9 files changed, 121 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 acec02778..f94eeea99 100644
--- a/app/presenters/instance_presenter.rb
+++ b/app/presenters/instance_presenter.rb
@@ -21,8 +21,8 @@ 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
diff --git a/config/initializers/inflections.rb b/config/initializers/inflections.rb
index bf0cb52a3..c65153b0a 100644
--- a/config/initializers/inflections.rb
+++ b/config/initializers/inflections.rb
@@ -18,4 +18,5 @@ ActiveSupport::Inflector.inflections(:en) do |inflect|
   inflect.acronym 'PubSubHubbub'
   inflect.acronym 'ActivityStreams'
   inflect.acronym 'JsonLd'
+  inflect.acronym 'NodeInfo'
 end
diff --git a/config/routes.rb b/config/routes.rb
index aae7e8767..26e5f3d09 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -21,10 +21,13 @@ Rails.application.routes.draw do
   end
 
   get '.well-known/host-meta', to: 'well_known/host_meta#show', as: :host_meta, defaults: { format: 'xml' }
+  get '.well-known/nodeinfo', to: 'well_known/nodeinfo#index', as: :nodeinfo, defaults: { format: 'json' }
   get '.well-known/webfinger', to: 'well_known/webfinger#show', as: :webfinger
   get '.well-known/change-password', to: redirect('/auth/edit')
   get '.well-known/keybase-proof-config', to: 'well_known/keybase_proof_config#show'
 
+  get '/nodeinfo/2.0', to: 'well_known/nodeinfo#show', as: :nodeinfo_schema
+
   get 'manifest', to: 'manifests#show', defaults: { format: 'json' }
   get 'intent', to: 'intents#show'
   get 'custom.css', to: 'custom_css#show', as: :custom_css
diff --git a/spec/controllers/well_known/nodeinfo_controller_spec.rb b/spec/controllers/well_known/nodeinfo_controller_spec.rb
new file mode 100644
index 000000000..12e1fa415
--- /dev/null
+++ b/spec/controllers/well_known/nodeinfo_controller_spec.rb
@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+describe WellKnown::NodeInfoController, type: :controller do
+  render_views
+
+  describe 'GET #index' do
+    it 'returns json document pointing to node info' do
+      get :index
+
+      expect(response).to have_http_status(200)
+      expect(response.content_type).to eq 'application/json'
+
+      json = body_as_json
+
+      expect(json[:links]).to be_an Array
+      expect(json[:links][0][:rel]).to eq 'http://nodeinfo.diaspora.software/ns/schema/2.0'
+      expect(json[:links][0][:href]).to include 'nodeinfo/2.0'
+    end
+  end
+
+  describe 'GET #show' do
+    it 'returns json document with node info properties' do
+      get :show
+
+      expect(response).to have_http_status(200)
+      expect(response.content_type).to eq 'application/json'
+
+      json = body_as_json
+
+      expect(json[:version]).to eq '2.0'
+      expect(json[:usage]).to be_a Hash
+      expect(json[:software]).to be_a Hash
+      expect(json[:protocols]).to be_an Array
+    end
+  end
+end