lib/activity.php

   1 <?php
   2 /**
   3  * StatusNet, the distributed open-source microblogging tool
   4  *
   5  * An activity
   6  *
   7  * PHP version 5
   8  *
   9  * LICENCE: This program is free software: you can redistribute it and/or modify
  10  * it under the terms of the GNU Affero General Public License as published by
  11  * the Free Software Foundation, either version 3 of the License, or
  12  * (at your option) any later version.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU Affero General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Affero General Public License
  20  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  21  *
  22  * @category  Feed
  23  * @package   StatusNet
  24  * @author    Evan Prodromou <evan@status.net>
  25  * @author    Zach Copley <zach@status.net>
  26  * @copyright 2010 StatusNet, Inc.
  27  * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPLv3
  28  * @link      http://status.net/
  29  */
  30
  31 if (!defined('STATUSNET')) {
  32     exit(1);
  33 }
  34
  35 /**
  36  * An activity in the ActivityStrea.ms world
  37  *
  38  * An activity is kind of like a sentence: someone did something
  39  * to something else.
  40  *
  41  * 'someone' is the 'actor'; 'did something' is the verb;
  42  * 'something else' is the object.
  43  *
  44  * @category  OStatus
  45  * @package   StatusNet
  46  * @author    Evan Prodromou <evan@status.net>
  47  * @copyright 2010 StatusNet, Inc.
  48  * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPLv3
  49  * @link      http://status.net/
  50  */
  51 class Activity
  52 {
  53     const SPEC   = 'http://activitystrea.ms/spec/1.0/';
  54     const SCHEMA = 'http://activitystrea.ms/schema/1.0/';
  55     const MEDIA  = 'http://purl.org/syndication/atommedia';
  56
  57     const VERB       = 'verb';
  58     const OBJECT     = 'object';
  59     const ACTOR      = 'actor';
  60     const SUBJECT    = 'subject';
  61     const OBJECTTYPE = 'object-type';
  62     const CONTEXT    = 'context';
  63     const TARGET     = 'target';
  64
  65     const ATOM = 'http://www.w3.org/2005/Atom';
  66
  67     const AUTHOR    = 'author';
  68     const PUBLISHED = 'published';
  69     const UPDATED   = 'updated';
  70
  71     const RSS = null; // no namespace!
  72
  73     const PUBDATE     = 'pubDate';
  74     const DESCRIPTION = 'description';
  75     const GUID        = 'guid';
  76     const SELF        = 'self';
  77     const IMAGE       = 'image';
  78     const URL         = 'url';
  79
  80     const DC = 'http://purl.org/dc/elements/1.1/';
  81
  82     const CREATOR = 'creator';
  83
  84     const CONTENTNS = 'http://purl.org/rss/1.0/modules/content/';
  85     const ENCODED = 'encoded';
  86
  87     public $actor;   // an ActivityObject
  88     public $verb;    // a string (the URL)
  89     public $objects = array();  // an array of ActivityObjects
  90     public $target;  // an ActivityObject
  91     public $context; // an ActivityObject
  92     public $time;    // Time of the activity
  93     public $link;    // an ActivityObject
  94     public $entry;   // the source entry
  95     public $feed;    // the source feed
  96
  97     public $summary; // summary of activity
  98     public $content; // HTML content of activity
  99     public $id;      // ID of the activity
 100     public $title;   // title of the activity
 101     public $categories = array(); // list of AtomCategory objects
 102     public $enclosures = array(); // list of enclosure URL references
 103     public $attachments = array(); // list of attachments
 104
 105     public $extra = array(); // extra elements as array(tag, attrs, content)
 106     public $source;  // ActivitySource object representing 'home feed'
 107     public $selfLink; // <link rel='self' type='application/atom+xml'>
 108     public $editLink; // <link rel='edit' type='application/atom+xml'>
 109
 110     /**
 111      * Turns a regular old Atom <entry> into a magical activity
 112      *
 113      * @param DOMElement $entry Atom entry to poke at
 114      * @param DOMElement $feed  Atom feed, for context
 115      */
 116     function __construct($entry = null, $feed = null)
 117     {
 118         if (is_null($entry)) {
 119             return;
 120         }
 121
 122         // Insist on a feed's root DOMElement; don't allow a DOMDocument
 123         if ($feed instanceof DOMDocument) {
 124             throw new ClientException(
 125                 // TRANS: Client exception thrown when a feed instance is a DOMDocument.
