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/wp-includes/ -> feed.php (source)

   1  <?php
   2  /**
   3   * WordPress Feed API
   4   *
   5   * Many of the functions used in here belong in The Loop, or The Loop for the
   6   * Feeds.
   7   *
   8   * @package WordPress
   9   * @subpackage Feed
  10   * @since 2.1.0
  11   */
  12  
  13  /**
  14   * Retrieves RSS container for the bloginfo function.
  15   *
  16   * You can retrieve anything that you can using the get_bloginfo() function.
  17   * Everything will be stripped of tags and characters converted, when the values
  18   * are retrieved for use in the feeds.
  19   *
  20   * @since 1.5.1
  21   *
  22   * @see get_bloginfo() For the list of possible values to display.
  23   *
  24   * @param string $show See get_bloginfo() for possible values.
  25   * @return string
  26   */
  27  function get_bloginfo_rss( $show = '' ) {
  28      $info = strip_tags( get_bloginfo( $show ) );
  29      /**
  30       * Filters the bloginfo for use in RSS feeds.
  31       *
  32       * @since 2.2.0
  33       *
  34       * @see convert_chars()
  35       * @see get_bloginfo()
  36       *
  37       * @param string $info Converted string value of the blog information.
  38       * @param string $show The type of blog information to retrieve.
  39       */
  40      return apply_filters( 'get_bloginfo_rss', convert_chars( $info ), $show );
  41  }
  42  
  43  /**
  44   * Displays RSS container for the bloginfo function.
  45   *
  46   * You can retrieve anything that you can using the get_bloginfo() function.
  47   * Everything will be stripped of tags and characters converted, when the values
  48   * are retrieved for use in the feeds.
  49   *
  50   * @since 0.71
  51   *
  52   * @see get_bloginfo() For the list of possible values to display.
  53   *
  54   * @param string $show See get_bloginfo() for possible values.
  55   */
  56  function bloginfo_rss( $show = '' ) {
  57      /**
  58       * Filters the bloginfo for display in RSS feeds.
  59       *
  60       * @since 2.1.0
  61       *
  62       * @see get_bloginfo()
  63       *
  64       * @param string $rss_container RSS container for the blog information.
  65       * @param string $show          The type of blog information to retrieve.
  66       */
  67      echo apply_filters( 'bloginfo_rss', get_bloginfo_rss( $show ), $show );
  68  }
  69  
  70  /**
  71   * Retrieves the default feed.
  72   *
  73   * The default feed is 'rss2', unless a plugin changes it through the
  74   * {@see 'default_feed'} filter.
  75   *
  76   * @since 2.5.0
  77   *
  78   * @return string Default feed, or for example 'rss2', 'atom', etc.
  79   */
  80  function get_default_feed() {
  81      /**
  82       * Filters the default feed type.
  83       *
  84       * @since 2.5.0
  85       *
  86       * @param string $feed_type Type of default feed. Possible values include 'rss2', 'atom'.
  87       *                          Default 'rss2'.
  88       */
  89      $default_feed = apply_filters( 'default_feed', 'rss2' );
  90  
  91      return ( 'rss' === $default_feed ) ? 'rss2' : $default_feed;
  92  }
  93  
  94  /**
  95   * Retrieves the blog title for the feed title.
  96   *
  97   * @since 2.2.0
  98   * @since 4.4.0 The optional `$sep` parameter was deprecated and renamed to `$deprecated`.
  99   *
 100   * @param string $deprecated Unused.
 101   * @return string The document title.
 102   */
 103  function get_wp_title_rss( $deprecated = '&#8211;' ) {
 104      if ( '&#8211;' !== $deprecated ) {
 105          /* translators: %s: 'document_title_separator' filter name. */
 106          _deprecated_argument( __FUNCTION__, '4.4.0', sprintf( __( 'Use the %s filter instead.' ), '<code>document_title_separator</code>' ) );
 107      }
 108  
 109      /**
 110       * Filters the blog title for use as the feed title.
