composer 自动加载源码解析

一直在用 composer，最近想看一下具体的原理是什么，就仔细阅读了一下源码，一下是个人理解。在看该文章前最好了解一下 PSR-4 自动加载规范

引入类自动加载文件

# 加载类自动加载文件
require __DIR__.'/../vendor/autoload.php';

# autoload.php 入口文件
require_once __DIR__ . '/composer/autoload_real.php';

return ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c::getLoader();

composer 目录文件

根目录 composer/

• autoload_namespaces.php 为需要加载的命名空间前缀定义路径
• autoload_classmap.php 为所有需要自动加载的类定义路径
• autoload_files.php 定义所有需要加载的配置文件
• autoload_psr4.php 根据 Psr4 规范定义命名空间前缀和路径
• autoload_static.php 包含所有需要加载的文件、类，内容包含以上文件
• autoload_real.php 自动加载配置
• ClassLoader.php 自动加载类

autoload_real.php 解析

<?php

// autoload_real.php @generated by Composer

class ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c
{
    private static $loader;

    public static function loadClassLoader($class)
    {
        // 调用自动加载类 ClassLoader.php
        if ('Composer\Autoload\ClassLoader' === $class) {
            require __DIR__ . '/ClassLoader.php';
        }
    }

	// 实例化 ClassLoader 类，并注册所有需要加载文件的地址
    public static function getLoader()
    {
        if (null !== self::$loader) {
            return self::$loader;
        }

        // 将 loadClassLoader 注册为 __autoload 函数
        spl_autoload_register(array('ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c', 'loadClassLoader'), true, true);
        // 实例化自动加载类
        self::$loader = $loader = new \Composer\Autoload\ClassLoader();
        // 注销 __autoload 函数
        spl_autoload_unregister(array('ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c', 'loadClassLoader'));

        // 判断 PHP 版本 以及 HHVM_VERSION
        $useStaticLoader = PHP_VERSION_ID >= 50600 && !defined('HHVM_VERSION') && (!function_exists('zend_loader_file_encoded') || !zend_loader_file_encoded());
        if ($useStaticLoader) {
            // autoload_static.php 为所有需要加载的文件
            require_once __DIR__ . '/autoload_static.php';

            // 初始化需要加载的数据，调用通过 autoload_static.php 中定义的值
            call_user_func(\Composer\Autoload\ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::getInitializer($loader));
        } else {
			// 加载的已定义命名空间
            $map = require __DIR__ . '/autoload_namespaces.php';
            foreach ($map as $namespace => $path) {
                $loader->set($namespace, $path);
            }

            // 加载已定义的命名空间前缀和路径
			$map = require __DIR__ . '/autoload_psr4.php';
            foreach ($map as $namespace => $path) {
                $loader->setPsr4($namespace, $path);
            }

            // 加载已定义的所有类
			$classMap = require __DIR__ . '/autoload_classmap.php';
            if ($classMap) {
                $loader->addClassMap($classMap);
            }
        }

        // 注册自动加载方法 __atuoload()
        $loader->register(true);

        if ($useStaticLoader) {
            // 加载基础配置文件
            $includeFiles = Composer\Autoload\ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$files;
        } else {
            $includeFiles = require __DIR__ . '/autoload_files.php';
        }
        foreach ($includeFiles as $fileIdentifier => $file) {
            composerRequire8ff9bdcc605ff8ad74a329b1634c155c($fileIdentifier, $file);
        }

        return $loader;
    }
}

function composerRequire8ff9bdcc605ff8ad74a329b1634c155c($fileIdentifier, $file)
{
    if (empty($GLOBALS['__composer_autoload_files'][$fileIdentifier])) {
        // 调用配置文件
        require $file;

        $GLOBALS['__composer_autoload_files'][$fileIdentifier] = true;
    }
}

autoload_static.php 解析

<?php

// autoload_static.php @generated by Composer

namespace Composer\Autoload;

class ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c
{
	// 基础文件
    public static $files = array (
        '0e6d7bf4a5811bfa5cf40c5ccd6fae6a' => __DIR__ . '/..' . '/custom/sub-custom/custom.php',
    );

	// 命名空间前缀及长度
    public static $prefixLengthsPsr4 = array (
		'p' =>
		array (
		'custom\\sub-custom\\' => 18,
		),
	);

	// 命名空间前缀及路径
	public static $prefixDirsPsr4 = array (
        'sustom\\sub-custom\\' =>
        array (
            0 => __DIR__ . '/..' . '/custom/sub-custom/custom',
        ),
	);

