bp_document_sideload_attachment( string $file )

function bp_document_sideload_attachment( $file ) {
	if ( empty( $file ) ) {
		return;
	}

	// Set variables for storage, fix file filename for query strings.
	preg_match( '/[^\?]+\.(jpe?g|jpe|gif|png|svg|bmp|mp4)\b/i', $file, $matches );
	$file_array = array();

	if ( empty( $matches ) ) {
		return;
	}

	$file_array['name'] = basename( $matches[0] );

	// Download file to temp location.
	$file = preg_replace( '/^:*?\/\//', $protocol = strtolower( substr( $_SERVER['SERVER_PROTOCOL'], 0, strpos( $_SERVER['SERVER_PROTOCOL'], '/' ) ) ) . '://', $file );

	if ( ! function_exists( 'download_url' ) ) {
		require_once ABSPATH . 'wp-admin' . '/includes/image.php';
		require_once ABSPATH . 'wp-admin' . '/includes/file.php';
		require_once ABSPATH . 'wp-admin' . '/includes/media.php';
	}
	$file_array['tmp_name'] = download_url( $file );

	// If error storing temporarily, return the error.
	if ( is_wp_error( $file_array['tmp_name'] ) ) {
		return;
	}

	// Do the validation and storage stuff.
	$id = bp_document_handle_sideload( $file_array );

	// If error storing permanently, unlink.
	if ( is_wp_error( $id ) ) {
		return;
	}

	return $id;
}