Add basic OEmbed provider API, fix #247

app/controllers/api/oembed_controller.rb

+# frozen_string_literal: true
+
+class Api::OembedController < ApiController
+  respond_to :json
+
+  def show
+    @stream_entry = stream_entry_from_url(params[:url])
+    @width        = [300, params[:maxwidth].to_i].min
+    @height       = [200, params[:maxheight].to_i].min
+  end
+
+  private
+
+  def stream_entry_from_url(url)
+    params = Rails.application.routes.recognize_path(url)
+
+    raise ActiveRecord::NotFound unless params[:controller] == 'stream_entries' && params[:action] == 'show'
+
+    StreamEntry.find(params[:id])
+  end
+end

app/helpers/api/oembed_helper.rb

+module Api::OembedHelper
+end

app/views/api/oembed/show.json.rabl

+# frozen_string_literal: true
+object @stream_entry
+
+node(:type) { 'rich' }
+node(:version) { '1.0' }
+node(:title, &:title)
+node(:author_name) { |entry| entry.account.display_name.blank? ? entry.account.username : entry.account.display_name }
+node(:author_url) { |entry| account_url(entry.account) }
+node(:provider_name) { Rails.configuration.x.local_domain }
+node(:provider_url) { root_url }
+node(:cache_age) { 86_400 }
+node(:html, &:content)
+node(:width) { @width }
+node(:height) { @height }

app/views/stream_entries/show.html.haml

 - content_for :header_tags do
   %link{ rel: 'alternate', type: 'application/atom+xml', href: account_stream_entry_url(@account, @stream_entry, format: 'atom') }/
+  %link{ rel: 'alternate', type: 'application/json+oembed', href: api_oembed_url(url: account_stream_entry_url(@account, @stream_entry), format: 'json') }/
+
   %meta{ name: 'og:site_name', content: 'Mastodon' }/
   %meta{ name: 'og:type', content: 'article' }/
+  %meta{ name: 'og:title', content: "#{@account.username} on #{Rails.configuration.x.local_domain}" }/
   %meta{ name: 'og:article:author', content: @account.username }/
+  %meta{ name: 'og:description', content: @stream_entry.activity.content }/
+  %meta{ name: 'og:image', content: @stream_entry.activity.is_a?(Status) && @stream_entry.activity.media_attachments.size > 0 ? full_asset_url(@stream_entry.activity.media_attachments.first.file.url(:preview)) : full_asset_url(@account.avatar.url(:large)) }/
 
 .activity-stream.activity-stream-headless
   = render partial: @type, locals: { @type.to_sym => @stream_entry.activity, include_threads: true }

config/routes.rb

@@ -60,6 +60,9 @@ Rails.application.routes.draw do
     # Salmon
     post '/salmon/:id', to: 'salmon#update', as: :salmon
 
+    # OEmbed
+    get '/oembed', to: 'oembed#show', as: :oembed
+
     # JSON / REST API
     namespace :v1 do
       resources :statuses, only: [:create, :show, :destroy] do

spec/controllers/api/oembed_controller_spec.rb

+require 'rails_helper'
+
+RSpec.describe Api::OembedController, type: :controller do
+
+end

spec/helpers/api/oembed_helper_spec.rb

+require 'rails_helper'
+
+# Specs in this file have access to a helper object that includes
+# the Api::OembedHelper. For example:
+#
+# describe Api::OembedHelper do
+#   describe "string concat" do
+#     it "concats two strings with spaces" do
+#       expect(helper.concat_strings("this","that")).to eq("this that")
+#     end
+#   end
+# end
+RSpec.describe Api::OembedHelper, type: :helper do
+  pending "add some examples to (or delete) #{__FILE__}"
+end