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
 104     public $extra = array(); // extra elements as array(tag, attrs, content)
 105     public $source;  // ActivitySource object representing 'home feed'
 106     public $selfLink; // <link rel='self' type='application/atom+xml'>
 107     public $editLink; // <link rel='edit' type='application/atom+xml'>
 108
 109     /**
 110      * Turns a regular old Atom <entry> into a magical activity
 111      *
 112      * @param DOMElement $entry Atom entry to poke at
 113      * @param DOMElement $feed  Atom feed, for context
 114      */
 115     function __construct($entry = null, $feed = null)
 116     {
 117         if (is_null($entry)) {
 118             return;
 119         }
 120
 121         // Insist on a feed's root DOMElement; don't allow a DOMDocument
 122         if ($feed instanceof DOMDocument) {
 123             throw new ClientException(
 124                 // TRANS: Client exception thrown when a feed instance is a DOMDocument.
 125                 _('Expecting a root feed element but got a whole XML document.')
 126             );
 127         }
 128
 129         $this->entry = $entry;
 130         $this->feed  = $feed;
 131
 132         if ($entry->namespaceURI == Activity::ATOM &&
 133             $entry->localName == 'entry') {
 134             $this->_fromAtomEntry($entry, $feed);
 135         } else if ($entry->namespaceURI == Activity::RSS &&
 136                    $entry->localName == 'item') {
 137             $this->_fromRssItem($entry, $feed);
 138         } else if ($entry->namespaceURI == Activity::SPEC &&
 139                    $entry->localName == 'object') {
 140             $this->_fromAtomEntry($entry, $feed);
 141         } else {
 142             // Low level exception. No need for i18n.
 143             throw new Exception("Unknown DOM element: {$entry->namespaceURI} {$entry->localName}");
 144         }
 145     }
 146
 147     function _fromAtomEntry($entry, $feed)
 148     {
 149         $pubEl = $this->_child($entry, self::PUBLISHED, self::ATOM);
 150
 151         if (!empty($pubEl)) {
 152             $this->time = strtotime($pubEl->textContent);
 153         } else {
 154             // XXX technically an error; being liberal. Good idea...?
 155             $updateEl = $this->_child($entry, self::UPDATED, self::ATOM);
 156             if (!empty($updateEl)) {
 157                 $this->time = strtotime($updateEl->textContent);
 158             } else {
 159                 $this->time = null;
 160             }
 161         }
 162
 163         $this->link = ActivityUtils::getPermalink($entry);
 164
 165         $verbEl = $this->_child($entry, self::VERB);
 166
 167         if (!empty($verbEl)) {
 168             $this->verb = trim($verbEl->textContent);
 169         } else {
 170             $this->verb = ActivityVerb::POST;
 171             // XXX: do other implied stuff here
 172         }
 173
 174         // get immediate object children
 175
 176         $objectEls = ActivityUtils::children($entry, self::OBJECT, self::SPEC);
 177
 178         if (count($objectEls) > 0) {
 179             foreach ($objectEls as $objectEl) {
 180                 // Special case for embedded activities
 181                 $objectType = ActivityUtils::childContent($objectEl, self::OBJECTTYPE, self::SPEC);
 182                 if (!empty($objectType) && $objectType == ActivityObject::ACTIVITY) {
 183                     $this->objects[] = new Activity($objectEl);
 184                 } else {
 185                     $this->objects[] = new ActivityObject($objectEl);
 186                 }
 187             }
 188         } else {
 189             // XXX: really?
 190             $this->objects[] = new ActivityObject($entry);
 191         }
 192
 193         $actorEl = $this->_child($entry, self::ACTOR);
 194
 195         if (!empty($actorEl)) {
 196             // Standalone <activity:actor> elements are a holdover from older
 197             // versions of ActivityStreams. Newer feeds should have this data
 198             // integrated straight into <atom:author>.
