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// Determines the current time (with a +/- 1 second tolerance) | |
// by making HTTP requests to the hosts specified in hostnames.txt. | |
// | |
// Assumes unanimity. If a single host's clock is off by more than | |
// two seconds, it'll invalidate the whole operation. | |
// | |
// $ node time.js | |
const fs = require('fs'); | |
const http = require('http'); | |
function getDateFromHost(hostname) { | |
return new Promise(function(resolve, reject) { | |
http.get({ hostname }, function(res) { | |
resolve(res.headers.date); | |
}).on('error', reject); | |
}); | |
} | |
function guessTimeFromInterwebz(hostnames) { | |
return Promise.all(hostnames.map(getDateFromHost)) | |
.then(function(dates) { | |
const times = dates | |
.filter(function(d) { return !!d; }) | |
.map( function(d) { return (new Date(d)).getTime() }); | |
const min = Math.min.apply(Math, times); | |
const max = Math.max.apply(Math, times); | |
const diff = max - min; | |
if (diff <= 2000) | |
return new Date((min + max) / 2); | |
else | |
return null; | |
}) | |
} | |
const hostnames = fs.readFileSync('hostnames.txt') | |
.toString() | |
.split("\n") | |
.filter(function(line) { | |
return line.length > 0; | |
}); | |
guessTimeFromInterwebz(hostnames) | |
.then(function(time) { | |
if (time) | |
console.log(time.toISOString()); | |
else | |
console.error('Could not accurately determine the time.'); | |
}) | |
.catch(console.error); |
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