remote_meta.php

/**
 * Get or update post meta via the WordPress REST API
 *
 * @param int   	$post_id	Post ID to get meta for.
 * @param bool|string 	$json_url 	Optional. Base URL for API. If false will use current site's API URL.
 * @param array     	$headers 	Headers to use in request. Must at least include authorization.
 * @param bool 		$update 	Optional. If true updates meta value, if false just returns current values.
 * @param bool|array 	$meta_data 	Optional, but required if updating. Array of key => value for meta ID being  updated.
 * @param bool|int	$meta_id 	Optional. ID of meta key to update. If not specified and updating an additional HTTP request is required to find it.
 *
 * @return string|WP_Error|JSON
 */
function jp_mini_rest_client_remote_meta( $post_id, $json_url = false, $headers, $update = true,  $meta_data = false, $meta_id = false ) {

	//get base URL if not provided
	if ( ! $json_url ) {
		//return error if no url provided and REST API isn't installed on this site
		if ( ! function_exists( 'json_url' ) ) {

			return __( 'You must provide a remote JSON url, or install the REST API plugin on this site.', 'jp-mini-rest-client' );

		}

		$json_url = json_url();
	}

	//begin setting up arguments for wp_remote_get()
	$args = array(
		'headers' => $headers,
		'method' => 'GET',
		'body' => '',
	);

	//add meta endpoint to url
	$json_url = trailingslashit( $json_url ). "posts/{$post_id}/meta/";

	//If trying to update, add the meta ID to url if we have it, if not retrieve it.
	if ( $update && $meta_id && intval( $meta_data ) > 0 ) {
		$json_url .= $meta_id;
	} else{
		$response = wp_remote_get( $json_url, $args );

		if ( ! is_wp_error( $response ) && ! is_null( $response ) ) {
			$response = json_decode( $response[ 'body' ] );

			foreach( $response as $meta ) {
				if ( isset( $meta->key ) && $meta->key === $meta_data[ 'key' ] ) {
					$meta_id = $meta->ID;
					break;
				}

			}
		}

		if ( ! $meta_id ) {
			$message =  __( sprintf( 'Meta key %1s does not appear to exist.', $meta_data[ 'key' ] ), 'jp-mini-rest' );
			return new WP_Error( 'no-key', $message );

		}

	}

	//if updating change to post, add the data to body and change endpoint to include ID.
	if ( $update && is_array( $meta_data ) ) {
		$args[ 'method' ] = 'POST';
		$args[ 'body' ] = json_encode( $meta_data );

		$json_url .= $meta_id;
	}

	//make request
	$response = wp_remote_post( $json_url, $args );

	//return if not error
	if ( ! is_wp_error( $response ) ) {

		return $response[ 'body' ];

	}
	else{
		if ( WP_DEBUG_DISPLAY ) {
			return $response;
		}
	}

}