	// 命名空间前缀及路径
	public static $prefixesPsr0 = array (
        'C' =>
        array (
            'Custom\\' =>
            array (
                0 => __DIR__ . '/..' . '/custom/sub-custom/custom',
            ),
        ),
	）

	// 所有需要自动加载的类
	public static $classMap = array (
        'Custom\\CustomController' => __DIR__ . '/../..' . 'Custom/CustomController.php',
	)

	public static function getInitializer(ClassLoader $loader)
    {
        return \Closure::bind(function () use ($loader) {
            $loader->prefixLengthsPsr4 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixLengthsPsr4;
            $loader->prefixDirsPsr4 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixDirsPsr4;
            $loader->prefixesPsr0 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixesPsr0;
            // 以上为 PHP 自动加载规范
            // 以下为需要加载的类
            $loader->classMap = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$classMap;

        }, null, ClassLoader::class);
    }

ClassLoader.php 解析

<?php
/*
 * This file is part of Composer.
 *
 * (c) Nils Adermann <naderman@naderman.de>
 *     Jordi Boggiano <j.boggiano@seld.be>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Composer\Autoload;

/**
 * ClassLoader implements a PSR-0, PSR-4 and classmap class loader.
 *
 *     $loader = new \Composer\Autoload\ClassLoader();
 *
 *     // register classes with namespaces
 *     $loader->add('Symfony\Component', __DIR__.'/component');
 *     $loader->add('Symfony',           __DIR__.'/framework');
 *
 *     // activate the autoloader
 *     $loader->register();
 *
 *     // to enable searching the include path (eg. for PEAR packages)
 *     $loader->setUseIncludePath(true);
 *
 * In this example, if you try to use a class in the Symfony\Component
 * namespace or one of its children (Symfony\Component\Console for instance),
 * the autoloader will first look for the class under the component/
 * directory, and it will then fallback to the framework/ directory if not
 * found before giving up.
 *
 * This class is loosely based on the Symfony UniversalClassLoader.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 * @author Jordi Boggiano <j.boggiano@seld.be>
 * @see    http://www.php-fig.org/psr/psr-0/
 * @see    http://www.php-fig.org/psr/psr-4/
 */
class ClassLoader
{
    // PSR-4
    private $prefixLengthsPsr4 = array();
    private $prefixDirsPsr4 = array();
    private $fallbackDirsPsr4 = array();

    // PSR-0
    private $prefixesPsr0 = array();
    private $fallbackDirsPsr0 = array();

    private $useIncludePath = false;
    private $classMap = array();
    private $classMapAuthoritative = false;
    private $missingClasses = array();
    private $apcuPrefix;

    public function getPrefixes()
    {
        if (!empty($this->prefixesPsr0)) {
            return call_user_func_array('array_merge', $this->prefixesPsr0);
        }

        return array();
    }

    public function getPrefixesPsr4()
    {
        return $this->prefixDirsPsr4;
    }

    public function getFallbackDirs()
    {
        return $this->fallbackDirsPsr0;
    }

    public function getFallbackDirsPsr4()
    {
        return $this->fallbackDirsPsr4;
    }

    public function getClassMap()
    {
        return $this->classMap;
    }

    /**
     * @param array $classMap Class to filename map
     */
    public function addClassMap(array $classMap)
    {
        if ($this->classMap) {
            $this->classMap = array_merge($this->classMap, $classMap);
        } else {
            $this->classMap = $classMap;
        }
    }

    /**
     * Registers a set of PSR-0 directories for a given prefix, either
     * appending or prepending to the ones previously set for this prefix.
     *
     * @param string       $prefix  The prefix
     * @param array|string $paths   The PSR-0 root directories
     * @param bool         $prepend Whether to prepend the directories
     */
    public function add($prefix, $paths, $prepend = false)
    {
        if (!$prefix) {
            if ($prepend) {
                $this->fallbackDirsPsr0 = array_merge(
                    (array) $paths,
                    $this->fallbackDirsPsr0
                );
            } else {
                $this->fallbackDirsPsr0 = array_merge(
                    $this->fallbackDirsPsr0,
                    (array) $paths
                );
            }

            return;
        }

        $first = $prefix[0];
        if (!isset($this->prefixesPsr0[$first][$prefix])) {
            $this->prefixesPsr0[$first][$prefix] = (array) $paths;

            return;
        }
        if ($prepend) {
            $this->prefixesPsr0[$first][$prefix] = array_merge(
                (array) $paths,
                $this->prefixesPsr0[$first][$prefix]
            );
        } else {
            $this->prefixesPsr0[$first][$prefix] = array_merge(
                $this->prefixesPsr0[$first][$prefix],
                (array) $paths
            );
        }
    }

