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     public $generator; // ActivityObject representing the generating application
 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'] = $this->content;
 368
 369         // generator
 370
 371         if (!empty($this->generator)) {
 372             $activity['generator'] = $this->generator->asArray();
 373         }
 374
 375         // icon <-- possibly a mini object representing verb?
 376
 377         // id
 378         $activity['id'] = $this->id;
 379
 380         // object
 381
 382         if (count($this->objects) == 0) {
 383             common_log(LOG_ERR, "Can't save " . $this->id);
 384         } else {
 385             if (count($this->objects) > 1) {
 386                 common_log(LOG_WARNING, "Ignoring " . (count($this->objects) - 1) . " extra objects in JSON output for activity " . $this->id);
 387             }
 388             $object = $this->objects[0];
 389
 390             if ($object instanceof Activity) {
 391                 // Sharing a post activity is more like sharing the original object
 392                 if ($this->verb == 'share' && $object->verb == 'post') {
 393                     // XXX: Here's one for the obfuscation record books
 394                     $object = $object->object;
 395                 }
 396             }
 397
 398             $activity['object'] = $object->asArray();
 399
 400             if ($object instanceof Activity) {
 401                 $activity['object']['objectType'] = 'activity';
 402             }
 403
 404             foreach ($this->attachments as $attachment) {
 405                 if (empty($activity['object']['attachments'])) {
 406                     $activity['object']['attachments'] = array();
 407                 }
 408                 $activity['object']['attachments'][] = $attachment->asArray();
 409             }
 410         }
 411
 412         // Context stuff.
 413
 414         if (!empty($this->context)) {
 415
 416             if (!empty($this->context->location)) {
 417                 $loc = $this->context->location;
 418
 419                 $activity['location'] = array(
 420                     'objectType' => 'place',
 421                     'position' => sprintf("%+02.5F%+03.5F/", $loc->lat, $loc->lon),
 422                     'lat' => $loc->lat,
 423                     'lon' => $loc->lon
 424                 );
 425
 426                 $name = $loc->getName();
 427
 428                 if ($name) {
 429                     $activity['location']['displayName'] = $name;
 430                 }
 431
 432                 $url = $loc->getURL();
 433
 434                 if ($url) {
 435                     $activity['location']['url'] = $url;
 436                 }
 437             }
 438
 439             $activity['to']      = $this->context->getToArray();
 440
 441             $ctxarr = $this->context->asArray();
 442
 443             if (array_key_exists('inReplyTo', $ctxarr)) {
 444                 $activity['object']['inReplyTo'] = $ctxarr['inReplyTo'];
 445                 unset($ctxarr['inReplyTo']);
 446             }
 447
 448             if (!array_key_exists('status_net', $activity)) {
 449                 $activity['status_net'] = array();
 450             }
 451
 452             foreach ($ctxarr as $key => $value) {
 453                 $activity['status_net'][$key] = $value;
 454             }
 455         }
 456
 457         // published
 458         $activity['published'] = self::iso8601Date($this->time);
 459
 460         // provider
 461         $provider = array(
 462             'objectType' => 'service',
 463             'displayName' => common_config('site', 'name'),
 464             'url' => common_root_url()
 465         );
 466
 467         $activity['provider'] = $provider;
 468
 469         // target
 470         if (!empty($this->target)) {
 471             $activity['target'] = $this->target->asArray();
 472         }
 473
 474         // title
 475         $activity['title'] = $this->title;
 476
 477         // updated <-- Optional. Should we use this to indicate the time we r
 478         //             eceived a remote notice? Probably not.
 479
 480         // verb
 481
 482         $activity['verb'] = ActivityVerb::canonical($this->verb);
 483
 484         // url
 485         if ($this->link) {
 486             $activity['url'] = $this->link;
 487         }
 488
 489         /* Purely extensions hereafter */
 490
 491         if ($activity['verb'] == 'post') {
 492             $tags = array();
 493             foreach ($this->categories as $cat) {
 494                 if (mb_strlen($cat->term) > 0) {
 495                     // Couldn't figure out which object type to use, so...
 496                     $tags[] = array('objectType' => 'http://activityschema.org/object/hashtag',
 497                                     'displayName' => $cat->term);
 498                 }
 499             }
 500             if (count($tags) > 0) {
 501                 $activity['object']['tags'] = $tags;
 502             }
 503         }
 504
 505         // XXX: a bit of a hack... Since JSON isn't namespaced we probably
 506         // shouldn't be using 'statusnet:notice_info', but this will work
 507         // for the moment.
