Introduce predictable environment slugs

If an environment slug is predictable given only the environment
name, we can use the environment slug earlier in the CI variable
evaluation process as we don't have to wait for the environment
record itself to be persisted.

1 files changed, 58 insertions, 0 deletions

diff --git a/lib/gitlab/slug/environment.rb b/lib/gitlab/slug/environment.rb
new file mode 100644
index 00000000000..1b87d3bb626
--- /dev/null
+++ b/lib/gitlab/slug/environment.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+# An environment name is not necessarily suitable for use in URLs, DNS
+# or other third-party contexts, so provide a slugified version. A slug has
+# the following properties:
+#   * contains only lowercase letters (a-z), numbers (0-9), and '-'
+#   * begins with a letter
+#   * has a maximum length of 24 bytes (OpenShift limitation)
+#   * cannot end with `-`
+module Gitlab
+  module Slug
+    class Environment
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+
+      def generate
+        # Lowercase letters and numbers only
+        slugified = name.to_s.downcase.gsub(/[^a-z0-9]/, '-')
+
+        # Must start with a letter
+        slugified = 'env-' + slugified unless slugified.match?(/^[a-z]/)
+
+        # Repeated dashes are invalid (OpenShift limitation)
+        slugified.squeeze!('-')
+
+        slugified =
+          if slugified.size > 24 || slugified != name
+            # Maximum length: 24 characters (OpenShift limitation)
+            shorten_and_add_suffix(slugified)
+          else
+            # Cannot end with a dash (Kubernetes label limitation)
+            slugified.chomp('-')
+          end
+
+        slugified
+      end
+
+      private
+
+      def shorten_and_add_suffix(slug)
+        slug = slug[0..16]
+        slug << '-' unless slug.ends_with?('-')
+        slug << suffix
+      end
+
+      # Slugifying a name may remove the uniqueness guarantee afforded by it being
+      # based on name (which must be unique). To compensate, we add a predictable
+      # 6-byte suffix in those circumstances. This is not *guaranteed* uniqueness,
+      # but the chance of collisions is vanishingly small
+      def suffix
+        Digest::SHA2.hexdigest(name.to_s).to_i(16).to_s(36).last(6)
+      end
+    end
+  end
+end