Persistent/keepalive HTTP with the PHP Curl library?

cURL PHP documentation (curl_setopt) says:

CURLOPT_FORBID_REUSE - TRUE to force the connection to explicitly close when it has finished processing, and not be pooled for reuse.

So:

1. Yes, actually it should re-use connections by default, as long as you re-use the cURL handle.
2. by default, cURL handles persistent connections by itself; should you need some special headers, check CURLOPT_HTTPHEADER
3. the server may send a keep-alive timeout (with default Apache install, it is 15 seconds or 100 requests, whichever comes first) - but cURL will just open another connection when that happens.

Curl sends the keep-alive header by default, but:

1. create a context using curl_init() without any parameters.
2. store the context in a scope where it will survive (not a local var)
3. use CURLOPT_URL option to pass the url to the context
4. execute the request using curl_exec()
5. don't close the connection with curl_close()

very basic example:

function get($url) {    global $context;    curl_setopt($context, CURLOPT_URL, $url);    return curl_exec($context);}$context = curl_init();//multiple calls to get() herecurl_close($context);

1. On the server you are accessing keep-alive must be enabled and maximum keep-alive requests should be reasonable. In the case of Apache, refer to the apache docs.

2. You have to be re-using the same cURL context.

3. When configuring the cURL context, enable keep-alive with timeout in the header:

   curl_setopt($curlHandle, CURLOPT_HTTPHEADER, array(    'Connection: Keep-Alive',    'Keep-Alive: 300'));