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{
  "name": "tracing_test",
  "version": "1.0.0",
  "main": "index.js",
  "author": "Leo Liang",
  "license": "MIT",
  "scripts": {
    "start": "node index.js"
  },
  "dependencies": {
    "async-local-storage": "^1.0.0"
  }
}

const context = require('async-local-storage');
const http = require('http');
const util = require('util');
const url = require('url');

function trace(...args) {
    let trace = context.get('trace');
    if (!trace) {
        trace = [];
        context.set('trace', trace);
    }
    const t = Date.now();
    trace.push(t + ': ' + args.join(' '));
}

function printTrace() {
    const trace = context.get('trace');
    const id = context.get('id');
    console.log('Trace of ID ', id);
    if (trace) {
        trace.forEach( line => console.log(line) );
    }
    console.log('-----');
}

const delay = util.promisify(setTimeout);

async function step1() {
    const id = context.get('id');
    trace('Step 1', id);
    await delay(Math.random() * 10000);
    return step2();
}

function step2() {
    const id = context.get('id');
    trace('Step 2', id);
    return 'Hello';
}

context.enable();

const server = http.createServer(async (req, res) => {
    const reqId = url.parse(req.url, true).query.id;
    trace('Received request. ID:', reqId);
    context.set('id', reqId);
    const content = await step1();
    res.write(content);
    res.end();
    trace('Response sent', reqId);
    printTrace();
});
server.listen(8080);

setInterval(() => {
    console.log('Number of contexts:', context.size());
}, 1000);

Trace of ID  1
1497340609369: Received request. ID: 1
1497340609369: Step 1 1
1497340610599: Step 2 1
1497340610602: Response sent 1
-----
Trace of ID  2
1497340606575: Received request. ID: 2
1497340606575: Step 1 2
1497340612700: Step 2 2
1497340612700: Response sent 2
-----