2ch API proxy

#!/usr/bin/env node

var createHmac = require('crypto').createHmac;
var fs = require('fs');
var https = require('https');
var http = require('http');
var path = require('path');
var stringify = require('querystring').stringify;
var url = require('url');

var USER_AGENT = 'Monazilla/1.00 (JaneStyle/3.81)';
var APP_KEY = 'aqMBM5paukkx5FOVcSfisMTMj8I4Dm';
var HM_KEY = 'CPGjWLXxFojVtO7tiu3Lrwm1yLqtk1';

var PORT = 8088;

var sessionFile = path.join(__dirname, 'session.txt');
var sessionExpire = 24 * 60 * 60 * 1000;
var headerList = [
  'accept-encoding',
  'if-modified-since',
  'range'
];

var _sid;

function authenticate() {
  var ct = '1234567890';
  var message = APP_KEY + ct;
  var hb = createHmac('sha256', HM_KEY).update(message).digest('hex');
  var data = { ID: '', PW: '', KY: APP_KEY, CT: ct, HB: hb };
  var headers = {
    'User-Agent': 'Monazilla/1.3',
    'X-2ch-UA': 'JaneStyle/3.81',
    'Content-Type': 'application/x-www-form-urlencoded'
  };
  var options = {
    'method': 'POST',
    'hostname': 'api.2ch.net',
    'path': '/v1/auth/',
    'headers': headers
  };

  https.request(options, function(response) {
    console.log('POST %s - %s', options.path, response.statusCode);

    var writeStream = fs.createWriteStream(sessionFile);
    writeStream.on('close', readSessionFile);
    response.pipe(writeStream);
  }).end(stringify(data));
}

function readSessionFile() {
  fs.readFile(sessionFile, { encoding: 'utf8' }, function(err, data) {
    _sid = data.split(':')[1];
  });
}

fs.stat(sessionFile, function(err, stat) {
  if (!err && stat && stat.mtime > new Date() - sessionExpire) {
    readSessionFile();
  } else {
    authenticate();
  }
});

var proxy = http.createServer(function(req, res) {
  var o = url.parse(req.url);
  if (o.href.match(/http:\/\/(\w+)\.2ch\.net\/(\w+)\/dat\/(\d+)\.dat/)) {
    var server = RegExp.$1;
    var board = RegExp.$2;
    var threadID = RegExp.$3;

    var message = '/v1/' + server + '/' + board + '/' + threadID;
    message += _sid + APP_KEY;
    var hobo = createHmac('sha256', HM_KEY).update(message).digest('hex');
    var data = { sid: _sid, hobo: hobo, appkey: APP_KEY };
    var headers = {
      'User-Agent': USER_AGENT,
      'Content-Type': 'application/x-www-form-urlencoded'
    };
    headerList.forEach(function(key) {
      if (key in req.headers) headers[key] = req.headers[key];
    });
    var options = {
      'method': 'POST',
      'hostname': 'api.2ch.net',
      'path': '/v1/' + server + '/' + board + '/' + threadID,
      'headers': headers
    };

    return https.request(options, function(response) {
      console.log('POST %s - %s', options.path, response.statusCode);

      res.writeHead(response.statusCode, response.headers);
      response.pipe(res);
    }).end(stringify(data));
  }

  o.method = req.method;
  o.headers = req.headers;
  req.pipe(http.request(o, function(response) {
    res.writeHead(response.statusCode, response.headers);
    response.pipe(res);
  }));
});

proxy.on('clientError', function(err, sock) {
  console.log(err);
  sock.end();
});

proxy.listen(PORT, function() {
  console.log('proxy server is listening on port %d', proxy.address().port);
});