 199
 200             $this->actor = new ActivityObject($actorEl);
 201
 202             // Cliqset has bad actor IDs (just nickname of user). We
 203             // work around it by getting the author data and using its
 204             // id instead
 205
 206             if (!preg_match('/^\w+:/', $this->actor->id)) {
 207                 $authorEl = ActivityUtils::child($entry, 'author');
 208                 if (!empty($authorEl)) {
 209                     $authorObj = new ActivityObject($authorEl);
 210                     $this->actor->id = $authorObj->id;
 211                 }
 212             }
 213         } else if ($authorEl = $this->_child($entry, self::AUTHOR, self::ATOM)) {
 214
 215             // An <atom:author> in the entry overrides any author info on
 216             // the surrounding feed.
 217             $this->actor = new ActivityObject($authorEl);
 218
 219         } else if (!empty($feed) &&
 220                    $subjectEl = $this->_child($feed, self::SUBJECT)) {
 221
 222             // Feed subject is used for things like groups.
 223             // Should actually possibly not be interpreted as an actor...?
 224             $this->actor = new ActivityObject($subjectEl);
 225
 226         } else if (!empty($feed) && $authorEl = $this->_child($feed, self::AUTHOR,
 227                                                               self::ATOM)) {
 228
 229             // If there's no <atom:author> on the entry, it's safe to assume
 230             // the containing feed's authorship info applies.
 231             $this->actor = new ActivityObject($authorEl);
 232         }
 233
 234         $contextEl = $this->_child($entry, self::CONTEXT);
 235
 236         if (!empty($contextEl)) {
 237             $this->context = new ActivityContext($contextEl);
 238         } else {
 239             $this->context = new ActivityContext($entry);
 240         }
 241
 242         $targetEl = $this->_child($entry, self::TARGET);
 243
 244         if (!empty($targetEl)) {
 245             $this->target = new ActivityObject($targetEl);
 246         }
 247
 248         $this->summary = ActivityUtils::childContent($entry, 'summary');
 249         $this->id      = ActivityUtils::childContent($entry, 'id');
 250         $this->content = ActivityUtils::getContent($entry);
 251
 252         $catEls = $entry->getElementsByTagNameNS(self::ATOM, 'category');
 253         if ($catEls) {
 254             for ($i = 0; $i < $catEls->length; $i++) {
 255                 $catEl = $catEls->item($i);
 256                 $this->categories[] = new AtomCategory($catEl);
 257             }
 258         }
 259
 260         foreach (ActivityUtils::getLinks($entry, 'enclosure') as $link) {
 261             $this->enclosures[] = $link->getAttribute('href');
 262         }
 263
 264         // From APP. Might be useful.
 265
 266         $this->selfLink = ActivityUtils::getLink($entry, 'self', 'application/atom+xml');
 267         $this->editLink = ActivityUtils::getLink($entry, 'edit', 'application/atom+xml');
 268     }
 269
 270     function _fromRssItem($item, $channel)
 271     {
 272         $verbEl = $this->_child($item, self::VERB);
 273
 274         if (!empty($verbEl)) {
 275             $this->verb = trim($verbEl->textContent);
 276         } else {
 277             $this->verb = ActivityVerb::POST;
 278             // XXX: do other implied stuff here
 279         }
 280
 281         $pubDateEl = $this->_child($item, self::PUBDATE, self::RSS);
 282
 283         if (!empty($pubDateEl)) {
 284             $this->time = strtotime($pubDateEl->textContent);
 285         }
 286
 287         if ($authorEl = $this->_child($item, self::AUTHOR, self::RSS)) {
 288             $this->actor = ActivityObject::fromRssAuthor($authorEl);
 289         } else if ($dcCreatorEl = $this->_child($item, self::CREATOR, self::DC)) {
 290             $this->actor = ActivityObject::fromDcCreator($dcCreatorEl);
 291         } else if ($posterousEl = $this->_child($item, ActivityObject::AUTHOR, ActivityObject::POSTEROUS)) {
 292             // Special case for Posterous.com
 293             $this->actor = ActivityObject::fromPosterousAuthor($posterousEl);
 294         } else if (!empty($channel)) {
 295             $this->actor = ActivityObject::fromRssChannel($channel);
 296         } else {
 297             // No actor!
 298         }
 299
 300         $this->title = ActivityUtils::childContent($item, ActivityObject::TITLE, self::RSS);
 301
 302         $contentEl = ActivityUtils::child($item, self::ENCODED, self::CONTENTNS);
 303
 304         if (!empty($contentEl)) {
 305             // <content:encoded> XML node's text content is HTML; no further processing needed.
