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     /**
 112      * Turns a regular old Atom <entry> into a magical activity
 113      *
 114      * @param DOMElement $entry Atom entry to poke at
 115      * @param DOMElement $feed  Atom feed, for context
 116      */
 117     function __construct($entry = null, $feed = null)
 118     {
 119         if (is_null($entry)) {
 120             return;
 121         }
 122
 123         // Insist on a feed's root DOMElement; don't allow a DOMDocument
 124         if ($feed instanceof DOMDocument) {
 125             throw new ClientException(
 126                 // TRANS: Client exception thrown when a feed instance is a DOMDocument.
 127                 _('Expecting a root feed element but got a whole XML document.')
 128             );
 129         }
 130
 131         $this->entry = $entry;
 132         $this->feed  = $feed;
 133
 134         if ($entry->namespaceURI == Activity::ATOM &&
 135             $entry->localName == 'entry') {
 136             $this->_fromAtomEntry($entry, $feed);
 137         } else if ($entry->namespaceURI == Activity::RSS &&
 138                    $entry->localName == 'item') {
 139             $this->_fromRssItem($entry, $feed);
 140         } else if ($entry->namespaceURI == Activity::SPEC &&
 141                    $entry->localName == 'object') {
 142             $this->_fromAtomEntry($entry, $feed);
 143         } else {
 144             // Low level exception. No need for i18n.
 145             throw new Exception("Unknown DOM element: {$entry->namespaceURI} {$entry->localName}");
 146         }
 147     }
 148
 149     function _fromAtomEntry($entry, $feed)
 150     {
 151         $pubEl = $this->_child($entry, self::PUBLISHED, self::ATOM);
 152
 153         if (!empty($pubEl)) {
 154             $this->time = strtotime($pubEl->textContent);
 155         } else {
 156             // XXX technically an error; being liberal. Good idea...?
 157             $updateEl = $this->_child($entry, self::UPDATED, self::ATOM);
 158             if (!empty($updateEl)) {
 159                 $this->time = strtotime($updateEl->textContent);
 160             } else {
 161                 $this->time = null;
 162             }
 163         }
 164
 165         $this->link = ActivityUtils::getPermalink($entry);
 166
 167         $verbEl = $this->_child($entry, self::VERB);
 168
 169         if (!empty($verbEl)) {
 170             $this->verb = trim($verbEl->textContent);
 171         } else {
 172             $this->verb = ActivityVerb::POST;
 173             // XXX: do other implied stuff here
 174         }
 175
 176         // get immediate object children
 177
 178         $objectEls = ActivityUtils::children($entry, self::OBJECT, self::SPEC);
 179
 180         if (count($objectEls) > 0) {
 181             foreach ($objectEls as $objectEl) {
 182                 // Special case for embedded activities
 183                 $objectType = ActivityUtils::childContent($objectEl, self::OBJECTTYPE, self::SPEC);
 184                 if (!empty($objectType) && $objectType == ActivityObject::ACTIVITY) {
 185                     $this->objects[] = new Activity($objectEl);
 186                 } else {
 187                     $this->objects[] = new ActivityObject($objectEl);
 188                 }
 189             }
 190         } else {
 191             // XXX: really?
 192             $this->objects[] = new ActivityObject($entry);
 193         }
 194
 195         $actorEl = $this->_child($entry, self::ACTOR);
 196
 197         if (!empty($actorEl)) {
 198             // Standalone <activity:actor> elements are a holdover from older
 199             // versions of ActivityStreams. Newer feeds should have this data
 200             // integrated straight into <atom:author>.
 201
 202             $this->actor = new ActivityObject($actorEl);
 203
 204             // Cliqset has bad actor IDs (just nickname of user). We
 205             // work around it by getting the author data and using its
 206             // id instead
 207
 208             if (!preg_match('/^\w+:/', $this->actor->id)) {
 209                 $authorEl = ActivityUtils::child($entry, 'author');
 210                 if (!empty($authorEl)) {
 211                     $authorObj = new ActivityObject($authorEl);
 212                     $this->actor->id = $authorObj->id;
 213                 }
 214             }
 215         } else if ($authorEl = $this->_child($entry, self::AUTHOR, self::ATOM)) {
 216
 217             // An <atom:author> in the entry overrides any author info on
 218             // the surrounding feed.