 126                 _('Expecting a root feed element but got a whole XML document.')
 127             );
 128         }
 129
 130         $this->entry = $entry;
 131         $this->feed  = $feed;
 132
 133         if ($entry->namespaceURI == Activity::ATOM &&
 134             $entry->localName == 'entry') {
 135             $this->_fromAtomEntry($entry, $feed);
 136         } else if ($entry->namespaceURI == Activity::RSS &&
 137                    $entry->localName == 'item') {
 138             $this->_fromRssItem($entry, $feed);
 139         } else if ($entry->namespaceURI == Activity::SPEC &&
 140                    $entry->localName == 'object') {
 141             $this->_fromAtomEntry($entry, $feed);
 142         } else {
 143             // Low level exception. No need for i18n.
 144             throw new Exception("Unknown DOM element: {$entry->namespaceURI} {$entry->localName}");
 145         }
 146     }
 147
 148     function _fromAtomEntry($entry, $feed)
 149     {
 150         $pubEl = $this->_child($entry, self::PUBLISHED, self::ATOM);
 151
 152         if (!empty($pubEl)) {
 153             $this->time = strtotime($pubEl->textContent);
 154         } else {
 155             // XXX technically an error; being liberal. Good idea...?
 156             $updateEl = $this->_child($entry, self::UPDATED, self::ATOM);
 157             if (!empty($updateEl)) {
 158                 $this->time = strtotime($updateEl->textContent);
 159             } else {
 160                 $this->time = null;
 161             }
 162         }
 163
 164         $this->link = ActivityUtils::getPermalink($entry);
 165
 166         $verbEl = $this->_child($entry, self::VERB);
 167
 168         if (!empty($verbEl)) {
 169             $this->verb = trim($verbEl->textContent);
 170         } else {
 171             $this->verb = ActivityVerb::POST;
 172             // XXX: do other implied stuff here
 173         }
 174
 175         // get immediate object children
 176
 177         $objectEls = ActivityUtils::children($entry, self::OBJECT, self::SPEC);
 178
 179         if (count($objectEls) > 0) {
 180             foreach ($objectEls as $objectEl) {
 181                 // Special case for embedded activities
 182                 $objectType = ActivityUtils::childContent($objectEl, self::OBJECTTYPE, self::SPEC);
 183                 if (!empty($objectType) && $objectType == ActivityObject::ACTIVITY) {
 184                     $this->objects[] = new Activity($objectEl);
 185                 } else {
 186                     $this->objects[] = new ActivityObject($objectEl);
 187                 }
 188             }
 189         } else {
 190             // XXX: really?
 191             $this->objects[] = new ActivityObject($entry);
 192         }
 193
 194         $actorEl = $this->_child($entry, self::ACTOR);
 195
 196         if (!empty($actorEl)) {
 197             // Standalone <activity:actor> elements are a holdover from older
 198             // versions of ActivityStreams. Newer feeds should have this data
 199             // integrated straight into <atom:author>.
 200
 201             $this->actor = new ActivityObject($actorEl);
 202
 203             // Cliqset has bad actor IDs (just nickname of user). We
 204             // work around it by getting the author data and using its
 205             // id instead
 206
 207             if (!preg_match('/^\w+:/', $this->actor->id)) {
 208                 $authorEl = ActivityUtils::child($entry, 'author');
 209                 if (!empty($authorEl)) {
 210                     $authorObj = new ActivityObject($authorEl);
 211                     $this->actor->id = $authorObj->id;
 212                 }
 213             }
 214         } else if ($authorEl = $this->_child($entry, self::AUTHOR, self::ATOM)) {
 215
 216             // An <atom:author> in the entry overrides any author info on
 217             // the surrounding feed.