 306             $this->content = $contentEl->textContent;
 307         } else {
 308             $descriptionEl = ActivityUtils::child($item, self::DESCRIPTION, self::RSS);
 309             if (!empty($descriptionEl)) {
 310                 // Per spec, <description> must be plaintext.
 311                 // In practice, often there's HTML... but these days good
 312                 // feeds are using <content:encoded> which is explicitly
 313                 // real HTML.
 314                 // We'll treat this following spec, and do HTML escaping
 315                 // to convert from plaintext to HTML.
 316                 $this->content = htmlspecialchars($descriptionEl->textContent);
 317             }
 318         }
 319
 320         $this->link = ActivityUtils::childContent($item, ActivityUtils::LINK, self::RSS);
 321
 322         // @fixme enclosures
 323         // @fixme thumbnails... maybe
 324
 325         $guidEl = ActivityUtils::child($item, self::GUID, self::RSS);
 326
 327         if (!empty($guidEl)) {
 328             $this->id = $guidEl->textContent;
 329
 330             if ($guidEl->hasAttribute('isPermaLink') && $guidEl->getAttribute('isPermaLink') != 'false') {
 331                 // overwrites <link>
 332                 $this->link = $this->id;
 333             }
 334         }
 335
 336         $this->objects[] = new ActivityObject($item);
 337         $this->context   = new ActivityContext($item);
 338     }
 339
 340     /**
 341      * Returns an Atom <entry> based on this activity
 342      *
 343      * @return DOMElement Atom entry
 344      */
 345
 346     function toAtomEntry()
 347     {
 348         return null;
 349     }
 350
 351     /**
 352      * Returns an array based on this activity suitable
 353      * for encoding as a JSON object
 354      *
 355      * @return array $activity
 356      */
 357
 358     function asArray()
 359     {
 360         $activity = array();
 361
 362         // actor
 363         $activity['actor'] = $this->actor->asArray();
 364
 365         // content
 366         $activity['content'] = $this->content;
 367
 368         // generator <-- We could use this when we know a notice is created
 369         //               locally. Or if we know the upstream Generator.
 370
 371         // icon <-- possibly a mini object representing verb?
 372
 373         // id
 374         $activity['id'] = $this->id;
 375
 376         // object
 377
 378         if (count($this->objects) == 0) {
 379             common_log(LOG_ERR, "Can't save " . $this->id);
 380         } else {
 381             if (count($this->objects) > 1) {
 382                 common_log(LOG_WARNING, "Ignoring " . (count($this->objects) - 1) . " extra objects in JSON output for activity " . $this->id);
 383             }
 384             $object = $this->objects[0];
 385
 386             if ($object instanceof Activity) {
 387                 // Sharing a post activity is more like sharing the original object
 388                 if ($this->verb == 'share' && $object->verb == 'post') {
 389                     // XXX: Here's one for the obfuscation record books
 390                     $object = $object->object;
 391                 }
 392             }
 393
 394             $activity['object'] = $object->asArray();
 395
 396             if ($object instanceof Activity) {
 397                 $activity['object']['objectType'] = 'activity';
 398             }
 399
 400
 401             // Instead of adding enclosures as an extension to JSON
 402             // Activities, it seems like we should be using the
 403             // attachements property of ActivityObject
 404
 405             $attachments = array();
 406
 407             // XXX: OK, this is kinda cheating. We should probably figure out
 408             // what kind of objects these are based on mime-type and then
 409             // create specific object types. Right now this rely on
 410             // duck-typing.  Also, we should include an embed code for
 411             // video attachments.
 412
 413             foreach ($this->enclosures as $enclosure) {
 414
 415                 if (is_string($enclosure)) {
 416
 417                     $attachments[]['id']  = $enclosure;
 418
 419                 } else {
 420
 421                     $attachments[]['id']  = $enclosure->url;
 422
 423                     $mediaLink = new ActivityStreamsMediaLink(
 424                         $enclosure->url,
 425                         null,
 426                         null,
 427                         $enclosure->mimetype
 428                         // XXX: Add 'size' as an extension to MediaLink?