 219             $this->actor = new ActivityObject($authorEl);
 220
 221         } else if (!empty($feed) &&
 222                    $subjectEl = $this->_child($feed, self::SUBJECT)) {
 223
 224             // Feed subject is used for things like groups.
 225             // Should actually possibly not be interpreted as an actor...?
 226             $this->actor = new ActivityObject($subjectEl);
 227
 228         } else if (!empty($feed) && $authorEl = $this->_child($feed, self::AUTHOR,
 229                                                               self::ATOM)) {
 230
 231             // If there's no <atom:author> on the entry, it's safe to assume
 232             // the containing feed's authorship info applies.
 233             $this->actor = new ActivityObject($authorEl);
 234         }
 235
 236         $contextEl = $this->_child($entry, self::CONTEXT);
 237
 238         if (!empty($contextEl)) {
 239             $this->context = new ActivityContext($contextEl);
 240         } else {
 241             $this->context = new ActivityContext($entry);
 242         }
 243
 244         $targetEl = $this->_child($entry, self::TARGET);
 245
 246         if (!empty($targetEl)) {
 247             $this->target = new ActivityObject($targetEl);
 248         } elseif (ActivityUtils::compareVerbs($this->verb, array(ActivityVerb::FAVORITE))) {
 249             // StatusNet didn't send a 'target' for their Favorite atom entries
 250             $this->target = clone($this->objects[0]);
 251         }
 252
 253         $this->summary = ActivityUtils::childContent($entry, 'summary');
 254         $this->id      = ActivityUtils::childContent($entry, 'id');
 255         $this->content = ActivityUtils::getContent($entry);
 256
 257         $catEls = $entry->getElementsByTagNameNS(self::ATOM, 'category');
 258         if ($catEls) {
 259             for ($i = 0; $i < $catEls->length; $i++) {
 260                 $catEl = $catEls->item($i);
 261                 $this->categories[] = new AtomCategory($catEl);
 262             }
 263         }
 264
 265         foreach (ActivityUtils::getLinks($entry, 'enclosure') as $link) {
 266             $this->enclosures[] = $link->getAttribute('href');
 267         }
 268
 269         // From APP. Might be useful.
 270
 271         $this->selfLink = ActivityUtils::getLink($entry, 'self', 'application/atom+xml');
 272         $this->editLink = ActivityUtils::getLink($entry, 'edit', 'application/atom+xml');
 273     }
 274
 275     function _fromRssItem($item, $channel)
 276     {
 277         $verbEl = $this->_child($item, self::VERB);
 278
 279         if (!empty($verbEl)) {
 280             $this->verb = trim($verbEl->textContent);
 281         } else {
 282             $this->verb = ActivityVerb::POST;
 283             // XXX: do other implied stuff here
 284         }
 285
 286         $pubDateEl = $this->_child($item, self::PUBDATE, self::RSS);
 287
 288         if (!empty($pubDateEl)) {
 289             $this->time = strtotime($pubDateEl->textContent);
 290         }
 291
 292         if ($authorEl = $this->_child($item, self::AUTHOR, self::RSS)) {
 293             $this->actor = ActivityObject::fromRssAuthor($authorEl);
 294         } else if ($dcCreatorEl = $this->_child($item, self::CREATOR, self::DC)) {
 295             $this->actor = ActivityObject::fromDcCreator($dcCreatorEl);
 296         } else if ($posterousEl = $this->_child($item, ActivityObject::AUTHOR, ActivityObject::POSTEROUS)) {
 297             // Special case for Posterous.com
 298             $this->actor = ActivityObject::fromPosterousAuthor($posterousEl);
 299         } else if (!empty($channel)) {
 300             $this->actor = ActivityObject::fromRssChannel($channel);
 301         } else {
 302             // No actor!