 111       *
 112       * @since 2.2.0
 113       * @since 4.4.0 The `$sep` parameter was deprecated and renamed to `$deprecated`.
 114       *
 115       * @param string $title      The current blog title.
 116       * @param string $deprecated Unused.
 117       */
 118      return apply_filters( 'get_wp_title_rss', wp_get_document_title(), $deprecated );
 119  }
 120  
 121  /**
 122   * Displays the blog title for display of the feed title.
 123   *
 124   * @since 2.2.0
 125   * @since 4.4.0 The optional `$sep` parameter was deprecated and renamed to `$deprecated`.
 126   *
 127   * @param string $deprecated Unused.
 128   */
 129  function wp_title_rss( $deprecated = '&#8211;' ) {
 130      if ( '&#8211;' !== $deprecated ) {
 131          /* translators: %s: 'document_title_separator' filter name. */
 132          _deprecated_argument( __FUNCTION__, '4.4.0', sprintf( __( 'Use the %s filter instead.' ), '<code>document_title_separator</code>' ) );
 133      }
 134  
 135      /**
 136       * Filters the blog title for display of the feed title.
 137       *
 138       * @since 2.2.0
 139       * @since 4.4.0 The `$sep` parameter was deprecated and renamed to `$deprecated`.
 140       *
 141       * @see get_wp_title_rss()
 142       *
 143       * @param string $wp_title_rss The current blog title.
 144       * @param string $deprecated   Unused.
 145       */
 146      echo apply_filters( 'wp_title_rss', get_wp_title_rss(), $deprecated );
 147  }
 148  
 149  /**
 150   * Retrieves the current post title for the feed.
 151   *
 152   * @since 2.0.0
 153   * @since 6.6.0 Added the `$post` parameter.
 154   *
 155   * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 156   * @return string Current post title.
 157   */
 158  function get_the_title_rss( $post = 0 ) {
 159      $title = get_the_title( $post );
 160  
 161      /**
 162       * Filters the post title for use in a feed.
 163       *
 164       * @since 1.2.0
 165       *
 166       * @param string $title The current post title.
 167       */
 168      return apply_filters( 'the_title_rss', $title );
 169  }
 170  
 171  /**
 172   * Displays the post title in the feed.
 173   *
 174   * @since 0.71
 175   */
 176  function the_title_rss() {
 177      echo get_the_title_rss();
 178  }
 179  
 180  /**
 181   * Retrieves the post content for feeds.
 182   *
 183   * @since 2.9.0
 184   *
 185   * @see get_the_content()
 186   *
 187   * @param string $feed_type The type of feed. rss2 | atom | rss | rdf
 188   * @return string The filtered content.
 189   */
 190  function get_the_content_feed( $feed_type = null ) {
 191      if ( ! $feed_type ) {
 192          $feed_type = get_default_feed();
 193      }
 194  
 195      /** This filter is documented in wp-includes/post-template.php */
 196      $content = apply_filters( 'the_content', get_the_content() );
 197      $content = str_replace( ']]>', ']]&gt;', $content );
 198  
 199      /**
 200       * Filters the post content for use in feeds.
 201       *
 202       * @since 2.9.0
 203       *
 204       * @param string $content   The current post content.
 205       * @param string $feed_type Type of feed. Possible values include 'rss2', 'atom'.
 206       *                          Default 'rss2'.
 207       */
 208      return apply_filters( 'the_content_feed', $content, $feed_type );
 209  }
 210  
 211  /**
 212   * Displays the post content for feeds.
 213   *
 214   * @since 2.9.0
 215   *
 216   * @param string $feed_type The type of feed. rss2 | atom | rss | rdf
 217   */
 218  function the_content_feed( $feed_type = null ) {
 219      echo get_the_content_feed( $feed_type );
 220  }
 221  
 222  /**
 223   * Displays the post excerpt for the feed.
