explore-services/services/cache/mecache/cache.js

'use strict';

let express = require('express');
let app = express();
let mcache = require('memory-cache');
const request = require('superagent');
const prom = require('prom-client');

let cors = require('cors');
app.use(cors());

const register = new prom.Registry();

const responses = new prom.Counter({
    name: 'cache_http_responses_total',
    help: 'A counter for cache response codes for every API request.',
    labelNames: ['url', 'code'],
    registers: [register]
});

const histogram = new prom.Histogram({
    name: 'cache_http_request_duration_seconds',
    help: 'A Histogram for cache. Providing information about API request and load latency in seconds.',
    labelNames: ['url'],
    registers: [register],
    buckets: [0.1, 0.2, 0.5, 1, 2]
});

let cache = (duration) => {
    return (req, res, next) => {
        let key = '__express__' + req.originalUrl || req.url
        console.log(req.originalUrl || req.url);
        let cachedBody = mcache.get(key);
        if (cachedBody) {
            res.send(JSON.parse(cachedBody))
        } else {
            res.sendResponse = res.send;
            res.send = (body) => {
                if (res.statusCode === 200) {
                    mcache.put(key, body, duration * 1000);
                }
                res.sendResponse(body)

            };
            next();
        }
    };
};


app.get('/metrics', (req, res) => {
    res.set('Content-Type', register.contentType);
    res.end(register.metrics());
});

app.get('/get', cache(30), cors(), (req, res) => {
    setTimeout(() => {
        const url = (req.query) ? req.query.url : null;
        if (!url) {
            responses.inc({url: null, code: 404});
            res.status(404).send(getResponse(404, "Not Found ")) //not found
        } else {
            request.get(url, function (err, response) {
                // res.header("Access-Control-Allow-Origin", "http://localhost:3000");
                res.header("Access-Control-Allow-Headers", "Origin, Content-Type,  Content-Length");
                res.header("Access-Control-Allow-Methods", "GET,  OPTIONS");
                res.header("Access-Control-Allow-Methods", "GET,  OPTIONS");
                res.header("Content-Type", "application/json");
                if (!response && err) {
                    res.status(500).send(getResponse(500, "An error occurred for " + url))
                } else {
                    const end = histogram.startTimer({url: url});
                    res.status(response.status).send(response.body);
                    res.on('finish', function () {
                        responses.inc({url: url, code: res.statusCode});
                        end();
                    });
                }
            })
        }
    })
});

app.use((req, res) => {
    res.status(404).send(getResponse(404, "Not Found")); //not found
});

app.listen((process.env.PORT) ? process.env.PORT : 3000, function () {
    console.log(`Example app listening on port ${process.env.PORT}!`)
});

function getResponse(code, message) {
    var response = {};
    response["code"] = code;
    response["message"] = message;
    return response;

}