    /**
     * Registers a set of PSR-4 directories for a given namespace, either
     * appending or prepending to the ones previously set for this namespace.
     *
     * @param string       $prefix  The prefix/namespace, with trailing '\\'
     * @param array|string $paths   The PSR-4 base directories
     * @param bool         $prepend Whether to prepend the directories
     *
     * @throws \InvalidArgumentException
     */
    public function addPsr4($prefix, $paths, $prepend = false)
    {
        if (!$prefix) {
            // Register directories for the root namespace.
            if ($prepend) {
                $this->fallbackDirsPsr4 = array_merge(
                    (array) $paths,
                    $this->fallbackDirsPsr4
                );
            } else {
                $this->fallbackDirsPsr4 = array_merge(
                    $this->fallbackDirsPsr4,
                    (array) $paths
                );
            }
        } elseif (!isset($this->prefixDirsPsr4[$prefix])) {
            // Register directories for a new namespace.
            $length = strlen($prefix);
            if ('\\' !== $prefix[$length - 1]) {
                throw new \InvalidArgumentException("A non-empty PSR-4 prefix must end with a namespace separator.");
            }
            $this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
            $this->prefixDirsPsr4[$prefix] = (array) $paths;
        } elseif ($prepend) {
            // Prepend directories for an already registered namespace.
            $this->prefixDirsPsr4[$prefix] = array_merge(
                (array) $paths,
                $this->prefixDirsPsr4[$prefix]
            );
        } else {
            // Append directories for an already registered namespace.
            $this->prefixDirsPsr4[$prefix] = array_merge(
                $this->prefixDirsPsr4[$prefix],
                (array) $paths
            );
        }
    }

    /**
     * Registers a set of PSR-0 directories for a given prefix,
     * replacing any others previously set for this prefix.
     *
     * @param string       $prefix The prefix
     * @param array|string $paths  The PSR-0 base directories
     */
    public function set($prefix, $paths)
    {
        if (!$prefix) {
            $this->fallbackDirsPsr0 = (array) $paths;
        } else {
            $this->prefixesPsr0[$prefix[0]][$prefix] = (array) $paths;
        }
    }

    /**
     * Registers a set of PSR-4 directories for a given namespace,
     * replacing any others previously set for this namespace.
     *
     * @param string       $prefix The prefix/namespace, with trailing '\\'
     * @param array|string $paths  The PSR-4 base directories
     *
     * @throws \InvalidArgumentException
     */
    public function setPsr4($prefix, $paths)
    {
        if (!$prefix) {
            $this->fallbackDirsPsr4 = (array) $paths;
        } else {
            $length = strlen($prefix);
            if ('\\' !== $prefix[$length - 1]) {
                throw new \InvalidArgumentException("A non-empty PSR-4 prefix must end with a namespace separator.");
            }
            $this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
            $this->prefixDirsPsr4[$prefix] = (array) $paths;
        }
    }

    /**
     * Turns on searching the include path for class files.
     *
     * @param bool $useIncludePath
     */
    public function setUseIncludePath($useIncludePath)
    {
        $this->useIncludePath = $useIncludePath;
    }

    /**
     * Can be used to check if the autoloader uses the include path to check
     * for classes.
     *
     * @return bool
     */
    public function getUseIncludePath()
    {
        return $this->useIncludePath;
    }

    /**
     * Turns off searching the prefix and fallback directories for classes
     * that have not been registered with the class map.
     *
     * @param bool $classMapAuthoritative
     */
    public function setClassMapAuthoritative($classMapAuthoritative)
    {
        $this->classMapAuthoritative = $classMapAuthoritative;
    }

    /**
     * Should class lookup fail if not found in the current class map?
     *
     * @return bool
     */
    public function isClassMapAuthoritative()
    {
        return $this->classMapAuthoritative;
    }

    /**
     * APCu prefix to use to cache found/not-found classes, if the extension is enabled.
     *
     * @param string|null $apcuPrefix
     */
    public function setApcuPrefix($apcuPrefix)
    {
        $this->apcuPrefix = function_exists('apcu_fetch') && ini_get('apc.enabled') ? $apcuPrefix : null;
    }