 429                     );
 430
 431                     $attachments[]['mediaLink'] = $mediaLink->asArray(); // extension
 432
 433                     if ($enclosure->title) {
 434                         $attachments[]['displayName'] = $enclosure->title;
 435                     }
 436                 }
 437             }
 438
 439             if (!empty($attachments)) {
 440                 $activity['object']['attachments'] = $attachments;
 441             }
 442         }
 443
 444         // Context stuff.
 445
 446         if (!empty($this->context)) {
 447
 448             if (!empty($this->context->location)) {
 449                 $loc = $this->context->location;
 450
 451                 $activity['location'] = array(
 452                     'objectType' => 'place',
 453                     'position' => sprintf("%+02.5F%+03.5F/", $loc->lat, $loc->lon),
 454                     'lat' => $loc->lat,
 455                     'lon' => $loc->lon
 456                 );
 457
 458                 $name = $loc->getName();
 459
 460                 if ($name) {
 461                     $activity['location']['displayName'] = $name;
 462                 }
 463
 464                 $url = $loc->getURL();
 465
 466                 if ($url) {
 467                     $activity['location']['url'] = $url;
 468                 }
 469             }
 470
 471             $activity['to']      = $this->context->getToArray();
 472
 473             $ctxarr = $this->context->asArray();
 474
 475             if (array_key_exists('inReplyTo', $ctxarr)) {
 476                 $activity['object']['inReplyTo'] = $ctxarr['inReplyTo'];
 477                 unset($ctxarr['inReplyTo']);
 478             }
 479
 480             if (!array_key_exists('status_net', $activity)) {
 481                 $activity['status_net'] = array();
 482             }
 483
 484             foreach ($ctxarr as $key => $value) {
 485                 $activity['status_net'][$key] = $value;
 486             }
 487         }
 488
 489         // published
 490         $activity['published'] = self::iso8601Date($this->time);
 491
 492         // provider
 493         $provider = array(
 494             'objectType' => 'service',
 495             'displayName' => common_config('site', 'name'),
 496             'url' => common_root_url()
 497         );
 498
 499         $activity['provider'] = $provider;
 500
 501         // target
 502         if (!empty($this->target)) {
 503             $activity['target'] = $this->target->asArray();
 504         }
 505
 506         // title
 507         $activity['title'] = $this->title;
 508
 509         // updated <-- Optional. Should we use this to indicate the time we r
 510         //             eceived a remote notice? Probably not.
 511
 512         // verb
 513
 514         $activity['verb'] = ActivityVerb::canonical($this->verb);
 515
 516         // url
 517         $activity['url'] = $this->id;
 518
 519         /* Purely extensions hereafter */
 520
 521         if ($activity['verb'] == 'post') {
 522             $tags = array();
 523             foreach ($this->categories as $cat) {
 524                 if (mb_strlen($cat->term) > 0) {
 525                     // Couldn't figure out which object type to use, so...
 526                     $tags[] = array('objectType' => 'http://activityschema.org/object/hashtag',
 527                                     'displayName' => $cat->term);
 528                 }
 529             }
 530             if (count($tags) > 0) {
 531                 $activity['object']['tags'] = $tags;
 532             }
 533         }
 534
 535         // XXX: a bit of a hack... Since JSON isn't namespaced we probably
 536         // shouldn't be using 'statusnet:notice_info', but this will work
 537         // for the moment.
