view rlgwebd.js @ 111:f56fdfeed01a

Replace taking over games with forced saves. Instead of reusing the id, just SIGHUP the game process. This works whether it is using polling, WebSockets, or dgamelaunch.
author John "Elwin" Edwards <elwin@sdf.org>
date Sun, 15 Jul 2012 22:33:44 -0700
parents 18a81cc0084b
children 4f2b89e6fde2
line wrap: on
line source

#!/usr/bin/env node

// If you can't quite trust node to find it on its own
var localModules = '/usr/local/lib/node_modules/';
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');
var daemon = require(path.join(localModules, "daemon"));
var pty = require(path.join(localModules, "pty.js"));
var WebSocketServer = require(path.join(localModules, "websocket")).server;

/* Configuration variables */
// These first two files are NOT in the chroot.
var ctlsocket = "/var/local/rlgwebd/ctl";
var logfile = "/var/local/rlgwebd/log";
var httpPort = 8080;
var chrootDir = "/var/dgl/";
var dropToUID = 501;
var dropToGID = 501;
var serveStaticRoot = "/var/www/"; // inside the chroot
var playtimeout = 3600000; // Idle time before games are autosaved, in ms

/* Data on the games available. */
var games = {
  "rogue3": {
    "name": "Rogue V3",
    "uname": "rogue3",
    "suffix": ".r3sav",
    "path": "/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": "/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": "/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": "/bin/srogue",
    "clear": new Buffer([27, 91, 72, 27, 91, 74]) // CSI H CSI J
  }
};

/* Global state */
var logins = {};
var sessions = {};
var clients = {};
var allowlogin = true;
var nextsession = 0;
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. */
  this.sessid = nextsession++;
  sessions[this.sessid] = 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 (index %d, pid %d)", this.pname, this.game.uname, 
            this.sessid, this.term.pid);
  this.emit('open', true, this.sessid);
  gamemux.emit('begin', this.sessid, this.pname, this.game.uname);
  /* Set up the lockfile and ttyrec */
  var ts = timestamp();
  var progressdir = "/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;
  logins[lkey].sessions.push(this.sessid);
  /* END setup */
  function ttyrec_chunk(datastr) {
    var ts = new Date();
    var buf = new Buffer(datastr);
    var chunk = new Buffer(buf.length + 12);
    /* TTYREC headers */
    chunk.writeUInt32LE(Math.floor(ts.getTime() / 1000), 0);
    chunk.writeUInt32LE(1000 * (ts.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 %d frame buffer at %d bytes", this.sessid, 
                this.framebuf.length);
      }
    }
    chunk.copy(this.framebuf, this.frameoff);
    this.frameoff += chunk.length;
  };
  this.write = function(data) {
    this.term.write(data);
  };
  // Teardown.
  this.term.on("exit", function () {
    fs.unlink(ss.lock);
    ss.record.end();
    ss.emit('exit');
    var id = ss.sessid;
    delete sessions[id];
    tslog("Game %s ended.", id);
    gamemux.emit('end', id);
  });
  this.close = function () {
    if (this.sessid in sessions)
      this.term.kill('SIGHUP');
  };
}
TermSession.prototype = new events.EventEmitter();

function Watcher(session) {
  var ss = this; // that
  this.session = session;
  this.alive = true;
  /* State for messaging. */
  this.nsend = 0;
  this.sendQ = [];
  /* Get a place in the table. */
  this.id = randkey(2);
  while (this.id in clients) {
    this.id = randkey(2);
  }
  clients[this.id] = this;
  /* Recreate the current screen state from the session's buffer. */
  this.sendQ.push({"t": "d", "n": this.nsend++, 
        "d": session.framebuf.toString("hex", 0, session.frameoff)});
  function dataH(buf) {
    var reply = {};
    reply.t = "d";
    reply.n = ss.nsend++;
    reply.d = buf.toString("hex");
    ss.sendQ.push(reply);
  }
  function exitH() {
    ss.alive = false;
    ss.sendQ.push({"t": "q"});
  }
  session.on('data', dataH);
  session.on('exit', exitH);
  this.read = function() {
    /* Returns an array of all outstanding messages, empty if none. */
    var temp = this.sendQ;
    this.sendQ = [];
    /* Clean up if finished. */
    if (!this.alive) {
      delete clients[this.id];
    }
    return temp;
  };
  this.quit = function() {
    this.session.removeListener('data', dataH);
    this.session.removeListener('exit', exitH);
    delete clients[this.id];
  };
}

