do_enclose

do_enclose: 这个钩子用来为一个文章打印一个封套。

检查内容中的视频和音频链接，以添加为附件。

不会添加已经添加过的附件，并且会删除已经不在文章中的附件。这就是所谓的pingbacks和trackbacks。

function do_enclose( $content, $post ) {
	global $wpdb;

	// @todo Tidy this code and make the debug code optional.
	include_once ABSPATH . WPINC . '/class-IXR.php';

	$post = get_post( $post );
	if ( ! $post ) {
		return false;
	}

	if ( null === $content ) {
		$content = $post->post_content;
	}

	$post_links = array();

	$pung = get_enclosed( $post->ID );

	$post_links_temp = wp_extract_urls( $content );

	foreach ( $pung as $link_test ) {
		// Link is no longer in post.
		if ( ! in_array( $link_test, $post_links_temp, true ) ) {
			$mids = $wpdb->get_col( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = 'enclosure' AND meta_value LIKE %s", $post->ID, $wpdb->esc_like( $link_test ) . '%' ) );
			foreach ( $mids as $mid ) {
				delete_metadata_by_mid( 'post', $mid );
			}
		}
	}

	foreach ( (array) $post_links_temp as $link_test ) {
		// If we haven't pung it already.
		if ( ! in_array( $link_test, $pung, true ) ) {
			$test = parse_url( $link_test );
			if ( false === $test ) {
				continue;
			}
			if ( isset( $test['query'] ) ) {
				$post_links[] = $link_test;
			} elseif ( isset( $test['path'] ) && ( '/' !== $test['path'] ) && ( '' !== $test['path'] ) ) {
				$post_links[] = $link_test;
			}
		}
	}

	/**
	 * Filters the list of enclosure links before querying the database.
	 *
	 * Allows for the addition and/or removal of potential enclosures to save
	 * to postmeta before checking the database for existing enclosures.
	 *
	 * @since 4.4.0
	 *
	 * @param string[] $post_links An array of enclosure links.
	 * @param int      $post_ID    Post ID.
	 */
	$post_links = apply_filters( 'enclosure_links', $post_links, $post->ID );

	foreach ( (array) $post_links as $url ) {
		$url = strip_fragment_from_url( $url );

		if ( '' !== $url && ! $wpdb->get_var( $wpdb->prepare( "SELECT post_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = 'enclosure' AND meta_value LIKE %s", $post->ID, $wpdb->esc_like( $url ) . '%' ) ) ) {

			$headers = wp_get_http_headers( $url );
			if ( $headers ) {
				$len           = isset( $headers['content-length'] ) ? (int) $headers['content-length'] : 0;
				$type          = isset( $headers['content-type'] ) ? $headers['content-type'] : '';
				$allowed_types = array( 'video', 'audio' );

				// Check to see if we can figure out the mime type from the extension.
				$url_parts = parse_url( $url );
				if ( false !== $url_parts && ! empty( $url_parts['path'] ) ) {
					$extension = pathinfo( $url_parts['path'], PATHINFO_EXTENSION );
					if ( ! empty( $extension ) ) {
						foreach ( wp_get_mime_types() as $exts => $mime ) {
							if ( preg_match( '!^(' . $exts . ')$!i', $extension ) ) {
								$type = $mime;
								break;
							}
						}
					}
				}

				if ( in_array( substr( $type, 0, strpos( $type, '/' ) ), $allowed_types, true ) ) {
					add_post_meta( $post->ID, 'enclosure', "$urln$lenn$mimen" );
				}
			}
		}
	}
}