How does cURL Keep-alive works? - php

Question

I've been working on this and couldn't find a way to understand it fully.
I have this code:
<?php
function get2($url) {
// Create a handle.
$handle = curl_init($url);
// Set options...
// Do the request.
$ret = curlExecWithMulti($handle);
// Do stuff with the results...
// Destroy the handle.
curl_close($handle);
}
function curlExecWithMulti($handle) {
// In real life this is a class variable.
static $multi = NULL;
// Create a multi if necessary.
if (empty($multi)) {
$multi = curl_multi_init();
}
// Add the handle to be processed.
curl_multi_add_handle($multi, $handle);
// Do all the processing.
$active = NULL;
do {
$ret = curl_multi_exec($multi, $active);
} while ($ret == CURLM_CALL_MULTI_PERFORM);
while ($active && $ret == CURLM_OK) {
if (curl_multi_select($multi) != -1) {
do {
$mrc = curl_multi_exec($multi, $active);
} while ($mrc == CURLM_CALL_MULTI_PERFORM);
}
}
// Remove the handle from the multi processor.
curl_multi_remove_handle($multi, $handle);
return TRUE;
}
?>
The above script is doing this: I run the PHP and it creates new TCP connection, it returns data and then it closes the connection.
The server is working on HTTP 1.1 and connection: keep-alive.
What i want is if i run the script will create connection, return data and NOT close the connection and when i run the PHP script again will use that same connection (of course if that connection didn't expire after the timeout of the sever).
Is that possible with cURL? Am I understanding the multi in cURL wrong?

Answer 1

When a program exits, all of its open sockets (indeed, all open files) are closed. There is no way to reuse a connection from one instance to another(*). You must re-open a new connection or loop within your application.
If you want to use HTTP Keep-Alive, your program must not exit.
(*) There are ways to keep a socket open inside one process and pass it to others via Unix domain sockets but that is an advanced topic I recommend against; I mention it only for completeness.