 538
 539         foreach ($this->extra as $e) {
 540             list($objectName, $props, $txt) = $e;
 541             if (!empty($objectName)) {
 542                 $parts = explode(":", $objectName);
 543                 if (count($parts) == 2 && $parts[0] == "statusnet") {
 544                     if (!array_key_exists('status_net', $activity)) {
 545                         $activity['status_net'] = array();
 546                     }
 547                     $activity['status_net'][$parts[1]] = $props;
 548                 } else {
 549                     $activity[$objectName] = $props;
 550                 }
 551             }
 552         }
 553
 554         return array_filter($activity);
 555     }
 556
 557     function asString($namespace=false, $author=true, $source=false)
 558     {
 559         $xs = new XMLStringer(true);
 560         $this->outputTo($xs, $namespace, $author, $source);
 561         return $xs->getString();
 562     }
 563
 564     function outputTo($xs, $namespace=false, $author=true, $source=false, $tag='entry')
 565     {
 566         if ($namespace) {
 567             $attrs = array('xmlns' => 'http://www.w3.org/2005/Atom',
 568                            'xmlns:thr' => 'http://purl.org/syndication/thread/1.0',
 569                            'xmlns:activity' => 'http://activitystrea.ms/spec/1.0/',
 570                            'xmlns:georss' => 'http://www.georss.org/georss',
 571                            'xmlns:ostatus' => 'http://ostatus.org/schema/1.0',
 572                            'xmlns:poco' => 'http://portablecontacts.net/spec/1.0',
 573                            'xmlns:media' => 'http://purl.org/syndication/atommedia',
 574                            'xmlns:statusnet' => 'http://status.net/schema/api/1/');
 575         } else {
 576             $attrs = array();
 577         }
 578
 579         $xs->elementStart($tag, $attrs);
 580
 581         if ($tag != 'entry') {
 582             $xs->element('activity:object-type', null, ActivityObject::ACTIVITY);
 583         }
 584
 585         if ($this->verb == ActivityVerb::POST && count($this->objects) == 1 && $tag == 'entry') {
 586
 587             $obj = $this->objects[0];
 588                         $obj->outputTo($xs, null);
 589
 590         } else {
 591             $xs->element('id', null, $this->id);
 592
 593             if ($this->title) {
 594                 $xs->element('title', null, $this->title);
 595             } else {
 596                 // Require element
 597                 $xs->element('title', null, "");
 598             }
 599
 600             $xs->element('content', array('type' => 'html'), $this->content);
 601
 602             if (!empty($this->summary)) {
 603                 $xs->element('summary', null, $this->summary);
 604             }
 605
 606             if (!empty($this->link)) {
 607                 $xs->element('link', array('rel' => 'alternate',
 608                                            'type' => 'text/html'),
 609                              $this->link);
 610             }
 611
 612         }
 613
 614         $xs->element('activity:verb', null, $this->verb);
 615
 616         $published = self::iso8601Date($this->time);
 617
 618         $xs->element('published', null, $published);
 619         $xs->element('updated', null, $published);
 620
 621         if ($author) {
 622             $this->actor->outputTo($xs, 'author');
 623         }
 624
 625         if ($this->verb != ActivityVerb::POST || count($this->objects) != 1 || $tag != 'entry') {
 626             foreach($this->objects as $object) {
 627                 if ($object instanceof Activity) {
 628                     $object->outputTo($xs, false, true, true, 'activity:object');
 629                 } else {
 630                     $object->outputTo($xs, 'activity:object');
 631                 }
 632             }
 633         }
 634
 635         if (!empty($this->context)) {
 636
 637             if (!empty($this->context->replyToID)) {
 638                 if (!empty($this->context->replyToUrl)) {
 639                     $xs->element('thr:in-reply-to',
 640                                  array('ref' => $this->context->replyToID,
 641                                        'href' => $this->context->replyToUrl));
 642                 } else {
 643                     $xs->element('thr:in-reply-to',
 644                                  array('ref' => $this->context->replyToID));
 645                 }
 646             }
 647
 648             if (!empty($this->context->replyToUrl)) {
 649                 $xs->element('link', array('rel' => 'related',
 650                                            'href' => $this->context->replyToUrl));
 651             }
 652
 653             if (!empty($this->context->conversation)) {
 654                 $xs->element('link', array('rel' => 'ostatus:conversation',
 655                                            'href' => $this->context->conversation));
 656             }
 657
 658             foreach ($this->context->attention as $attnURI) {
 659                 $xs->element('link', array('rel' => 'ostatus:attention',
 660                                            'href' => $attnURI));
