Difference between revisions of "Mediawiki LocalServer"

Revision as of 20:37, 26 March 2008

Mediawiki offline support thanks to Google Gears

This is an attempt to provide an offline version of the wiki using Google Gears LocalServer.
Inspired by this blog post

To be able to use Mediawiki offline, the Mediawiki website has to have this extension installed and the browser has to have the Google Gears extension.

The original blog post was quick and dirty (do it in less than one hour), but too dirty for me:

There was always a complete replication of the full wiki as soon as some change occurred
There was no way to know if we were viewing the offline or the online version of a page
There was no way to temporarily disable the offline pages
It implied hacking the Mediawiki code

So I rewrote it as a Mediawiki extension and tried to overcome the mentioned problems.
Note that it is done for the default style MonoBook.

Documentation

Bits I found useful for this task:

the original idea
http://code.google.com/apis/gears/api_localserver.html
The Google Gears inspector:

svn checkout http://google-gears.googlecode.com/svn/trunk/gears/inspector google-gears-read-only

http://www.mediawiki.org/wiki/Manual:MediaWiki_hooks

Google Gears browser extension

You must first install the plugin available here, note that it does a stupid browser detection and refuses my Iceweasel 2.0 so I had to cheat with my User Agent Switch extension and mimick Firefox 2.0 ;-)

Google Gears LocalServer extension

/extensions/GGears/

Create a folder GGears in your MediaWiki extensions directory
As I'm using rewriting rules, I had to add to /etc/apache2/sites-available/wiki.yobi.be:

RewriteCond %{REQUEST_URI} !/GGears/

gears_init.js

Download the gears_init.js from the Google Gears web site and place it in the newly created folder

localserver.js

Create localserver.js:

// Change this to set the name of the managed resource store to create.
// You use the name with the createManagedStore, and removeManagedStore,
// and openManagedStore APIs. It isn't visible to the user.
var STORE_NAME = "yobiwiki";

// Change this to set the URL of tha manifest file, which describe which
// URLs to capture. It can be relative to the current page, or an
// absolute URL.
var MANIFEST_FILENAME = "/extensions/GGears/manifest.php";

var localServer;
var store;
var blink=false;

// Called onload to initialize local server and store variables
function initStore() {
  if (!window.google || !google.gears) {
//    textOut("Google Gears not found");
  return;
  }
  localServer = google.gears.factory.create("beta.localserver");
  store = localServer.openManagedStore(STORE_NAME);
  if (!store) {
    textOut("No store found");
  } else {
    // Here is the place to touch the manifestUrl, if required
    textOut("");
  }
  menuStore();
}

// Create (or open&update) the managed resource store
function createStore() {
  if (!window.google || !google.gears) {
    alert("You must install Google Gears first.");
    return;
  }
  store = localServer.createManagedStore(STORE_NAME);
  if (!store) {
    textOut("Error creating store");
  } else {
    store.manifestUrl = MANIFEST_FILENAME;
    textOut("Downloading...");
    hideItem("t-createStore");
    showItem("t-removeStore");
  }
  updateStore();
}

// Update the managed resource store
function updateStore() {
  if (!window.google || !google.gears) {
    alert("You must install Google Gears first.");
    return;
  }

  store.checkForUpdate();

  var timerId = window.setInterval(function() {
    // When the currentVersion property has a value, all of the resources
    // listed in the manifest file for that version are captured. There is
    // an open bug to surface this state change as an event.
    if (store.currentVersion) {
      window.clearInterval(timerId);
      textOut("Sync done!\n" +
              "Version: " +
              store.currentVersion + "\n" +
              "Refreshing...");
      menuStore();
      setTimeout("location.reload(true)", 2000);
    } else if (store.updateStatus == 3) {
      window.clearInterval(timerId);
      textOut("Error: " + store.lastErrorMessage);
    } else {
      textBlink();
    }
  }, 500);
}

