koa实现请求转发

## koa实现请求转发

首先我们来用koa创建一个简单的服务：

```js
const Koa = require('koa')
const app = new Koa()
const port = process.env.PORT || 3000

app.listen(port, () => {
	console.log(`启动地址: http://localhost:${port}`)
})
```

给服务添加跨域需要的响应头：

```js
app.use(async (ctx, next) => {
	ctx.set("Access-Control-Allow-Origin", '*');
	ctx.set("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");
	ctx.set('Access-Control-Allow-Headers', '*');
	ctx.set("Access-Control-Allow-Credentials", "true");
    await next()
})
```

> 浏览器在跨域请求的时候会有`OPTIONS`预检请求

处理`OPTIONS`预检请求

```js
// ……
if (ctx.method === 'OPTIONS') {
    ctx.body = 200
} else {
    await next()
}
// ……
```

接下来我们使用 `http-proxy-middleware` 处理转发

```js
const { createProxyMiddleware } = require('http-proxy-middleware')
const k2c = require('koa2-connect')
const proxyList = [
	// 需要转发的请求地址
	'http://www.xxxx.com'
]
// ……

app.use(async (ctx, next) => {
	const url = ctx.path

if (url.startsWith('/_')) {
		ctx.response = false
		await k2c(
			createProxyMiddleware({
				target: proxyList[0],
				changeOrigin: true,
				ws: false,
				secure: false,
				pathRewrite: {
					'^/_': '/'
				}
			}),
		)(ctx, next)

return await next()
	}

return await next()
})
```

最终的代码
```js
const Koa = require('koa')
const { createProxyMiddleware } = require('http-proxy-middleware')
const k2c = require('koa2-connect')
const proxyList = [
	// 需要转发的请求地址
	'http://www.xxxx.com'
]
const port = process.env.PORT || 3000

const app = new Koa()

app.use(async (ctx, next) => {
	ctx.set("Access-Control-Allow-Origin", '*');
	ctx.set("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");
	ctx.set('Access-Control-Allow-Headers', '*');
	ctx.set("Access-Control-Allow-Credentials", "true");
	if (ctx.method === 'OPTIONS') {
		ctx.body = 200
	} else {
		await next()
	}
})

app.use(async (ctx, next) => {
	const url = ctx.path

return await next()
	}

return await next()
})

app.listen(port, () => {
	console.log(`启动地址: http://localhost:${port}`)
})
```

## nginx配置请求转发
nginx请求转发的配置详见另一篇文章
[nginx配置请求转发](https://nothankyou.cn/index.php/archives/83/)

本文由 tutustack 创作，采用知识共享署名4.0 国际许可协议进行许可
本站文章除注明转载/出处外，均为本站原创或翻译，转载前请务必署名