 218             $this->actor = new ActivityObject($authorEl);
 219
 220         } else if (!empty($feed) &&
 221                    $subjectEl = $this->_child($feed, self::SUBJECT)) {
 222
 223             // Feed subject is used for things like groups.
 224             // Should actually possibly not be interpreted as an actor...?
 225             $this->actor = new ActivityObject($subjectEl);
 226
 227         } else if (!empty($feed) && $authorEl = $this->_child($feed, self::AUTHOR,
 228                                                               self::ATOM)) {
 229
 230             // If there's no <atom:author> on the entry, it's safe to assume
 231             // the containing feed's authorship info applies.
 232             $this->actor = new ActivityObject($authorEl);
 233         }
 234
 235         $contextEl = $this->_child($entry, self::CONTEXT);
 236
 237         if (!empty($contextEl)) {
 238             $this->context = new ActivityContext($contextEl);
 239         } else {
 240             $this->context = new ActivityContext($entry);
 241         }
 242
 243         $targetEl = $this->_child($entry, self::TARGET);
 244
 245         if (!empty($targetEl)) {
 246             $this->target = new ActivityObject($targetEl);
 247         }
 248
 249         $this->summary = ActivityUtils::childContent($entry, 'summary');
 250         $this->id      = ActivityUtils::childContent($entry, 'id');
 251         $this->content = ActivityUtils::getContent($entry);
 252
 253         $catEls = $entry->getElementsByTagNameNS(self::ATOM, 'category');
 254         if ($catEls) {
 255             for ($i = 0; $i < $catEls->length; $i++) {
 256                 $catEl = $catEls->item($i);
 257                 $this->categories[] = new AtomCategory($catEl);
 258             }
 259         }
 260
 261         foreach (ActivityUtils::getLinks($entry, 'enclosure') as $link) {
 262             $this->enclosures[] = $link->getAttribute('href');
 263         }
 264
 265         // From APP. Might be useful.
 266
 267         $this->selfLink = ActivityUtils::getLink($entry, 'self', 'application/atom+xml');
 268         $this->editLink = ActivityUtils::getLink($entry, 'edit', 'application/atom+xml');
 269     }
 270
 271     function _fromRssItem($item, $channel)
 272     {
 273         $verbEl = $this->_child($item, self::VERB);
 274
 275         if (!empty($verbEl)) {
 276             $this->verb = trim($verbEl->textContent);
 277         } else {
 278             $this->verb = ActivityVerb::POST;
 279             // XXX: do other implied stuff here
 280         }
 281
 282         $pubDateEl = $this->_child($item, self::PUBDATE, self::RSS);
 283
 284         if (!empty($pubDateEl)) {
 285             $this->time = strtotime($pubDateEl->textContent);
 286         }
 287
 288         if ($authorEl = $this->_child($item, self::AUTHOR, self::RSS)) {
 289             $this->actor = ActivityObject::fromRssAuthor($authorEl);
 290         } else if ($dcCreatorEl = $this->_child($item, self::CREATOR, self::DC)) {
 291             $this->actor = ActivityObject::fromDcCreator($dcCreatorEl);
 292         } else if ($posterousEl = $this->_child($item, ActivityObject::AUTHOR, ActivityObject::POSTEROUS)) {
 293             // Special case for Posterous.com
 294             $this->actor = ActivityObject::fromPosterousAuthor($posterousEl);
 295         } else if (!empty($channel)) {
 296             $this->actor = ActivityObject::fromRssChannel($channel);
 297         } else {
 298             // No actor!
