读 Slim 框架代码（1）

一直都想找个PHP 的 web 框架的代码来读读，好学习一下 web 框架都是怎么写的。但是一般的 PHP 框架好像都比较傲复杂。之前在 Mysapce 实习的时候用过一套自己写的非常简单的 MVC 框架，只是很薄的包了一层，把 Model，View 和 Controller 分开，我自己平时写 PHP 应用也是用这种方法写的。凭着记忆，把当时用的那套东西重现了一下（github）。

前几天在 github 上发现一个叫 Slim 的框架，star 和 fork 数都不算少，也号称非常轻量级，打算看一看它的源代码。

Hello World

Slim Framework 的文档第一个例子依然是 Hello World。先结合这个例子来看一看 Slim 的实现方法。

第一步：创建 Slim 对象

第一行代码是：

    $app = new \Slim\Slim();

这一行代码对应的 Slim 代码如下：

    public function __construct(array $userSettings = array())
    {
        // Setup IoC container
        $this->container = new \Slim\Helper\Set();
        $this->container['settings'] = array_merge(static::getDefaultSettings(), $userSettings);

        // Default environment
        $this->container->singleton('environment', function ($c) {
            return \Slim\Environment::getInstance();
        });

        // Default request
        $this->container->singleton('request', function ($c) {
            return new \Slim\Http\Request($c['environment']);
        });

        // Default response
        $this->container->singleton('response', function ($c) {
            return new \Slim\Http\Response();
        });

        // Default router
        $this->container->singleton('router', function ($c) {
            return new \Slim\Router();
        });

        // Default view
        $this->container->singleton('view', function ($c) {
            $viewClass = $c['settings']['view'];

            return ($viewClass instanceOf \Slim\View) ? $viewClass : new $viewClass;
        });

        // Default log writer
        $this->container->singleton('logWriter', function ($c) {
            $logWriter = $c['settings']['log.writer'];

            return is_object($logWriter) ? $logWriter : new \Slim\LogWriter($c['environment']['slim.errors']);
        });

        // Default log
        $this->container->singleton('log', function ($c) {
            $log = new \Slim\Log($c['logWriter']);
            $log->setEnabled($c['settings']['log.enabled']);
            $log->setLevel($c['settings']['log.level']);
            $env = $c['environment'];
            $env['slim.log'] = $log;

            return $log;
        });

        // Default mode
        $this->container['mode'] = function ($c) {
            $mode = $c['settings']['mode'];

            if (isset($_ENV['SLIM_MODE'])) {
                $mode = $_ENV['SLIM_MODE'];
            } else {
                $envMode = getenv('SLIM_MODE');
                if ($envMode !== false) {
                    $mode = $envMode;
                }
            }

            return $mode;
        };

        // Define default middleware stack
        $this->middleware = array($this);
        $this->add(new \Slim\Middleware\Flash());
        $this->add(new \Slim\Middleware\MethodOverride());

        // Make default if first instance
        if (is_null(static::getInstance())) {
            $this->setName('default');
        }
    }

• Environment 对象中包含 REQUEST_METHO，REMOTE_ADD，REQUEST_URI 等各种 $_SERVER 环境变量
• Request 对象中包含 REQUEST_METHOD，QUERY_STRING，HTTP_COOKIE 及各种 HTTP 请求头内容
• Response 对象包含响应状态码，header 及 body
• Router 对象会解析请求的 URI 并关联到对应的响应函数
• View 对象可以从 HTML 模板渲染页面
• LogWriter 和 Log 主要用来写 log
• Middle 数组是一串 middle，每个请求过来会一次执行 Middle 对象的 call 方法

第二步：指定 route 和 callback

这一步对应的代码是：

    $app->get('/hello/:name', function ($name) {
        echo "Hello, $name";
    });

此时会执行 Slim 对象的 mapRoute 方法，并关联请求方法：

    public function get()
    {
        $args = func_get_args();

        return $this->mapRoute($args)->via(\Slim\Http\Request::METHOD_GET, \Slim\Http\Request::METHOD_HEAD);
    }

在 mapRoute 方法中，会创建一个 Route 对象，将 “/hello/:name” 作为 Route 对象的 pattern，将第二个参数（一个函数）作为 Route 对象的 callable，并将这个 Route 对象加入到 Router 对象的 routes 数组中。

    protected function mapRoute($args)
    {
        $pattern = array_shift($args);
        $callable = array_pop($args);
        $route = new \Slim\Route($pattern, $callable);
        $this->router->map($route);
        if (count($args) > 0) {
            $route->setMiddleware($args);
        }

        return $route;
    }

Route 对象的 via 方法

    public function via()
    {
        $args = func_get_args();
        $this->methods = array_merge($this->methods, $args);

        return $this;
    }

第三步：执行

最后可以执行代码生成 reponse：

    $app->run();

