Post Meta Viewer

post-meta-viewer.php

<?php
/**
 * Plugin Name: Post Meta Viewer
 * Description: Allows to view the post meta.
 */

/**
 * Add Post Meta Viewer submenu under Tools menu.
 *
 * @return void
 */
function pmv_admin_init() {

	add_submenu_page( 'options-general.php', 'Post Meta Viewer', 'Post Meta Viewer', 'manage_options', 'post-meta-viewer', 'pmv_page' );

	add_filter( 'page_row_actions', 'pmv_row_action', 10, 2 );
	add_filter( 'post_row_actions', 'pmv_row_action', 10, 2 );

}
add_action( 'admin_menu', 'pmv_admin_init' );

/**
 * Add "View Meta" row action.
 *
 * @param array   $actions An array of row action links.
 * @param WP_Post $post    The post object.
 *
 * @return array
 */
function pmv_row_action( $actions, $post ) {

	$actions['pmv'] = sprintf( '<a href="%s">View Meta</a>', esc_url( add_query_arg( 'post_id', $post->ID, menu_page_url( 'post-meta-viewer', false ) ) ) );

	return $actions;

}

/**
 * Display the post meta of selected post ID.
 *
 * @return void
 */
function pmv_page() {

	$post_id = '';
	$post_meta = [];

		if ( ! empty( $_REQUEST['post_id'] ) && is_numeric( $_REQUEST['post_id'] ) ) {
			$post_id = $_REQUEST['post_id'];
			$post_meta = get_post_meta( $_REQUEST['post_id'] );
		}

	?>

	<style>
		.pmv pre {
			margin-top: 8px;
		}
	</style>

	<div class="wrap pmv">

		<h1><?php echo esc_html( get_admin_page_title() ); ?></h1>

		<form action="" method="post">
			<table class="form-table" role="presentation">
				<tbody>
					<th scope="row"><label for="pmv_post_id">Enter Post ID</label></th>
					<td><input type="text" id="pmv_post_id" class="medium-text" name="post_id" required value="<?php echo esc_attr( $post_id ); ?>" /></td>
				</tbody>
			</table>
			<p class="submit">
				<input type="submit" class="button button-primary" value="View" />
			</p>
		</form>

		<?php
		if ( ! empty( $post_meta ) && is_array( $post_meta ) ) {

			echo '<table class="form-table" role="presentation"><tbody>';

			foreach ( $post_meta as $meta_key => $meta_value ) {

				$meta_value = is_array( $meta_value ) ? $meta_value [0] : $meta_value;

				// Check if meta value is in JSON format.
				if ( ! empty( json_decode( $meta_value ) ) ) {
					$meta_value = json_decode( $meta_value, true );
				} else {
					$meta_value = maybe_unserialize( $meta_value );
				}

				echo '<tr>';

				printf( '<th scope="row"><label>%s</label></th>', esc_html( $meta_key ) );

				if ( is_array( $meta_value ) ) {
					printf( '<td><pre>%s</pre></td>', esc_html( print_r( $meta_value, true ) ) );
				} else {
					printf( '<td><pre>%s</pre></td>', esc_html( print_r( $meta_value, true ) ) );
				}

				echo '</tr>';

			}

			echo '</tbody></table>';

		} elseif ( ! empty( $post_id ) ) {
			echo '<p>No post meta found.</p>';
		}
		?>

	</div>

	<?php

}