1、下面以koa2为例
var koa = require('koa'); var app = new koa(); var router = require('koa-router')(); // CORS是一个W3C标准,全称是"跨域资源共享"(Cross-origin resource sharing)。 // 下面以koa2-cors为例, const cors = require('koa2-cors'); // 具体参数我们在后面进行解释 app.use(cors({ origin: function (ctx) { if (ctx.url === '/test') { return "*"; // 允许来自所有域名请求 } return 'http://localhost:8080'; / 这样就能只允许 http://localhost:8080 这个域名的请求了 }, exposeHeaders: ['WWW-Authenticate', 'Server-Authorization'], maxAge: 5, credentials: true, allowMethods: ['GET', 'POST', 'DELETE'], allowHeaders: ['Content-Type', 'Authorization', 'Accept'], })) router.post('/', async function (ctx) { ctx.body = '恭喜 __小简__ 你成功登陆了' }); app .use(router.routes()) .use(router.allowedMethods()); app.listen(3000);
2、下面我们在http://localhost:8080发送请求进行测试
this.$axios.post('http://172.16.186.50:3000/', {}) .then((response) => { console.log(response) }) .catch(function (error) { console.log(error); });
3、下面我们以具体的请求头信息解释上面的代码,也就是cors具体的实现过程
// 我们可以用下面的中间件理解app.use(cors({}))
app.use(async (ctx, next) => { // 允许来自所有域名请求 ctx.set("Access-Control-Allow-Origin", "*"); // 这样就能只允许 http://localhost:8080 这个域名的请求了 // ctx.set("Access-Control-Allow-Origin", "http://localhost:8080"); // 设置所允许的HTTP请求方法 ctx.set("Access-Control-Allow-Methods", "OPTIONS, GET, PUT, POST, DELETE"); // 字段是必需的。它也是一个逗号分隔的字符串,表明服务器支持的所有头信息字段. ctx.set("Access-Control-Allow-Headers", "x-requested-with, accept, origin, content-type"); // 服务器收到请求以后,检查了Origin、Access-Control-Request-Method和Access-Control-Request-Headers字段以后,确认允许跨源请求,就可以做出回应。 // Content-Type表示具体请求中的媒体类型信息 ctx.set("Content-Type", "application/json;charset=utf-8"); // 该字段可选。它的值是一个布尔值,表示是否允许发送Cookie。默认情况下,Cookie不包括在CORS请求之中。 // 当设置成允许请求携带cookie时,需要保证"Access-Control-Allow-Origin"是服务器有的域名,而不能是"*"; ctx.set("Access-Control-Allow-Credentials", true); // 该字段可选,用来指定本次预检请求的有效期,单位为秒。 // 当请求方法是PUT或DELETE等特殊方法或者Content-Type字段的类型是application/json时,服务器会提前发送一次请求进行验证 // 下面的的设置只本次验证的有效时间,即在该时间段内服务端可以不用进行验证 ctx.set("Access-Control-Max-Age", 300); /* CORS请求时,XMLHttpRequest对象的getResponseHeader()方法只能拿到6个基本字段: Cache-Control、 Content-Language、 Content-Type、 Expires、 Last-Modified、 Pragma。 */ // 需要获取其他字段时,使用Access-Control-Expose-Headers, // getResponseHeader('myData')可以返回我们所需的值 ctx.set("Access-Control-Expose-Headers", "myData"); await next(); })
源码:
/** * CORS middleware for koa2 * * @param {Object} [options] * - {String|Function(ctx)} origin `Access-Control-Allow-Origin`, default is request Origin header * - {Array} exposeHeaders `Access-Control-Expose-Headers` * - {String|Number} maxAge `Access-Control-Max-Age` in seconds * - {Boolean} credentials `Access-Control-Allow-Credentials` * - {Array} allowMethods `Access-Control-Allow-Methods`, * default is ['GET', 'PUT', 'POST', 'PATCH', 'DELETE', 'HEAD', 'OPTIONS'] * - {Array} allowHeaders `Access-Control-Allow-Headers` * @return {Function} * @api public */ module.exports = function crossOrigin(options = {}) { const defaultOptions = { allowMethods: ['GET', 'PUT', 'POST', 'PATCH', 'DELETE', 'HEAD', 'OPTIONS'], }; // set defaultOptions to options options = Object.assign({}, defaultOptions, options); // eslint-disable-line no-param-reassign // eslint-disable-next-line consistent-return return async function cors(ctx, next) { // always set vary Origin Header // https://github.com/rs/cors/issues/10 ctx.vary('Origin'); let origin; if (typeof options.origin === 'function') { origin = options.origin(ctx); } else { origin = options.origin || ctx.get('Origin') || '*'; } if (!origin) { return await next(); } // Access-Control-Allow-Origin ctx.set('Access-Control-Allow-Origin', origin); if (ctx.method === 'OPTIONS') { // Preflight Request if (!ctx.get('Access-Control-Request-Method')) { return await next(); } // Access-Control-Max-Age if (options.maxAge) { ctx.set('Access-Control-Max-Age', String(options.maxAge)); } // Access-Control-Allow-Credentials if (options.credentials === true) { // When used as part of a response to a preflight request, // this indicates whether or not the actual request can be made using credentials. ctx.set('Access-Control-Allow-Credentials', 'true'); } // Access-Control-Allow-Methods if (options.allowMethods) { ctx.set('Access-Control-Allow-Methods', options.allowMethods.join(',')); } // Access-Control-Allow-Headers if (options.allowHeaders) { ctx.set('Access-Control-Allow-Headers', options.allowHeaders.join(',')); } else { ctx.set('Access-Control-Allow-Headers', ctx.get('Access-Control-Request-Headers')); } ctx.status = 204; // No Content } else { // Request // Access-Control-Allow-Credentials if (options.credentials === true) { if (origin === '*') { // `credentials` can't be true when the `origin` is set to `*` ctx.remove('Access-Control-Allow-Credentials'); } else { ctx.set('Access-Control-Allow-Credentials', 'true'); } } // Access-Control-Expose-Headers if (options.exposeHeaders) { ctx.set('Access-Control-Expose-Headers', options.exposeHeaders.join(',')); } try { await next(); } catch (err) { throw err; } } }; };
参考:https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Headers/Access-Control-Request-Headers