// Remove the managed resource store.
function removeStore() {
  if (!window.google || !google.gears || !store) {
    return;
  }
  localServer.removeManagedStore(STORE_NAME);
  textOut("Store removed\n" +
          "Refreshing...");
  hideItem("t-createStore");
  hideItem("t-updateStore");
  hideItem("t-removeStore");
  hideItem("t-enableStore");
  hideItem("t-disableStore");
  setTimeout("location.reload(true)", 2000);
}

function enableStore() {
  if (!window.google || !google.gears || !store) {
    return;
  }
  store.enabled = true;
  menuStore();
  setTimeout("location.reload(true)", 5);
}

function disableStore() {
  if (!window.google || !google.gears || !store) {
    return;
  }
  store.enabled = false;
  menuStore();
  setTimeout("location.reload(true)", 5);
}

// Utility function to output some status text.
function textOut(s) {
 var elm = document.getElementById("t-textStore");
  while (elm.firstChild) {
    elm.removeChild(elm.firstChild);
  } 
  elm.appendChild(document.createTextNode(s));
  elm.style.fontWeight='normal';
  blink=false;
}

function textBlink() {
 var elm = document.getElementById("t-textStore");
  if (blink) {
    elm.style.fontWeight='normal';
    blink=false;
  } else {
    elm.style.fontWeight='bold';
    blink=true;
  }
}

// update the menu entries according to the current state
function menuStore() {
  showItem("p-ggears");
  if (!store) {
    showItem("t-createStore");
    hideItem("t-updateStore");
    hideItem("t-removeStore");
    hideItem("t-enableStore");
    hideItem("t-disableStore");
  } else {
    hideItem("t-createStore");
    showItem("t-updateStore");
    showItem("t-removeStore");
    if (store.enabled) {
      hideItem("t-enableStore");
      showItem("t-disableStore");
    } else {
      hideItem("t-disableStore");
      showItem("t-enableStore");
    }
  }
}

function showItem(s) {
 var elm = document.getElementById(s);
  elm.style.display='';
}

function hideItem(s) {
 var elm = document.getElementById(s);
  elm.style.display='none';
}

Modify the store name in this localserver.js to what you want:

var STORE_NAME = "mymediawiki";

manifest.php

Create the manifest.php that will create the file list on the fly (based on access to the database):
Make sure to list all your static resources (css, js, images,...)

{
  "betaManifestVersion": 1,
<?php
require_once("../../DBSettings.php");

$l = mysql_connect($wgDBserver,$wgDBuser,$wgDBpassword);
mysql_selectdb($wgDBname);
$q = "SELECT max(rc_timestamp) from ".$wgDBprefix."recentchanges";
$r = mysql_query($q);
$t = mysql_fetch_row($r);
echo '  "version": "' . $t[0] . 'a",';
?>

  "entries": [
<?php
$q = "SELECT page_title FROM ".$wgDBprefix."page;";
$r = mysql_query($q);
while ($t = mysql_fetch_row($r))
{
    echo '    { "url": "/wiki/' . $t[0] . '" },'."\n";
}
?>
    { "url": "/skins/common/shared.css?97"},
    { "url": "/skins/common/commonPrint.css?97"},
    { "url": "/skins/common/wikibits.js?97"},
    { "url": "/skins/common/ajax.js?97"},
    { "url": "/skins/common/ajaxsearch.js?97"},
    { "url": "/skins/common/ajaxwatch.js?97"},
    { "url": "/skins/common/images/poweredby_mediawiki_88x31.png"},
    { "url": "/skins/common/images/gnu-fdl.png"},
    { "url": "/skins/monobook/main.css?97"},
    { "url": "/skins/monobook/headbg.jpg"},
    { "url": "/skins/monobook/external.png"},
    { "url": "/skins/monobook/bullet.gif"},
    { "url": "/skins/monobook/user.gif"},
    { "url": "/index.php?title=-&action=raw&smaxage=0&gen=js&useskin=monobook"},
    { "url": "/index.php?title=MediaWiki:Common.css&usemsgcache=yes&action=raw&ctype=text/css&smaxage=18000"},
    { "url": "/index.php?title=MediaWiki:Monobook.css&usemsgcache=yes&action=raw&ctype=text/css&smaxage=18000"},
    { "url": "/index.php?title=-&action=raw&gen=css&maxage=18000&smaxage=0"},
    { "url": "/local/yobiwiki-pub.png"},
    { "url": "/extensions/GGears/localserver.js"},
    { "url": "/extensions/GGears/gears_init.js"}
  ]
}