 224   *
 225   * @since 0.71
 226   */
 227  function the_excerpt_rss() {
 228      $output = get_the_excerpt();
 229      /**
 230       * Filters the post excerpt for a feed.
 231       *
 232       * @since 1.2.0
 233       *
 234       * @param string $output The current post excerpt.
 235       */
 236      echo apply_filters( 'the_excerpt_rss', $output );
 237  }
 238  
 239  /**
 240   * Displays the permalink to the post for use in feeds.
 241   *
 242   * @since 2.3.0
 243   */
 244  function the_permalink_rss() {
 245      /**
 246       * Filters the permalink to the post for use in feeds.
 247       *
 248       * @since 2.3.0
 249       *
 250       * @param string $post_permalink The current post permalink.
 251       */
 252      echo esc_url( apply_filters( 'the_permalink_rss', get_permalink() ) );
 253  }
 254  
 255  /**
 256   * Outputs the link to the comments for the current post in an XML safe way.
 257   *
 258   * @since 3.0.0
 259   */
 260  function comments_link_feed() {
 261      /**
 262       * Filters the comments permalink for the current post.
 263       *
 264       * @since 3.6.0
 265       *
 266       * @param string $comment_permalink The current comment permalink with
 267       *                                  '#comments' appended.
 268       */
 269      echo esc_url( apply_filters( 'comments_link_feed', get_comments_link() ) );
 270  }
 271  
 272  /**
 273   * Displays the feed GUID for the current comment.
 274   *
 275   * @since 2.5.0
 276   *
 277   * @param int|WP_Comment $comment_id Optional comment object or ID. Defaults to global comment object.
 278   */
 279  function comment_guid( $comment_id = null ) {
 280      echo esc_url( get_comment_guid( $comment_id ) );
 281  }
 282  
 283  /**
 284   * Retrieves the feed GUID for the current comment.
 285   *
 286   * @since 2.5.0
 287   *
 288   * @param int|WP_Comment $comment_id Optional comment object or ID. Defaults to global comment object.
 289   * @return string|false GUID for comment on success, false on failure.
 290   */
 291  function get_comment_guid( $comment_id = null ) {
 292      $comment = get_comment( $comment_id );
 293  
 294      if ( ! is_object( $comment ) ) {
 295          return false;
 296      }
 297  
 298      return get_the_guid( $comment->comment_post_ID ) . '#comment-' . $comment->comment_ID;
 299  }
 300  
 301  /**
 302   * Displays the link to the comments.
 303   *
 304   * @since 1.5.0
 305   * @since 4.4.0 Introduced the `$comment` argument.
 306   *
 307   * @param int|WP_Comment $comment Optional. Comment object or ID. Defaults to global comment object.
 308   */
 309  function comment_link( $comment = null ) {
 310      /**
 311       * Filters the current comment's permalink.
 312       *
 313       * @since 3.6.0
 314       *
 315       * @see get_comment_link()
 316       *
 317       * @param string $comment_permalink The current comment permalink.
 318       */
 319      echo esc_url( apply_filters( 'comment_link', get_comment_link( $comment ) ) );
 320  }
 321  
 322  /**
 323   * Retrieves the current comment author for use in the feeds.
 324   *
 325   * @since 2.0.0
 326   *
 327   * @return string Comment Author.
 328   */
 329  function get_comment_author_rss() {
 330      /**
 331       * Filters the current comment author for use in a feed.
 332       *
 333       * @since 1.5.0
 334       *
 335       * @see get_comment_author()
 336       *
 337       * @param string $comment_author The current comment author.
 338       */
 339      return apply_filters( 'comment_author_rss', get_comment_author() );
 340  }
 341  
 342  /**
 343   * Displays the current comment author in the feed.
