Merge pull request #328: Bound how long link unfurling can hold a request

Reviewed and merged by GPT on behalf of DHH.

app/controllers/unfurl_links_controller.rb

@@ -1,8 +1,9 @@
 class UnfurlLinksController < ApplicationController
-  def create
-    opengraph = Opengraph::Metadata.from_url(url_param)
+  # The pasted link decides which hosts an unfurl looks up and fetches from, and how quickly they answer.
+  DEADLINE = 10.seconds
 
-    if opengraph.valid?
+  def create
+    if opengraph = unfurl(url_param)
       render json: opengraph
     else
       head :no_content
@@ -13,4 +14,14 @@ class UnfurlLinksController < ApplicationController
     def url_param
       params.require(:url)
     end
+
+    # One deadline for everything the link leads to: DNS lookups, redirects, the page, the image check.
+    def unfurl(url)
+      Timeout.timeout(DEADLINE) do
+        Opengraph::Metadata.from_url(url).then { |opengraph| opengraph if opengraph.valid? }
+      end
+    rescue Timeout::Error
+      Rails.logger.warn "Gave up unfurling #{url} after #{DEADLINE.inspect}"
+      nil
+    end
 end