 508
 509         foreach ($this->extra as $e) {
 510             list($objectName, $props, $txt) = $e;
 511             if (!empty($objectName)) {
 512                 $parts = explode(":", $objectName);
 513                 if (count($parts) == 2 && $parts[0] == "statusnet") {
 514                     if (!array_key_exists('status_net', $activity)) {
 515                         $activity['status_net'] = array();
 516                     }
 517                     $activity['status_net'][$parts[1]] = $props;
 518                 } else {
 519                     $activity[$objectName] = $props;
 520                 }
 521             }
 522         }
 523
 524         return array_filter($activity);
 525     }
 526
 527     function asString($namespace=false, $author=true, $source=false)
 528     {
 529         $xs = new XMLStringer(true);
 530         $this->outputTo($xs, $namespace, $author, $source);
 531         return $xs->getString();
 532     }
 533
 534     function outputTo($xs, $namespace=false, $author=true, $source=false, $tag='entry')
 535     {
 536         if ($namespace) {
 537             $attrs = array('xmlns' => 'http://www.w3.org/2005/Atom',
 538                            'xmlns:thr' => 'http://purl.org/syndication/thread/1.0',
 539                            'xmlns:activity' => 'http://activitystrea.ms/spec/1.0/',
 540                            'xmlns:georss' => 'http://www.georss.org/georss',
 541                            'xmlns:ostatus' => 'http://ostatus.org/schema/1.0',
 542                            'xmlns:poco' => 'http://portablecontacts.net/spec/1.0',
 543                            'xmlns:media' => 'http://purl.org/syndication/atommedia',
 544                            'xmlns:statusnet' => 'http://status.net/schema/api/1/');
 545         } else {
 546             $attrs = array();
 547         }
 548
 549         $xs->elementStart($tag, $attrs);
 550
 551         if ($tag != 'entry') {
 552             $xs->element('activity:object-type', null, ActivityObject::ACTIVITY);
 553         }
 554
 555         if ($this->verb == ActivityVerb::POST && count($this->objects) == 1 && $tag == 'entry') {
 556
 557             $obj = $this->objects[0];
 558                         $obj->outputTo($xs, null);
 559
 560         } else {
 561             $xs->element('id', null, $this->id);
 562
 563             if ($this->title) {
 564                 $xs->element('title', null, $this->title);
 565             } else {
 566                 // Require element
 567                 $xs->element('title', null, "");
 568             }
 569
 570             $xs->element('content', array('type' => 'html'), $this->content);
 571
 572             if (!empty($this->summary)) {
 573                 $xs->element('summary', null, $this->summary);
 574             }
 575
 576             if (!empty($this->link)) {
 577                 $xs->element('link', array('rel' => 'alternate',
 578                                            'type' => 'text/html'),
 579                              $this->link);
 580             }
 581
 582         }
 583
 584         $xs->element('activity:verb', null, $this->verb);
 585
 586         $published = self::iso8601Date($this->time);
 587
 588         $xs->element('published', null, $published);
 589         $xs->element('updated', null, $published);
 590
 591         if ($author) {
 592             $this->actor->outputTo($xs, 'author');
 593         }
 594
 595         if ($this->verb != ActivityVerb::POST || count($this->objects) != 1 || $tag != 'entry') {
 596             foreach($this->objects as $object) {
 597                 if ($object instanceof Activity) {
 598                     $object->outputTo($xs, false, true, true, 'activity:object');
 599                 } else {
 600                     $object->outputTo($xs, 'activity:object');
 601                 }
 602             }
 603         }
 604
 605         if (!empty($this->context)) {
 606
 607             if (!empty($this->context->replyToID)) {
 608                 if (!empty($this->context->replyToUrl)) {
 609                     $xs->element('thr:in-reply-to',
 610                                  array('ref' => $this->context->replyToID,
 611                                        'href' => $this->context->replyToUrl));
 612                 } else {
 613                     $xs->element('thr:in-reply-to',
 614                                  array('ref' => $this->context->replyToID));
 615                 }
 616             }
 617
 618             if (!empty($this->context->replyToUrl)) {
 619                 $xs->element('link', array('rel' => 'related',
 620                                            'href' => $this->context->replyToUrl));
 621             }
 622
 623             if (!empty($this->context->conversation)) {
 624                 $xs->element('link', array('rel' => 'ostatus:conversation',
 625                                            'href' => $this->context->conversation));
 626             }
 627
 628             foreach ($this->context->attention as $attnURI) {
 629                 $xs->element('link', array('rel' => 'ostatus:attention',
 630                                            'href' => $attnURI));