 344   *
 345   * @since 1.0.0
 346   */
 347  function comment_author_rss() {
 348      echo get_comment_author_rss();
 349  }
 350  
 351  /**
 352   * Displays the current comment content for use in the feeds.
 353   *
 354   * @since 1.0.0
 355   */
 356  function comment_text_rss() {
 357      $comment_text = get_comment_text();
 358      /**
 359       * Filters the current comment content for use in a feed.
 360       *
 361       * @since 1.5.0
 362       *
 363       * @param string $comment_text The content of the current comment.
 364       */
 365      $comment_text = apply_filters( 'comment_text_rss', $comment_text );
 366      echo $comment_text;
 367  }
 368  
 369  /**
 370   * Retrieves all of the post categories, formatted for use in feeds.
 371   *
 372   * All of the categories for the current post in the feed loop, will be
 373   * retrieved and have feed markup added, so that they can easily be added to the
 374   * RSS2, Atom, or RSS1 and RSS0.91 RDF feeds.
 375   *
 376   * @since 2.1.0
 377   *
 378   * @param string $type Optional, default is the type returned by get_default_feed().
 379   * @return string All of the post categories for displaying in the feed.
 380   */
 381  function get_the_category_rss( $type = null ) {
 382      if ( empty( $type ) ) {
 383          $type = get_default_feed();
 384      }
 385      $categories = get_the_category();
 386      $tags       = get_the_tags();
 387      $the_list   = '';
 388      $cat_names  = array();
 389  
 390      $filter = 'rss';
 391      if ( 'atom' === $type ) {
 392          $filter = 'raw';
 393      }
 394  
 395      if ( ! empty( $categories ) ) {
 396          foreach ( (array) $categories as $category ) {
 397              $cat_names[] = sanitize_term_field( 'name', $category->name, $category->term_id, 'category', $filter );
 398          }
 399      }
 400  
 401      if ( ! empty( $tags ) ) {
 402          foreach ( (array) $tags as $tag ) {
 403              $cat_names[] = sanitize_term_field( 'name', $tag->name, $tag->term_id, 'post_tag', $filter );
 404          }
 405      }
 406  
 407      $cat_names = array_unique( $cat_names );
 408  
 409      foreach ( $cat_names as $cat_name ) {
 410          if ( 'rdf' === $type ) {
 411              $the_list .= "\t\t<dc:subject><![CDATA[$cat_name]]></dc:subject>\n";
 412          } elseif ( 'atom' === $type ) {
 413              $the_list .= sprintf( '<category scheme="%1$s" term="%2$s" />', esc_attr( get_bloginfo_rss( 'url' ) ), esc_attr( $cat_name ) );
 414          } else {
 415              $the_list .= "\t\t<category><![CDATA[" . html_entity_decode( $cat_name, ENT_COMPAT, get_option( 'blog_charset' ) ) . "]]></category>\n";
 416          }
 417      }
 418  
 419      /**
 420       * Filters all of the post categories for display in a feed.
 421       *
 422       * @since 1.2.0
 423       *
 424       * @param string $the_list All of the RSS post categories.
 425       * @param string $type     Type of feed. Possible values include 'rss2', 'atom'.
 426       *                         Default 'rss2'.
 427       */
 428      return apply_filters( 'the_category_rss', $the_list, $type );
 429  }
 430  
 431  /**
 432   * Displays the post categories in the feed.
 433   *
 434   * @since 0.71
 435   *
 436   * @see get_the_category_rss() For better explanation.
 437   *
 438   * @param string $type Optional, default is the type returned by get_default_feed().
 439   */
 440  function the_category_rss( $type = null ) {
 441      echo get_the_category_rss( $type );
 442  }
 443  
 444  /**
 445   * Displays the HTML type based on the blog setting.
 446   *
 447   * The two possible values are either 'xhtml' or 'html'.