 303         }
 304
 305         $this->title = ActivityUtils::childContent($item, ActivityObject::TITLE, self::RSS);
 306
 307         $contentEl = ActivityUtils::child($item, self::ENCODED, self::CONTENTNS);
 308
 309         if (!empty($contentEl)) {
 310             // <content:encoded> XML node's text content is HTML; no further processing needed.
 311             $this->content = $contentEl->textContent;
 312         } else {
 313             $descriptionEl = ActivityUtils::child($item, self::DESCRIPTION, self::RSS);
 314             if (!empty($descriptionEl)) {
 315                 // Per spec, <description> must be plaintext.
 316                 // In practice, often there's HTML... but these days good
 317                 // feeds are using <content:encoded> which is explicitly
 318                 // real HTML.
 319                 // We'll treat this following spec, and do HTML escaping
 320                 // to convert from plaintext to HTML.
 321                 $this->content = htmlspecialchars($descriptionEl->textContent);
 322             }
 323         }
 324
 325         $this->link = ActivityUtils::childContent($item, ActivityUtils::LINK, self::RSS);
 326
 327         // @fixme enclosures
 328         // @fixme thumbnails... maybe
 329
 330         $guidEl = ActivityUtils::child($item, self::GUID, self::RSS);
 331
 332         if (!empty($guidEl)) {
 333             $this->id = $guidEl->textContent;
 334
 335             if ($guidEl->hasAttribute('isPermaLink') && $guidEl->getAttribute('isPermaLink') != 'false') {
 336                 // overwrites <link>
 337                 $this->link = $this->id;
 338             }
 339         }
 340
 341         $this->objects[] = new ActivityObject($item);
 342         $this->context   = new ActivityContext($item);
 343     }
 344
 345     /**
 346      * Returns an Atom <entry> based on this activity
 347      *
 348      * @return DOMElement Atom entry
 349      */
 350
 351     function toAtomEntry()
 352     {
 353         return null;
 354     }
 355
 356     /**
 357      * Returns an array based on this activity suitable
 358      * for encoding as a JSON object
 359      *
 360      * @return array $activity
 361      */
 362
 363     function asArray()
 364     {
 365         $activity = array();
 366
 367         // actor
 368         $activity['actor'] = $this->actor->asArray();
 369
 370         // content
 371         $activity['content'] = $this->content;
 372
 373         // generator
 374
 375         if (!empty($this->generator)) {
 376             $activity['generator'] = $this->generator->asArray();
 377         }
 378
 379         // icon <-- possibly a mini object representing verb?
 380
 381         // id
 382         $activity['id'] = $this->id;
 383
 384         // object
 385
 386         if (count($this->objects) == 0) {
 387             common_log(LOG_ERR, "Can't save " . $this->id);
 388         } else {
 389             if (count($this->objects) > 1) {
 390                 common_log(LOG_WARNING, "Ignoring " . (count($this->objects) - 1) . " extra objects in JSON output for activity " . $this->id);
 391             }
 392             $object = $this->objects[0];
 393
 394             if ($object instanceof Activity) {
 395                 // Sharing a post activity is more like sharing the original object
 396                 if (ActivityVerb::canonical($this->verb) == ActivityVerb::canonical(ActivityVerb::SHARE) &&
 397                     ActivityVerb::canonical($object->verb) == ActivityVerb::canonical(ActivityVerb::POST)) {
 398                     // XXX: Here's one for the obfuscation record books
 399                     $object = $object->objects[0];
 400                 }
 401             }
 402
 403             $activity['object'] = $object->asArray();
 404
 405             if ($object instanceof Activity) {
 406                 $activity['object']['objectType'] = 'activity';
 407             }
 408
 409             foreach ($this->attachments as $attachment) {
 410                 if (empty($activity['object']['attachments'])) {
 411                     $activity['object']['attachments'] = array();
 412                 }
 413                 $activity['object']['attachments'][] = $attachment->asArray();
 414             }
 415         }
 416
 417         // Context stuff.
