feat: add OAS 3.2 additionalOperations support

Process operations defined under path_item.additionalOperations
(OAS 3.2.0 field for non-standard HTTP methods like COPY, LINK).

Extract register_operation helper from the REQUEST_METHODS loop
to share logic between standard methods and additionalOperations.
Method keys from additionalOperations are downcased to match the
router's internal UPPERCASE convention (router.route_at upcases).

3 tests: COPY method routed, GET still works, undefined LINK rejected.
570 examples, 0 failures, 100% line + branch coverage.

Authored by: Aaron Lippold<lippold@gmail.com>

Author: aaronlippold

lib/openapi_first/builder.rb

@@ -66,33 +66,42 @@ def router # rubocop:disable Metrics/MethodLength
         path_parameters = path_item_object['parameters'] || []
         path_item_object.resolved.keys.intersection(REQUEST_METHODS).map do |request_method|
           operation_object = path_item_object[request_method]
-          operation_parameters = operation_object['parameters'] || []
-          parameters = parse_parameters(operation_parameters.chain(path_parameters))
-
-          build_requests(path:, request_method:, operation_object:,
-                         parameters:).each do |request|
-            router.add_request(
-              request,
-              request_method:,
-              path:,
-              content_type: request.content_type,
-              allow_empty_content: request.allow_empty_content?
-            )
-            build_responses(request:, responses: operation_object['responses']).each do |response|
-              router.add_response(
-                response,
-                request_method:,
-                path:,
-                status: response.status,
-                response_content_type: response.content_type
-              )
-            end
-          end
+          register_operation(router, path:, request_method:, operation_object:, path_parameters:)
+        end
+
+        path_item_object['additionalOperations']&.each do |request_method, operation_object|
+          register_operation(router, path:, request_method: request_method.downcase,
+                                    operation_object:, path_parameters:)
         end
       end
       router
     end
 
+    def register_operation(router, path:, request_method:, operation_object:, path_parameters:)
+      operation_parameters = operation_object['parameters'] || []
+      parameters = parse_parameters(operation_parameters.chain(path_parameters))
+
+      build_requests(path:, request_method:, operation_object:,
+                     parameters:).each do |request|
+        router.add_request(
+          request,
+          request_method:,
+          path:,
+          content_type: request.content_type,
+          allow_empty_content: request.allow_empty_content?
+        )
+        build_responses(request:, responses: operation_object['responses']).each do |response|
+          router.add_response(
+            response,
+            request_method:,
+            path:,
+            status: response.status,
+            response_content_type: response.content_type
+          )
+        end
+      end
+    end
+
     def parse_parameters(parameters)
       grouped_parameters = group_parameters(parameters)
       ParsedParameters.new(

spec/definition_spec.rb

@@ -49,6 +49,50 @@ def build_request(path, method: 'GET')
     end
   end
 
+  describe 'OAS 3.2 additionalOperations' do
+    let(:definition) do
+      OpenapiFirst.parse({
+                           'openapi' => '3.2.0',
+                           'info' => { 'title' => 'Test', 'version' => '1.0' },
+                           'paths' => {
+                             '/files/{id}' => {
+                               'get' => {
+                                 'operationId' => 'getFile',
+                                 'responses' => { '200' => { 'description' => 'OK' } }
+                               },
+                               'additionalOperations' => {
+                                 'COPY' => {
+                                   'operationId' => 'copyFile',
+                                   'responses' => { '200' => { 'description' => 'Copied' } }
+                                 }
+                               }
+                             }
+                           }
+                         })
+    end
+
+    it 'routes requests using non-standard HTTP methods from additionalOperations' do
+      request = build_request('/files/123', method: 'COPY')
+      validated = definition.validate_request(request)
+      expect(validated.error).to be_nil
+      expect(validated.operation_id).to eq('copyFile')
+    end
+
+    it 'does not break standard method routing alongside additionalOperations' do
+      request = build_request('/files/123', method: 'GET')
+      validated = definition.validate_request(request)
+      expect(validated.error).to be_nil
+      expect(validated.operation_id).to eq('getFile')
+    end
+
+    it 'returns method_not_allowed for undefined additional methods' do
+      request = build_request('/files/123', method: 'LINK')
+      validated = definition.validate_request(request)
+      expect(validated.error).not_to be_nil
+      expect(validated.error.type).to eq(:method_not_allowed)
+    end
+  end
+
   describe '#title' do
     it 'returns the title from info.title' do
       definition = OpenapiFirst.parse({