 448   *
 449   * @since 2.2.0
 450   */
 451  function html_type_rss() {
 452      $type = get_bloginfo( 'html_type' );
 453      if ( str_contains( $type, 'xhtml' ) ) {
 454          $type = 'xhtml';
 455      } else {
 456          $type = 'html';
 457      }
 458      echo $type;
 459  }
 460  
 461  /**
 462   * Displays the rss enclosure for the current post.
 463   *
 464   * Uses the global $post to check whether the post requires a password and if
 465   * the user has the password for the post. If not then it will return before
 466   * displaying.
 467   *
 468   * Also uses the function get_post_custom() to get the post's 'enclosure'
 469   * metadata field and parses the value to display the enclosure(s). The
 470   * enclosure(s) consist of enclosure HTML tag(s) with a URI and other
 471   * attributes.
 472   *
 473   * @since 1.5.0
 474   */
 475  function rss_enclosure() {
 476      if ( post_password_required() ) {
 477          return;
 478      }
 479  
 480      foreach ( (array) get_post_custom() as $key => $val ) {
 481          if ( 'enclosure' === $key ) {
 482              foreach ( (array) $val as $enc ) {
 483                  $enclosure = explode( "\n", $enc );
 484  
 485                  if ( count( $enclosure ) < 3 ) {
 486                      continue;
 487                  }
 488  
 489                  // Only get the first element, e.g. 'audio/mpeg' from 'audio/mpeg mpga mp2 mp3'.
 490                  $t    = preg_split( '/[ \t]/', trim( $enclosure[2] ) );
 491                  $type = $t[0];
 492  
 493                  /**
 494                   * Filters the RSS enclosure HTML link tag for the current post.
 495                   *
 496                   * @since 2.2.0
 497                   *
 498                   * @param string $html_link_tag The HTML link tag with a URI and other attributes.
 499                   */
 500                  echo apply_filters( 'rss_enclosure', '<enclosure url="' . esc_url( trim( $enclosure[0] ) ) . '" length="' . absint( trim( $enclosure[1] ) ) . '" type="' . esc_attr( $type ) . '" />' . "\n" );
 501              }
 502          }
 503      }
 504  }
 505  
 506  /**
 507   * Displays the atom enclosure for the current post.
 508   *
 509   * Uses the global $post to check whether the post requires a password and if
 510   * the user has the password for the post. If not then it will return before
 511   * displaying.
 512   *
 513   * Also uses the function get_post_custom() to get the post's 'enclosure'
 514   * metadata field and parses the value to display the enclosure(s). The
 515   * enclosure(s) consist of link HTML tag(s) with a URI and other attributes.
 516   *
 517   * @since 2.2.0
 518   */
 519  function atom_enclosure() {
 520      if ( post_password_required() ) {
 521          return;
 522      }
 523  
 524      foreach ( (array) get_post_custom() as $key => $val ) {
 525          if ( 'enclosure' === $key ) {
 526              foreach ( (array) $val as $enc ) {
 527                  $enclosure = explode( "\n", $enc );
 528  
 529                  $url    = '';
 530                  $type   = '';
 531                  $length = 0;
 532  
 533                  $mimes = get_allowed_mime_types();
 534  
 535                  // Parse URL.
 536                  if ( isset( $enclosure[0] ) && is_string( $enclosure[0] ) ) {
 537                      $url = trim( $enclosure[0] );
 538                  }
 539  
 540                  // Parse length and type.
 541                  for ( $i = 1; $i <= 2; $i++ ) {
 542                      if ( isset( $enclosure[ $i ] ) ) {
 543                          if ( is_numeric( $enclosure[ $i ] ) ) {
 544                              $length = trim( $enclosure[ $i ] );
 545                          } elseif ( in_array( $enclosure[ $i ], $mimes, true ) ) {
 546                              $type = trim( $enclosure[ $i ] );
 547                          }
 548                      }
 549                  }
 550  
 551                  $html_link_tag = sprintf(
 552                      "<link href=\"%s\" rel=\"enclosure\" length=\"%d\" type=\"%s\" />\n",
 553                      esc_url( $url ),
 554                      esc_attr( $length ),
 555                      esc_attr( $type )
 556                  );
 557  
 558                  /**
 559                   * Filters the atom enclosure HTML link tag for the current post.
