Configurable setting for max text size for highlighting

changelogs/unreleased/gmh-ensure-highlighting-limits-are-configurable-and-documented.yml

+---
+title: Ensure highlighting limits are documented, configurable, and monitorable
+merge_request: 60445
+author:
+type: added

config/gitlab.yml.example

@@ -1270,6 +1270,10 @@ production: &base
     # matomo_site_id: '_your_matomo_site_id'
     # matomo_disable_cookies: false
 
+    ## Maximum file size for syntax highlighting
+    ## https://docs.gitlab.com/ee/user/project/highlighting.html
+    # maximum_text_highlight_size_kilobytes: 512
+
   rack_attack:
     git_basic_auth:
       # Rack Attack IP banning enabled

config/initializers/1_settings.rb

@@ -856,6 +856,7 @@ Settings['extra'] ||= Settingslogic.new({})
 Settings.extra['matomo_site_id'] ||= Settings.extra['piwik_site_id'] if Settings.extra['piwik_site_id'].present?
 Settings.extra['matomo_url'] ||= Settings.extra['piwik_url'] if Settings.extra['piwik_url'].present?
 Settings.extra['matomo_disable_cookies'] = false if Settings.extra['matomo_disable_cookies'].nil?
+Settings.extra['maximum_text_highlight_size_kilobytes'] = Settings.extra.fetch('maximum_text_highlight_size_kilobytes', 512).kilobytes
 
 #
 # Rack::Attack settings

lib/gitlab/highlight.rb

@@ -4,7 +4,6 @@ module Gitlab
   class Highlight
     TIMEOUT_BACKGROUND = 30.seconds
     TIMEOUT_FOREGROUND = 1.5.seconds
-    MAXIMUM_TEXT_HIGHLIGHT_SIZE = 512.kilobytes
 
     def self.highlight(blob_name, blob_content, language: nil, plain: false)
       new(blob_name, blob_content, language: language)
@@ -23,7 +22,7 @@ module Gitlab
     def highlight(text, continue: false, plain: false, context: {})
       @context = context
 
-      plain ||= text.length > MAXIMUM_TEXT_HIGHLIGHT_SIZE
+      plain ||= text.length > maximum_text_highlight_size
 
       highlighted_text = highlight_text(text, continue: continue, plain: plain)
       highlighted_text = link_dependencies(text, highlighted_text) if blob_name
@@ -78,5 +77,9 @@ module Gitlab
     def link_dependencies(text, highlighted_text)
       Gitlab::DependencyLinker.link(blob_name, text, highlighted_text)
     end
+
+    def maximum_text_highlight_size
+      Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
+    end
   end
 end

spec/lib/gitlab/highlight_spec.rb

@@ -47,8 +47,9 @@ RSpec.describe Gitlab::Highlight do
     end
 
     it 'returns plain version for long content' do
-      stub_const('Gitlab::Highlight::MAXIMUM_TEXT_HIGHLIGHT_SIZE', 1)
-      result = described_class.highlight(file_name, content)
+      stub_config(extra: { 'maximum_text_highlight_size_kilobytes' => 0.0001 } ) # 1.024 bytes
+
+      result = described_class.highlight(file_name, content) # content is 44 bytes
 
       expect(result).to eq(%[<span id="LC1" class="line" lang="">(make-pathname :defaults name</span>\n<span id="LC2" class="line" lang="">:type "assem")</span>])
     end