Allow default headers passed to Granola::Rack#json

❤️ @lucasefe for the idea. See #2 for discussion.

lib/granola/rack.rb

@@ -15,6 +15,11 @@ def self.included(base)
   # Granola::Serializer. This takes care of setting the `Last-Modified` and
   # `ETag` headers if appropriate.
   #
+  # You can customize the response tuple by passing the status and the default
+  # headers, as in the following example:
+  #
+  #   json(user, status: 400, headers: { "X-Error" => "Boom!" })
+  #
   # object - An object to serialize into JSON.
   #
   # Keywords:
@@ -23,15 +28,15 @@ def self.included(base)
   #                   serializer class.
   #   status:         The HTTP status to return on stale responses. Defaults to
   #                   `200`.
+  #   headers:        A Hash of default HTTP headers. Defaults to an empty Hash.
   #   **json_options: Any other keywords passed will be forwarded to the
   #                   serializer's `#to_json` call.
   #
   # Raises NameError if no specific serializer is provided and we fail to infer
   #   one for this object.
   # Returns a Rack response tuple.
-  def json(object, with: nil, status: 200, **json_options)
+  def json(object, with: nil, status: 200, headers: {}, **json_options)
     serializer = serializer_for(object, with: with)
-    headers = {}
 
     if serializer.last_modified
       headers["Last-Modified".freeze] = serializer.last_modified.httpdate

test/rack_test.rb

@@ -50,3 +50,11 @@ def initialize(env = {})
   expected_last_modified = Time.at(987654321).httpdate
   assert_equal expected_last_modified, headers["Last-Modified"]
 end
+
+test "allows passing default headers" do |context|
+  default_headers = { "Other-Header" => "Meow" }
+  status, headers, body = context.json(@person, headers: default_headers)
+
+  assert_equal "application/json", headers["Content-Type"]
+  assert_equal "Meow", headers["Other-Header"]
+end