 560                   *
 561                   * @since 2.2.0
 562                   *
 563                   * @param string $html_link_tag The HTML link tag with a URI and other attributes.
 564                   */
 565                  echo apply_filters( 'atom_enclosure', $html_link_tag );
 566              }
 567          }
 568      }
 569  }
 570  
 571  /**
 572   * Determines the type of a string of data with the data formatted.
 573   *
 574   * Tell whether the type is text, HTML, or XHTML, per RFC 4287 section 3.1.
 575   *
 576   * In the case of WordPress, text is defined as containing no markup,
 577   * XHTML is defined as "well formed", and HTML as tag soup (i.e., the rest).
 578   *
 579   * Container div tags are added to XHTML values, per section 3.1.1.3.
 580   *
 581   * @link http://www.atomenabled.org/developers/syndication/atom-format-spec.php#rfc.section.3.1
 582   *
 583   * @since 2.5.0
 584   *
 585   * @param string $data Input string.
 586   * @return array array(type, value)
 587   */
 588  function prep_atom_text_construct( $data ) {
 589      if ( ! str_contains( $data, '<' ) && ! str_contains( $data, '&' ) ) {
 590          return array( 'text', $data );
 591      }
 592  
 593      if ( ! function_exists( 'xml_parser_create' ) ) {
 594          wp_trigger_error( '', __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML extension." ) );
 595  
 596          return array( 'html', "<![CDATA[$data]]>" );
 597      }
 598  
 599      $parser = xml_parser_create();
 600      xml_parse( $parser, '<div>' . $data . '</div>', true );
 601      $code = xml_get_error_code( $parser );
 602      xml_parser_free( $parser );
 603      unset( $parser );
 604  
 605      if ( ! $code ) {
 606          if ( ! str_contains( $data, '<' ) ) {
 607              return array( 'text', $data );
 608          } else {
 609              $data = "<div xmlns='http://www.w3.org/1999/xhtml'>$data</div>";
 610              return array( 'xhtml', $data );
 611          }
 612      }
 613  
 614      if ( ! str_contains( $data, ']]>' ) ) {
 615          return array( 'html', "<![CDATA[$data]]>" );
 616      } else {
 617          return array( 'html', htmlspecialchars( $data ) );
 618      }
 619  }
 620  
 621  /**
 622   * Displays Site Icon in atom feeds.
 623   *
 624   * @since 4.3.0
 625   *
 626   * @see get_site_icon_url()
 627   */
 628  function atom_site_icon() {
 629      $url = get_site_icon_url( 32 );
 630      if ( $url ) {
 631          echo '<icon>' . convert_chars( $url ) . "</icon>\n";
 632      }
 633  }
 634  
 635  /**
 636   * Displays Site Icon in RSS2.
 637   *
 638   * @since 4.3.0
 639   */
 640  function rss2_site_icon() {
 641      $rss_title = get_wp_title_rss();
 642      if ( empty( $rss_title ) ) {
 643          $rss_title = get_bloginfo_rss( 'name' );
 644      }
 645  
 646      $url = get_site_icon_url( 32 );
 647      if ( $url ) {
 648          echo '
 649  <image>
 650      <url>' . convert_chars( $url ) . '</url>
 651      <title>' . $rss_title . '</title>
 652      <link>' . get_bloginfo_rss( 'url' ) . '</link>
 653      <width>32</width>
 654      <height>32</height>
 655  </image> ' . "\n";
 656      }
 657  }
 658  
 659  /**
 660   * Returns the link for the currently displayed feed.
