#!/usr/bin/env node

var http = require('http');
var net = require('net');
var url = require('url');
var path = require('path');
var fs = require('fs');
var events = require('events');
var child_process = require('child_process');
// Dependencies
var posix = require("posix");
var pty = require("pty.js");
var WebSocketServer = require("websocket").server;

/* Configuration variables */
// The first file is NOT in the chroot.
var ctlsocket = "/var/local/rlgwebd/ctl";
var httpPort = 8080;
var chrootDir = "/var/dgl/";
var dropToUser = "rodney";
var serveStaticRoot = "/var/www/"; // inside the chroot

/* Data on the games available. */
var games = {
  "rogue3": {
    "name": "Rogue V3",
    "uname": "rogue3",
    "suffix": ".r3sav",
    "path": "/usr/bin/rogue3",
    "clear": new Buffer([27, 91, 72, 27, 91, 50, 74]) // CSI H CSI 2J
  },
  "rogue4": {
    "name": "Rogue V4",
    "uname": "rogue4",
    "suffix": ".r4sav",
    "path": "/usr/bin/rogue4",
    "clear": new Buffer([27, 91, 72, 27, 91, 50, 74]) // CSI H CSI 2J
  },
  "rogue5": {
    "name": "Rogue V5",
    "uname": "rogue5",
    "suffix": ".r5sav",
    "path": "/usr/bin/rogue5",
    "clear": new Buffer([27, 91, 72, 27, 91, 50, 74]) // CSI H CSI 2J
  },
  "srogue": {
    "name": "Super-Rogue",
    "uname": "srogue",
    "suffix": ".srsav",
    "path": "/usr/bin/srogue",
    "clear": new Buffer([27, 91, 72, 27, 91, 50, 74]) // CSI H CSI 2J
  },
  "arogue5": {
    "name": "Advanced Rogue 5",
    "uname": "arogue5",
    "suffix": ".ar5sav",
    "path": "/usr/bin/arogue5",
    "clear": new Buffer([27, 91, 72, 27, 91, 50, 74]) // CSI H CSI 2J
  }
};

/* Global state */
var logins = {};
var sessions = {};
var dglgames = {};
var allowlogin = true;
var gamemux = new events.EventEmitter();

