Render calendar feed inline when accessed from GitLab

With text/calendar as Content-Type, the browser always downloads the
content as a file (even ignoring the Content-Disposition header). We
want to display the content inline when accessed from GitLab, similarly
to the RSS feed.

2 files changed, 26 insertions, 10 deletions

diff --git a/app/controllers/concerns/issues_action.rb b/app/controllers/concerns/issues_action.rb
index b6eb7d292fc..9d58656773d 100644
--- a/app/controllers/concerns/issues_action.rb
+++ b/app/controllers/concerns/issues_action.rb
@@ -1,6 +1,7 @@
 module IssuesAction
   extend ActiveSupport::Concern
   include IssuableCollections
+  include IssuesCalendar
 
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def issues
@@ -17,18 +18,9 @@ module IssuesAction
   end
   # rubocop:enable Gitlab/ModuleWithInstanceVariables
 
-  # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def issues_calendar
-    @issues = issuables_collection
-                  .non_archived
-                  .with_due_date
-                  .limit(100)
-
-    respond_to do |format|
-      format.ics { response.headers['Content-Disposition'] = 'inline' }
-    end
+    render_issues_calendar(issuables_collection)
   end
-  # rubocop:enable Gitlab/ModuleWithInstanceVariables
 
   private
 
diff --git a/app/controllers/concerns/issues_calendar.rb b/app/controllers/concerns/issues_calendar.rb
new file mode 100644
index 00000000000..671a204621d
--- /dev/null
+++ b/app/controllers/concerns/issues_calendar.rb
@@ -0,0 +1,24 @@
+module IssuesCalendar
+  extend ActiveSupport::Concern
+
+  # rubocop:disable Gitlab/ModuleWithInstanceVariables
+  def render_issues_calendar(issuables)
+    @issues = issuables
+                  .non_archived
+                  .with_due_date
+                  .limit(100)
+
+    respond_to do |format|
+      format.ics do
+        # NOTE: with text/calendar as Content-Type, the browser always downloads
+        #       the content as a file (even ignoring the Content-Disposition
+        #       header). We want to display the content inline when accessed
+        #       from GitLab, similarly to the RSS feed.
+        if request.referer&.start_with?(::Settings.gitlab.base_url)
+          response.headers['Content-Type'] = 'text/plain'
+        end
+      end
+    end
+  end
+  # rubocop:enable Gitlab/ModuleWithInstanceVariables
+end