.status)) if stream_entry.account.local?
+    else
+      serialize_status_attributes(entry, stream_entry.status)
+    end
+
+    append_element(entry, 'link', nil, rel: :alternate, type: 'text/html', href: ::TagManager.instance.url_for(stream_entry.status))
+    append_element(entry, 'link', nil, rel: :self, type: 'application/atom+xml', href: account_stream_entry_url(stream_entry.account, stream_entry, format: 'atom'))
+    append_element(entry, 'thr:in-reply-to', nil, ref: OStatus::TagManager.instance.uri_for(stream_entry.thread), href: ::TagManager.instance.url_for(stream_entry.thread)) if stream_entry.threaded?
+    append_element(entry, 'ostatus:conversation', nil, ref: conversation_uri(stream_entry.status.conversation)) unless stream_entry&.status&.conversation_id.nil?
+
+    entry
+  end
+
+  def object(status)
+    object = Ox::Element.new('activity:object')
+
+    append_element(object, 'id', OStatus::TagManager.instance.uri_for(status))
+    append_element(object, 'published', status.created_at.iso8601)
+    append_element(object, 'updated', status.updated_at.iso8601)
+    append_element(object, 'title', status.title)
+
+    object << author(status.account)
+
+    append_element(object, 'activity:object-type', OStatus::TagManager::TYPES[status.object_type])
+    append_element(object, 'activity:verb', OStatus::TagManager::VERBS[status.verb])
+
+    serialize_status_attributes(object, status)
+
+    append_element(object, 'link', nil, rel: :alternate, type: 'text/html', href: ::TagManager.instance.url_for(status))
+    append_element(object, 'thr:in-reply-to', nil, ref: OStatus::TagManager.instance.uri_for(status.thread), href: ::TagManager.instance.url_for(status.thread)) unless status.thread.nil?
+    append_element(object, 'ostatus:conversation', nil, ref: conversation_uri(status.conversation)) unless status.conversation_id.nil?
+
+    object
+  end
+
+  def follow_salmon(follow)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{follow.account.acct} started following #{follow.target_account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(follow.created_at, follow.id, 'Follow'))
+    append_element(entry, 'title', description)
+    append_element(entry, 'content', description, type: :html)
+
+    entry << author(follow.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:follow])
+
+    object = author(follow.target_account)
+    object.value = 'activity:object'
+
+    entry << object
+    entry
+  end
+
+  def follow_request_salmon(follow_request)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(follow_request.created_at, follow_request.id, 'FollowRequest'))
+    append_element(entry, 'title', "#{follow_request.account.acct} requested to follow #{follow_request.target_account.acct}")
+
+    entry << author(follow_request.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:request_friend])
+
+    object = author(follow_request.target_account)
+    object.value = 'activity:object'
+
+    entry << object
+    entry
+  end
+
+  def authorize_follow_request_salmon(follow_request)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, follow_request.id, 'FollowRequest'))
+    append_element(entry, 'title', "#{follow_request.target_account.acct} authorizes follow request by #{follow_request.account.acct}")
+
+    entry << author(follow_request.target_account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:authorize])
+
+    object = Ox::Element.new('activity:object')
+    object << author(follow_request.account)
+
+    append_element(object, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(object, 'activity:verb', OStatus::TagManager::VERBS[:request_friend])
+
+    inner_object = author(follow_request.target_account)
+    inner_object.value = 'activity:object'
+
+    object << inner_object
+    entry  << object
+    entry
+  end
+
+  def reject_follow_request_salmon(follow_request)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, follow_request.id, 'FollowRequest'))
+    append_element(entry, 'title', "#{follow_request.target_account.acct} rejects follow request by #{follow_request.account.acct}")
+
+    entry << author(follow_request.target_account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:reject])
+
+    object = Ox::Element.new('activity:object')
+    object << author(follow_request.account)
+
+    append_element(object, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(object, 'activity:verb', OStatus::TagManager::VERBS[:request_friend])
+
+    inner_object = author(follow_request.target_account)
+    inner_object.value = 'activity:object'
+
+    object << inner_object
+    entry  << object
+    entry
+  end
+
+  def unfollow_salmon(follow)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{follow.account.acct} is no longer following #{follow.target_account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, follow.id, 'Follow'))