/* Constructor.  A TermSession handles a pty and the game running on it.
 *   game: (String) Name of the game to launch.
 *   lkey: (String, key) The user's id, a key into logins.
 *   dims: (Array [Number, Number]) Height and width of the pty.
 *   handlers: (Object) Key-value pairs, event names and functions to
 *           install to handle them.
 *  Events:
 *   "open": Emitted on startup.  Parameters: success (Boolean)
 *   "data": Data generated by child. Parameters: buf (Buffer)
 *   "exit": Child terminated. Parameters: none
 */
function TermSession(game, lkey, dims, handlers) {
  var ss = this;
  /* Subclass EventEmitter to do the hard work. */
  events.EventEmitter.call(this);
  for (var evname in handlers)
    this.on(evname, handlers[evname]);
  /* Don't launch anything that's not a real game. */
  if (game in games) {
    this.game = games[game];
  }
  else {
    this.emit('open', false);
    return;
  }
  if (lkey in logins) {
    this.key = lkey;
    this.pname = logins[lkey].name;
  }
  else {
    this.emit('open', false);
    return;
  }
  /* Grab a spot in the sessions table. */
  sessions[this.game.uname + "/" + this.pname] = this;
  /* Set up the sizes. */
  this.w = Math.floor(Number(dims[1]));
  if (!(this.w > 0 && this.w < 256))
    this.w = 80;
  this.h = Math.floor(Number(dims[0]));
  if (!(this.h > 0 && this.h < 256))
    this.h = 24;
  /* Environment. */
  var childenv = {};
  for (var key in process.env) {
    childenv[key] = process.env[key];
  }
  var args = ["-n", this.pname];
  var spawnopts = {"env": childenv, "cwd": "/", "rows": this.h, "cols": this.w,
                   "name": "xterm-256color"};
  this.term = pty.spawn(this.game.path, args, spawnopts);
  tslog("%s playing %s (pid %d)", this.pname, this.game.uname, this.term.pid);
  this.emit('open', true, this.game.uname, this.pname);
  gamemux.emit('begin', this.game.uname, this.pname);
  /* Set up the lockfile and ttyrec */
  this.lasttime = new Date();
  var ts = timestamp(this.lasttime);
  var progressdir = path.join("/dgldir/inprogress", this.game.uname);
  this.lock = path.join(progressdir, this.pname + ":node:" + ts + ".ttyrec");
  var lmsg = this.term.pid.toString() + '\n' + this.h + '\n' + this.w + '\n'; 
  fs.writeFile(this.lock, lmsg, "utf8"); 
  var ttyrec = path.join("/dgldir/ttyrec", this.pname, this.game.uname, 
               ts + ".ttyrec");
  this.record = fs.createWriteStream(ttyrec, { mode: 0664 });
  /* Holds the output since the last screen clear, so watchers can begin
   * with a complete screen. */
  this.framebuf = new Buffer(1024);
  this.frameoff = 0;
  /* END setup */
  function ttyrec_chunk(datastr) {
    ss.lasttime = new Date();
    var buf = new Buffer(datastr);
    var chunk = new Buffer(buf.length + 12);
    /* TTYREC headers */
    chunk.writeUInt32LE(Math.floor(ss.lasttime.getTime() / 1000), 0);
    chunk.writeUInt32LE(1000 * (ss.lasttime.getTime() % 1000), 4);
    chunk.writeUInt32LE(buf.length, 8);
    buf.copy(chunk, 12);
    ss.record.write(chunk);
    ss.framepush(buf);
    ss.emit('data', buf);
  }
  this.term.on("data", ttyrec_chunk);
  this.framepush = function(chunk) {
    /* If this chunk resets the screen, discard what preceded it. */
    if (bufncmp(chunk, this.game.clear, this.game.clear.length)) {
      this.framebuf = new Buffer(1024);
      this.frameoff = 0;
    }
    /* Make sure there's space. */
    while (this.framebuf.length < chunk.length + this.frameoff) {
      var nbuf = new Buffer(this.framebuf.length * 2);
      this.framebuf.copy(nbuf, 0, 0, this.frameoff);
      this.framebuf = nbuf;
      if (this.framebuf.length > 65536) {
        tslog("Warning: Game %s frame buffer at %d bytes", this.tag(), 
                this.framebuf.length);
      }
    }
    chunk.copy(this.framebuf, this.frameoff);
    this.frameoff += chunk.length;
  };
  this.write = function(data) {
    this.term.write(data);
  };
  this.tag = function() {
    return this.game.uname + "/" + this.pname;
  };
  // Teardown.
  this.term.on("exit", function () {
    var tag = ss.tag();
    fs.unlink(ss.lock);
    ss.record.end();
    ss.emit('exit');
    gamemux.emit('end', ss.game.uname, ss.pname);
    delete sessions[tag];
    tslog("Game %s ended.", tag);
  });
  this.close = function () {
    if (this.tag() in sessions)
      this.term.kill('SIGHUP');
  };
}
TermSession.prototype = new events.EventEmitter();

