Add a nodeinfo endpoint (#12002)

* Add nodeinfo endpoint

* dont commit stuff from my local dev

* consistant naming since we implimented 2.1 schema

* Add some additional node info stuff

* Add nodeinfo endpoint

* dont commit stuff from my local dev

* consistant naming since we implimented 2.1 schema

* expanding this to include federation info

* codeclimate feedback

* CC feedback

* using activeserializers seems like a good idea...

* get rid of draft 2.1 version

* Reimplement 2.1, also fix metaData -> metadata

* Fix metaData -> metadata here too

* Fix nodeinfo 2.1 tests

* Implement cache for monthly user aggregate

* Useless

* Remove ostatus from the list of supported protocols

* Fix nodeinfo's open_registration reading obsolete setting variable

* Only serialize domain blocks with user-facing limitations

* Do not needlessly list noop severity in nodeinfo

* Only serialize domain blocks info in nodeinfo when they are set to be displayed to everyone

* Enable caching for nodeinfo endpoints

* Fix rendering nodeinfo

* CodeClimate fixes

* Please CodeClimate

* Change InstancePresenter#active_user_count_months for clarity

* Refactor NodeInfoSerializer#metadata

* Remove nodeinfo 2.1 support as the schema doesn't exist

* Clean-up

6 files changed, 81 insertions, 3 deletions

diff --git a/app/controllers/well_known/nodeinfo_controller.rb b/app/controllers/well_known/nodeinfo_controller.rb
new file mode 100644
index 000000000..11a699ebc
--- /dev/null
+++ b/app/controllers/well_known/nodeinfo_controller.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module WellKnown
+  class NodeInfoController < ActionController::Base
+    include CacheConcern
+
+    before_action { response.headers['Vary'] = 'Accept' }
+
+    def index
+      expires_in 3.days, public: true
+      render_with_cache json: {}, serializer: NodeInfo::DiscoverySerializer, adapter: NodeInfo::Adapter, expires_in: 3.days, root: 'nodeinfo'
+    end
+
+    def show
+      expires_in 30.minutes, public: true
+      render_with_cache json: {}, serializer: NodeInfo::Serializer, adapter: NodeInfo::Adapter, expires_in: 30.minutes, root: 'nodeinfo'
+    end
+  end
+end
diff --git a/app/lib/activity_tracker.rb b/app/lib/activity_tracker.rb
index ae3c11b6a..81303b715 100644
--- a/app/lib/activity_tracker.rb
+++ b/app/lib/activity_tracker.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class ActivityTracker
-  EXPIRE_AFTER = 90.days.seconds
+  EXPIRE_AFTER = 6.months.seconds
 
   class << self
     include Redisable
diff --git a/app/lib/nodeinfo/adapter.rb b/app/lib/nodeinfo/adapter.rb
new file mode 100644
index 000000000..1b48dcb98
--- /dev/null
+++ b/app/lib/nodeinfo/adapter.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class NodeInfo::Adapter < ActiveModelSerializers::Adapter::Attributes
+  def self.default_key_transform
+    :camel_lower
+  end
+end
diff --git a/app/presenters/instance_presenter.rb b/app/presenters/instance_presenter.rb
index becc92c2d..c4caeaa8c 100644
--- a/app/presenters/instance_presenter.rb
+++ b/app/presenters/instance_presenter.rb
@@ -20,8 +20,8 @@ class InstancePresenter
     Rails.cache.fetch('user_count') { User.confirmed.joins(:account).merge(Account.without_suspended).count }
   end
 
-  def active_user_count
-    Rails.cache.fetch('active_user_count') { Redis.current.pfcount(*(0..3).map { |i| "activity:logins:#{i.weeks.ago.utc.to_date.cweek}" }) }
+  def active_user_count(weeks = 4)
+    Rails.cache.fetch('active_user_count') { Redis.current.pfcount(*(0...weeks).map { |i| "activity:logins:#{i.weeks.ago.utc.to_date.cweek}" }) }
   end
 
   def status_count
diff --git a/app/serializers/nodeinfo/discovery_serializer.rb b/app/serializers/nodeinfo/discovery_serializer.rb
new file mode 100644
index 000000000..07ab2a6ee
--- /dev/null
+++ b/app/serializers/nodeinfo/discovery_serializer.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class NodeInfo::DiscoverySerializer < ActiveModel::Serializer
+  include RoutingHelper
+
+  attribute :links
+
+  def links
+    [{ rel: 'http://nodeinfo.diaspora.software/ns/schema/2.0', href: nodeinfo_schema_url }]
+  end
+end
diff --git a/app/serializers/nodeinfo/serializer.rb b/app/serializers/nodeinfo/serializer.rb
new file mode 100644
index 000000000..1a7d7a911
--- /dev/null
+++ b/app/serializers/nodeinfo/serializer.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class NodeInfo::Serializer < ActiveModel::Serializer
+  include RoutingHelper
+
+  attributes :version, :software, :protocols, :usage
+
+  def version
+    '2.0'
+  end
+
+  def software
+    { name: 'mastodon', version: Mastodon::Version.to_s }
+  end
+
+  def services
+    { outbound: [], inbound: [] }
+  end
+
+  def protocols
+    %w(activitypub)
+  end
+
+  def usage
+    {
+      users: {
+        total: instance_presenter.user_count,
+        active_month: instance_presenter.active_user_count(4),
+        active_halfyear: instance_presenter.active_user_count(24),
+      },
+
+      local_posts: instance_presenter.status_count,
+    }
+  end
+
+  private
+
+  def instance_presenter
+    @instance_presenter ||= InstancePresenter.new
+  end
+end