Web servers typically log request details, so that you can perform tasks such as analytics, identification of invalid requests, and more.

Out-of-the-box, Swoole does not do this. As such, we provide these capabilities with this integration.

We log a number of items:

  • When the web server starts, indicating the host and port on which it is running.
  • When workers start, including the working directory and worker ID.
  • When the web server stops.
  • When the web server reloads workers.
  • Each request (more on this below)

By default, logging is performed to STDOUT, using an internal logger. However, you can use any PSR-3 compliant logger to log application details. We emit logs detailing server operations using the priority Psr\Log\LogLevel::NOTICE (unless detailing an error, such as inability to reload)), while Psr\Log\LogLevel::INFO and Psr\Log\LogLevel::ERROR are used to log requests (errors are used for response statuses greater than or equal to 400).

Access Logs

Technically, the SwooleRequestHandlerRunner doesn't use PSR-3 loggers directly, but, rather, instances of Zend\Expressive\Swoole\Log\AccessLogInterface. This package-specific interface extends the PSR-3 interface to add two methods:

use Psr\Http\Message\ResponseInterface;
use Psr\Log\LoggerInterface;
use Swoole\Http\Request;
use Zend\Expressive\Swoole\StaticResourceHandler\StaticResourceResponse;

interface AccessLogInterface extends LoggerInterface
    public function logAccessForStaticResource(
        Request $request,
        StaticResourceResponse $response
    ) : void;

    public function logAccessForPsr7Resource(
        Request $request,
        ResponseInterface $response
    ) : void;

To allow usage of a standard PSR-3 logger, we also provide a decorator, Zend\Expressive\Swoole\Log\Psr3AccessLogDecorator, which decorates the PSR-3 logger and provides a standard implementation for the two methods listed above. If you have defined a PSR-3 LoggerInterface service in your application, it will be used automatically.

Formatting logs

The Apache web server has long provided flexible and robust logging capabilities, and its formats are used across a variety of web servers and logging platforms. As such, we have chosen to use its formats for our standard implementation. However, we allow you to plug in your own system as needed.

You can refer to the Apache mod_log_config documentation in order to understand the available placeholders available for format strings.

Formatting is provided to the Psr3AccessLogDecorator via instances of the interface Zend\Expressive\Swoole\Log\AccessLogFormatterInterface:

interface AccessLogFormatterInterface
    public function format(AccessLogDataMap $map) : string;

AccessLogDataMap is a class used internally by the Psr3AccessLogDecorator in order to map Apache log placeholders to request/response values.

Our default AccessLogFormatterInterface implementation, AccessLogFormatter, provides constants referencing the most common formats, but also allows you to use arbitrary log formats that use the standard Apache placeholders. The formats we include by default are:

  • AccessLogFormatter::FORMAT_COMMON: Apache common log format: %h %l %u %t "%r" %>s %b
  • AccessLogFormatter::FORMAT_COMMON_VHOST: Apache common log format + vhost: %v %h %l %u %t "%r" %>s %b
  • AccessLogFormatter::FORMAT_COMBINED: Apache combined log format: %h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"
  • AccessLogFormatter::FORMAT_REFERER: %{Referer}i -> %U
  • AccessLogFormatter::FORMAT_AGENT: %{User-Agent}i
  • AccessLogFormatter::FORMAT_VHOST: Alternative Apache vhost format: '%v %l %u %t "%r" %>s %b';
  • AccessLogFormatter::FORMAT_COMMON_DEBIAN: Debian variant of common log format: %h %l %u %t “%r” %>s %O;
  • AccessLogFormatter::FORMAT_COMBINED_DEBIAN: Debian variant of combined log format: %h %l %u %t “%r” %>s %O “%{Referer}i” “%{User-Agent}i”;
  • AccessLogFormatter::FORMAT_VHOST_COMBINED_DEBIAN: Debian variant of combined log format + vhost: %v:%p %h %l %u %t “%r” %>s %O “%{Referer}i” “%{User-Agent}i";

Configuring a logger

You may subsitute your own logger implementation into the Swoole request handler runner.

Manual usage

If you are manually instantiating a Zend\Expressive\Swoole\SwooleRequestHandlerRunner instance, you may provide it as the seventh argument to the constructor:

use Zend\Expressive\Swoole\SwooleRequestHandlerRunner;

$runner = new SwooleRequestHandlerRunner(
    $logger // <-- AccessLoggerInterface instance

Container usage

If you are using a PSR-11 container, the SwooleRequestHandlerRunnerFactory will retrieve a log instance using the Zend\Expressive\Swoole\Log\AccessLogInterface service.

You have two options for substituting your own logger from there.

First, if you already have a service which resolves to a Psr\Log\LoggerInterface instance, you can configure it by providing its name:

'zend-expressive-swoole' => [
    'swoole-http-server' => [
        'logger' => [
            'logger-name' => 'my_logger', // define the logger service name here

If you don't want to manually provide the service name but you are okay with re-using your existing PSR-3 logger, the provided Zend\Expressive\Swoole\Log\AccessLogFactory will use the Psr\Log\LoggerInterface service to create a Psr3AccessLogDecorator instance.

Since 2.4.0, the Zend\Expressive\Swoole\Log\AccessLogFactory will resolve the logger instance by using the Zend\Expressive\Swoole\Log\SwooleLogger service. If you were manually using this factory, you should register the service to the Zend\Expressive\Swoole\Log\SwooleLoggerFactory.

This factory also allows you to specify a custom AccessLogFormatterInterface instance if you want. It will look up a service by the fully-qualified interface name, and use it if present. Otherwise, it creates an AccessLogFormatter instance for you.

In both cases the factory will also look at the following configuration values:

'zend-expressive-swoole' => [
    'swoole-http-server' => [
        'logger' => [
            'format' => string, // one of the AccessLogFormatter::FORMAT_*
                                // constants, or a custom format string
            'use-hostname-lookups' => bool, // Set to true to enable hostname lookups

Using Monolog as a PSR-3 logger

When using Monolog with a StreamHandler, you must supply a file or a stream resource descriptor. We recommend using one of the following:

  • php://stdout is a good choice, as this will generally write to the current console.

  • php://stderr is also a good choice, as this will generally write to the current console, and allows you to filter based on that output stream.

  • When using Docker, generally one of either /proc/1/fd/1 or /proc/1/fd/2 can be used, and are analogous to STDOUT and STDERR, respectively. We recommend using php://stdout and php://stderr instead, as these will be mapped to the correct locations by the language.


If you plan to write to STDERR, you might consider instead using the Monolog ErrorLogHandler, as this will use PHP's error_log() mechanism to write to the configured PHP error log. You can then either introspect that location, or configure the error_log php.ini setting to point to either /dev/stderr or, if on Docker, /proc/1/fd/2.

Additionally, we recommend using the PsrLogMessageProcessor with any Monolog handler to ensure that any templated parameters are expanded by the logger.

As an example, the following is a factory that wires a StreamHandler to a Monolog\Logger instance.

use Psr\Container\ContainerInterface;
use Psr\Log\LoggerInterface;
use Monolog\Handler\StreamHandler;
use Monolog\Logger;
use Monolog\Processor\PsrLogMessageProcessor;

class LoggerFactory
    public function __invoke(ContainerInterface $container) : LoggerInterface
        $logger = new Logger('swoole-http-server');
        $logger->pushHandler(new StreamHandler(
            $bubble = true,
            $expandNewLines = true
        $logger->pushProcessor(new PsrLogMessageProcessor());
        return $logger;

If you then wire this to the Psr\Log\LoggerInterface service, it will be used by Swoole for the purposes of access logs as well.

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