function DglSession(filename) {
  var ss = this;
  events.EventEmitter.call(this);
  var pathcoms = filename.split('/');
  this.gname = pathcoms[pathcoms.length - 2];
  if (!(this.gname in games)) {
    ss.emit('open', false);
    return;
  }
  var basename = pathcoms[pathcoms.length - 1];
  var firstsep = basename.indexOf(':');
  this.pname = basename.slice(0, firstsep);
  var fname = basename.slice(firstsep + 1);
  this.ttyrec = path.join("/dgldir/ttyrec", this.pname, this.gname, fname);
  /* Flag to prevent multiple handlers from reading simultaneously and
   * getting into a race. */
  this.reading = false;
  this.framebuf = new Buffer(1024);
  this.frameoff = 0;
  this.framepush = function(chunk) {
    /* If this chunk resets the screen, discard what preceded it. */
    var cgame = games[this.gname];
    if (bufncmp(chunk, cgame.clear, cgame.clear.length)) {
      tslog("DGL %s: clearing frame", ss.tag());
      this.framebuf = new Buffer(1024);
      this.frameoff = 0;
    }
    /* Make sure there's space. */
    while (this.framebuf.length < chunk.length + this.frameoff) {
      var nbuf = new Buffer(this.framebuf.length * 2);
      this.framebuf.copy(nbuf, 0, 0, this.frameoff);
      this.framebuf = nbuf;
      if (this.framebuf.length > 65536) {
        tslog("Warning: DGL %s frame buffer at %d bytes", this.tag(), 
                this.framebuf.length);
      }
    }
    chunk.copy(this.framebuf, this.frameoff);
    this.frameoff += chunk.length;
  };
  this.readchunk = function () {
    if (this.reading)
      return;
    this.reading = true;
    var header = new Buffer(12);
    fs.read(ss.fd, header, 0, 12, null, function (err, n, buf) {
      /* Stop recursion if end of file has been reached. */
      if (err || n < 12) {
        ss.reading = false;
        return;
      }
      var datalen = buf.readUInt32LE(8);
      //tslog("Allocating %d bytes", datalen);
      var databuf = new Buffer(datalen);
      fs.read(ss.fd, databuf, 0, datalen, null, function (err, n, buf) {
        ss.reading = false;
        if (err || n < datalen) {
          return;
        }
        /* Process the data */
        ss.framepush(buf);
        ss.emit("data", buf);
        tslog("DGL %s: %d bytes", ss.tag(), buf.length);
        /* Recurse. */
        ss.readchunk();
      });
    });
  };
  fs.readFile(filename, {encoding: "utf8"}, function (err, data) {
    if (err) {
      ss.emit('open', false);
      return;
    }
    var lines = data.split('\n');
    ss.h = Number(lines[1]);
    ss.w = Number(lines[2]);
    fs.open(ss.ttyrec, "r", function(err, fd) {
      if (err) {
        ss.emit('open', false);
      }
      else {
        ss.fd = fd;
        ss.emit('open', true);
        tslog("DGL %s: open", ss.tag());
        ss.readchunk();
        ss.watcher = fs.watch(ss.ttyrec, function (ev, finame) {
          if (ev == "change")
            ss.readchunk();
        });
      }
    });
  });
  this.tag = function () {
    return this.gname + "/" + this.pname;
  };
  this.close = function () {
    this.watcher.close()
    /* Ensure all data is handled before quitting. */
    this.readchunk();
    fs.close(this.fd);
    this.emit("close");
    tslog("DGL %s: closed", ss.tag());
  };
}
DglSession.prototype = new events.EventEmitter();

// Also known as WebSocketAndTermSessionClosureGlueFactory
function wsWatcher(conn, session) {
  var ss = this; // is this even needed?
  var dataH = function(buf) {
    conn.sendUTF(JSON.stringify({"t": "d", "d": buf.toString("hex")}));
  };
  var exitH = function() {
    if (conn.connected)
      conn.close();
  }
  session.on('data', dataH);
  session.on('exit', exitH);
  conn.on('close', function(code, desc) {
    session.removeListener('data', dataH);
    session.removeListener('exit', exitH);
    if (session.tag() in sessions)
      tslog("A WebSocket watcher has left game %s", session.tag());
  });
  conn.sendUTF(JSON.stringify({
            "t": "w", "w": session.w, "h": session.h, 
            "p": session.pname, "g": session.game.uname
  }));
  conn.sendUTF(JSON.stringify({"t": "d",
        "d": session.framebuf.toString("hex", 0, session.frameoff)}));
}

function wsPlay(wsReq, game, lkey, dims) {
  var conn;
  var session;
  /* Listeners on the WebSocket */
  function messageH(message) {
    var parsedMsg = getMsgWS(message);
    if (parsedMsg.t == 'q') {
      session.close();
    }
    else if (parsedMsg.t == 'd') {
      var hexstr = parsedMsg.d.replace(/[^0-9a-f]/gi, "");
      if (hexstr.length % 2 != 0) {
        hexstr = hexstr.slice(0, -1);
      }
      var keybuf = new Buffer(hexstr, "hex");
      session.write(keybuf);
    }
  }
  function closeH() {
    session.close();
  }
  /* These listen on the TermSession. */
  function openH(success, gname, pname) {
    if (success) {
      var tag = gname + "/" + pname;
      var reply = {"t": "s", "tag": tag, "w": sessions[tag].w, "h": 
                   sessions[tag].h, "p": pname, "g": gname};
      conn = wsReq.accept(null, wsReq.origin);
      conn.sendUTF(JSON.stringify(reply));
      conn.on('message', messageH);
      conn.on('close', closeH);
    }
    else {
      wsReq.reject(500, errorcodes[5]);
      tslog("Unable to allocate TTY for %s", game);
    }
  }
  function dataH(chunk) {
    var msg = {};
    msg.t = "d";
    msg.d = chunk.toString("hex");
    conn.sendUTF(JSON.stringify(msg));
  }
  function exitH() {
    if (conn.connected)
      conn.sendUTF(JSON.stringify({"t": "q"}));
    conn.close();
    session.removeListener('open', openH);
    session.removeListener('data', dataH);
    session.removeListener('exit', exitH);
  }
  var handlers = {'open': openH, 'data': dataH, 'exit': exitH};
  session = new TermSession(game, lkey, dims, handlers);
}

