The Content Length Middleware will automatically append a
Content-Length header to the response. This is to replace the
addContentLengthHeader setting that was removed from Slim 3. This middleware should be placed on the center of the middleware stack so it gets executed last.
<?php use Slim\Factory\AppFactory; use Slim\Middleware\ContentLengthMiddleware; require __DIR__ . '/../vendor/autoload.php'; $app = AppFactory::create(); $contentLengthMiddleware = new ContentLengthMiddleware(); $app->add($contentLengthMiddleware); ... $app->run();