浏览器同源策略实现原理

发布时间: 2025-03-23 16:02

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# 浏览器同源策略实现原理

## 概述

同源策略(Same-Origin Policy)是浏览器安全的基石,它限制了一个源(origin)的文档或脚本如何与另一个源的资源进行交互。本文将深入探讨浏览器如何实现同源策略,以及相关的安全机制。

## 基本概念

### 1. 源的定义

```javascript
// URL解析器
class URLParser {
  constructor(url) {
    this.url = new URL(url);
  }

getOrigin() {
    return {
      protocol: this.url.protocol,
      hostname: this.url.hostname,
      port: this.url.port || this.getDefaultPort()
    };
  }

getDefaultPort() {
    switch(this.url.protocol) {
      case 'http:':
        return '80';
      case 'https:':
        return '443';
      default:
        return '';
    }
  }

toString() {
    const origin = this.getOrigin();
    return `${origin.protocol}//${origin.hostname}:${origin.port}`;
  }
}
```

### 2. 源的比较

```javascript
// 源比较器
class OriginComparator {
  constructor() {
    this.parser = new URLParser();
  }

isSameOrigin(url1, url2) {
    const origin1 = this.parser.constructor(url1).getOrigin();
    const origin2 = this.parser.constructor(url2).getOrigin();
    
    return origin1.protocol === origin2.protocol &&
           origin1.hostname === origin2.hostname &&
           origin1.port === origin2.port;
  }

checkAccess(sourceUrl, targetUrl) {
    if (this.isSameOrigin(sourceUrl, targetUrl)) {
      return true;
    }
    
    // 检查是否允许跨域访问
    return this.checkCORSPolicy(sourceUrl, targetUrl);
  }

checkCORSPolicy(sourceUrl, targetUrl) {
    // CORS策略检查实现
    return false; // 默认禁止跨域访问
  }
}
```

## 实现机制

### 1. DOM访问控制

```javascript
// DOM访问控制器
class DOMAccessController {
  constructor() {
    this.comparator = new OriginComparator();
  }

canAccessDOM(sourceWindow, targetWindow) {
    try {
      if (!this.comparator.isSameOrigin(
        sourceWindow.location.href,
        targetWindow.location.href
      )) {
        throw new Error('跨域DOM访问被拒绝');
      }
      return true;
    } catch(error) {
      console.error('DOM访问错误:', error);
      return false;
    }
  }

wrapDOMAccess(window) {
    const controller = this;
    
    // 代理DOM访问
    return new Proxy(window, {
      get(target, property) {
        if (controller.canAccessDOM(window, target)) {
          return target[property];
        }
        return undefined;
      }
    });
  }
}
```

### 2. XMLHttpRequest控制

```javascript
// XHR请求控制器
class XHRController {
  constructor() {
    this.comparator = new OriginComparator();
  }

createSecureXHR() {
    const controller = this;
    const xhr = new XMLHttpRequest();
    
    // 包装open方法
    const originalOpen = xhr.open;
    xhr.open = function(method, url, ...args) {
      if (!controller.canMakeRequest(url)) {
        throw new Error('跨域XHR请求被拒绝');
      }
      return originalOpen.call(this, method, url, ...args);
    };
    
    return xhr;
  }

canMakeRequest(targetUrl) {
    return this.comparator.checkAccess(
      window.location.href,
      targetUrl
    );
  }
}
```

### 3. Cookie访问控制

```javascript
// Cookie控制器
class CookieController {
  constructor() {
    this.parser = new URLParser();
  }

canAccessCookie(domain) {
    const currentDomain = this.parser
      .constructor(window.location.href)
      .getOrigin()
      .hostname;
    
    return this.isDomainMatch(currentDomain, domain);
  }

isDomainMatch(currentDomain, cookieDomain) {
    // 检查域名匹配
    return currentDomain.endsWith(cookieDomain);
  }

setCookie(name, value, options = {}) {
    if (!this.canAccessCookie(options.domain)) {
      throw new Error('Cookie域设置被拒绝');
    }
    
    // 设置Cookie
    document.cookie = this.formatCookie(name, value, options);
  }

formatCookie(name, value, options) {
    const parts = [`${name}=${value}`];
    
    if (options.domain) {
      parts.push(`domain=${options.domain}`);
    }
    if (options.path) {
      parts.push(`path=${options.path}`);
    }
    if (options.secure) {
      parts.push('secure');
    }
    if (options.sameSite) {
      parts.push(`samesite=${options.sameSite}`);
    }
    
    return parts.join('; ');
  }
}
```