 299         }
 300
 301         $this->title = ActivityUtils::childContent($item, ActivityObject::TITLE, self::RSS);
 302
 303         $contentEl = ActivityUtils::child($item, self::ENCODED, self::CONTENTNS);
 304
 305         if (!empty($contentEl)) {
 306             // <content:encoded> XML node's text content is HTML; no further processing needed.
 307             $this->content = $contentEl->textContent;
 308         } else {
 309             $descriptionEl = ActivityUtils::child($item, self::DESCRIPTION, self::RSS);
 310             if (!empty($descriptionEl)) {
 311                 // Per spec, <description> must be plaintext.
 312                 // In practice, often there's HTML... but these days good
 313                 // feeds are using <content:encoded> which is explicitly
 314                 // real HTML.
 315                 // We'll treat this following spec, and do HTML escaping
 316                 // to convert from plaintext to HTML.
 317                 $this->content = htmlspecialchars($descriptionEl->textContent);
 318             }
 319         }
 320
 321         $this->link = ActivityUtils::childContent($item, ActivityUtils::LINK, self::RSS);
 322
 323         // @fixme enclosures
 324         // @fixme thumbnails... maybe
 325
 326         $guidEl = ActivityUtils::child($item, self::GUID, self::RSS);
 327
 328         if (!empty($guidEl)) {
 329             $this->id = $guidEl->textContent;
 330
 331             if ($guidEl->hasAttribute('isPermaLink') && $guidEl->getAttribute('isPermaLink') != 'false') {
 332                 // overwrites <link>
 333                 $this->link = $this->id;
 334             }
 335         }
 336
 337         $this->objects[] = new ActivityObject($item);
 338         $this->context   = new ActivityContext($item);
 339     }
 340
 341     /**
 342      * Returns an Atom <entry> based on this activity
 343      *
 344      * @return DOMElement Atom entry
 345      */
 346
 347     function toAtomEntry()
 348     {
 349         return null;
 350     }
 351
 352     /**
 353      * Returns an array based on this activity suitable
 354      * for encoding as a JSON object
 355      *
 356      * @return array $activity
 357      */
 358
 359     function asArray()
 360     {
 361         $activity = array();
 362
 363         // actor
 364         $activity['actor'] = $this->actor->asArray();
 365
 366         // content
 367         $activity['content'] = $this->content;
 368
 369         // generator <-- We could use this when we know a notice is created
 370         //               locally. Or if we know the upstream Generator.
 371
 372         // icon <-- possibly a mini object representing verb?
 373
 374         // id
 375         $activity['id'] = $this->id;
 376
 377         // object
 378
 379         if (count($this->objects) == 0) {
 380             common_log(LOG_ERR, "Can't save " . $this->id);
 381         } else {
 382             if (count($this->objects) > 1) {
 383                 common_log(LOG_WARNING, "Ignoring " . (count($this->objects) - 1) . " extra objects in JSON output for activity " . $this->id);
 384             }
 385             $object = $this->objects[0];
 386
 387             if ($object instanceof Activity) {
 388                 // Sharing a post activity is more like sharing the original object
 389                 if ($this->verb == 'share' && $object->verb == 'post') {
 390                     // XXX: Here's one for the obfuscation record books
 391                     $object = $object->object;
 392                 }
 393             }
 394
 395             $activity['object'] = $object->asArray();
 396
 397             if ($object instanceof Activity) {
 398                 $activity['object']['objectType'] = 'activity';
 399             }
 400
 401             foreach ($this->attachments as $attachment) {
 402                 if (empty($activity['object']['attachments'])) {
 403                     $activity['object']['attachments'] = array();
 404                 }
 405                 $activity['object']['attachments'][] = $attachment->asArray();
 406             }
 407         }
 408
 409         // Context stuff.
