WordPress at a glance
filter is not described

upgrader_pre_download filter-hook . WP 3.7.0

Filters whether to return the package.

Usage

add_filter( 'upgrader_pre_download', 'filter_function_name_1021', 10, 3 );
function filter_function_name_1021( $reply, $package, $this ){
	// filter...

	return $reply;
}
$reply(true/false)
Whether to bail without returning the package.
Default: false
$package(string)
The package file name.
$this(WP_Upgrader)
The WP_Upgrader instance.

Where the hook is called

WP_Upgrader::download_package()
wp-admin/includes/class-wp-upgrader.php 254
$reply = apply_filters( 'upgrader_pre_download', false, $package, $this );

Where the hook is used (in WP core)

Does not used.