PHP RFC: ext/curl HTTP/2 Server Push Support


With the introduction of HTTP/2 support in libcurl, PHP 7.0 now has some support for HTTP/2 requests, but it does not yet support one of the (potentially) most powerful features: Server push.

Server push allows the server to push additional resources relevant to the requested resource directly to the client proactively.

Server push is available in libcurl since 7.44.0, but broken till the as-yet-unreleased 7.46.0 (See: this and this github issues for details).

Libcurl Implementation

libcurl supports registering a callback for multi handlers to handle server pushes via the CURLMOPT_PUSHFUNCTION and CURLMOPT_PUSHDATA options for curl_multi_setopt().

The callback will be passed the parent curl handle (the request the client made), a new curl handle for the pushed request, the number of headers, the PUSH_PROMISE headers, and a user-defined pointer (set using CURLMOPT_PUSHDATA).

The callback then returns either CURL_PUSH_OK if can handle the push, or CURL_PUSH_DENY to reject it.

The new curl handle is then added to the multi handler and is then included in the handling of multiple requests.

Suggested Implementation

$transfers = 1;
$callback = function($parent_ch, $pushed_ch, array $headers) use (&$transfers) {
	$transfers++; // increment to keep track of the number of concurrent requests
	return CURL_PUSH_OK;
$mh = curl_multi_init();
curl_multi_setopt($mh, CURLMOPT_PUSHFUNCTION, $callback);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://localhost:8080/index.html");
curl_setopt($ch, CURLOPT_HTTP_VERSION, 3);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
// Debugging/Local stuff
//curl_setopt($ch, CURLOPT_VERBOSE, 1); // will output curl debugging information
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0); // self-signed cert
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); // self-signed cert
curl_multi_add_handle($mh, $ch);
$active = null;
do {
    $status = curl_multi_exec($mh, $active);
    do {
        $info = curl_multi_info_read($mh);
        if (false !== $info && $info['msg'] == CURLMSG_DONE) {
            $handle = $info['handle'];
            if ($handle !== null) {
                $transfers--; // decrement remaining requests
		$out = curl_multi_getcontent($info['handle']); // Response body
                curl_multi_remove_handle($mh, $handle);
    } while ($info);
} while ($transfers);


Within the PHP implementation of curl_multi_setopt() (referenced as php\curl_multi_setopt()) there is a switch that handles different options. When CURLMOPT_PUSHFUNCTION is set a C callback is registered that will call the callable set in php\curl_multi_setopt() (and passed to the C callback using curls CURLMOPT_PUSHDATA).

We do not support CURLMOPT_PUSHDATA. Instead, the user can use closures and use with references to replicate this behavior.

libcurl exposes the push headers with two functions functions curl_pushheader_bynum() and curl_pushheader_byname(). We can use curl_pushheader_bynum() to create an array of header lines. These would then be parsed in user land (as with regular request headers).

Backward Incompatible Changes

No breaks

Proposed PHP Version(s)

PHP 7.1

RFC Impact


No impact

To Existing Extensions

No impact outside of BC compatible changes to ext/curl

To Opcache

No impact on Opcache

New Constants


These are directly exposed from libcurl, and documentation can be taken from there.

php.ini Defaults


Open Issues

Possibly a memory leak in libcurl

Future Scope

This change should track libcurl.


Simple Yes/No option. Requires 50%+1 to be accepted.

This vote will close on 13:00 UTC on Wed 2015-12-23

Add HTTP/2 Server Push Support to ext/curl
Real name Yes No
ajf (ajf)  
bwoebi (bwoebi)  
colinodell (colinodell)  
davey (davey)  
galvao (galvao)  
ircmaxell (ircmaxell)  
jpauli (jpauli)  
keyur (keyur)  
marcio (marcio)  
mariuz (mariuz)  
mattwil (mattwil)  
mbeccati (mbeccati)  
mike (mike)  
mj (mj)  
oliviergarcia (oliviergarcia)  
pajoye (pajoye)  
patrickallaert (patrickallaert)  
pollita (pollita)  
ramsey (ramsey)  
rdohms (rdohms)  
remi (remi)  
santiagolizardo (santiagolizardo)  
tpunt (tpunt)  
trowski (trowski)  
zeev (zeev)  
zimt (zimt)  
Final result: 26 0
This poll has been closed.

Patches and Tests

  1. Working patch can be found here
  2. Docker container for easy testing can be found here


Server push support has been implemented in PHP 7.1 with commit ad15e1cc, and is documented in the curl_multi_setopt man page.

The language specification is not affected by this RFC.


Rejected Features


rfc/curl_http2_push.txt · Last modified: 2017/09/22 13:28 by