modifying controller functions to make html preview

app/controllers/annotations_controller.rb

@@ -34,7 +34,7 @@ def add_existing_annotation
         page: params[:page],
         **base_attributes
       )
-    elsif submission_file.is_pynb?
+    elsif submission_file.is_pynb? || submission_file.is_rmd?
       @annotation = result.annotations.create!(
         type: 'HtmlAnnotation',
         start_node: params[:start_node],
@@ -107,7 +107,7 @@ def create
         page: params[:page],
         **base_attributes
       )
-    elsif submission_file.is_pynb?
+    elsif submission_file.is_pynb? || submission_file.is_rmd?
       @annotation = result.annotations.create!(
         type: 'HtmlAnnotation',
         start_node: params[:start_node],

app/controllers/submissions_controller.rb

@@ -18,7 +18,9 @@ class SubmissionsController < ApplicationController
     p.frame_src(*PERMITTED_IFRAME_SRC)
   end
 
-  content_security_policy_report_only only: :html_content
+  content_security_policy only: :html_content do |p|
+    p.style_src :self, "'unsafe-inline'"
+  end
 
   def index
     respond_to do |format|
@@ -55,9 +57,9 @@ def repo_browser
         end
         # store the displayed revision
         if @revision.nil? && ((params[:revision_identifier] &&
-            params[:revision_identifier] == revision.revision_identifier.to_s) ||
-            (params[:revision_timestamp] &&
-              Time.zone.parse(params[:revision_timestamp]).in_time_zone >= revision.server_timestamp))
+          params[:revision_identifier] == revision.revision_identifier.to_s) ||
+          (params[:revision_timestamp] &&
+            Time.zone.parse(params[:revision_timestamp]).in_time_zone >= revision.server_timestamp))
           @revision = revision
         end
       end
@@ -482,7 +484,8 @@ def download_file
       return head :not_found
     end
 
-    if params[:show_in_browser] == 'true' && file.is_pynb? && Rails.application.config.nbconvert_enabled
+    if params[:show_in_browser] == 'true' &&
+      ((file.is_pynb? && Rails.application.config.nbconvert_enabled) || file.is_rmd?)
       redirect_to html_content_course_assignment_submissions_url(current_course,
                                                                  record.grouping.assignment,
                                                                  select_file_id: params[:select_file_id])
@@ -559,8 +562,9 @@ def download_file_zip
   def download
     preview = params[:preview] == 'true'
     nbconvert_enabled = Rails.application.config.nbconvert_enabled
+    file_type = FileHelper.get_file_type(params[:file_name])
 
-    if FileHelper.get_file_type(params[:file_name]) == 'jupyter-notebook' && preview && nbconvert_enabled
+    if ((file_type == 'jupyter-notebook' && nbconvert_enabled) || file_type == 'markdown') && preview
       redirect_to action: :html_content,
                   course_id: current_course.id,
                   assignment_id: params[:assignment_id],
@@ -678,7 +682,11 @@ def html_content
     else
       sanitized_filename = ActiveStorage::Filename.new("#{filename}.#{revision_identifier}").sanitized
       unique_path = File.join(grouping.group.repo_name, path, sanitized_filename)
-      @html_content = notebook_to_html(file_contents, unique_path, @file_type)
+      if @file_type == 'markdown'
+        @html_content = rmd_to_html(file_contents, unique_path)
+      else
+        @html_content = notebook_to_html(file_contents, unique_path, @notebook_type)
+      end
     end
     render layout: 'html_content'
   end
@@ -945,6 +953,43 @@ def notebook_to_html(file_contents, unique_path, type)
     File.read(cache_file)
   end
 
+  def rmd_to_html(file_contents, unique_path)
+    cache_file = Pathname.new('tmp/rmd_html_cache') + "#{unique_path}.html"
+    unless File.exist? cache_file
+      FileUtils.mkdir_p(cache_file.dirname)
+      begin
+        temp_rmd_file = Tempfile.new(['temp_rmd_content', '.Rmd'], 'tmp/rmd_html_cache')
+        file_contents.gsub!(/```{r[^\}]*?(echo|eval|include)\s*=\s*(TRUE|FALSE)[^\}]*?}/, '```{r}')
+        temp_rmd_file.write(file_contents)
+        temp_rmd_file.close
+
+        args = [
+          'Rscript', '-e',
+          "library(rmarkdown); library(knitr); knitr::opts_chunk$set(eval = FALSE, echo = TRUE, include = TRUE); \
+          rmarkdown::render('#{temp_rmd_file.path}', output_format = 'html_document', \
+          output_file = '#{Rails.root.join(cache_file)}')"
+        ]
+
+        _stdout, stderr, status = Open3.capture3(*args)
+        return "#{I18n.t('submissions.cannot_display')}<br/><br/>#{stderr.lines.last}" unless status.exitstatus.zero?
+      rescue StandardError => e
+        return "#{I18n.t('submissions.invalid_rmd_content')}: #{e}"
+      ensure
+        temp_rmd_file&.unlink
+      end
+
+      html = Nokogiri::HTML.parse(File.read(cache_file))
+      current_ids = html.xpath('//*[@id]').pluck(:id).to_set # rubocop:disable Rails/PluckId
+      html.xpath('//*[not(@id)]').map do |elem|
+        unique_id = elem.path
+        unique_id += '-next' while current_ids.include? unique_id
+        elem.set_attribute(:id, unique_id)
+      end
+      File.write(cache_file, html.to_html)
+    end
+    File.read(cache_file)
+  end
+
   # Return a relative path to a temporary zip file (which may or may not exists).
   # The name of this file is unique by the +assignment+ and current user.
   def zipped_grouping_file_name(assignment)