自动设置内容里的第一张图片为特色图片，并上传到Aliyun OSS

本文章测试于 WordPress 4.4.2

这儿需要用的两个插件

阿里云附件存储 [http://yii.im/posts/aliyun-oss-support-plugin-for-wordpress]
Auto Post Thumbnail [https://wordpress.org/plugins/auto-post-thumbnail/]

接下来要对 auto post thumbnail 里的函数 apt_generate_post_thumb 稍作修改，将文件下载保存在本地替换成使用 wp_handle_sideload 上传到OSS

/**
 * Function to fetch the image from URL and generate the required thumbnails
 */
function apt_generate_post_thumb($matches, $key, $post_content, $post_id)
{
    // Make sure to assign correct title to the image. Extract it from img tag
    $imageTitle = '';
    preg_match_all('/<\s*img [^\>]*title\s*=\s*[\""\']?([^\""\'>]*)/i', $post_content, $matchesTitle);

    if (count($matchesTitle) && isset($matchesTitle[1])) {
        $imageTitle = $matchesTitle[1][$key];
    }

    // Get the URL now for further processing
    $imageUrl = $matches[1][$key];

    // Get the file name
    $filename = substr($imageUrl, (strrpos($imageUrl, '/'))+1);

    if (!(($uploads = wp_upload_dir(current_time('mysql')) ) && false === $uploads['error'])) {
        return null;
    }

    // Generate unique file name
    $filename = wp_unique_filename( $uploads['path'], $filename );


    // gives us access to the download_url() and wp_handle_sideload() functions
    if ( ! function_exists( 'download_url' ) ) {
        require_once( ABSPATH . 'wp-admin/includes/file.php' );
    }

    $timeout_seconds = 5;
    // download file to temp dir
    $temp_file = download_url( $imageUrl, $timeout_seconds );

    if (!is_wp_error( $temp_file )) {
        // array based on $_FILE as seen in PHP file uploads
        $file = array(
            'name' => basename($imageUrl), // ex: wp-header-logo.png
            'type' => 'image/png',
            'tmp_name' => $temp_file,
            'error' => 0,
            'size' => filesize($temp_file),
        );

        $overrides = array(
            // tells WordPress to not look for the POST form
            // fields that would normally be present, default is true,
            // we downloaded the file from a remote server, so there
            // will be no form fields
            'test_form' => false,

            // setting this to false lets WordPress allow empty files, not recommended
            'test_size' => true,

            // A properly uploaded file will pass this test.
            // There should be no reason to override this one.
            'test_upload' => true,
        );

        // move the temporary file into the uploads directory
        $results = wp_handle_sideload( $file, $overrides );

        if (!empty($results['error'])) {
            // insert any error handling here
            return null;
        } else {

            $filename   = $results['file']; // full path to the file
            $local_url  = $results['url']; // URL to the file in the uploads dir
            $type       = $results['type']; // MIME type of the file

            $attachment = array(
                'post_mime_type' => $type,
                'guid' => $local_url,
                'post_parent' => null,
                'post_title' => $imageTitle,
                'post_content' => '',
            );

            $thumb_id = wp_insert_attachment($attachment, $filename, $post_id);

            if ( !is_wp_error($thumb_id) ) {
                require_once(ABSPATH . '/wp-admin/includes/image.php');

                // Added fix by misthero as suggested
                wp_update_attachment_metadata( $thumb_id, wp_generate_attachment_metadata( $thumb_id, $filename ) );
                update_attached_file( $thumb_id, $filename );

                return $thumb_id;
            }
        }
    }
    return null;
}