 661   *
 662   * @since 5.3.0
 663   *
 664   * @return string Correct link for the atom:self element.
 665   */
 666  function get_self_link() {
 667      $parsed = parse_url( home_url() );
 668  
 669      $domain = $parsed['host'];
 670      if ( isset( $parsed['port'] ) ) {
 671          $domain .= ':' . $parsed['port'];
 672      }
 673  
 674      return set_url_scheme( 'http://' . $domain . wp_unslash( $_SERVER['REQUEST_URI'] ) );
 675  }
 676  
 677  /**
 678   * Displays the link for the currently displayed feed in a XSS safe way.
 679   *
 680   * Generate a correct link for the atom:self element.
 681   *
 682   * @since 2.5.0
 683   */
 684  function self_link() {
 685      /**
 686       * Filters the current feed URL.
 687       *
 688       * @since 3.6.0
 689       *
 690       * @see set_url_scheme()
 691       * @see wp_unslash()
 692       *
 693       * @param string $feed_link The link for the feed with set URL scheme.
 694       */
 695      echo esc_url( apply_filters( 'self_link', get_self_link() ) );
 696  }
 697  
 698  /**
 699   * Gets the UTC time of the most recently modified post from WP_Query.
 700   *
 701   * If viewing a comment feed, the time of the most recently modified
 702   * comment will be returned.
 703   *
 704   * @since 5.2.0
 705   *
 706   * @global WP_Query $wp_query WordPress Query object.
 707   *
 708   * @param string $format Date format string to return the time in.
 709   * @return string|false The time in requested format, or false on failure.
 710   */
 711  function get_feed_build_date( $format ) {
 712      global $wp_query;
 713  
 714      $datetime          = false;
 715      $max_modified_time = false;
 716      $utc               = new DateTimeZone( 'UTC' );
 717  
 718      if ( ! empty( $wp_query ) && $wp_query->have_posts() ) {
 719          // Extract the post modified times from the posts.
 720          $modified_times = wp_list_pluck( $wp_query->posts, 'post_modified_gmt' );
 721  
 722          // If this is a comment feed, check those objects too.
 723          if ( $wp_query->is_comment_feed() && $wp_query->comment_count ) {
 724              // Extract the comment modified times from the comments.
 725              $comment_times = wp_list_pluck( $wp_query->comments, 'comment_date_gmt' );
 726  
 727              // Add the comment times to the post times for comparison.
 728              $modified_times = array_merge( $modified_times, $comment_times );
 729          }
 730  
 731          // Determine the maximum modified time.
 732          $datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', max( $modified_times ), $utc );
 733      }
 734  
 735      if ( false === $datetime ) {
 736          // Fall back to last time any post was modified or published.
 737          $datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', get_lastpostmodified( 'GMT' ), $utc );
 738      }
 739  
 740      if ( false !== $datetime ) {
 741          $max_modified_time = $datetime->format( $format );
 742      }
 743  
 744      /**
 745       * Filters the date the last post or comment in the query was modified.
 746       *
 747       * @since 5.2.0
 748       *
 749       * @param string|false $max_modified_time Date the last post or comment was modified in the query, in UTC.
 750       *                                        False on failure.
 751       * @param string       $format            The date format requested in get_feed_build_date().
 752       */
 753      return apply_filters( 'get_feed_build_date', $max_modified_time, $format );
 754  }
 755  
 756  /**
 757   * Returns the content type for specified feed type.
 758   *
 759   * @since 2.8.0
 760   *
 761   * @param string $type Type of feed. Possible values include 'rss', rss2', 'atom', and 'rdf'.
 762   * @return string Content type for specified feed type.