 418
 419         if (!empty($this->context)) {
 420
 421             if (!empty($this->context->location)) {
 422                 $loc = $this->context->location;
 423
 424                 $activity['location'] = array(
 425                     'objectType' => 'place',
 426                     'position' => sprintf("%+02.5F%+03.5F/", $loc->lat, $loc->lon),
 427                     'lat' => $loc->lat,
 428                     'lon' => $loc->lon
 429                 );
 430
 431                 $name = $loc->getName();
 432
 433                 if ($name) {
 434                     $activity['location']['displayName'] = $name;
 435                 }
 436
 437                 $url = $loc->getURL();
 438
 439                 if ($url) {
 440                     $activity['location']['url'] = $url;
 441                 }
 442             }
 443
 444             $activity['to']      = $this->context->getToArray();
 445
 446             $ctxarr = $this->context->asArray();
 447
 448             if (array_key_exists('inReplyTo', $ctxarr)) {
 449                 $activity['object']['inReplyTo'] = $ctxarr['inReplyTo'];
 450                 unset($ctxarr['inReplyTo']);
 451             }
 452
 453             if (!array_key_exists('status_net', $activity)) {
 454                 $activity['status_net'] = array();
 455             }
 456
 457             foreach ($ctxarr as $key => $value) {
 458                 $activity['status_net'][$key] = $value;
 459             }
 460         }
 461
 462         // published
 463         $activity['published'] = self::iso8601Date($this->time);
 464
 465         // provider
 466         $provider = array(
 467             'objectType' => 'service',
 468             'displayName' => common_config('site', 'name'),
 469             'url' => common_root_url()
 470         );
 471
 472         $activity['provider'] = $provider;
 473
 474         // target
 475         if (!empty($this->target)) {
 476             $activity['target'] = $this->target->asArray();
 477         }
 478
 479         // title
 480         $activity['title'] = $this->title;
 481
 482         // updated <-- Optional. Should we use this to indicate the time we r
 483         //             eceived a remote notice? Probably not.
 484
 485         // verb
 486
 487         $activity['verb'] = ActivityVerb::canonical($this->verb);
 488
 489         // url
 490         if ($this->link) {
 491             $activity['url'] = $this->link;
 492         }
 493
 494         /* Purely extensions hereafter */
 495
 496         if ($activity['verb'] == 'post') {
 497             $tags = array();
 498             foreach ($this->categories as $cat) {
 499                 if (mb_strlen($cat->term) > 0) {
 500                     // Couldn't figure out which object type to use, so...
 501                     $tags[] = array('objectType' => 'http://activityschema.org/object/hashtag',
 502                                     'displayName' => $cat->term);
 503                 }
 504             }
 505             if (count($tags) > 0) {
 506                 $activity['object']['tags'] = $tags;
 507             }
 508         }
 509
 510         // XXX: a bit of a hack... Since JSON isn't namespaced we probably
 511         // shouldn't be using 'statusnet:notice_info', but this will work
 512         // for the moment.