这行代码在 Slim.php 中对应：

    public function run()
    {
        set_error_handler(array('\Slim\Slim', 'handleErrors'));

        //Apply final outer middleware layers
        if ($this->config('debug')) {
            //Apply pretty exceptions only in debug to avoid accidental information leakage in production
            $this->add(new \Slim\Middleware\PrettyExceptions());
        }

        //Invoke middleware and application stack
        $this->middleware[0]->call();

        //Fetch status, header, and body
        list($status, $headers, $body) = $this->response->finalize();

        // Serialize cookies (with optional encryption)
        \Slim\Http\Util::serializeCookies($headers, $this->response->cookies, $this->settings);

        //Send headers
        if (headers_sent() === false) {
            //Send status
            if (strpos(PHP_SAPI, 'cgi') === 0) {
                header(sprintf('Status: %s', \Slim\Http\Response::getMessageForCode($status)));
            } else {
                header(sprintf('HTTP/%s %s', $this->config('http.version'), \Slim\Http\Response::getMessageForCode($status)));
            }

            //Send headers
            foreach ($headers as $name => $value) {
                $hValues = explode("\n", $value);
                foreach ($hValues as $hVal) {
                    header("$name: $hVal", false);
                }
            }
        }

        //Send body, but only if it isn't a HEAD request
        if (!$this->request->isHead()) {
            echo $body;
        }

        restore_error_handler();
    }

由于 Slim 对象的最后一个 Middle 是本身，所以在执行完一堆 Middle 的 call 方法后会执行自己的 call 方法：

    public function call()
    {
        try {
            if (isset($this->environment['slim.flash'])) {
                $this->view()->setData('flash', $this->environment['slim.flash']);
            }
            $this->applyHook('slim.before');
            ob_start();
            $this->applyHook('slim.before.router');
            $dispatched = false;
            $matchedRoutes = $this->router->getMatchedRoutes($this->request->getMethod(), $this->request->getResourceUri());
            foreach ($matchedRoutes as $route) {
                try {
                    $this->applyHook('slim.before.dispatch');
                    $dispatched = $route->dispatch();
                    $this->applyHook('slim.after.dispatch');
                    if ($dispatched) {
                        break;
                    }
                } catch (\Slim\Exception\Pass $e) {
                    continue;
                }
            }
            if (!$dispatched) {
                $this->notFound();
            }
            $this->applyHook('slim.after.router');
            $this->stop();
        } catch (\Slim\Exception\Stop $e) {
            $this->response()->write(ob_get_clean());
            $this->applyHook('slim.after');
        } catch (\Exception $e) {
            if ($this->config('debug')) {
                throw $e;
            } else {
                try {
                    $this->error($e);
                } catch (\Slim\Exception\Stop $e) {
                    // Do nothing
                }
            }
        }
    }

在 Router 的 getMatchedRoutes 方法中会针对请求的 URI，用正则表达式匹配是否有合适的 Route 对象，并且匹配出其中传进来的参数

    public function getMatchedRoutes($httpMethod, $resourceUri, $reload = false)
    {
        if ($reload || is_null($this->matchedRoutes)) {
            $this->matchedRoutes = array();
            foreach ($this->routes as $route) {
                if (!$route->supportsHttpMethod($httpMethod) && !$route->supportsHttpMethod("ANY")) {
                    continue;
                }

                if ($route->matches($resourceUri)) {
                    $this->matchedRoutes[] = $route;
                }
            }
        }

        return $this->matchedRoutes;
    }

    public function matches($resourceUri)
    {
        //Convert URL params into regex patterns, construct a regex for this route, init params
        $patternAsRegex = preg_replace_callback(
            '#:([\w]+)\+?#',
            array($this, 'matchesCallback'),
            str_replace(')', ')?', (string) $this->pattern)
        );
        if (substr($this->pattern, -1) === '/') {
            $patternAsRegex .= '?';
        }

        //Cache URL params' names and values if this route matches the current HTTP request
        if (!preg_match('#^' . $patternAsRegex . '$#', $resourceUri, $paramValues)) {
            return false;
        }
        foreach ($this->paramNames as $name) {
            if (isset($paramValues[$name])) {
                if (isset($this->paramNamesPath[ $name ])) {
                    $this->params[$name] = explode('/', urldecode($paramValues[$name]));
                } else {
                    $this->params[$name] = urldecode($paramValues[$name]);
                }
            }
        }

        return true;
    }

最后执行 Route 对象的 dispatch 方法，就是将匹配出来的参数传到 callable 然后执行。

    public function dispatch()
    {
        foreach ($this->middleware as $mw) {
            call_user_func_array($mw, array($this));
        }

        $return = call_user_func_array($this->getCallable(), array_values($this->getParams()));
        return ($return === false)? false : true;
    }