Update "show as HTML" attachment controller action

This updates `AttachmentController#show_as_html` to do attachment
masking in the background.

Our "view attachments in the browser" feature, or "view as HTML", is
doing a lot of processing inline in the web processes and this sometimes
causes memory issues on the server and results in oom-kill running.

Uses the same logic as the `#show` action to check an attachment is
masked before proceeding with the action. This means it will time outs
after 5 seconds and then redirect the `AttachmentMaskController` to wait
for the job to complete before rendering a view saying the attachment is
now viewable.

Fixes #7977

app/controllers/attachments_controller.rb

@@ -16,7 +16,7 @@ class AttachmentsController < ApplicationController
   before_action :authenticate_attachment
   before_action :authenticate_attachment_as_html, only: :show_as_html
 
-  around_action :ensure_masked, only: :show
+  around_action :ensure_masked
   around_action :cache_attachments, only: :show_as_html
 
   def show

app/views/attachment_masks/_download.html.erb

@@ -0,0 +1,11 @@
+<% @title = _('Attachment available for download.') %>
+<h1><%= @title %></h1>
+
+<p>
+  <%= _('The attachment has now been processed and is available for ' \
+        'download.') %>
+</p>
+
+<p>
+  <%= link_to _('Download attachment'), @referer, class: 'button' %>
+</p>

app/views/attachment_masks/_viewing.html.erb

@@ -0,0 +1,11 @@
+<% @title = _('Attachment available for viewing.') %>
+<h1><%= @title %></h1>
+
+<p>
+  <%= _('The attachment has now been processed and is available for ' \
+        'viewing.') %>
+</p>
+
+<p>
+  <%= link_to _('View attachment'), @referer, class: 'button' %>
+</p>

app/views/attachment_masks/done.html.erb

@@ -1,11 +1,5 @@
-<% @title = _('Attachment available for download.') %>
-<h1><%= @title %></h1>
-
-<p>
-  <%= _('The attachment has now been processed and is available for ' \
-        'download.') %>
-</p>
-
-<p>
-  <%= link_to _('Download attachment'), @referer, class: 'button' %>
-</p>
+<% if @referer =~ %r(/request/\d+/response/\d+/attach/html/) %>
+  <%= render partial: 'viewing' %>
+<% else %>
+  <%= render partial: 'download' %>
+<% end %>

spec/controllers/attachments_controller_spec.rb

@@ -450,6 +450,69 @@ def show_as_html(params = {})
         .to raise_error(ActiveRecord::RecordNotFound)
     end
 
+    context 'when attachment has not been masked' do
+      let(:attachment) do
+        FactoryBot.create(
+          :body_text, :unmasked,
+          incoming_message: message,
+          prominence: attachment_prominence
+        )
+      end
+
+      context 'when masked attachment is available before timing out' do
+        before do
+          allow(IncomingMessage).to receive(
+            :get_attachment_by_url_part_number_and_filename!
+          ).and_return(attachment)
+          allow(attachment).to receive(:masked?).and_return(false, true)
+        end
+
+        it 'queues FoiAttachmentMaskJob' do
+          expect(FoiAttachmentMaskJob).to receive(:perform_later).
+            with(attachment)
+          show_as_html
+        end
+
+        it 'redirects to show action' do
+          show_as_html
+          expect(response).to redirect_to(request.fullpath)
+        end
+      end
+
+      context 'when response times out waiting for masked attachment' do
+        before do
+          allow(Timeout).to receive(:timeout).and_raise(Timeout::Error)
+        end
+
+        it 'queues FoiAttachmentMaskJob' do
+          expect(FoiAttachmentMaskJob).to receive(:perform_later).
+            with(attachment)
+          show_as_html
+        end
+
+        it 'redirects to wait for attachment mask route' do
+          allow_any_instance_of(FoiAttachment).to receive(:to_signed_global_id).
+            and_return('ABC')
+
+          verifier = double('ActiveSupport::MessageVerifier')
+          allow(controller).to receive(:verifier).and_return(verifier)
+          allow(verifier).to receive(:generate).with(
+            get_attachment_as_html_path(
+              incoming_message_id: attachment.incoming_message_id,
+              id: info_request.id,
+              part: attachment.url_part_number,
+              file_name: attachment.filename
+            )
+          ).and_return('DEF')
+
+          show_as_html
+          expect(response).to redirect_to(
+            wait_for_attachment_mask_path('ABC', referer: 'DEF')
+          )
+        end
+      end
+    end
+
     context 'when request is embargoed' do
       let(:info_request) { FactoryBot.create(:embargoed_request) }
 

spec/integration/incoming_mail_spec.rb

@@ -64,25 +64,35 @@
   it "generates a valid HTML verson of plain text attachments" do
     receive_incoming_mail('incoming-request-two-same-name.email',
                           email_to: info_request.incoming_email)
-    visit get_attachment_as_html_path(
+    attachment_path = get_attachment_as_html_path(
       incoming_message_id: info_request.incoming_messages.first.id,
       id: info_request.id,
       part: 2,
       file_name: 'hello world.txt.html',
       skip_cache: 1)
+
+    visit attachment_path
+    perform_enqueued_jobs
+
+    visit attachment_path
     expect(page.response_headers['Content-Type']).to eq("text/html; charset=utf-8")
     expect(page).to have_content "Second hello"
   end
 
   it "generates a valid HTML verson of PDF attachments" do
     receive_incoming_mail('incoming-request-pdf-attachment.email',
                           email_to: info_request.incoming_email)
-    visit get_attachment_as_html_path(
+    attachment_path = get_attachment_as_html_path(
       incoming_message_id: info_request.incoming_messages.first.id,
       id: info_request.id,
       part: 2,
       file_name: 'fs 50379341.pdf.html',
       skip_cache: 1)
+
+    visit attachment_path
+    perform_enqueued_jobs
+
+    visit attachment_path
     expect(page.response_headers['Content-Type']).to eq("text/html; charset=utf-8")
     expect(page).to have_content "Walberswick Parish Council"
   end