+    append_element(entry, 'title', description)
+    append_element(entry, 'content', description, type: :html)
+
+    entry << author(follow.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:unfollow])
+
+    object = author(follow.target_account)
+    object.value = 'activity:object'
+
+    entry << object
+    entry
+  end
+
+  def block_salmon(block)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{block.account.acct} no longer wishes to interact with #{block.target_account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, block.id, 'Block'))
+    append_element(entry, 'title', description)
+
+    entry << author(block.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:block])
+
+    object = author(block.target_account)
+    object.value = 'activity:object'
+
+    entry << object
+    entry
+  end
+
+  def unblock_salmon(block)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{block.account.acct} no longer blocks #{block.target_account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, block.id, 'Block'))
+    append_element(entry, 'title', description)
+
+    entry << author(block.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:unblock])
+
+    object = author(block.target_account)
+    object.value = 'activity:object'
+
+    entry << object
+    entry
+  end
+
+  def favourite_salmon(favourite)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{favourite.account.acct} favorited a status by #{favourite.status.account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(favourite.created_at, favourite.id, 'Favourite'))
+    append_element(entry, 'title', description)
+    append_element(entry, 'content', description, type: :html)
+
+    entry << author(favourite.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:favorite])
+
+    entry << object(favourite.status)
+
+    append_element(entry, 'thr:in-reply-to', nil, ref: OStatus::TagManager.instance.uri_for(favourite.status), href: ::TagManager.instance.url_for(favourite.status))
+
+    entry
+  end
+
+  def unfavourite_salmon(favourite)
+    entry = Ox::Element.new('entry')
+    add_namespaces(entry)
+
+    description = "#{favourite.account.acct} no longer favorites a status by #{favourite.status.account.acct}"
+
+    append_element(entry, 'id', OStatus::TagManager.instance.unique_tag(Time.now.utc, favourite.id, 'Favourite'))
+    append_element(entry, 'title', description)
+    append_element(entry, 'content', description, type: :html)
+
+    entry << author(favourite.account)
+
+    append_element(entry, 'activity:object-type', OStatus::TagManager::TYPES[:activity])
+    append_element(entry, 'activity:verb', OStatus::TagManager::VERBS[:unfavorite])
+
+    entry << object(favourite.status)
+
+    append_element(entry, 'thr:in-reply-to', nil, ref: OStatus::TagManager.instance.uri_for(favourite.status), href: ::TagManager.instance.url_for(favourite.status))
+
+    entry
+  end
+
+  private
+
+  def append_element(parent, name, content = nil, **attributes)
+    element = Ox::Element.new(name)
+    attributes.each { |k, v| element[k] = sanitize_str(v) }
+    element << sanitize_str(content) unless content.nil?
+    parent  << element
+  end
+
+  def sanitize_str(raw_str)
+    raw_str.to_s
+  end
+
+  def conversation_uri(conversation)
+    return conversation.uri if conversation.uri?
+    OStatus::TagManager.instance.unique_tag(conversation.created_at, conversation.id, 'Conversation')
+  end
+
+  def add_namespaces(parent)
+    parent['xmlns']          = OStatus::TagManager::XMLNS
+    parent['xmlns:thr']      = OStatus::TagManager::THR_XMLNS
+    parent['xmlns:activity'] = OStatus::TagManager::AS_XMLNS
+    parent['xmlns:poco']     = OStatus::TagManager::POCO_XMLNS
+    parent['xmlns:media']    = OStatus::TagManager::MEDIA_XMLNS
+    parent['xmlns:ostatus']  = OStatus::TagManager::OS_XMLNS
+    parent['xmlns:gabsocial'] = OStatus::TagManager::GABSCL_XMLNS
+  end
+
+  def serialize_status_attributes(entry, status)
+    append_element(entry, 'link', nil, rel: :alternate, type: 'application/activity+json', href: ActivityPub::TagManager.instance.uri_for(status)) if status.account.local?
+
+    append_element(entry, 'summary', status.spoiler_text, 'xml:lang': status.language) if status.spoiler_text?
+    append_element(entry, 'content', Formatter.instance.format(status, inline_poll_options: true).to_str || '.', type: 'html', 'xml:lang': status.language)
+
+    status.active_mentions.sort_by(&:id).each do |mentioned|
+      append_element(entry, 'link', nil, rel: :mentioned, 'ostatus:object-type': OStatus::TagManager::TYPES[:person], href: OStatus::TagManager.instance.uri_for(mentioned.account))
+    end
+
+    append_element(entry, 'link', nil, rel: :mentioned, 'ostatus:object-type': OStatus::TagManager::TYPES[:collection], href: OStatus::TagManager::COLLECTIONS[:public]) if status.public_visibility?