 513
 514         foreach ($this->extra as $e) {
 515             list($objectName, $props, $txt) = $e;
 516             if (!empty($objectName)) {
 517                 $parts = explode(":", $objectName);
 518                 if (count($parts) == 2 && $parts[0] == "statusnet") {
 519                     if (!array_key_exists('status_net', $activity)) {
 520                         $activity['status_net'] = array();
 521                     }
 522                     $activity['status_net'][$parts[1]] = $props;
 523                 } else {
 524                     $activity[$objectName] = $props;
 525                 }
 526             }
 527         }
 528
 529         return array_filter($activity);
 530     }
 531
 532     function asString($namespace=false, $author=true, $source=false)
 533     {
 534         $xs = new XMLStringer(true);
 535         $this->outputTo($xs, $namespace, $author, $source);
 536         return $xs->getString();
 537     }
 538
 539     function outputTo($xs, $namespace=false, $author=true, $source=false, $tag='entry')
 540     {
 541         if ($namespace) {
 542             $attrs = array('xmlns' => 'http://www.w3.org/2005/Atom',
 543                            'xmlns:thr' => 'http://purl.org/syndication/thread/1.0',
 544                            'xmlns:activity' => 'http://activitystrea.ms/spec/1.0/',
 545                            'xmlns:georss' => 'http://www.georss.org/georss',
 546                            'xmlns:ostatus' => 'http://ostatus.org/schema/1.0',
 547                            'xmlns:poco' => 'http://portablecontacts.net/spec/1.0',
 548                            'xmlns:media' => 'http://purl.org/syndication/atommedia',
 549                            'xmlns:statusnet' => 'http://status.net/schema/api/1/');
 550         } else {
 551             $attrs = array();
 552         }
 553
 554         $xs->elementStart($tag, $attrs);
 555
 556         if ($tag != 'entry') {
 557             $xs->element('activity:object-type', null, ActivityObject::ACTIVITY);
 558         }
 559
 560         if ($this->verb == ActivityVerb::POST && count($this->objects) == 1 && $tag == 'entry') {
 561
 562             $obj = $this->objects[0];
 563                         $obj->outputTo($xs, null);
 564
 565         } else {
 566             $xs->element('id', null, $this->id);
 567
 568             if ($this->title) {
 569                 $xs->element('title', null, $this->title);
 570             } else {
 571                 // Require element
 572                 $xs->element('title', null, "");
 573             }
 574
 575             $xs->element('content', array('type' => 'html'), $this->content);
 576
 577             if (!empty($this->summary)) {
 578                 $xs->element('summary', null, $this->summary);
 579             }
 580
 581             if (!empty($this->link)) {
 582                 $xs->element('link', array('rel' => 'alternate',
 583                                            'type' => 'text/html',
 584                                            'href' => $this->link));
 585             }
 586
 587         }
 588
 589         $xs->element('activity:verb', null, $this->verb);
 590
 591         $published = self::iso8601Date($this->time);
 592
 593         $xs->element('published', null, $published);
 594         $xs->element('updated', null, $published);
 595
 596         if ($author) {
 597             $this->actor->outputTo($xs, 'author');
 598         }
 599
 600         if ($this->verb != ActivityVerb::POST || count($this->objects) != 1 || $tag != 'entry') {
 601             foreach($this->objects as $object) {
 602                 if ($object instanceof Activity) {
 603                     $object->outputTo($xs, false, true, true, 'activity:object');
 604                 } else {
 605                     $object->outputTo($xs, 'activity:object');
 606                 }
 607             }
 608         }
 609
 610         if (!empty($this->context)) {
 611
 612             if (!empty($this->context->replyToID)) {
 613                 if (!empty($this->context->replyToUrl)) {
 614                     $xs->element('thr:in-reply-to',
 615                                  array('ref' => $this->context->replyToID,
 616                                        'href' => $this->context->replyToUrl));
 617                 } else {
 618                     $xs->element('thr:in-reply-to',
 619                                  array('ref' => $this->context->replyToID));
 620                 }
 621             }
 622
 623             if (!empty($this->context->replyToUrl)) {
 624                 $xs->element('link', array('rel' => 'related',
 625                                            'href' => $this->context->replyToUrl));
 626             }
 627
 628             if (!empty($this->context->conversation)) {
 629                 $xs->element('link', array('rel' => ActivityContext::CONVERSATION,
 630                                            'href' => $this->context->conversation));
 631                 $xs->element(ActivityContext::CONVERSATION, null, $this->context->conversation);
 632                 /* Since we use XMLWriter we just use the previously hardcoded prefix for ostatus,
