gistfile1.js

/*
 * RSS Subscription Count Node.js Proxy Server
 * Devon Govett
 * Public Domain
 *
 * This script is a simple proxy server for my blog's RSS feed that keeps track of requests
 * to the feed and attempts to guess a subscriber count.
 * Google Reader represents the majority of my subscriber base, and they give you actual
 * subscriber numbers when their spider requests your feed.  Other aggregators do something similar.
 * Otherwise, this script tracks unique IP addresses over a 24 hour period.
 *
 * Data is saved on an hourly basis into data.json, as well as when the script is about to exit.
 * When it is relaunched, it attempts to restore the information in that file.
 * Once per day, a log of the subscriber information for that day is appended to subscribers.txt.
 *
 * Hopefully this script is of use to others.  I'm sure it can be improved, so feel free to fork away!
 */

// configuration
var USERNAME = 'username';
var PASSWORD = 'password';
var RSS_URL  = 'http://example.com/feed.xml';

var express = require('express');
var request = require('request');
var fs = require('fs');

var ONE_DAY = 1000 * 60 * 60 * 24;
var data = {
    ips: {},
    googleReader: {},
    otherAgs: {}
};

// try reading current subscriber data from the file
try {
    data = JSON.parse(fs.readFileSync('data.json'));
    var stat = fs.statSync('data.json');
    
    // clear IPs if too old
    if (stat.mtime < Date.now() - ONE_DAY) {
        data.ips = {};
    }
} catch (e) {};

var app = express();
app.get('/', function(req, res) {
    var userAgent = req.headers['user-agent'];
    var match;
    
    // Google Reader sends subscriber count in the User-Agent header
    // It also sends a feed-id parameter for uniqueness
    // see http://support.google.com/reader/bin/answer.py?hl=en&answer=70001
    if (userAgent && (match = userAgent.match(/([0-9]+) subscribers?; feed-id=([0-9]+)/i))) {
        var subscribers = match[1], feedId = match[2];
        data.googleReader[feedId] = +subscribers;
    }

    // Some other aggregators send the subscribers but no feed-id
    else if (userAgent && (match = userAgent.match(/([0-9]+) (?:subscribers?|readers?)/i))) {
        var subscribers = match[1];
        data.otherAgs[userAgent.replace(/([0-9]+) (?:subscribers?|readers?)/i, '')] = +subscribers;
    }
    
    // Otherwise, track unique IP addresses
    else {
        // use the x-forwarded-for header if you're behind a reverse proxy like I am
        data.ips[req.headers['x-forwarded-for'] || req.connection.remoteAddress] = 1;
    }
    
    // Send the actual feed
    req.pipe(request(RSS_URL)).pipe(res);
});

// right aligns a number
function pad(s) {
    return (Array(7).join(' ') + s).slice(-7);
}

// sums the values of an object
function sum(o) {
    var sum = 0;
    for (var k in o)
        sum += o[k];
    
    return sum;
}

// stats page (up to the minute)
app.get('/stats', express.basicAuth(USERNAME, PASSWORD), function(req, res) {
    var googleReader = sum(data.googleReader),
        otherAgs = sum(data.otherAgs),
        direct = sum(data.ips),
        total = googleReader + otherAgs + direct;
        
    res.type('text');

    res.write('Subscribers For Today:\n');
    res.write('--------------------------\n');
    res.write('Google Reader:     ' + pad(googleReader) + '\n');
    res.write('Other aggregators: ' + pad(otherAgs) + '\n');
    res.write('Direct:            ' + pad(direct) + '\n');
    res.write('--------------------------\n');
    res.write('TOTAL:             ' + pad(total));

    res.end();
});

// clear the unique IP addresses and write subscriber logs once per day
setInterval(function() {
    // write subscriber logs
    var fd = fs.openSync('subscribers.txt', 'a');
    
    var googleReader = sum(data.googleReader),
        otherAgs = sum(data.otherAgs),
        direct = sum(data.ips),
        total = googleReader + otherAgs + direct;
    
    fs.writeSync(fd,
        new Date() + 
        ' -- Google Reader: ' + googleReader +
        ', Other aggregators: ' + otherAgs +
        ', Direct: ' + direct +
        ', TOTAL: ' + total +
        '\n'
    );
                
    fs.closeSync(fd);
    
    // clear IPS
    data.ips = {};
}, ONE_DAY);

// write the current data to a file once an hour, and when the program exits
function write() {
    fs.writeFileSync('data.json', JSON.stringify(data));
}

setInterval(write, 1000 * 60 * 60);
process.on('SIGINT', function() {
    write();
    process.exit();
});

app.listen(3000);