 763   */
 764  function feed_content_type( $type = '' ) {
 765      if ( empty( $type ) ) {
 766          $type = get_default_feed();
 767      }
 768  
 769      $types = array(
 770          'rss'      => 'application/rss+xml',
 771          'rss2'     => 'application/rss+xml',
 772          'rss-http' => 'text/xml',
 773          'atom'     => 'application/atom+xml',
 774          'rdf'      => 'application/rdf+xml',
 775      );
 776  
 777      $content_type = ( ! empty( $types[ $type ] ) ) ? $types[ $type ] : 'application/octet-stream';
 778  
 779      /**
 780       * Filters the content type for a specific feed type.
 781       *
 782       * @since 2.8.0
 783       *
 784       * @param string $content_type Content type indicating the type of data that a feed contains.
 785       * @param string $type         Type of feed. Possible values include 'rss', rss2', 'atom', and 'rdf'.
 786       */
 787      return apply_filters( 'feed_content_type', $content_type, $type );
 788  }
 789  
 790  /**
 791   * Builds SimplePie object based on RSS or Atom feed from URL.
 792   *
 793   * @since 2.8.0
 794   *
 795   * @param string|string[] $url URL of feed to retrieve. If an array of URLs, the feeds are merged
 796   *                             using SimplePie's multifeed feature.
 797   *                             See also {@link http://simplepie.org/wiki/faq/typical_multifeed_gotchas}
 798   * @return SimplePie\SimplePie|WP_Error SimplePie object on success or WP_Error object on failure.
 799   */
 800  function fetch_feed( $url ) {
 801      if ( ! class_exists( 'SimplePie\SimplePie', false ) ) {
 802          require_once  ABSPATH . WPINC . '/class-simplepie.php';
 803      }
 804  
 805      require_once  ABSPATH . WPINC . '/class-wp-feed-cache-transient.php';
 806      require_once  ABSPATH . WPINC . '/class-wp-simplepie-file.php';
 807      require_once  ABSPATH . WPINC . '/class-wp-simplepie-sanitize-kses.php';
 808  
 809      $feed = new SimplePie\SimplePie();
 810  
 811      $feed->set_sanitize_class( 'WP_SimplePie_Sanitize_KSES' );
 812      /*
 813       * We must manually overwrite $feed->sanitize because SimplePie's constructor
 814       * sets it before we have a chance to set the sanitization class.
 815       */
 816      $feed->sanitize = new WP_SimplePie_Sanitize_KSES();
 817  
 818      // Register the cache handler using the recommended method for SimplePie 1.3 or later.
 819      if ( method_exists( 'SimplePie_Cache', 'register' ) ) {
 820          SimplePie_Cache::register( 'wp_transient', 'WP_Feed_Cache_Transient' );
 821          $feed->set_cache_location( 'wp_transient' );
 822      } else {
 823          // Back-compat for SimplePie 1.2.x.
 824          require_once  ABSPATH . WPINC . '/class-wp-feed-cache.php';
 825          $feed->set_cache_class( 'WP_Feed_Cache' );
 826      }
 827  
 828      $feed->set_file_class( 'WP_SimplePie_File' );
 829  
 830      $feed->set_feed_url( $url );
 831      /** This filter is documented in wp-includes/class-wp-feed-cache-transient.php */
 832      $feed->set_cache_duration( apply_filters( 'wp_feed_cache_transient_lifetime', 12 * HOUR_IN_SECONDS, $url ) );
 833  
 834      /**
 835       * Fires just before processing the SimplePie feed object.
 836       *
 837       * @since 3.0.0
 838       *
 839       * @param SimplePie\SimplePie $feed SimplePie feed object (passed by reference).
 840       * @param string|string[]     $url  URL of feed or array of URLs of feeds to retrieve.
 841       */
 842      do_action_ref_array( 'wp_feed_options', array( &$feed, $url ) );
 843  
 844      $feed->init();
 845      $feed->set_output_encoding( get_bloginfo( 'charset' ) );
 846  
 847      if ( $feed->error() ) {
 848          return new WP_Error( 'simplepie-error', $feed->error() );
 849      }
 850  
 851      return $feed;
 852  }


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