Source

File: wp-admin/includes/class-wp-filesystem-ftpext.php

public function dirlist( $path = '.', $include_hidden = true, $recursive = false ) {
		if ( $this->is_file( $path ) ) {
			$limit_file = basename( $path );
			$path       = dirname( $path ) . '/';
		} else {
			$limit_file = false;
		}

		$pwd = ftp_pwd( $this->link );

		if ( ! @ftp_chdir( $this->link, $path ) ) { // Can't change to folder = folder doesn't exist.
			return false;
		}

		$list = ftp_rawlist( $this->link, '-a', false );

		@ftp_chdir( $this->link, $pwd );

		if ( empty( $list ) ) { // Empty array = non-existent folder (real folder will show . at least).
			return false;
		}

		$dirlist = array();

		foreach ( $list as $k => $v ) {
			$entry = $this->parselisting( $v );

			if ( empty( $entry ) ) {
				continue;
			}

			if ( '.' === $entry['name'] || '..' === $entry['name'] ) {
				continue;
			}

			if ( ! $include_hidden && '.' === $entry['name'][0] ) {
				continue;
			}

			if ( $limit_file && $entry['name'] != $limit_file ) {
				continue;
			}

			$dirlist[ $entry['name'] ] = $entry;
		}

		$ret = array();

		foreach ( (array) $dirlist as $struc ) {
			if ( 'd' === $struc['type'] ) {
				if ( $recursive ) {
					$struc['files'] = $this->dirlist( $path . '/' . $struc['name'], $include_hidden, $recursive );
				} else {
					$struc['files'] = array();
				}
			}

			$ret[ $struc['name'] ] = $struc;
		}

		return $ret;
	}