+
+    status.tags.each do |tag|
+      append_element(entry, 'category', nil, term: tag.name)
+    end
+
+    status.media_attachments.each do |media|
+      append_element(entry, 'link', nil, rel: :enclosure, type: media.file_content_type, length: media.file_file_size, href: full_asset_url(media.file.url(:original, false)))
+    end
+
+    append_element(entry, 'category', nil, term: 'nsfw') if status.sensitive? && status.media_attachments.any?
+    append_element(entry, 'gabsocial:scope', status.visibility)
+
+    status.emojis.each do |emoji|
+      append_element(entry, 'link', nil, rel: :emoji, href: full_asset_url(emoji.image.url), name: emoji.shortcode)
+    end
+  end
+end

app/lib/ostatus/tag_manager.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+class OStatus::TagManager
+  include Singleton
+  include RoutingHelper
+
+  VERBS = {
+    post:           'http://activitystrea.ms/schema/1.0/post',
+    share:          'http://activitystrea.ms/schema/1.0/share',
+    favorite:       'http://activitystrea.ms/schema/1.0/favorite',
+    unfavorite:     'http://activitystrea.ms/schema/1.0/unfavorite',
+    delete:         'http://activitystrea.ms/schema/1.0/delete',
+    follow:         'http://activitystrea.ms/schema/1.0/follow',
+    request_friend: 'http://activitystrea.ms/schema/1.0/request-friend',
+    authorize:      'http://activitystrea.ms/schema/1.0/authorize',
+    reject:         'http://activitystrea.ms/schema/1.0/reject',
+    unfollow:       'http://ostatus.org/schema/1.0/unfollow',
+    block:          'http://gab.com/schema/1.0/block',
+    unblock:        'http://gab.com/schema/1.0/unblock',
+  }.freeze
+
+  TYPES = {
+    activity:   'http://activitystrea.ms/schema/1.0/activity',
+    note:       'http://activitystrea.ms/schema/1.0/note',
+    comment:    'http://activitystrea.ms/schema/1.0/comment',
+    person:     'http://activitystrea.ms/schema/1.0/person',
+    collection: 'http://activitystrea.ms/schema/1.0/collection',
+    group:      'http://activitystrea.ms/schema/1.0/group',
+  }.freeze
+
+  COLLECTIONS = {
+    public: 'http://activityschema.org/collection/public',
+  }.freeze
+
+  XMLNS        = 'http://www.w3.org/2005/Atom'
+  MEDIA_XMLNS  = 'http://purl.org/syndication/atommedia'
+  AS_XMLNS     = 'http://activitystrea.ms/spec/1.0/'
+  THR_XMLNS    = 'http://purl.org/syndication/thread/1.0'
+  POCO_XMLNS   = 'http://portablecontacts.net/spec/1.0'
+  DFRN_XMLNS   = 'http://purl.org/macgirvin/dfrn/1.0'
+  OS_XMLNS     = 'http://ostatus.org/schema/1.0'
+  GABSCL_XMLNS = 'http://gab.com/schema/1.0'
+
+  def unique_tag(date, id, type)
+    "tag:#{Rails.configuration.x.local_domain},#{date.strftime('%Y-%m-%d')}:objectId=#{id}:objectType=#{type}"
+  end
+
+  def unique_tag_to_local_id(tag, expected_type)
+    return nil unless local_id?(tag)
+
+    if ActivityPub::TagManager.instance.local_uri?(tag)
+      ActivityPub::TagManager.instance.uri_to_local_id(tag)
+    else
+      matches = Regexp.new("objectId=([\\d]+):objectType=#{expected_type}").match(tag)
+      return matches[1] unless matches.nil?
+    end
+  end
+
+  def local_id?(id)
+    id.start_with?("tag:#{Rails.configuration.x.local_domain}") || ActivityPub::TagManager.instance.local_uri?(id)
+  end
+
+  def uri_for(target)
+    return target.uri if target.respond_to?(:local?) && !target.local?
+
+    case target.object_type
+    when :person
+      account_url(target)
+    when :note, :comment, :activity
+      target.uri || unique_tag(target.created_at, target.id, 'Status')
+    end
+  end
+end