function Player(gamename, lkey, dims, callback) {
  var ss = this;
  this.alive = false;
  /* State for messaging. */
  this.nsend = 0;
  this.nrecv = 0;
  this.sendQ = [];
  this.recvQ = []
  this.Qtimeout = null;
  /* Get a place in the table. */
  this.id = randkey(2);
  while (this.id in clients) {
    this.id = randkey(2);
  }
  clients[this.id] = this;

  this.read = function() {
    var temp = this.sendQ;
    this.sendQ = [];
    /* Clean up if finished. */
    if (!this.alive) {
      clearTimeout(this.Qtimeout);
      delete clients[this.id];
    }
    return temp;
  };
  this.write = function (data, n) {
    if (!this.alive || typeof (n) != "number") {
      return;
    }
    var oindex = n - this.nrecv;
    if (oindex === 0) {
      this.session.write(data);
      this.nrecv++;
      var next;
      while ((next = this.recvQ.shift()) !== undefined) {
        this.session.write(next);
        this.nrecv++;
      }
      if (this.recvQ.length == 0 && this.Qtimeout) {
        clearTimeout(this.Qtimeout);
        this.Qtimeout = null;
      }
    }
    else if (oindex > 0 && oindex <= 1024) {
      tslog("Client %s: Stashing message %d at %d", this.id,  n, oindex - 1);
      this.recvQ[oindex - 1] = data;
      if (!this.Qtimeout) {
        var nextn = this.nrecv + this.recvQ.length + 1;
        this.Qtimeout = setTimeout(this.flushQ, 30000, this, nextn);
      }
    }
    /* Otherwise, discard it */
    return;
  };
  this.flushQ = function (client, n) {
    /* Callback for when an unreceived message times out.
     * n is the first empty space that will not be given up on. */
    if (!client.alive || client.nrecv >= n)
      return;
    client.nrecv++;
    var next;
    /* Clear the queue up to n */
    while (client.nrecv < n) {
      next = client.recvQ.shift();
      if (next !== undefined)
        client.session.write(next);
      client.nrecv++;
    }
    /* Clear out anything that's ready. */
    while ((next = client.recvQ.shift()) !== undefined) {
      client.session.write(next);
      client.nrecv++;
    }
    /* Now set another timeout if necessary. */
    if (client.recvQ.length != 0) {
      var nextn = client.nrecv + client.recvQ.length + 1;
      client.Qtimeout = setTimeout(client.flushQ, 30000, client, nextn);
    }
    tslog("Flushing queue for player %s", player.id);
  };
  this.reset = function () {
    /* To be called when the game is taken over. */
    if (this.Qtimeout) {
      clearTimeout(this.Qtimeout);
      this.Qtimeout = null;
    }
    for (var i = 0; i < this.recvQ.length; i++) {
      if (this.recvQ[i] !== undefined) {
        this.session.write(this.recvQ[i]);
      }
    }
    this.recvQ = [];
    this.nrecv = 0;
    this.nsend = 0;
    this.sendQ = [{"t": "d", "n": this.nsend++, 
        "d": this.session.framebuf.toString("hex", 0, this.session.frameoff)}];
  };
  this.quit = function() {
    if (this.alive)
      this.session.close();
  };
  function openH(success, id) {
    if (success) {
      ss.alive = true;
      ss.session = sessions[id];
      ss.h = sessions[id].h;
      ss.w = sessions[id].w;
    }
    callback(ss, success);
  }
  function dataH(chunk) {
    var reply = {};
    reply.t = "d";
    reply.n = ss.nsend++;
    reply.d = chunk.toString("hex");
    ss.sendQ.push(reply);
  }
  function exitH() {
    ss.alive = false;
    ss.sendQ.push({"t": "q"});
  }
  var handlers = {'open': openH, 'data': dataH, 'exit': exitH};
  this.session = new TermSession(gamename, lkey, dims, handlers);
}