 410
 411         if (!empty($this->context)) {
 412
 413             if (!empty($this->context->location)) {
 414                 $loc = $this->context->location;
 415
 416                 $activity['location'] = array(
 417                     'objectType' => 'place',
 418                     'position' => sprintf("%+02.5F%+03.5F/", $loc->lat, $loc->lon),
 419                     'lat' => $loc->lat,
 420                     'lon' => $loc->lon
 421                 );
 422
 423                 $name = $loc->getName();
 424
 425                 if ($name) {
 426                     $activity['location']['displayName'] = $name;
 427                 }
 428
 429                 $url = $loc->getURL();
 430
 431                 if ($url) {
 432                     $activity['location']['url'] = $url;
 433                 }
 434             }
 435
 436             $activity['to']      = $this->context->getToArray();
 437
 438             $ctxarr = $this->context->asArray();
 439
 440             if (array_key_exists('inReplyTo', $ctxarr)) {
 441                 $activity['object']['inReplyTo'] = $ctxarr['inReplyTo'];
 442                 unset($ctxarr['inReplyTo']);
 443             }
 444
 445             if (!array_key_exists('status_net', $activity)) {
 446                 $activity['status_net'] = array();
 447             }
 448
 449             foreach ($ctxarr as $key => $value) {
 450                 $activity['status_net'][$key] = $value;
 451             }
 452         }
 453
 454         // published
 455         $activity['published'] = self::iso8601Date($this->time);
 456
 457         // provider
 458         $provider = array(
 459             'objectType' => 'service',
 460             'displayName' => common_config('site', 'name'),
 461             'url' => common_root_url()
 462         );
 463
 464         $activity['provider'] = $provider;
 465
 466         // target
 467         if (!empty($this->target)) {
 468             $activity['target'] = $this->target->asArray();
 469         }
 470
 471         // title
 472         $activity['title'] = $this->title;
 473
 474         // updated <-- Optional. Should we use this to indicate the time we r
 475         //             eceived a remote notice? Probably not.
 476
 477         // verb
 478
 479         $activity['verb'] = ActivityVerb::canonical($this->verb);
 480
 481         // url
 482         $activity['url'] = $this->id;
 483
 484         /* Purely extensions hereafter */
 485
 486         if ($activity['verb'] == 'post') {
 487             $tags = array();
 488             foreach ($this->categories as $cat) {
 489                 if (mb_strlen($cat->term) > 0) {
 490                     // Couldn't figure out which object type to use, so...
 491                     $tags[] = array('objectType' => 'http://activityschema.org/object/hashtag',
 492                                     'displayName' => $cat->term);
 493                 }
 494             }
 495             if (count($tags) > 0) {
 496                 $activity['object']['tags'] = $tags;
 497             }
 498         }
 499
 500         // XXX: a bit of a hack... Since JSON isn't namespaced we probably
 501         // shouldn't be using 'statusnet:notice_info', but this will work
 502         // for the moment.
 503
 504         foreach ($this->extra as $e) {
 505             list($objectName, $props, $txt) = $e;
 506             if (!empty($objectName)) {
 507                 $parts = explode(":", $objectName);
 508                 if (count($parts) == 2 && $parts[0] == "statusnet") {
 509                     if (!array_key_exists('status_net', $activity)) {
 510                         $activity['status_net'] = array();
 511                     }
 512                     $activity['status_net'][$parts[1]] = $props;
 513                 } else {
 514                     $activity[$objectName] = $props;
 515                 }
 516             }
 517         }
 518
 519         return array_filter($activity);
 520     }
 521
 522     function asString($namespace=false, $author=true, $source=false)
 523     {
 524         $xs = new XMLStringer(true);
 525         $this->outputTo($xs, $namespace, $author, $source);
 526         return $xs->getString();
 527     }
 528
 529     function outputTo($xs, $namespace=false, $author=true, $source=false, $tag='entry')
 530     {
 531         if ($namespace) {
 532             $attrs = array('xmlns' => 'http://www.w3.org/2005/Atom',
 533                            'xmlns:thr' => 'http://purl.org/syndication/thread/1.0',