## 跨域通信

### 1. postMessage机制

```javascript
// 跨域消息控制器
class PostMessageController {
  constructor() {
    this.setupMessageListener();
  }

setupMessageListener() {
    window.addEventListener('message', event => {
      this.handleMessage(event);
    });
  }

handleMessage(event) {
    // 验证消息来源
    if (!this.isValidSource(event.origin)) {
      return;
    }
    
    try {
      const message = this.parseMessage(event.data);
      this.processMessage(message, event.source);
    } catch(error) {
      console.error('消息处理错误:', error);
    }
  }

isValidSource(origin) {
    // 检查消息源是否在白名单中
    const whitelist = this.getOriginWhitelist();
    return whitelist.includes(origin);
  }

getOriginWhitelist() {
    // 配置允许的源
    return [
      'https://trusted-domain.com',
      'https://api.trusted-domain.com'
    ];
  }

sendMessage(targetWindow, message, targetOrigin) {
    if (targetOrigin === '*') {
      console.warn('不建议使用通配符源');
    }
    
    targetWindow.postMessage(
      this.formatMessage(message),
      targetOrigin
    );
  }

formatMessage(message) {
    return JSON.stringify({
      data: message,
      timestamp: Date.now()
    });
  }

parseMessage(data) {
    return JSON.parse(data);
  }

processMessage(message, source) {
    // 处理接收到的消息
    console.log('收到消息:', message);
  }
}
```

### 2. CORS配置

```javascript
// CORS控制器
class CORSController {
  constructor() {
    this.config = this.getDefaultConfig();
  }

getDefaultConfig() {
    return {
      allowedOrigins: ['https://trusted-domain.com'],
      allowedMethods: ['GET', 'POST'],
      allowedHeaders: ['Content-Type'],
      exposedHeaders: [],
      allowCredentials: false,
      maxAge: 86400
    };
  }

setCORSHeaders(request, response) {
    const origin = request.headers.get('Origin');
    
    if (this.isAllowedOrigin(origin)) {
      this.applyHeaders(response, origin);
    }
  }

isAllowedOrigin(origin) {
    return this.config.allowedOrigins.includes(origin);
  }

applyHeaders(response, origin) {
    // 设置CORS响应头
    response.headers.set(
      'Access-Control-Allow-Origin',
      origin
    );
    
    if (this.config.allowCredentials) {
      response.headers.set(
        'Access-Control-Allow-Credentials',
        'true'
      );
    }
    
    response.headers.set(
      'Access-Control-Allow-Methods',
      this.config.allowedMethods.join(', ')
    );
    
    response.headers.set(
      'Access-Control-Allow-Headers',
      this.config.allowedHeaders.join(', ')
    );
    
    if (this.config.exposedHeaders.length > 0) {
      response.headers.set(
        'Access-Control-Expose-Headers',
        this.config.exposedHeaders.join(', ')
      );
    }
    
    response.headers.set(
      'Access-Control-Max-Age',
      this.config.maxAge.toString()
    );
  }

handlePreflight(request, response) {
    // 处理预检请求
    if (request.method === 'OPTIONS') {
      this.setCORSHeaders(request, response);
      return new Response(null, {
        status: 204,
        headers: response.headers
      });
    }
    return null;
  }
}
```

## 最佳实践

### 1. 安全配置

```javascript
// 安全配置管理器
class SecurityManager {
  constructor() {
    this.corsController = new CORSController();
    this.cookieController = new CookieController();
  }

configureSecurityHeaders(response) {
    // 设置安全响应头
    response.headers.set(
      'Content-Security-Policy',
      this.getCSPPolicy()
    );
    
    response.headers.set(
      'X-Frame-Options',
      'SAMEORIGIN'
    );
    
    response.headers.set(
      'X-Content-Type-Options',
      'nosniff'
    );
  }

getCSPPolicy() {
    return [
      "default-src 'self'",
      "script-src 'self' 'unsafe-inline'",
      "style-src 'self' 'unsafe-inline'",
      "img-src 'self' data: https:",
      "connect-src 'self' https://api.trusted-domain.com"
    ].join('; ');
  }

configureCookie(name, value, options = {}) {
    // 设置安全Cookie
    const secureOptions = {
      ...options,
      secure: true,
      sameSite: 'Strict',
      path: '/'
    };
    
    this.cookieController.setCookie(
      name,
      value,
      secureOptions
    );
  }
}
```

### 2. 错误处理

```javascript
// 错误处理器
class ErrorHandler {
  constructor() {
    this.setupErrorListeners();
  }

setupErrorListeners() {
    window.addEventListener('error', event => {
      this.handleError(event.error);
    });
    
    window.addEventListener('unhandledrejection', event => {
      this.handlePromiseError(event.reason);
    });
  }

handleError(error) {
    if (this.isCORSError(error)) {
      console.error('跨域错误:', {
        message: error.message,
        source: error.filename,
        line: error.lineno
      });
      return;
    }
    
    // 处理其他错误
    console.error('应用错误:', error);
  }

handlePromiseError(reason) {
    console.error('Promise错误:', reason);
  }

isCORSError(error) {
    return error instanceof DOMException &&
           error.name === 'SecurityError';
  }
}
```

## 总结

本文详细介绍了浏览器同源策略的实现原理,包括:

1. 源的定义和比较机制
2. DOM访问控制
3. XMLHttpRequest请求控制
4. Cookie访问控制
5. 跨域通信机制
6. CORS配置
7. 安全最佳实践

通过理解这些核心概念和实现细节,开发者可以更好地处理跨域问题,构建安全的Web应用。在实际开发中,应当谨慎配置跨域策略,采用最小权限原则,确保应用的安全性。

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