function wsStart(wsReq) {
  var playmatch = wsReq.resourceURL.pathname.match(/^\/play\/([^\/]*)$/);
  if (!playmatch[1] || !(playmatch[1] in games)) {
    wsReq.reject(404, errorcodes[2]);
    return;
  }
  var gname = playmatch[1];
  if (!allowlogin) {
    wsReq.reject(404, errorcodes[6]);
    return;
  }
  if (!("key" in wsReq.resourceURL.query)) {
    wsReq.reject(404, "No key given.");
    return;
  }
  var lkey = wsReq.resourceURL.query["key"];
  if (!(lkey in logins)) {
    wsReq.reject(404, errorcodes[1]);
    return;
  }
  var pname = logins[lkey].name;
  var dims = [wsReq.resourceURL.query.h, wsReq.resourceURL.query.w];
  function progcallback(err, fname) {
    if (fname) {
      wsReq.reject(404, errorcodes[4]);
      tslog("%s is already playing %s", pname, gname);
    }
    else
      wsPlay(wsReq, gname, lkey, dims);
  };
  checkprogress(pname, games[gname], progcallback, []);
}

/* Some functions which check whether a player is currently playing or 
 * has a saved game.  Maybe someday they will provide information on 
 * the game. */
function checkprogress(user, game, callback, args) {
  var progressdir = path.join("/dgldir/inprogress", game.uname);
  fs.readdir(progressdir, function(err, files) {
    if (err) {
      args.unshift(err, null);
      callback.apply(null, args);
      return;
    }
    var fre = RegExp("^" + user + ":");
    for (var i = 0; i < files.length; i++) {
      if (files[i].match(fre)) {
        args.unshift(null, files[i]);
        callback.apply(null, args);
        return;
      }
    }
    args.unshift(null, false);
    callback.apply(null, args);
  });
}

function checksaved(user, game, callback, args) {
  var savedirc = game.uname + "save";
  var basename = String(pwent.uid) + "-" + user + game.suffix;
  var savefile = path.join("/var/games/roguelike", savedirc, basename);
  fs.exists(savefile, function (exist) {
    args.unshift(exist);
    callback.apply(null, args);
  });
}

function playerstatus(user, callback) {
  var sdata = {};
  function finishp() {
    for (var gname in games) {
      if (!(gname in sdata))
        return;
    }
    callback(sdata);
  }
  function regsaved(exists, game) {
    if (exists)
      sdata[game.uname] = "s";
    else
      sdata[game.uname] = "0";
    finishp();
  }
  function regactive(err, filename, game) {
    if (!err && filename) {
      if (filename.match(/^[^:]*:node:/))
        sdata[game.uname] = "p";
      else
        sdata[game.uname] = "d";
      finishp();
    }
    else
      checksaved(user, game, regsaved, [game]);
  }
  for (var gname in games) {
    checkprogress(user, games[gname], regactive, [games[gname]]);
  }
}

/* A few utility functions */
function timestamp(dd) {
  if (!(dd instanceof Date)) {
    dd = new Date();
  }
  sd = dd.toISOString();
  sd = sd.slice(0, sd.indexOf("."));
  return sd.replace("T", ".");
}

function randkey(words) {
  if (!words || !(words > 0))
    words = 1;
  function rand32() {
    rnum = Math.floor(Math.random() * 65536 * 65536);
    hexstr = rnum.toString(16);
    while (hexstr.length < 8)
      hexstr = "0" + hexstr;
    return hexstr;
  }
  var key = "";
  for (var i = 0; i < words; i++)
    key += rand32();
  return key;
}

/* Compares two buffers, returns true for equality up to index n */
function bufncmp(buf1, buf2, n) {
  if (!Buffer.isBuffer(buf1) || !Buffer.isBuffer(buf2))
    return false;
  for (var i = 0; i < n; i++) {
    if (i == buf1.length && i == buf2.length)
      return true;
    if (i == buf1.length || i == buf2.length)
      return false;
    if (buf1[i] != buf2[i])
      return false;
  }
  return true;
}

function tslog() {
  arguments[0] = new Date().toISOString() + ": " + String(arguments[0]);
  console.log.apply(console, arguments);
}