 534                            'xmlns:activity' => 'http://activitystrea.ms/spec/1.0/',
 535                            'xmlns:georss' => 'http://www.georss.org/georss',
 536                            'xmlns:ostatus' => 'http://ostatus.org/schema/1.0',
 537                            'xmlns:poco' => 'http://portablecontacts.net/spec/1.0',
 538                            'xmlns:media' => 'http://purl.org/syndication/atommedia',
 539                            'xmlns:statusnet' => 'http://status.net/schema/api/1/');
 540         } else {
 541             $attrs = array();
 542         }
 543
 544         $xs->elementStart($tag, $attrs);
 545
 546         if ($tag != 'entry') {
 547             $xs->element('activity:object-type', null, ActivityObject::ACTIVITY);
 548         }
 549
 550         if ($this->verb == ActivityVerb::POST && count($this->objects) == 1 && $tag == 'entry') {
 551
 552             $obj = $this->objects[0];
 553                         $obj->outputTo($xs, null);
 554
 555         } else {
 556             $xs->element('id', null, $this->id);
 557
 558             if ($this->title) {
 559                 $xs->element('title', null, $this->title);
 560             } else {
 561                 // Require element
 562                 $xs->element('title', null, "");
 563             }
 564
 565             $xs->element('content', array('type' => 'html'), $this->content);
 566
 567             if (!empty($this->summary)) {
 568                 $xs->element('summary', null, $this->summary);
 569             }
 570
 571             if (!empty($this->link)) {
 572                 $xs->element('link', array('rel' => 'alternate',
 573                                            'type' => 'text/html'),
 574                              $this->link);
 575             }
 576
 577         }
 578
 579         $xs->element('activity:verb', null, $this->verb);
 580
 581         $published = self::iso8601Date($this->time);
 582
 583         $xs->element('published', null, $published);
 584         $xs->element('updated', null, $published);
 585
 586         if ($author) {
 587             $this->actor->outputTo($xs, 'author');
 588         }
 589
 590         if ($this->verb != ActivityVerb::POST || count($this->objects) != 1 || $tag != 'entry') {
 591             foreach($this->objects as $object) {
 592                 if ($object instanceof Activity) {
 593                     $object->outputTo($xs, false, true, true, 'activity:object');
 594                 } else {
 595                     $object->outputTo($xs, 'activity:object');
 596                 }
 597             }
 598         }
 599
 600         if (!empty($this->context)) {
 601
 602             if (!empty($this->context->replyToID)) {
 603                 if (!empty($this->context->replyToUrl)) {
 604                     $xs->element('thr:in-reply-to',
 605                                  array('ref' => $this->context->replyToID,
 606                                        'href' => $this->context->replyToUrl));
 607                 } else {
 608                     $xs->element('thr:in-reply-to',
 609                                  array('ref' => $this->context->replyToID));
 610                 }
 611             }
 612
 613             if (!empty($this->context->replyToUrl)) {
 614                 $xs->element('link', array('rel' => 'related',
 615                                            'href' => $this->context->replyToUrl));
 616             }
 617
 618             if (!empty($this->context->conversation)) {
 619                 $xs->element('link', array('rel' => 'ostatus:conversation',
 620                                            'href' => $this->context->conversation));
 621             }
 622
 623             foreach ($this->context->attention as $attnURI) {
 624                 $xs->element('link', array('rel' => 'ostatus:attention',
 625                                            'href' => $attnURI));
 626                 $xs->element('link', array('rel' => 'mentioned',
 627                                            'href' => $attnURI));
 628             }
 629
 630             // XXX: shoulda used ActivityVerb::SHARE
 631
 632             if (!empty($this->context->forwardID)) {
 633                 if (!empty($this->context->forwardUrl)) {
 634                     $xs->element('ostatus:forward',
 635                                  array('ref' => $this->context->forwardID,
 636                                        'href' => $this->context->forwardUrl));
 637                 } else {
 638                     $xs->element('ostatus:forward',
