1 files changed, 51 insertions, 0 deletions
diff --git a/lib/gitlab/pages/random_domain.rb b/lib/gitlab/pages/random_domain.rb
new file mode 100644
index 00000000000..8aa7611c910
--- /dev/null
+++ b/lib/gitlab/pages/random_domain.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Pages
+    class RandomDomain
+      PROJECT_PATH_LIMIT = 48
+      SUBDOMAIN_LABEL_LIMIT = 63
+
+      def self.generate(project_path:, namespace_path:)
+        new(project_path: project_path, namespace_path: namespace_path).generate
+      end
+
+      def initialize(project_path:, namespace_path:)
+        @project_path = project_path
+        @namespace_path = namespace_path
+      end
+
+      # Subdomains have a limit of 63 bytes (https://www.freesoft.org/CIE/RFC/1035/9.htm)
+      # For this reason we're limiting each part of the unique subdomain
+      #
+      # The domain is made up of 3 parts, like: projectpath-namespacepath-randomstring
+      # - project path: between 1 and 48 chars
+      # - namespace path: when the project path has less than 48 chars,
+      #   the namespace full path will be used to fill the value up to 48 chars
+      # - random hexadecimal: to ensure a random value, the domain is then filled
+      #   with a random hexadecimal value to complete 63 chars
+      def generate
+        domain = project_path.byteslice(0, PROJECT_PATH_LIMIT)
+
+        # if the project_path has less than PROJECT_PATH_LIMIT chars,
+        # fill the domain with the parent full_path up to 48 chars like:
+        # projectpath-namespacepath
+        if domain.length < PROJECT_PATH_LIMIT
+          namespace_size = PROJECT_PATH_LIMIT - domain.length - 1
+          domain.concat('-', namespace_path.byteslice(0, namespace_size))
+        end
+
+        # Complete the domain with random hexadecimal values util it is 63 chars long
+        # PS.: SecureRandom.hex return an string twice the size passed as argument.
+        domain.concat('-', SecureRandom.hex(SUBDOMAIN_LABEL_LIMIT - domain.length - 1))
+
+        # Slugify ensures the format and size (63 chars) of the given string
+        Gitlab::Utils.slugify(domain)
+      end
+
+      private
+
+      attr_reader :project_path, :namespace_path
+    end
+  end
+end