/* Returns a list of the cookies in the request, obviously. */
function getCookies(req) {
  cookies = [];
  if ("cookie" in req.headers) {
    cookstrs = req.headers["cookie"].split("; ");
    for (var i = 0; i < cookstrs.length; i++) {
      eqsign = cookstrs[i].indexOf("=");
      if (eqsign > 0) {
        name = cookstrs[i].slice(0, eqsign).toLowerCase();
        val = cookstrs[i].slice(eqsign + 1);
        cookies[name] = val;
      }
      else if (eqsign < 0)
        cookies[cookstrs[i]] = null;
    }
  }
  return cookies;
}

function getMsg(posttext) {
  var jsonobj;
  if (!posttext)
    return {};
  try {
    jsonobj = JSON.parse(posttext);
  }
  catch (e) {
    if (e instanceof SyntaxError)
      return {};
  }
  if (typeof(jsonobj) != "object")
    return {};
  return jsonobj;
}

function getMsgWS(msgObj) {
  if (msgObj.type != "utf8")
    return {};
  return getMsg(msgObj.utf8Data);
}

function login(req, res, formdata) {
  if (!allowlogin) {
    sendError(res, 6, null, false);
    return;
  }
  if (!("name" in formdata)) {
    sendError(res, 2, "Username not given.", false);
    return;
  }
  else if (!("pw" in formdata)) {
    sendError(res, 2, "Password not given.", false);
    return;
  }
  var username = String(formdata["name"]);
  var password = String(formdata["pw"]);
  function checkit(code, signal) {
    /* Checks the exit status, see sqlickrypt.c for details. */
    if (code != 0) {
      sendError(res, 3);
      if (code == 1)
        tslog("Password check failed for user %s", username);
      else if (code == 2)
        tslog("Attempted login by nonexistent user %s", username);
      else
        tslog("Login failed: sqlickrypt error %d", code);
      return;
    }
    var lkey = randkey(2);
    while (lkey in logins)
      lkey = randkey(2);
    logins[lkey] = {"name": username, "ts": new Date()};
    res.writeHead(200, {'Content-Type': 'application/json'});
    var reply = {"t": "l", "k": lkey, "u": username};
    res.write(JSON.stringify(reply));
    res.end();
    tslog("%s has logged in (key %s)", username, lkey);
    return;
  }
  /* Launch the sqlickrypt utility to check the password. */
  var pwchecker = child_process.spawn("/bin/sqlickrypt", ["check"]);
  pwchecker.on("exit", checkit);
  pwchecker.stdin.end(username + '\n' + password + '\n', "utf8");
  return;
}

/* Sets things up for a new user, like dgamelaunch's commands[register] */
function regsetup(username) {
  function regsetup_l2(err) {
    for (var g in games) {
      fs.mkdir(path.join("/dgldir/ttyrec", username, games[g].uname), 0755);
    }
  }
  fs.mkdir(path.join("/dgldir/userdata", username), 0755);
  fs.mkdir(path.join("/dgldir/ttyrec/", username), 0755, regsetup_l2);
}

function register(req, res, formdata) {
  var uname, passwd, email;
  if (typeof (formdata.name) != "string" || formdata.name === "") {
    sendError(res, 2, "No name given.");
    return;
  }
  else
    uname = formdata["name"];
  if (typeof (formdata.pw) != "string" || formdata.pw === "") {
    sendError(res, 2, "No password given.");
    return;
  }
  else
    passwd = formdata["pw"];
  if (typeof (formdata.email) != "string" || formdata.email === "") {
    /* E-mail is optional */
    email = "nobody@nowhere.not";
  }
  else
    email = formdata["email"];
  function checkreg(code, signal) {
    if (code === 0) {
      var lkey = randkey(2);
      while (lkey in logins)
        lkey = randkey(2);
      logins[lkey] = {"name": uname, "ts": new Date()};
      var reply = {"t": "r", "k": lkey, "u": uname};
      res.writeHead(200, {'Content-Type': 'application/json'});
      res.write(JSON.stringify(reply));
      res.end();
      tslog("Added new user: %s", uname);
      regsetup(uname);
    }
    else if (code == 4) {
      sendError(res, 2, "Invalid characters in name or email.");
      tslog("Attempted registration: %s %s", uname, email);
    }
    else if (code == 1) {
      sendError(res, 2, "Username " + uname + " is already being used.");
      tslog("Attempted duplicate registration: %s", uname);
    }
    else {
      sendError(res, 0, null);
      tslog("sqlickrypt register failed with code %d", code);
    }
  }
  var child_adder = child_process.spawn("/bin/sqlickrypt", ["register"]);
  child_adder.on("exit", checkreg);
  child_adder.stdin.end(uname + '\n' + passwd + '\n' + email + '\n', "utf8");
  return;
}

