Adds content length to Lighthouse POST responses.

AddContentLengthLighthouse.php

<?php

// Thanks to: https://laracasts.com/discuss/channels/general-discussion/add-content-length-header-on-views
// In relation to a bug for graphql code generator in an upstream dependency, I needed to add a Content-Length header.
// Temporary workaround for this.
// See: https://github.com/dotansimha/graphql-code-generator/issues/7934
// See: https://github.com/nodejs/undici/issues/1414
// https://github.com/nodejs/undici/issues/1490
namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\Request;

class AddContentLengthLighthouse
{

    /**
     * Handle an incoming request.
     *
     * @param  Request  $request
     * @param  Closure  $next
     *
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $response = $next($request);
        $method = $request->method();

       if ($method === 'POST' && $request->getRequestUri() === config('lighthouse.route.uri', '/graphql')) {
            // to be sure nothing was already output (by an echo statement or something)
            if (headers_sent() || ob_get_contents() != '') {
                return $response;
            }

            $content = $response->content();
            $contentLength = mb_strlen($content);
            $useCompressedOutput = ($contentLength && isset($_SERVER['HTTP_ACCEPT_ENCODING'])
                && strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== false);

            if ($useCompressedOutput) {
                // In order to accurately set Content-Length, we have to compress the data ourselves
                // rather than letting PHP do it automatically.
                $compressedContent = gzencode($content, 9, FORCE_GZIP);
                $compressedContentLength = strlen($compressedContent);
                if ($compressedContentLength / $contentLength < 0.9) {
                    if (ini_get('zlib.output_compression')) {
                        ini_set('zlib.output_compression', false);
                    }
                    $response->header('Content-Encoding', 'gzip');
                    $response->setContent($compressedContent);
                    $contentLength = $compressedContentLength;
                }
            }

            // compressed or not, sets the Content-Length
            $response->header('Content-Length', $contentLength);
        }

        return $response;
    }
}