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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: github issue 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, int $num_headers, 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

Some memory leaks

Future Scope

This change should track libcurl.

Proposed Voting Choices

Two choices: Add, Deny 50% required as this is not a language change

Patches and Tests

(rough) Working patch can be found here


After the project is implemented, this section should contain

  1. the version(s) it was merged to
  2. a link to the git commit(s)
  3. a link to the PHP manual entry for the feature


Rejected Features

Keep this updated with features that were discussed on the mail lists.

rfc/curl_http2_push.1447906702.txt.gz · Last modified: 2017/09/22 13:28 (external edit)