Note that I moved my DB settings from LocalSettings.php to DBSettings.php, replaced now by a

require_once("DBSettings.php");

Otherwise you've to duplicate the following vars in your manifest.php:

$wgDBserver
$wgDBuser
$wgDBpassword
$wgDBname
$wgDBprefix

localserver.php

Create the localserver.php as our Mediawiki extension:

<?php

if (defined('MEDIAWIKI')) {


function fnMyGGearsHookStyle() {
    return <<<EOS
<style type='text/css'>
#t-offStore {
  color: #7d7d7d;
}
#t-textStore {
  color: #ba0000;
}
#p-ggears {
  display: none;
}
</style>
EOS;
}

function fnMyGGearsHookJS($out) {
    $gearjs='<script type="text/javascript" src="/extensions/GGears/gears_init.js"></script>';
    $out->addScript($gearjs);
    $gearjs='<script type="text/javascript" src="/extensions/GGears/localserver.js"></script>';
    $out->addScript($gearjs);
    $out->addHeadItem('myggearsstyle', fnMyGGearsHookStyle());
    return true;
}

function fnMyGGearsHookBox() {
    echo "\n".'</ul>'."\n";
    echo '</div>'."\n";
    echo '</div>'."\n";
    echo '<div class="portlet" id="p-ggears">'."\n";
    echo '<h5>Gears LocalServer</h5>'."\n";
    echo '<div id="t-ggears" class="pBody">'."\n";
    echo '<ul>'."\n";
    echo '<li id="t-createStore"><a href="#" onclick="createStore();">create Store</a></li>'."\n";
    echo '<li id="t-updateStore"><a href="#" onclick="createStore();">update Store</a></li>'."\n";
    echo '<li id="t-enableStore"><a href="#" onclick="enableStore();">enable Store</a></li>'."\n";
    echo '<li id="t-disableStore"><a href="#" onclick="disableStore();">disable Store</a></li>'."\n";
    echo '<li id="t-removeStore"><a href="#" onclick="removeStore();">remove Store</a></li>'."\n";
    echo '<span id="t-offStore">'."\n";
    // If we are called by Google Gears, let's stamp the page as "OFFLINE"
    if (isset($_SERVER['HTTP_X_GEARS_GOOGLE'])) {
        define('GGearsOffline');
        echo 'OFFLINE copy<br>'."\n";
    }
    echo '</span>'."\n";
    echo '<span id="t-textStore"></span>'."\n";
    echo '<script type="text/javascript">/*<![CDATA[*/ initStore(); /*]]>*/</script>'."\n";
    return true;
}

$wgExtensionCredits['other'][] = array('name' => 'GGears',
                           'version' => '0.1',
                           'author' => 'Philippe Teuwen',
//                         'url' => 'http://www.mediawiki.org/wiki/Extension:LocalServer',
                           'url' => 'http://wiki.yobi.be/Mediawiki_LocalServer',
                           'description' => 'Allows to work offline with Google Gears');
$wgHooks['BeforePageDisplay'][] = 'fnMyGGearsHookJS';
$wgHooks['MonoBookTemplateToolboxEnd'][] = 'fnMyGGearsHookBox';
}

?>

At the end of LocalSettings.php, add a link to the new extension:

require_once("$IP/extensions/GGears/localserver.php");

What is missing

What I wanted

What is crudely missing in the Google Gears API is a way to avoid to fetch all the pages at each new revision of the manifest.
Initially I made a manifest which accepts as argument the current version of the local Store and produces a list of the pages new or changed since.
But then GGears deletes all the other pages from the Store :-(

See this discussion

What I'd like to see:

One version per URL instead of one per manifest
- Very clean solution, manifest independent of the client state
Or sth like that: given the version of the client Store the manifest could be generated on-the-fly with some:

{ "url": "/path/to/page","refresh": false }

Current hack

So the current solution cannot avoid fetching all pages, the best we can achieve is to return a HTTP/1.0 304 Not Modified as often as possible.

