nodeJs--koa2 REST API

 

REST API规范

编写REST API，实际上就是编写处理HTTP请求的async函数，不过，REST请求和普通的HTTP请求有几个特殊的地方：

1. REST请求仍然是标准的HTTP请求，但是，除了GET请求外，POST、PUT等请求的body是JSON数据格式，请求的Content-Type为application/json；
2. REST响应返回的结果是JSON数据格式，因此，响应的Content-Type也是application/json。

1、工程结构

2、目录详解

package.json:项目描叙

{
    "name": "rest-koa",
    "version": "1.0.0",
    "description": "rest-koa project",
    "main": "app.js",
    "scripts": {
        "dev": "node --use_strict app.js"
    },
    "keywords": [
        "koa",
        "rest",
        "api"
    ],
    "author": "david pan",
    "dependencies": {
        "koa": "2.0.0",
        "koa-bodyparser": "3.2.0",
        "koa-router": "7.0.0"
    }
}

(1). controller.js--- 路由集中处理

const fs = require('fs');

// add url-route in /controllers:

function addMapping(router, mapping) {
    for (var url in mapping) {
        if (url.startsWith('GET ')) {
            var path = url.substring(4);
            router.get(path, mapping[url]);
            console.log(`register URL mapping: GET ${path}`);
        } else if (url.startsWith('POST ')) {
            var path = url.substring(5);
            router.post(path, mapping[url]);
            console.log(`register URL mapping: POST ${path}`);
        } else if (url.startsWith('PUT ')) {
            var path = url.substring(4);
            router.put(path, mapping[url]);
            console.log(`register URL mapping: PUT ${path}`);
        } else if (url.startsWith('DELETE ')) {
            var path = url.substring(7);
            router.del(path, mapping[url]);
            console.log(`register URL mapping: DELETE ${path}`);
        } else {
            console.log(`invalid URL: ${url}`);
        }
    }
}

function addControllers(router, dir) {
    fs.readdirSync(__dirname + '/' + dir).filter((f) => {
        return f.endsWith('.js');
    }).forEach((f) => {
        console.log(`process controller: ${f}...`);
        let mapping = require(__dirname + '/' + dir + '/' + f);
        addMapping(router, mapping);
    });
}

module.exports = function (dir) {
    let
        controllers_dir = dir || 'controllers',
        router = require('koa-router')();
    addControllers(router, controllers_dir);
    return router.routes();
};

(2). rest.js--- 支持rest的中间件middleware

a.定义错误码的统一处理

b.统一输出REST

如果每个异步函数都编写下面这样的代码：

// 设置Content-Type:
ctx.response.type = 'application/json';
// 设置Response Body:
ctx.response.body = {
    products: products
};

很显然，这样的重复代码很容易导致错误，例如，写错了字符串'application/json'，或者漏写了ctx.response.type = 'application/json'，都会导致浏览器得不到JSON数据。

写这个中间件给ctx添加一个rest()方法，直接输出JSON数据

module.exports = {
    APIError: function (code, message) {
        this.code = code || 'internal:unknown_error';
        this.message = message || '';
    },
    restify: (pathPrefix) => {
        pathPrefix = pathPrefix || '/api/';
        return async (ctx, next) => {
            if (ctx.request.path.startsWith(pathPrefix)) {
                console.log(`Process API ${ctx.request.method} ${ctx.request.url}...`);
                ctx.rest = (data) => {
                    ctx.response.type = 'application/json';
                    ctx.response.body = data;
                }
                try {
                    await next();
                } catch (e) {
                    console.log('Process API error...');
                    ctx.response.status = 400;
                    ctx.response.type = 'application/json';
                    ctx.response.body = {
                        code: e.code || 'internal:unknown_error',
                        message: e.message || ''
                    };
                }
            } else {
                await next();
            }
        };
    }
};

(3). controllers/api.js--- rest api的定义

具体的api定义，这里可以优化下：不同模块建立文件夹，如products/Api.js, car/api.js ...这样更清晰

const products = require('../model/products');

const APIError = require('../rest').APIError;

module.exports = {
    'GET /api/products': async (ctx, next) => {
        ctx.rest({
            products: products.getProducts()
        });
    },

    'POST /api/products': async (ctx, next) => {
        var p = products.createProduct(ctx.request.body.name, ctx.request.body.manufacturer, parseFloat(ctx.request.body.price));
        ctx.rest(p);
    },

    'DELETE /api/products/:id': async (ctx, next) => {
        console.log(`delete product ${ctx.params.id}...`);
        var p = products.deleteProduct(ctx.params.id);
        if (p) {
            ctx.rest(p);
        } else {
            throw new APIError('400', 'product not found by id.');
        }
    }
};

(4). model/products.js--- 具体的model逻辑处理

模拟数据库操作

// store products as database:

var id = 0;

function nextId() {
    id++;
    return 'p' + id;
}

function Product(name, manufacturer, price) {
    this.id = nextId();
    this.name = name;
    this.manufacturer = manufacturer;
    this.price = price;
}

var products = [
    new Product('iPhone 7', 'Apple', 6800),
    new Product('ThinkPad T440', 'Lenovo', 5999),
    new Product('LBP2900', 'Canon', 1099)
];

module.exports = {
    getProducts: () => {
        return products;
    },

    getProduct: (id) => {
        var i;
        for (i = 0; i < products.length; i++) {
            if (products[i].id === id) {
                return products[i];
            }
        }
        return null;
    },

    createProduct: (name, manufacturer, price) => {
        var p = new Product(name, manufacturer, price);
        products.push(p);
        return p;
    },

    deleteProduct: (id) => {
        var
            index = -1,
            i;
        for (i = 0; i < products.length; i++) {
            if (products[i].id === id) {
                index = i;
                break;
            }
        }
        if (index >= 0) {
            // remove products[index]:
            return products.splice(index, 1)[0];
        }
        return null;
    }
};

3、postman调试

npm run dev

postman测试增、查、删