 661                 $xs->element('link', array('rel' => 'mentioned',
 662                                            'href' => $attnURI));
 663             }
 664
 665             // XXX: shoulda used ActivityVerb::SHARE
 666
 667             if (!empty($this->context->forwardID)) {
 668                 if (!empty($this->context->forwardUrl)) {
 669                     $xs->element('ostatus:forward',
 670                                  array('ref' => $this->context->forwardID,
 671                                        'href' => $this->context->forwardUrl));
 672                 } else {
 673                     $xs->element('ostatus:forward',
 674                                  array('ref' => $this->context->forwardID));
 675                 }
 676             }
 677
 678             if (!empty($this->context->location)) {
 679                 $loc = $this->context->location;
 680                 $xs->element('georss:point', null, $loc->lat . ' ' . $loc->lon);
 681             }
 682         }
 683
 684         if ($this->target) {
 685             $this->target->outputTo($xs, 'activity:target');
 686         }
 687
 688         foreach ($this->categories as $cat) {
 689             $cat->outputTo($xs);
 690         }
 691
 692         // can be either URLs or enclosure objects
 693
 694         foreach ($this->enclosures as $enclosure) {
 695             if (is_string($enclosure)) {
 696                 $xs->element('link', array('rel' => 'enclosure',
 697                                            'href' => $enclosure));
 698             } else {
 699                 $attributes = array('rel' => 'enclosure',
 700                                     'href' => $enclosure->url,
 701                                     'type' => $enclosure->mimetype,
 702                                     'length' => $enclosure->size);
 703                 if ($enclosure->title) {
 704                     $attributes['title'] = $enclosure->title;
 705                 }
 706                 $xs->element('link', $attributes);
 707             }
 708         }
 709
 710         // Info on the source feed
 711
 712         if ($source && !empty($this->source)) {
 713             $xs->elementStart('source');
 714
 715             $xs->element('id', null, $this->source->id);
 716             $xs->element('title', null, $this->source->title);
 717
 718             if (array_key_exists('alternate', $this->source->links)) {
 719                 $xs->element('link', array('rel' => 'alternate',
 720                                            'type' => 'text/html',
 721                                            'href' => $this->source->links['alternate']));
 722             }
 723
 724             if (array_key_exists('self', $this->source->links)) {
 725                 $xs->element('link', array('rel' => 'self',
 726                                            'type' => 'application/atom+xml',
 727                                            'href' => $this->source->links['self']));
 728             }
 729
 730             if (array_key_exists('license', $this->source->links)) {
 731                 $xs->element('link', array('rel' => 'license',
 732                                            'href' => $this->source->links['license']));
 733             }
 734
 735             if (!empty($this->source->icon)) {
 736                 $xs->element('icon', null, $this->source->icon);
 737             }
 738
 739             if (!empty($this->source->updated)) {
 740                 $xs->element('updated', null, $this->source->updated);
 741             }
 742
 743             $xs->elementEnd('source');
 744         }
 745
 746         if (!empty($this->selfLink)) {
 747             $xs->element('link', array('rel' => 'self',
 748                                        'type' => 'application/atom+xml',
 749                                        'href' => $this->selfLink));
 750         }
 751
 752         if (!empty($this->editLink)) {
 753             $xs->element('link', array('rel' => 'edit',
 754                                        'type' => 'application/atom+xml',
 755                                        'href' => $this->editLink));
 756         }
 757
 758         // For throwing in extra elements; used for statusnet:notice_info
 759
 760         foreach ($this->extra as $el) {
 761             list($tag, $attrs, $content) = $el;
 762             $xs->element($tag, $attrs, $content);
 763         }
 764
 765         $xs->elementEnd($tag);
 766
 767         return;
 768     }
 769
 770     private function _child($element, $tag, $namespace=self::SPEC)
 771     {
 772         return ActivityUtils::child($element, $tag, $namespace);
 773     }
 774
 775     /**
 776      * For consistency, we'll always output UTC rather than local time.
 777      * Note that clients *should* accept any timezone we give them as long
 778      * as it's properly formatted.
 779      *
 780      * @param int $tm Unix timestamp
 781      * @return string
 782      */
 783     static function iso8601Date($tm)
 784     {
 785         $dateStr = date('d F Y H:i:s', $tm);
 786         $d = new DateTime($dateStr, new DateTimeZone('UTC'));
 787         return $d->format('c');
 788     }
 789 }