 633                     otherwise we should use something like this:
 634                 $xs->elementNS(array(ActivityContext::OSTATUS => 'ostatus'),    // namespace
 635                                 'conversation',  // tag (or the element name from ActivityContext::CONVERSATION)
 636                                 null,   // attributes
 637                                 $this->context->conversation);  // content
 638                 */
 639             }
 640
 641             foreach ($this->context->attention as $attnURI=>$type) {
 642                 $xs->element('link', array('rel' => ActivityContext::MENTIONED,
 643                                            ActivityContext::OBJECTTYPE => $type,  // FIXME: undocumented
 644                                            'href' => $attnURI));
 645             }
 646
 647             if (!empty($this->context->location)) {
 648                 $loc = $this->context->location;
 649                 $xs->element('georss:point', null, $loc->lat . ' ' . $loc->lon);
 650             }
 651         }
 652
 653         if ($this->target) {
 654             $this->target->outputTo($xs, 'activity:target');
 655         }
 656
 657         foreach ($this->categories as $cat) {
 658             $cat->outputTo($xs);
 659         }
 660
 661         // can be either URLs or enclosure objects
 662
 663         foreach ($this->enclosures as $enclosure) {
 664             if (is_string($enclosure)) {
 665                 $xs->element('link', array('rel' => 'enclosure',
 666                                            'href' => $enclosure));
 667             } else {
 668                 $attributes = array('rel' => 'enclosure',
 669                                     'href' => $enclosure->url,
 670                                     'type' => $enclosure->mimetype,
 671                                     'length' => $enclosure->size);
 672                 if ($enclosure->title) {
 673                     $attributes['title'] = $enclosure->title;
 674                 }
 675                 $xs->element('link', $attributes);
 676             }
 677         }
 678
 679         // Info on the source feed
 680
 681         if ($source && !empty($this->source)) {
 682             $xs->elementStart('source');
 683
 684             $xs->element('id', null, $this->source->id);
 685             $xs->element('title', null, $this->source->title);
 686
 687             if (array_key_exists('alternate', $this->source->links)) {
 688                 $xs->element('link', array('rel' => 'alternate',
 689                                            'type' => 'text/html',
 690                                            'href' => $this->source->links['alternate']));
 691             }
 692
 693             if (array_key_exists('self', $this->source->links)) {
 694                 $xs->element('link', array('rel' => 'self',
 695                                            'type' => 'application/atom+xml',
 696                                            'href' => $this->source->links['self']));
 697             }
 698
 699             if (array_key_exists('license', $this->source->links)) {
 700                 $xs->element('link', array('rel' => 'license',
 701                                            'href' => $this->source->links['license']));
 702             }
 703
 704             if (!empty($this->source->icon)) {
 705                 $xs->element('icon', null, $this->source->icon);
 706             }
 707
 708             if (!empty($this->source->updated)) {
 709                 $xs->element('updated', null, $this->source->updated);
 710             }
 711
 712             $xs->elementEnd('source');
 713         }
 714
 715         if (!empty($this->selfLink)) {
 716             $xs->element('link', array('rel' => 'self',
 717                                        'type' => 'application/atom+xml',
 718                                        'href' => $this->selfLink));
 719         }
 720
 721         if (!empty($this->editLink)) {
 722             $xs->element('link', array('rel' => 'edit',
 723                                        'type' => 'application/atom+xml',
 724                                        'href' => $this->editLink));
 725         }
 726
 727         // For throwing in extra elements; used for statusnet:notice_info
 728
 729         foreach ($this->extra as $el) {
 730             list($tag, $attrs, $content) = $el;
 731             $xs->element($tag, $attrs, $content);
 732         }
 733
 734         $xs->elementEnd($tag);
 735
 736         return;
 737     }
 738
 739     private function _child($element, $tag, $namespace=self::SPEC)
 740     {
 741         return ActivityUtils::child($element, $tag, $namespace);
 742     }
 743
 744     /**
 745      * For consistency, we'll always output UTC rather than local time.
 746      * Note that clients *should* accept any timezone we give them as long
 747      * as it's properly formatted.
 748      *
 749      * @param int $tm Unix timestamp
 750      * @return string
 751      */
 752     static function iso8601Date($tm)
 753     {
 754         $dateStr = date('d F Y H:i:s', $tm);
 755         $d = new DateTime($dateStr, new DateTimeZone('UTC'));
 756         return $d->format('c');
 757     }
 758 }