Reading document 是培養耐心的一種修煉…

本文大綱

Laravel 文件

怎麼會開始看文件呢？事發總有個原因XD 原因是被問到 Laravel 運作進入的順序，我大概只能回答出 middleware -> route -> controllers。

但其實這中間還有很多細節我並不知道的，我過去學習方式是以實戰下去學習，可以動就好，後來看到 Laravel conference 優美的架構後，才發現魔鬼藏在細節裡，養成良好的閱讀習慣。 以下用閱讀隨筆方式紀錄，如有錯誤，再煩請告知，不定期更新與整理。

Lifecycle

  1. public/index.php，為什麼 request 入口是 public/index.php，因為 server(Apache/Nginx) configuration 設定的。
  2. vendor/autoload.php -> /composer/autoload_real.php 會去載入官方與常用套件，分成以下三種
    (1) autoload_namespaces : 幫助日後使用 library 呼叫方便，對應其原來 library
    (2) autoload_psr4 : 將一些常用的 packages 對應其原先 packages 位置，以便後續使用方便
    (3) autoload_classmap : 同樣將其常用的 packages 對應其原先 packages 位置，以便後續使用方便

What is autoloading? PHP autoload best practices

What is autoloading? Every time you want to use a new class in your PHP project, first you need to include this class (using include or require language construct, that’s right this are not functions). However if you have __autoload function defined, inclusion will handle itself.

實際上去翻 laravel project 內容如下，看過這些底層後，我對 autoload 的認知是將有需要的 package & cutomized files 利用 autoload file 去 map 絕對路徑與命名，autoload_classmap 對應命名與實際存放位置。

autoload_real.php
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// vendor/autoload.php
require_once __DIR__ . '/composer/autoload_real.php';
// autoload_real.php
    public static function loadClassLoader($class)
    {
        if ('Composer\Autoload\ClassLoader' === $class) {
            require __DIR__ . '/ClassLoader.php';
        }
    }

    /**
     * @return \Composer\Autoload\ClassLoader
     */
    public static function getLoader()
    {
        if (null !== self::$loader) {
            return self::$loader;
        }

        require __DIR__ . '/platform_check.php';

        spl_autoload_register(array('ComposerAutoloaderInit5c55c31ecadb260233c7b285c5f084a8', 'loadClassLoader'), true, true);
        self::$loader = $loader = new \Composer\Autoload\ClassLoader(\dirname(\dirname(__FILE__)));
        spl_autoload_unregister(array('ComposerAutoloaderInit5c55c31ecadb260233c7b285c5f084a8', 'loadClassLoader'));

        $useStaticLoader = PHP_VERSION_ID >= 50600 && !defined('HHVM_VERSION') && (!function_exists('zend_loader_file_encoded') || !zend_loader_file_encoded());
        if ($useStaticLoader) {
            require __DIR__ . '/autoload_static.php';

            call_user_func(\Composer\Autoload\ComposerStaticInit5c55c31ecadb260233c7b285c5f084a8::getInitializer($loader));
        } else {
            $map = require __DIR__ . '/autoload_namespaces.php';
            foreach ($map as $namespace => $path) {
                $loader->set($namespace, $path);
            }

            $map = require __DIR__ . '/autoload_psr4.php';
            foreach ($map as $namespace => $path) {
                $loader->setPsr4($namespace, $path);
            }

            $classMap = require __DIR__ . '/autoload_classmap.php';
            if ($classMap) {
                $loader->addClassMap($classMap);
            }
        }

        $loader->register(true);

        if ($useStaticLoader) {
            $includeFiles = Composer\Autoload\ComposerStaticInit5c55c31ecadb260233c7b285c5f084a8::$files;
        } else {
            $includeFiles = require __DIR__ . '/autoload_files.php';
        }
        foreach ($includeFiles as $fileIdentifier => $file) {
            composerRequire5c55c31ecadb260233c7b285c5f084a8($fileIdentifier, $file);
        }

        return $loader;
    }
3. bootstrap/app.php，會去拿所有 instance of Laravel application，第一個動作就是創建 service container。 4. HTTP kernnel / console kernel
app/Http/Kernel.php bootstrapper 會在 require 前就執行，其會設定 error handling/logging/env 環境設定 HTTP kernel 定義在進入 application 前要進入的 middleware。 這些 middleware 處理讀寫 HTTP session、驗證 CSRF token

