1 files changed, 33 insertions, 0 deletions
diff --git a/lib/gitlab/json.rb b/lib/gitlab/json.rb
index 8565f664cd4..b51c0a33457 100644
--- a/lib/gitlab/json.rb
+++ b/lib/gitlab/json.rb
@@ -186,9 +186,14 @@ module Gitlab
       # The `env` param is ignored because it's not needed in either our formatter or Grape's,
       # but it is passed through for consistency.
       #
+      # If explicitly supplied with a `PrecompiledJson` instance it will skip conversion
+      # and return it directly. This is mostly used in caching.
+      #
       # @param object [Object]
       # @return [String]
       def self.call(object, env = nil)
+        return object.to_s if object.is_a?(PrecompiledJson)
+
         if Feature.enabled?(:grape_gitlab_json, default_enabled: true)
           Gitlab::Json.dump(object)
         else
@@ -197,6 +202,34 @@ module Gitlab
       end
     end
 
+    # Wrapper class used to skip JSON dumping on Grape endpoints.
+
+    class PrecompiledJson
+      UnsupportedFormatError = Class.new(StandardError)
+
+      # @overload PrecompiledJson.new("foo")
+      #   @param value [String]
+      #
+      # @overload PrecompiledJson.new(["foo", "bar"])
+      #   @param value [Array<String>]
+      def initialize(value)
+        @value = value
+      end
+
+      # Convert the value to a String. This will invoke
+      # `#to_s` on the members of the value if it's an array.
+      #
+      # @return [String]
+      # @raise [NoMethodError] if the objects in an array doesn't support to_s
+      # @raise [PrecompiledJson::UnsupportedFormatError] if the value is neither a String or Array
+      def to_s
+        return @value if @value.is_a?(String)
+        return "[#{@value.join(',')}]" if @value.is_a?(Array)
+
+        raise UnsupportedFormatError
+      end
+    end
+
     class LimitedEncoder
       LimitExceeded = Class.new(StandardError)