WordPress函数wp_generate_attachment_metadata()获取一个附件(图片/文件)的meta信息

描述：

获取一个附件(图片/文件)的meta信息

用法：

<?php wp_generate_attachment_metadata( $attachment_id, $file ); ?>

参数：

$attachment_id

(int) (必填) 要处理的附件ID。

默认值: None

$file

(string) (必填) 文件在服务器上的位置。使用绝对路径而不是文件的URI。文件必须在uploads目录中。请参阅wp_upload_dir()

默认值: None

源文件：

/**
 * Generate post thumbnail attachment meta data.
 *
 * @since 2.1.0
 *
 * @global array $_wp_additional_image_sizes
 *
 * @param int $attachment_id Attachment Id to process.
 * @param string $file Filepath of the Attached image.
 * @return mixed Metadata for attachment.
 */
function wp_generate_attachment_metadata( $attachment_id, $file ) {
	$attachment = get_post( $attachment_id );

	$metadata = array();
	$support = false;
	if ( preg_match('!^image/!', get_post_mime_type( $attachment )) && file_is_displayable_image($file) ) {
		$imagesize = getimagesize( $file );
		$metadata['width'] = $imagesize[0];
		$metadata['height'] = $imagesize[1];

		// Make the file path relative to the upload dir.
		$metadata['file'] = _wp_relative_upload_path($file);

		// Make thumbnails and other intermediate sizes.
		global $_wp_additional_image_sizes;

		$sizes = array();
		foreach ( get_intermediate_image_sizes() as $s ) {
			$sizes[$s] = array( 'width' => '', 'height' => '', 'crop' => false );
			if ( isset( $_wp_additional_image_sizes[$s]['width'] ) )
				$sizes[$s]['width'] = intval( $_wp_additional_image_sizes[$s]['width'] ); // For theme-added sizes
			else
				$sizes[$s]['width'] = get_option( "{$s}_size_w" ); // For default sizes set in options
			if ( isset( $_wp_additional_image_sizes[$s]['height'] ) )
				$sizes[$s]['height'] = intval( $_wp_additional_image_sizes[$s]['height'] ); // For theme-added sizes
			else
				$sizes[$s]['height'] = get_option( "{$s}_size_h" ); // For default sizes set in options
			if ( isset( $_wp_additional_image_sizes[$s]['crop'] ) )
				$sizes[$s]['crop'] = $_wp_additional_image_sizes[$s]['crop']; // For theme-added sizes
			else
				$sizes[$s]['crop'] = get_option( "{$s}_crop" ); // For default sizes set in options
		}

		/**
		 * Filter the image sizes automatically generated when uploading an image.
		 *
		 * @since 2.9.0
		 *
		 * @param array $sizes An associative array of image sizes.
		 */
		$sizes = apply_filters( 'intermediate_image_sizes_advanced', $sizes );

		if ( $sizes ) {
			$editor = wp_get_image_editor( $file );

			if ( ! is_wp_error( $editor ) )
				$metadata['sizes'] = $editor->multi_resize( $sizes );
		} else {
			$metadata['sizes'] = array();
		}

		// Fetch additional metadata from EXIF/IPTC.
		$image_meta = wp_read_image_metadata( $file );
		if ( $image_meta )
			$metadata['image_meta'] = $image_meta;

	} elseif ( wp_attachment_is( 'video', $attachment ) ) {
		$metadata = wp_read_video_metadata( $file );
		$support = current_theme_supports( 'post-thumbnails', 'attachment:video' ) || post_type_supports( 'attachment:video', 'thumbnail' );
	} elseif ( wp_attachment_is( 'audio', $attachment ) ) {
		$metadata = wp_read_audio_metadata( $file );
		$support = current_theme_supports( 'post-thumbnails', 'attachment:audio' ) || post_type_supports( 'attachment:audio', 'thumbnail' );
	}

	if ( $support && ! empty( $metadata['image']['data'] ) ) {
		// Check for existing cover.
		$hash = md5( $metadata['image']['data'] );
		$posts = get_posts( array(
			'fields' => 'ids',
			'post_type' => 'attachment',
			'post_mime_type' => $metadata['image']['mime'],
			'post_status' => 'inherit',
			'posts_per_page' => 1,
			'meta_key' => '_cover_hash',
			'meta_value' => $hash
		) );
		$exists = reset( $posts );

		if ( ! empty( $exists ) ) {
			update_post_meta( $attachment_id, '_thumbnail_id', $exists );
		} else {
			$ext = '.jpg';
			switch ( $metadata['image']['mime'] ) {
			case 'image/gif':
				$ext = '.gif';
				break;
			case 'image/png':
				$ext = '.png';
				break;
			}
			$basename = str_replace( '.', '-', basename( $file ) ) . '-image' . $ext;
			$uploaded = wp_upload_bits( $basename, '', $metadata['image']['data'] );
			if ( false === $uploaded['error'] ) {
				$image_attachment = array(
					'post_mime_type' => $metadata['image']['mime'],
					'post_type' => 'attachment',
					'post_content' => '',
				);
				/**
				 * Filter the parameters for the attachment thumbnail creation.
				 *
				 * @since 3.9.0
				 *
				 * @param array $image_attachment An array of parameters to create the thumbnail.
				 * @param array $metadata         Current attachment metadata.
				 * @param array $uploaded         An array containing the thumbnail path and url.
				 */
				$image_attachment = apply_filters( 'attachment_thumbnail_args', $image_attachment, $metadata, $uploaded );

				$sub_attachment_id = wp_insert_attachment( $image_attachment, $uploaded['file'] );
				add_post_meta( $sub_attachment_id, '_cover_hash', $hash );
				$attach_data = wp_generate_attachment_metadata( $sub_attachment_id, $uploaded['file'] );
				wp_update_attachment_metadata( $sub_attachment_id, $attach_data );
				update_post_meta( $attachment_id, '_thumbnail_id', $sub_attachment_id );
			}
		}
	}

	// Remove the blob of binary data from the array.
	unset( $metadata['image']['data'] );

	/**
	 * Filter the generated attachment meta data.
	 *
	 * @since 2.1.0
	 *
	 * @param array $metadata      An array of attachment meta data.
	 * @param int   $attachment_id Current attachment ID.
	 */
	return apply_filters( 'wp_generate_attachment_metadata', $metadata, $attachment_id );
}