/* Stops a running game if the request has the proper key. */
function stopgame(res, formdata) {
  if (!("key" in formdata) || !(formdata["key"] in logins)) {
    sendError(res, 1);
    return;
  }
  var pname = logins[formdata["key"]].name;
  if (!("g" in formdata) || !(formdata["g"] in games)) {
    sendError(res, 2, "No such game.");
    return;
  }
  var gname = formdata["g"];
  function checkback(err, fname) {
    if (!fname) {
      sendError(res, 7);
      return;
    }
    var fullfile = path.join("/dgldir/inprogress", gname, fname);
    fs.readFile(fullfile, "utf8", function(err, fdata) {
      if (err) {
        sendError(res, 7);
        return;
      }
      var pid = parseInt(fdata.split('\n')[0], 10);
      try {
        process.kill(pid, 'SIGHUP');
      }
      catch (err) {
        /* If the PID is invalid, the lockfile is stale. */
        if (err.code == "ESRCH") {
          var nodere = RegExp("^" + pname + ":node:");
          if (fname.match(nodere)) {
            fs.unlink(fullfile);
          }
        }
      }
      /* The response doesn't mean that the game is gone.  The only way
       * to make sure a dgamelaunch-supervised game is over would be to
       * poll fname until it disappears. */
      res.writeHead(200, {'Content-Type': 'application/json'});
      res.write(JSON.stringify({"t": "q"}));
      res.end();
    });
  }
  checkprogress(pname, games[gname], checkback, []);
}

function startProgressWatcher() {
  var watchdirs = [];
  for (var gname in games) {
    watchdirs.push(path.join("/dgldir/inprogress", gname));
  }
  var subproc = child_process.spawn("/bin/watcher", watchdirs);
  subproc.stdout.setEncoding('utf8');
  subproc.stdout.on('data', function (chunk) {
    var fname = chunk.slice(2, -1);
    var filere = /.*\/([^\/]*)\/([^\/:]*):(node:)?(.*)/;
    var matchresult = fname.match(filere);
    if (!matchresult || matchresult[3])
      return;
    var gname = matchresult[1];
    var pname = matchresult[2];
    var tag = gname + "/" + pname;
    if (chunk[0] == "E") {
      tslog("DGL: %s is playing %s: %s", pname, gname, fname)
      dglgames[tag] = new DglSession(fname);
    }
    else if (chunk[0] == "C") {
      tslog("DGL: %s started playing %s: %s", pname, gname, fname)
      dglgames[tag] = new DglSession(fname);
    }
    else if (chunk[0] == "D") {
      tslog("DGL: %s finished playing %s: %s", pname, gname, fname)
      dglgames[tag].close();
      delete dglgames[tag];
    }
    else {
      tslog("Watcher says: %s", chunk)
    }
  });
  subproc.stdout.resume();
  return subproc;
}

function serveStatic(req, res, fname) {
  var nname = path.normalize(fname);
  if (nname == "" || nname == "/")
    nname = "index.html";
  if (nname.match(/\/$/))
    path.join(nname, "index.html"); /* it was a directory */
  var realname = path.join(serveStaticRoot, nname);
  var extension = path.extname(realname);
  fs.exists(realname, function (exists) {
    var resheaders = {};
    if (!exists || !extension || extension == ".html")
      resheaders["Content-Type"] = "text/html; charset=utf-8";
    else if (extension == ".png")
      resheaders["Content-Type"] = "image/png";
    else if (extension == ".css")
      resheaders["Content-Type"] = "text/css";
    else if (extension == ".js")
      resheaders["Content-Type"] = "text/javascript";
    else if (extension == ".svg")
      resheaders["Content-Type"] = "image/svg+xml";
    else
      resheaders["Content-Type"] = "application/octet-stream";
    if (exists) {
      fs.readFile(realname, function (error, data) {
        if (error) {
          res.writeHead(500, {});
          res.end();
        }
        else {
          res.writeHead(200, resheaders);
          if (req.method != 'HEAD')
            res.write(data);
          res.end();
        }
      });
    }
    else {
      send404(res, nname, req.method == 'HEAD');
    }
  });
  return;
}

/* Currently, this doesn't do anything blocking, but keep the callback */