文件中提到將 kernel 想成一個黑盒子去說明你整個應用服務，因此 kernel 就是輸入 HTTP request，其回 HTTP response

Service Provider

kernel bootstrapping 工作是為你的服務載入 service providers，啟動服務前要去 config/app.php 設定 providers，遍歷 provider 去啟動 instance，register 這些 providers。

看完文件後，仍有點抽象，Service Provider 是可以讓開發者依賴綁定服務到 container 內，我不需要做太多實例化(instantiate)、或宣告， Service Provider 負責啟動各服務元件、設定 Alias 的對照表，例如：讓你在 controllers 可以直接使用 Request

在 Laravel 如何實現依賴注入 中有一個很好的比喻，Service Provider 像是點餐機器，提供你這項服務的各種功能，包含點餐、收款、付錢，Service Container 就是這個冷冰冰的機器實體，在還沒載入任何程式前，它就是普通的 POS 機台。

以下是 config/app.php 的 code

app.php
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    // ... 以上省略，包含一些名稱、時區等
    'providers' => [
        /*
         * Laravel Framework Service Providers...
         */
        Illuminate\Auth\AuthServiceProvider::class,
        Illuminate\Broadcasting\BroadcastServiceProvider::class,
        Illuminate\Bus\BusServiceProvider::class,
        Illuminate\Cache\CacheServiceProvider::class,
        Illuminate\Foundation\Providers\ConsoleSupportServiceProvider::class,
        Illuminate\Cookie\CookieServiceProvider::class,
        Illuminate\Database\DatabaseServiceProvider::class,
        Illuminate\Encryption\EncryptionServiceProvider::class,
        Illuminate\Filesystem\FilesystemServiceProvider::class,
        Illuminate\Foundation\Providers\FoundationServiceProvider::class,
        Illuminate\Hashing\HashServiceProvider::class,
        Illuminate\Mail\MailServiceProvider::class,
        Illuminate\Notifications\NotificationServiceProvider::class,
        Illuminate\Pagination\PaginationServiceProvider::class,
        Illuminate\Pipeline\PipelineServiceProvider::class,
        Illuminate\Queue\QueueServiceProvider::class,
        Illuminate\Redis\RedisServiceProvider::class,
        Illuminate\Auth\Passwords\PasswordResetServiceProvider::class,
        Illuminate\Session\SessionServiceProvider::class,
        Illuminate\Translation\TranslationServiceProvider::class,
        Illuminate\Validation\ValidationServiceProvider::class,
        Illuminate\View\ViewServiceProvider::class,

        /*
         * Package Service Providers...
         */

        /*
         * Application Service Providers...
         */
        App\Providers\AppServiceProvider::class,
        App\Providers\AuthServiceProvider::class,
        // App\Providers\BroadcastServiceProvider::class,
        App\Providers\EventServiceProvider::class,
        App\Providers\RouteServiceProvider::class,

    ],

    /*
    |--------------------------------------------------------------------------
    | Class Aliases
    |--------------------------------------------------------------------------
    |
    | This array of class aliases will be registered when this application
    | is started. However, feel free to register as many as you wish as
    | the aliases are "lazy" loaded so they don't hinder performance.
    |
    */

