Sending HTTP/2 request using PHP - php

Question

My problem statement is similar to the one mentioned here , except that the request type I need server to respond to is HTTP/2.
I am opening a telnet connection through a PHP script and sending a request:
<?php
$fp = fsockopen("10.20.0.120", 80, $errno, $errstr, 30);
if (!$fp) {
echo "$errstr ($errno)<br />\n";
} else {
$out = "GET /mng/1000.txt HTTP/2 \r\n";
$out .= "Host: 10.20.0.120\r\n";
$out .= "Connection: Close\r\n";
fwrite($fp, $out);
$out = "\r\n";
$out .= "\r\n";
fwrite($fp, $out);
while (!feof($fp)) {
echo fgets($fp, 128);
}
fclose($fp);
}
?>
I am aware that in case of HTTP/2 the header frame must be in binary format, hence I need to know if I could do it using PHP.
I tried with PHPs pack method, but it didn't work. When I execute the above script, this is the output it gives:
Client(root)#php above_file.php
HTTP/1.1 400 Bad Request
Content-Length: 0
...and when the request is of type HTTP/1.1 (and executed on another setup replacing HTTP/2 with HTTP/1.1), the output I receive is as expected:
Client(root)#php above_file.php
HTTP/1.1 200 OK
Date: Wed, 27 Sep 2017 11:31:57 GMT
Server: Apache/2.2.22 (Fedora)
Last-Modified: Wed, 20 Feb 2013 21:27:15 GMT
ETag: "a4f5b-3e8-4d62e9f40f9be"
Accept-Ranges: bytes
Content-Length: 12
Connection: close
Content-Type: text/plain; charset=UTF-8
Hello world!