Ticket #43691: 43691.2.diff

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -405 +405 @@
                          */
                         $result = apply_filters( 'rest_pre_echo_response', $result, $this, $request );
 
+                        // The 204 response shouldn't have a body.
+                        if ( 204 === $code || null === $result ) {
+                                return null;
+                        }
+
                         $result = wp_json_encode( $result );
 
                         $json_error_message = $this->get_json_last_error();

tests/phpunit/tests/rest-api/rest-server.php

@@ -1144 +1144 @@
                 $this->assertEquals( 200, $response->get_status() );
         }
 
+        /**
+         * @ticket 43691
+         */
+        public function test_does_not_echo_body_for_null_responses() {
+                register_rest_route(
+                        'test-ns',
+                        '/test',
+                        array(
+                                'methods'  => array( 'GET' ),
+                                'callback' => function () {
+                                        return new WP_REST_Response();
+                                },
+                        )
+                );
+
+                $result = rest_get_server()->serve_request( '/test-ns/test' );
+
+                $this->assertNull( $result );
+                $this->assertEquals( '', rest_get_server()->sent_body );
+        }
+
+        /**
+         * @ticket 43691
+         */
+        public function test_does_not_echo_body_for_responses_with_204_status() {
+                register_rest_route(
+                        'test-ns',
+                        '/test',
+                        array(
+                                'methods'  => array( 'GET' ),
+                                'callback' => function () {
+                                        return new WP_REST_Response( 'data', 204 );
+                                },
+                        )
+                );
+
+                $result = rest_get_server()->serve_request( '/test-ns/test' );
+
+                $this->assertNull( $result );
+                $this->assertEquals( '', rest_get_server()->sent_body );
+        }
+
         public function _validate_as_integer_123( $value, $request, $key ) {
                 if ( ! is_int( $value ) ) {
                         return new WP_Error( 'some-error', 'This is not valid!' );