    'aliases' => [

        'App' => Illuminate\Support\Facades\App::class,
        'Arr' => Illuminate\Support\Arr::class,
        'Artisan' => Illuminate\Support\Facades\Artisan::class,
        'Auth' => Illuminate\Support\Facades\Auth::class,
        'Blade' => Illuminate\Support\Facades\Blade::class,
        'Broadcast' => Illuminate\Support\Facades\Broadcast::class,
        'Bus' => Illuminate\Support\Facades\Bus::class,
        'Cache' => Illuminate\Support\Facades\Cache::class,
        'Config' => Illuminate\Support\Facades\Config::class,
        'Cookie' => Illuminate\Support\Facades\Cookie::class,
        'Crypt' => Illuminate\Support\Facades\Crypt::class,
        'Date' => Illuminate\Support\Facades\Date::class,
        'DB' => Illuminate\Support\Facades\DB::class,
        'Eloquent' => Illuminate\Database\Eloquent\Model::class,
        'Event' => Illuminate\Support\Facades\Event::class,
        'File' => Illuminate\Support\Facades\File::class,
        'Gate' => Illuminate\Support\Facades\Gate::class,
        'Hash' => Illuminate\Support\Facades\Hash::class,
        'Http' => Illuminate\Support\Facades\Http::class,
        'Lang' => Illuminate\Support\Facades\Lang::class,
        'Log' => Illuminate\Support\Facades\Log::class,
        'Mail' => Illuminate\Support\Facades\Mail::class,
        'Notification' => Illuminate\Support\Facades\Notification::class,
        'Password' => Illuminate\Support\Facades\Password::class,
        'Queue' => Illuminate\Support\Facades\Queue::class,
        'RateLimiter' => Illuminate\Support\Facades\RateLimiter::class,
        'Redirect' => Illuminate\Support\Facades\Redirect::class,
        // 'Redis' => Illuminate\Support\Facades\Redis::class,
        'Request' => Illuminate\Support\Facades\Request::class,
        'Response' => Illuminate\Support\Facades\Response::class,
        'Route' => Illuminate\Support\Facades\Route::class,
        'Schema' => Illuminate\Support\Facades\Schema::class,
        'Session' => Illuminate\Support\Facades\Session::class,
        'Storage' => Illuminate\Support\Facades\Storage::class,
        'Str' => Illuminate\Support\Str::class,
        'URL' => Illuminate\Support\Facades\URL::class,
        'Validator' => Illuminate\Support\Facades\Validator::class,
        'View' => Illuminate\Support\Facades\View::class,

    ],

就拿其載入的 App\Providers\AppServiceProvider::class 來說，裡面可以 register 自己定義的 provider，第一步事先 service provider register 被調用，
一但 all service provider 完成 register 後， boot 才被調用

AppServiceProvider.php
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    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->bind(TodoRepositoryInterface::class, TodoRepository::class);
        $this->app->bind(AssignerRepositoryInterface::class, AssignerRepository::class);
    }

service provider 提供不同 library, validator, router 等，只要 activate serivce provider 就可以使用 Laravel 所有功能。 因此當 application instance 創建後，serivce provider 就被註冊，請求被啟動後，其 controllers 就可以 use 這些功能。

Routing

文件中寫到 App\Providers\RouteServiceProvider 這個檔案紀錄 service providers，有哪些內容，讓我們看看程式…

RouteServiceProvider.php
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    public function boot()
    {
        $this->configureRateLimiting();

        $this->routes(function () {
            Route::prefix('api')
                ->middleware('api')
                ->namespace($this->namespace)
                ->group(base_path('routes/api.php'));

            Route::middleware('web')
                ->namespace($this->namespace)
                ->group(base_path('routes/web.php'));
        });
    }

我們發現其會先進入 routes/api.php 再去 routes/web.php，並載入這些 routes 所對應的 controllers，因此一切都串連起來了！ routes 會去 handle 要配發至哪個 controllers，再根據 controllers 互動 views & models，因此就連接起了 MVC 架構。

值得一提的是在跑進這些 routes 前會經過 middleware，middleware 提供一層過濾 HTTP requests，有種保護層的概念，可以在這裡做身份認證等。

總結與心得

因此 Laravel 的 LifeCycle 為 public/index.php -> autoload.php -> HTTP kernnel / console kernel -> Service Container & Providers -> Routing -> Middleware -> Controllers，這些其實都可以由文件與查詢底層 Code 去了解更多，沒有去細細看文件，也不會去查找這些 folder 裝什麼XD 補充： AppServiceProvider 可以加入你增加的 application’s bootstrapping & service container bindings。

心得

在某次面談中，被問到深層的意義才赫然發現，其實我不知道 Laravel 運作機制，就只是按照 SOP 流程寫作 Controllers & register routes，實際上我不知道中間發生什麼事情，只是會動，然後顯示出我想要的畫面，但其餘的我其實一無所知。

John Snow: You know nothing. King Snow 死於微小沒觀察到的互動，也可以去說明，如果掌握好細節，在這個遊戲中，更能翻轉自如！

參考連結