websocket 2 rest api

需要开发一个prometheus 的exporter 使用jmespath 获取对应metrics的数据，并进行转换处理，但是因为那个服务
提供的接口是通过websoket 的实时api，所以基于node 进行了简单的包装处理，暴露为一个直接可以使用的rest api
同时保留了数据的实效性

实现技术

很简单，通过express 暴露一个rest api，通过websocket client 连接已有websocket 服务，并使用全局变量存储数据即可
后边对应的exporter 直接获取数据进行处理就可以了

项目结构

• 代码结构

├── Dockerfile
├── README.md
├── app.env
├── docker-compose.yaml
├── index.js
├── package.json

• 代码说明
  Dockerfile

FROM node:alpine
WORKDIR /app
COPY . /app
LABEL NORE="ws 2 rest"
ENV NODE_ENV=production
ENV WSADDRESS=ws://localhost:7890/
LABEL AUTHOR="1141591465@qq.com"
EXPOSE 3000
RUN yarn
CMD [ "yarn", "start"]

index.js: 核心处理代码，和简单，就是包装了websocket 服务

const express = require('express')
const app = express()

var realtimeMetrics ={};
const WebSocketClient = require('websocket').client;

// 通过环境变量配置websocket 服务的地址
const wsAddress = process.env.WSADDRESS || "ws://localhost:7890/"
const client = new WebSocketClient();

client.on('connectFailed', function(error) {
    console.log('Connect Error: ' + error.toString());
});

client.on('connect', function(connection) {
    console.log('WebSocket Client Connected');
    connection.on('error', function(error) {
        console.log("Connection Error: " + error.toString());
    });
    connection.on('close', function() {
        console.log('echo-protocol Connection Closed');
    });
    client.onopen = function() {
        console.log('WebSocket Client Connected');

        function sendNumber() {
            if (client.readyState === client.OPEN) {
                var number = Math.round(Math.random() * 0xFFFFFF);
                client.send(number.toString());
                setTimeout(sendNumber, 1000);
            }
        }
        sendNumber();
    };
    connection.on('message', function(message) {
        if (message.type === 'utf8') {
            console.log("Received: '" + message.utf8Data + "'");
            realtimeMetrics = message.utf8Data;
        }
    });
});

client.connect(wsAddress);
app.get('/', function (req, res) {
    res.contentType("application/json")
    res.send(realtimeMetrics)
})

app.listen(3000)

pacakge.json 内容: 主要是npn 包的引用以及npm script 配置，这个包含了几个多余的依赖，但是不影响使用
可以直接删除

{
  "dependencies": {
    "express": "^4.16.4",
    "jmespath": "^0.15.0",
    "node-fetch": "^2.3.0",
    "websocket": "^1.0.28"
  },
  "scripts": {
    "start":"node index.js"
  }
}

docker-compose.yaml

version: "3"
services:
    ws2rest:
      image: dalongrong/simplews2rest
      build: ./
      ports:
      - "3000:3000"
      env_file: 
      - app.env

app.env ： 主要是方便扩展的

WSADDRESS=ws://server:port/

使用此服务的demo

• docker-compose 文件

version: "3"
services:
  metrics:
   image: dalongrong/promethues-jmespath-exporter
   volumes: 
   - "./conf/config.yaml:/etc/prometheus-jsonpath-exporter/config.yml"
   ports:
   - "9158:9158"
   command: /etc/prometheus-jsonpath-exporter/config.yml
  ws2rest:
   image: dalongrong/simplews2rest
   environment:
   - "WSADDRESS=ws://server:7890/"
   ports: 
   - "3000:3000"

参考资料

https://github.com/rongfengliang/ws-rest
https://github.com/rongfengliang/promethues-jmespath-exporter-demo