Guzzle 6 Circuit-Breaker Middleware

This is a Guzzle 6 middleware that integrates https://github.com/ejsmont-artur/php-circuit-breaker.

Contents

• Requirements
  • Hard Dependencies
• Installation
• Usage
  • Example
• Testing
  • Unit tests, Coding standards and static analysis
• Contributing

Requirements

Dependencies

Dependency	Version	Reason
php	~7.0	Anything lower has (almost) reached EOL
guzzlephp/promises	~6.2	Middlewares pass Promises around
psr/http-message	~1.0	Standardization, doh
ejsmont-artur/php-circuit-breaker	~0.1	Simple and robust Circuit Breaker implementation for PHP

Installation

This library is installed via composer.

composer require "flix-tech/guzzle-circuit-breaker-middleware=~1.0"

Usage

NOTE It is recommended that this middleware is on top of the stack so that if a service is unavailable, it can instantly reject without going further down the chain.

With the default configuration, this middleware will inspect the PSR-7 requests for either a transport option key "circuit_breaker.requested_service_name" exposed via Middleware::CB_TRANSFER_OPTION_KEY in the request options array, or a request header "X-CB-Service-Name" exposed via Middleware::CB_SERVICE_NAME_HEADER. You can pass an own service name extractor callable that takes the form f(RequestInterface $request, array $requestOptions): string.

The service name will be used to look up the availability in the circuit breaker. If it is not available, it will be instantly rejected with a CircuitBreakerIsClosedException.

If the request was successful, the middleware will report a success to the circuit breaker for the given service. Otherwise it will report a failure and pass the rejection further down the chain.

You can pass a custom exception map into the middleware with which you can control which exception types and values should actually trigger a failure report. I.e. a 404 might be a failed configuration issue and might not trigger failure reports. The exception map callback takes the form f($rejectedValue): bool.

Example

<?php

use Ejsmont\CircuitBreaker\Factory;
use FlixTech\CircuitBreakerMiddleware\Middleware;
use GuzzleHttp\Client;
use GuzzleHttp\Exception\RequestException;
use GuzzleHttp\HandlerStack;
use GuzzleHttp\Handler\CurlHandler;
use Psr\Http\Message\RequestInterface;

$circuitBreaker = Factory::getSingleApcInstance();

$serviceNameExtractor = function (RequestInterface $request, array $options) {
    if (\array_key_exists('my_custom_option_key', $options)) {
        return $options['my_custom_option_key'];
    }
    
    return null;
};

$exceptionMap = function ($rejectedValue) {
    if ($rejectedValue instanceof RequestException && $rejectedValue->getResponse()) {
        return 404 !== $rejectedValue->getResponse()->getStatusCode();
    }
    
    return true;
};

$middleware = new Middleware(
    $circuitBreaker,
    $serviceNameExtractor,
    $exceptionMap
);

$handlerStack = HandlerStack::create(new CurlHandler());
$handlerStack->push($middleware);

$client = new Client(['handler' => $handlerStack]);

Testing

To run the tests, just run ./vendor/bin/phpunit from the root of the project after installing the dev requirements.

Contributing

In order to contribute to this library, follow this workflow:

• Fork the repository
• Create a feature branch
• Work on the feature
• Run tests to verify that the tests are passing
• Open a PR to the upstream master branch
• See any Travis CI messages popping up on your PR
• Be happy about contributing to open source!