    /**
     * The APCu prefix in use, or null if APCu caching is not enabled.
     *
     * @return string|null
     */
    public function getApcuPrefix()
    {
        return $this->apcuPrefix;
    }

    /**
     * Registers this instance as an autoloader.
     *
     * @param bool $prepend Whether to prepend the autoloader or not
     */
    public function register($prepend = false)
    {
        spl_autoload_register(array($this, 'loadClass'), true, $prepend);
    }

    /**
     * Unregisters this instance as an autoloader.
     */
    public function unregister()
    {
        spl_autoload_unregister(array($this, 'loadClass'));
    }

    /**
     * Loads the given class or interface.
     *
     * @param  string    $class The name of the class
     * @return bool|null True if loaded, null otherwise
     */
    public function loadClass($class)
    {
        if ($file = $this->findFile($class)) {
            includeFile($file);

            return true;
        }
    }

    /**
     * Finds the path to the file where the class is defined.
     *
     * @param string $class The name of the class
     *
     * @return string|false The path if found, false otherwise
     */
    public function findFile($class)
    {
        // class map lookup
        // 如果存在直接返回
        if (isset($this->classMap[$class])) {
            return $this->classMap[$class];
        }
        if ($this->classMapAuthoritative || isset($this->missingClasses[$class])) {
            return false;
        }
        if (null !== $this->apcuPrefix) {
            $file = apcu_fetch($this->apcuPrefix.$class, $hit);
            if ($hit) {
                return $file;
            }
        }

        // 没有在 classMap中找到，重新查找
        $file = $this->findFileWithExtension($class, '.php');

        // Search for Hack files if we are running on HHVM
        if (false === $file && defined('HHVM_VERSION')) {
            $file = $this->findFileWithExtension($class, '.hh');
        }

        if (null !== $this->apcuPrefix) {
            apcu_add($this->apcuPrefix.$class, $file);
        }

        if (false === $file) {
            // Remember that this class does not exist.
            $this->missingClasses[$class] = true;
        }

        return $file;
    }

    private function findFileWithExtension($class, $ext)
    {
        // PSR-4 lookup
        $logicalPathPsr4 = strtr($class, '\\', DIRECTORY_SEPARATOR) . $ext;

        $first = $class[0];
        if (isset($this->prefixLengthsPsr4[$first])) {
            $subPath = $class;
            while (false !== $lastPos = strrpos($subPath, '\\')) {
                $subPath = substr($subPath, 0, $lastPos);
                $search = $subPath.'\\';
                if (isset($this->prefixDirsPsr4[$search])) {
                    foreach ($this->prefixDirsPsr4[$search] as $dir) {
                        $length = $this->prefixLengthsPsr4[$first][$search];
                        if (file_exists($file = $dir . DIRECTORY_SEPARATOR . substr($logicalPathPsr4, $length))) {
                            return $file;
                        }
                    }
                }
            }
        }

        // PSR-4 fallback dirs
        foreach ($this->fallbackDirsPsr4 as $dir) {
            if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr4)) {
                return $file;
            }
        }

        // PSR-0 lookup
        if (false !== $pos = strrpos($class, '\\')) {
            // namespaced class name
            $logicalPathPsr0 = substr($logicalPathPsr4, 0, $pos + 1)
                . strtr(substr($logicalPathPsr4, $pos + 1), '_', DIRECTORY_SEPARATOR);
        } else {
            // PEAR-like class name
            $logicalPathPsr0 = strtr($class, '_', DIRECTORY_SEPARATOR) . $ext;
        }

        if (isset($this->prefixesPsr0[$first])) {
            foreach ($this->prefixesPsr0[$first] as $prefix => $dirs) {
                if (0 === strpos($class, $prefix)) {
                    foreach ($dirs as $dir) {
                        if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
                            return $file;
                        }
                    }
                }
            }
        }

        // PSR-0 fallback dirs
        foreach ($this->fallbackDirsPsr0 as $dir) {
            if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
                return $file;
            }
        }

        // PSR-0 include paths.
        if ($this->useIncludePath && $file = stream_resolve_include_path($logicalPathPsr0)) {
            return $file;
        }

        return false;
    }
}

/**
 * Scope isolated include.
 *
 * Prevents access to $this/self from included files.
 */
function includeFile($file)
{
    include $file;
}