 639                                  array('ref' => $this->context->forwardID));
 640                 }
 641             }
 642
 643             if (!empty($this->context->location)) {
 644                 $loc = $this->context->location;
 645                 $xs->element('georss:point', null, $loc->lat . ' ' . $loc->lon);
 646             }
 647         }
 648
 649         if ($this->target) {
 650             $this->target->outputTo($xs, 'activity:target');
 651         }
 652
 653         foreach ($this->categories as $cat) {
 654             $cat->outputTo($xs);
 655         }
 656
 657         // can be either URLs or enclosure objects
 658
 659         foreach ($this->enclosures as $enclosure) {
 660             if (is_string($enclosure)) {
 661                 $xs->element('link', array('rel' => 'enclosure',
 662                                            'href' => $enclosure));
 663             } else {
 664                 $attributes = array('rel' => 'enclosure',
 665                                     'href' => $enclosure->url,
 666                                     'type' => $enclosure->mimetype,
 667                                     'length' => $enclosure->size);
 668                 if ($enclosure->title) {
 669                     $attributes['title'] = $enclosure->title;
 670                 }
 671                 $xs->element('link', $attributes);
 672             }
 673         }
 674
 675         // Info on the source feed
 676
 677         if ($source && !empty($this->source)) {
 678             $xs->elementStart('source');
 679
 680             $xs->element('id', null, $this->source->id);
 681             $xs->element('title', null, $this->source->title);
 682
 683             if (array_key_exists('alternate', $this->source->links)) {
 684                 $xs->element('link', array('rel' => 'alternate',
 685                                            'type' => 'text/html',
 686                                            'href' => $this->source->links['alternate']));
 687             }
 688
 689             if (array_key_exists('self', $this->source->links)) {
 690                 $xs->element('link', array('rel' => 'self',
 691                                            'type' => 'application/atom+xml',
 692                                            'href' => $this->source->links['self']));
 693             }
 694
 695             if (array_key_exists('license', $this->source->links)) {
 696                 $xs->element('link', array('rel' => 'license',
 697                                            'href' => $this->source->links['license']));
 698             }
 699
 700             if (!empty($this->source->icon)) {
 701                 $xs->element('icon', null, $this->source->icon);
 702             }
 703
 704             if (!empty($this->source->updated)) {
 705                 $xs->element('updated', null, $this->source->updated);
 706             }
 707
 708             $xs->elementEnd('source');
 709         }
 710
 711         if (!empty($this->selfLink)) {
 712             $xs->element('link', array('rel' => 'self',
 713                                        'type' => 'application/atom+xml',
 714                                        'href' => $this->selfLink));
 715         }
 716
 717         if (!empty($this->editLink)) {
 718             $xs->element('link', array('rel' => 'edit',
 719                                        'type' => 'application/atom+xml',
 720                                        'href' => $this->editLink));
 721         }
 722
 723         // For throwing in extra elements; used for statusnet:notice_info
 724
 725         foreach ($this->extra as $el) {
 726             list($tag, $attrs, $content) = $el;
 727             $xs->element($tag, $attrs, $content);
 728         }
 729
 730         $xs->elementEnd($tag);
 731
 732         return;
 733     }
 734
 735     private function _child($element, $tag, $namespace=self::SPEC)
 736     {
 737         return ActivityUtils::child($element, $tag, $namespace);
 738     }
 739
 740     /**
 741      * For consistency, we'll always output UTC rather than local time.
 742      * Note that clients *should* accept any timezone we give them as long
 743      * as it's properly formatted.
 744      *
 745      * @param int $tm Unix timestamp
 746      * @return string
 747      */
 748     static function iso8601Date($tm)
 749     {
 750         $dateStr = date('d F Y H:i:s', $tm);
 751         $d = new DateTime($dateStr, new DateTimeZone('UTC'));
 752         return $d->format('c');
 753     }
 754 }