By default Mediawiki honors properly If-Modified-Since except that for logged users it invalidates the cache for all the pages every time one page is edited :-(
This is supposedly to refresh all the things around a wikipage (headers, menus, footers,...) but for our offline version we prefer not to fetch the whole wiki just because we saved one single page.
So the ugly hack (ugly because not possible from the extension hooks): modify includes/User.php:

function validateCache( $timestamp ) {
    $this->load();
    // If we are called by Google Gears, don't care about minor modifs
    // concerning the current user.
    if (isset($_SERVER['HTTP_X_GEARS_GOOGLE']))
        return true;
    return ($timestamp >= $this->mTouched);
}

This still requires about 30s to query 200 of my wiki pages (instead of 85s + some more bandwidth for the initial download)
That means after every single edition I've to wait 30s then to reload the current page to see my changes :-(

Archived manifest.php, for the future?

Just in case, here is the manifest.php I tried to make with those assumptions in mind:

{
  "betaManifestVersion": 1,
<?php
require_once("../../DBSettings.php");
// We can get the version of the current DB to output only the
// pages changes since then, otherwise we dump all pages
$since = 0;
if (isset($_GET['since']) && is_numeric($_GET['since'])) {
    $since = $_GET['since'];
}
//error_log(date(DATE_RFC822).": since: ". $since . "\n", 3, './log.txt');

$l = mysql_connect($wgDBserver,$wgDBuser,$wgDBpassword);
mysql_selectdb($wgDBname);
$q = "SELECT max(rc_timestamp) from ".$wgDBprefix."recentchanges";
$r = mysql_query($q);
$t = mysql_fetch_row($r);
echo '  "version": "' . $t[0] . 'a",';
?>

  "entries": [
<?php
$q = "SELECT page_title FROM ".$wgDBprefix."page WHERE page_touched > ".$since.";";
$r = mysql_query($q);
while ($t = mysql_fetch_row($r))
{
    echo '    { "url": "/wiki/' . $t[0] . '" },'."\n";
}

// Just removing unchanged pages is not ok as they will be removed from the Store :-(
$q = "SELECT page_title FROM ".$wgDBprefix."page WHERE page_touched <= ".$since.";";
$r = mysql_query($q);
while ($t = mysql_fetch_row($r))
{
// Ideally I'd like to see sth like that to tell to keep the current page from the Store:
//    echo '    { "url": "/wiki/' . $t[0] . '","refresh": false },'."\n";
// But since the option doesn't exist in GGears, we've to fetch all pages again...
    echo '    { "url": "/wiki/' . $t[0] . '" },'."\n";
}
// Add also all the static ressources: css, images, js,...
?>
    { "url": "/extensions/GGears/localserver.js"},
    { "url": "/extensions/GGears/gears_init.js"}
  ]
}

With in initStore() and createStore() (localserver.js):

store.manifestUrl = MANIFEST_FILENAME + '?since=' + store.currentVersion;

BTW I tried another hack with some

   { "url": "/wiki/OnePage", "src": ".../notmodified.php" },

and notmodified.php being a simple script returning a 304 error

<php header( "HTTP/1.0 304 Not Modified" ); ?>

but GGears stores locally under the name of the src and not the name of the url (which makes some sense), so this attempt failed too.

TODO

check on clients who don't have ggears
check on clients who have ggears but don't use it on this wiki
check on clients who don't have javascript (#p-ggears {display:none} by default & remove it from js?)
on saving page: the page displayed is not up-to-date, we've to wait for the full sync and then only a refresh will display the latest revision.
We can get it faster by disabling the Store but then subsequent editions won't update the store anymore.
Maybe we could work (when online) always with Store disabled and with forced uploadStore() on save page...
could we find weird but cleaner way to return the error 304 via mediawiki extension hooks?
see Google Gears + Greasemonkey to take Wikipedia offline