Source

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

public function __construct( $opt = '' ) {
		$this->method = 'ftpext';
		$this->errors = new WP_Error();

		// Check if possible to use ftp functions.
		if ( ! extension_loaded( 'ftp' ) ) {
			$this->errors->add( 'no_ftp_ext', __( 'The ftp PHP extension is not available' ) );
			return;
		}

		// This class uses the timeout on a per-connection basis, others use it on a per-action basis.
		if ( ! defined( 'FS_TIMEOUT' ) ) {
			define( 'FS_TIMEOUT', 240 );
		}

		if ( empty( $opt['port'] ) ) {
			$this->options['port'] = 21;
		} else {
			$this->options['port'] = $opt['port'];
		}

		if ( empty( $opt['hostname'] ) ) {
			$this->errors->add( 'empty_hostname', __( 'FTP hostname is required' ) );
		} else {
			$this->options['hostname'] = $opt['hostname'];
		}

		// Check if the options provided are OK.
		if ( empty( $opt['username'] ) ) {
			$this->errors->add( 'empty_username', __( 'FTP username is required' ) );
		} else {
			$this->options['username'] = $opt['username'];
		}

		if ( empty( $opt['password'] ) ) {
			$this->errors->add( 'empty_password', __( 'FTP password is required' ) );
		} else {
			$this->options['password'] = $opt['password'];
		}

		$this->options['ssl'] = false;

		if ( isset( $opt['connection_type'] ) && 'ftps' === $opt['connection_type'] ) {
			$this->options['ssl'] = true;
		}
	}