The previous section implemented the express middleware. This section implements the error handling middleware.
If an error occurs during a certain step, it is uniformly stipulated that the parameter passed by calling next is the error message.
Let’s first look at the demo implemented by express
const express = require("express");
const app = express();
app.use("/", (req, res, next) => {
console.log("中间件1");
// next();
next("中间件1出错了");
});
app.use("/", (req, res, next) => {
console.log("中间件2");
next();
// next("中间件2出错了");
});
app.use("/", (req, res, next) => {
console.log("中间件3");
next();
// next("中间件3出错了");
});
app.get(
"/",
(req, res, next) => {
console.log("路由1");
next();
},
(req, res, next) => {
res.end("出错了 *****");
}
);
app.listen(3000, () => {
console.log(`server start 3000`);
console.log(`在线访问地址：http://localhost:3000/`);
});
Then go visit:http://localhost:3000/
The error handling intermediate price must have 4 parameters (take the length of the function) and put them at the bottom of the stack.
app.use((err, req, res, next) => {
res.end(err);
})
The processing logic is implemented below
router/index.js
const url = require("url");
const Route = require("./route");
const Layer = require("./layer");
const methods = require("methods");
function Router() {
// 维护所有的路由
this.stack = [];
}
Router.prototype.route = function (path) {
// 产生 route
let route = new Route();
// 产生 layer 让 layer 跟 route 进行关联
let layer = new Layer(path, route.dispatch.bind(route));
// 每个路由都具备一个 route 属性，稍后路径匹配到后会调用 route 中的每一层
layer.route = route;
// 把 layer 放到路由的栈中
this.stack.push(layer);
return route;
};
methods.forEach((method) => {
Router.prototype[method] = function (path, handlers) {
// 1.用户调用 method 时，需要保存成一个 layer 当道栈中
// 2.产生一个 Route 实例和当前的 layer 创造关系
// 3.要将 route 的 dispatch 方法存到 layer 上
let route = this.route(path);
// 让 route 记录用户传入的 handler 并且标记这个 handler 是什么方法
route[method](handlers);
};
});
Router.prototype.use = function (path, ...handlers) {
// 默认第一个是路径，后面是一个个的方法，路径可以不传
if (typeof path === "function") {
handlers.unshift(path);
path = "/";
}
// 如果是多个函数需要循环添加层
for (let i = 0; i < handlers.length; i++) {
let layer = new Layer(path, handlers[i]);
// 中间件不需要 route 属性
layer.route = undefined;
this.stack.push(layer);
}
};
Router.prototype.handle = function (req, res, out) {
console.log("请求到了");
// 需要取出路由系统中 Router 存放的 layer 依次执行
const {
pathname } = url.parse(req.url);
let idx = 0;
let next = (err) => {
// 遍历完后没有找到就直接走出路由系统
if (idx >= this.stack.length) return out();
let layer = this.stack[idx++];
if (err) {
console.log("统一对中间件跟路由错误处理");
// 找错误处理中间件
if (!layer.route) {
// 如果是中间件自己处理
layer.handle_error(err, req, res, next);
} else {
// 路由则跳过，继续携带错误向下执行
next(err);
}
} else {
// 需要判断 layer 上的 path 和当前请求路由是否一致，一致就执行 dispatch 方法
if (layer.match(pathname)) {
// 中间件没有方法可以匹配，不能是错误处理中间件
if (!layer.route) {
if (layer.handler.length !== 4) {
layer.handle_request(req, res, next);
} else {
next();
}
} else {
// 将遍历路由系统中下一层的方法传入
// 加速匹配，如果用户注册过这个类型的方法在去执行
if (layer.route.methods[req.method.toLowerCase()]) {
layer.handle_request(req, res, next);
} else {
next();
}
}
} else {
next();
}
}
};
next();
};
module.exports = Router;
layer.js
function Layer(path, handler) {
this.path = path;
this.handler = handler;
}
Layer.prototype.match = function (pathname) {
if (this.path === pathname) {
return true;
}
// 如果是中间件，进行中间件的匹配规则
if (!this.route) {
if (this.path == "/") {
return true;
}
// /aaaa/b 需要 /aaaa/ 才能匹配上
return pathname.startsWith(this.path + "/");
}
return false;
};
Layer.prototype.handle_error = function (err, req, res, next) {
if (this.handler.length === 4) {
// 调用错误处理中间件
return this.handler(err, req, res, next);
}
next(err); // 普通的中间件
};
Layer.prototype.handle_request = function (req, res, next) {
this.handler(req, res, next);
};
module.exports = Layer;
route.js
const Layer = require("./layer");
const methods = require("methods");
function Route() {
this.stack = [];
// 用来描述内部存过哪些方法
this.methods = {
};
}
Route.prototype.dispatch = function (req, res, out) {
// 稍后调用此方法时，回去栈中拿出对应的 handler 依次执行
let idx = 0;
console.log("this.stack----->", this.stack);
let next = (err) => {
// 如果内部迭代的时候出现错误，直接到外层的 stack 中
err && out(err);
// 遍历完后没有找到就直接走出路由系统
if (idx >= this.stack.length) return out();
let layer = this.stack[idx++];
console.log("dispatch----->", layer.method);
if (layer.method === req.method.toLowerCase()) {
layer.handle_request(req, res, next);
} else {
next();
}
};
next();
};
methods.forEach((method) => {
Route.prototype[method] = function (handlers) {
console.log("handlers----->", handlers);
handlers.forEach((handler) => {
// 这里的路径没有意义
let layer = new Layer("/", handler);
layer.method = method;
// 做个映射表
this.methods[method] = true;
this.stack.push(layer);
});
};
});
module.exports = Route;
test demo
const express = require("./kaimo-express");
const app = express();
app.use("/", (req, res, next) => {
console.log("中间件1");
next();
// next("中间件1出错了");
});
app.use("/", (req, res, next) => {
console.log("中间件2");
// next();
next("中间件2出错了");
});
app.use("/", (req, res, next) => {
console.log("中间件3");
next();
// next("中间件3出错了");
});
app.get(
"/",
(req, res, next) => {
console.log("路由1");
next();
},
(req, res, next) => {
res.end("出错了 *****");
}
);
// 错误处理中间价
app.use((err, req, res, next) => {
console.log("错误处理中间价----->", err);
res.end(err);
});
app.listen(3000, () => {
console.log(`server start 3000`);
console.log(`在线访问地址：http://localhost:3000/`);
});