// 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.sessid in sessions)
      tslog("A WebSocket watcher has left game %d", session.sessid);
  });
  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, id) {
    if (success) {
      var reply = {"t": "s", "id": id, "w": sessions[id].w, "h": 
                   sessions[id].h, "p": sessions[id].pname, "g": game};
      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 = "/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(dropToUID) + "-" + 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 = 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 reaper() {
  var now = new Date();
  function reapcheck(session) {
    fs.fstat(session.record.fd, function (err, stats) {
      if (!err && now - stats.mtime > playtimeout) {
        tslog("Reaping session %s", session.sessid);
        /* Dissociate it with its login name. */
        var sn = logins[session.key].sessions.indexOf(session.sessid);
        if (sn >= 0) {
          logins[session.key].sessions.splice(sn, 1);
          if (now - logins[session.key].ts > playtimeout)
            logins[session.key].ts = new Date(now - playtimeout);
        }
        /* Shut it down. */
        session.close();
      }
    });
  }
  for (var sessid in sessions) {
    reapcheck(sessions[sessid]);
  }
  /* HELPME this is about as clever as I can code, so I can't tell whether
   * there are any bugs. */
  for (var lkey in logins) {
    if (logins[lkey].sessions.length == 0) {
      /* A login with no current games can be killed for inactivity. */
      if (now - logins[lkey].ts > playtimeout * 4) {
        tslog("Login for %s (key %s) timed out", logins[lkey].name, lkey);
        delete logins[lkey];
      }
    }
    else {
      /* Check for games that have terminated normally, and update
       * the timestamp. */
      var expired = [];
      var targarray = logins[lkey].sessions;
      /* Let's not find out what happens if you modify an array
       * you're iterating through. */
      for (var i = 0; i < targarray.length; i++) {
        if (!(targarray[i] in sessions))
          expired.push(targarray[i]);
      }
      if (expired.length > 0) {
        logins[lkey].ts = new Date(now);
        for (var j = 0; j < expired.length; j++) {
          targarray.splice(targarray.indexOf(expired[j]), 1);
        }
      }
    }
  }
}

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(), "sessions": []};
    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;
}

function startgame(req, res, formdata) {
  if (!allowlogin) {
    sendError(res, 6, null);
    return;
  }
  if (!("key" in formdata)) {
    sendError(res, 2, "No key given.");
    return;
  }
  else if (!("game" in formdata)) {
    sendError(res, 2, "No game specified.");
    return;
  }
  var lkey = String(formdata["key"]);
  if (!(lkey in logins)) {
    sendError(res, 1, null);
    return;
  }
  else {
    logins[lkey].ts = new Date();
  }
  var username = logins[lkey].name;
  var gname = formdata["game"];
  // If dims are not given or invalid, the constructor will handle it.
  var dims = [formdata["h"], formdata["w"]];
  if (!(gname in games)) {
    sendError(res, 2, "No such game: " + gname);
    tslog("Request for nonexistant game \"%s\"", gname);
    return;
  }
  // A callback to pass to the game-in-progress checker.
  var launch = function(err, fname) {
    var nodematch = new RegExp("^" + username + ":node:");
    if (fname && (fname.match(nodematch) === null)) {
      /* It's being played in dgamelaunch. */
      sendError(res, 4, "dgamelaunch");
      tslog("%s is already playing %s", username, gname);
      return;
    }
    // Game starting has been approved.
    var respondlaunch = function(nclient, success) {
      if (success) {
        res.writeHead(200, {'Content-Type': 'application/json'});
        var reply = {"t": "s", "id": nclient.id, "w": nclient.w, "h": 
                     nclient.h, "p": username, "g": gname};
        res.write(JSON.stringify(reply));
        res.end();
      }
      else {
        sendError(res, 5, "Failed to open TTY");
        tslog("Unable to allocate TTY for %s", gname);
      }
    };
    if (fname) {
      for (var cid in clients) {
        cli = clients[cid];
        if ((cli instanceof Player) && 
             cli.session.pname == username &&
             cli.session.game.uname == gname) {
          cli.reset();
          respondlaunch(cli, true);
          tslog("Game %d has been taken over.", cli.session.sessid);
          return;
        }
      }
      /* If there's no player, it's a WebSocket game, and shouldn't be 
       * seized. */
      sendError(res, 4, "WebSocket");
    }
    else {
      new Player(gname, lkey, dims, respondlaunch);
    }
  };
  checkprogress(username, games[gname], launch, []);
}

function watch(req, res, formdata) {
  if (!("n" in formdata)) {
    sendError(res, 2, "Game number not given");
    return;
  }
  var gamenumber = Number(formdata["n"]);
  if (!(gamenumber in sessions)) {
    sendError(res, 7);
    return;
  }
  var session = sessions[gamenumber];
  var watch = new Watcher(session);
  var reply = {"t": "w", "id": watch.id, "w": session.w, "h": session.h, 
               "p": session.pname, "g": session.game.uname};
  res.writeHead(200, {'Content-Type': 'application/json'});
  res.write(JSON.stringify(reply));
  res.end();
  tslog("Game %d is being watched (key %s)", gamenumber, watch.id);
}

/* Sets things up for a new user, like dgamelaunch's commands[register] */