WordPress at a glance
action is not described

http_api_curl action-hook . WP 2.8.0

Fires before the cURL request is executed.

Cookies are not currently handled by the HTTP API. This action allows plugins to handle cookies themselves.

Usage

add_action( 'http_api_curl', 'action_function_name_5442', 10, 3 );
function action_function_name_5442( $handle, $r, $url ){
	// action...
}
$handle(resource)
The cURL handle returned by curl_init() (passed by reference).
$r(array)
The HTTP request arguments.
$url(string)
The request URL.

Where the hook is called

WP_Http_Curl::request()
WP_HTTP_Requests_Hooks::dispatch()
wp-includes/class-wp-http-curl.php 220
do_action_ref_array( 'http_api_curl', array( &$handle, $r, $url ) );
wp-includes/class-wp-http-requests-hooks.php 57
do_action_ref_array( 'http_api_curl', array( &$parameters[0], $this->request, $this->url ) );

Where the hook is used (in WP core)

Does not used.