 631                 $xs->element('link', array('rel' => 'mentioned',
 632                                            'href' => $attnURI));
 633             }
 634
 635             // XXX: shoulda used ActivityVerb::SHARE
 636
 637             if (!empty($this->context->forwardID)) {
 638                 if (!empty($this->context->forwardUrl)) {
 639                     $xs->element('ostatus:forward',
 640                                  array('ref' => $this->context->forwardID,
 641                                        'href' => $this->context->forwardUrl));
 642                 } else {
 643                     $xs->element('ostatus:forward',
 644                                  array('ref' => $this->context->forwardID));
 645                 }
 646             }
 647
 648             if (!empty($this->context->location)) {
 649                 $loc = $this->context->location;
 650                 $xs->element('georss:point', null, $loc->lat . ' ' . $loc->lon);
 651             }
 652         }
 653
 654         if ($this->target) {
 655             $this->target->outputTo($xs, 'activity:target');
 656         }
 657
 658         foreach ($this->categories as $cat) {
 659             $cat->outputTo($xs);
 660         }
 661
 662         // can be either URLs or enclosure objects
 663
 664         foreach ($this->enclosures as $enclosure) {
 665             if (is_string($enclosure)) {
 666                 $xs->element('link', array('rel' => 'enclosure',
 667                                            'href' => $enclosure));
 668             } else {
 669                 $attributes = array('rel' => 'enclosure',
 670                                     'href' => $enclosure->url,
 671                                     'type' => $enclosure->mimetype,
 672                                     'length' => $enclosure->size);
 673                 if ($enclosure->title) {
 674                     $attributes['title'] = $enclosure->title;
 675                 }
 676                 $xs->element('link', $attributes);
 677             }
 678         }
 679
 680         // Info on the source feed
 681
 682         if ($source && !empty($this->source)) {
 683             $xs->elementStart('source');
 684
 685             $xs->element('id', null, $this->source->id);
 686             $xs->element('title', null, $this->source->title);
 687
 688             if (array_key_exists('alternate', $this->source->links)) {
 689                 $xs->element('link', array('rel' => 'alternate',
 690                                            'type' => 'text/html',
 691                                            'href' => $this->source->links['alternate']));
 692             }
 693
 694             if (array_key_exists('self', $this->source->links)) {
 695                 $xs->element('link', array('rel' => 'self',
 696                                            'type' => 'application/atom+xml',
 697                                            'href' => $this->source->links['self']));
 698             }
 699
 700             if (array_key_exists('license', $this->source->links)) {
 701                 $xs->element('link', array('rel' => 'license',
 702                                            'href' => $this->source->links['license']));
 703             }
 704
 705             if (!empty($this->source->icon)) {
 706                 $xs->element('icon', null, $this->source->icon);
 707             }
 708
 709             if (!empty($this->source->updated)) {
 710                 $xs->element('updated', null, $this->source->updated);
 711             }
 712
 713             $xs->elementEnd('source');
 714         }
 715
 716         if (!empty($this->selfLink)) {
 717             $xs->element('link', array('rel' => 'self',
 718                                        'type' => 'application/atom+xml',
 719                                        'href' => $this->selfLink));
 720         }
 721
 722         if (!empty($this->editLink)) {
 723             $xs->element('link', array('rel' => 'edit',
 724                                        'type' => 'application/atom+xml',
 725                                        'href' => $this->editLink));
 726         }
 727
 728         // For throwing in extra elements; used for statusnet:notice_info
 729
 730         foreach ($this->extra as $el) {
 731             list($tag, $attrs, $content) = $el;
 732             $xs->element($tag, $attrs, $content);
 733         }
 734
 735         $xs->elementEnd($tag);
 736
 737         return;
 738     }
 739
 740     private function _child($element, $tag, $namespace=self::SPEC)
 741     {
 742         return ActivityUtils::child($element, $tag, $namespace);
 743     }
 744
 745     /**
 746      * For consistency, we'll always output UTC rather than local time.
 747      * Note that clients *should* accept any timezone we give them as long
 748      * as it's properly formatted.
 749      *
 750      * @param int $tm Unix timestamp
 751      * @return string
 752      */
 753     static function iso8601Date($tm)
 754     {
 755         $dateStr = date('d F Y H:i:s', $tm);
 756         $d = new DateTime($dateStr, new DateTimeZone('UTC'));
 757         return $d->format('c');
 758     }
 759 }