See https://github.com/php/php-src/pull/3216

wsainfo_echo_server.php

<?php

error_reporting(E_ALL);
set_time_limit(0);
ob_implicit_flush();

$is_master_proc = !isset($argv[1]) || !$argv[1];

if ($is_master_proc) {
	$address = 'localhost';
	//$address = '::1';
	$port = 10000;

	if (($sock = socket_create(AF_INET, SOCK_STREAM, SOL_TCP)) === false) {
	//if (($sock = socket_create(AF_INET6, SOCK_STREAM, SOL_TCP)) === false) {
		fprintf(STDERR, "socket_create() failed: reason: " . socket_strerror(socket_last_error()) . "\n");
	}

	if (socket_bind($sock, $address, $port) === false) {
		fprintf(STDERR, "socket_bind() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\n");
	}

	if (socket_listen($sock, 5) === false) {
		fprintf(STDERR, "socket_listen() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\n");
	}

	echo "parent: ", getmypid(), PHP_EOL; 

	$cwd = getcwd();
	$env = getenv();

	$descriptorspec = array(
		0 => array("pipe", "r"),
		1 => array("pipe", "w"),
		2 => array("pipe", "a"),
	);

	$cmd = PHP_BINARY . " -n -c " . php_ini_loaded_file() . " " . $_SERVER["PHP_SELF"] . " 1";
	$extra = array("bypass_shell" => true);
	$process = proc_open($cmd, $descriptorspec, $pipes, $cwd, $env, $extra);

	if (is_resource($process)) {
		$status = proc_get_status($process);

		$pid = $status["pid"];
		echo "child: ", $pid, PHP_EOL; 

		$info = socket_wsaprotocol_info_export($sock, $pid);
		fwrite($pipes[0], $info);
		fflush($pipes[0]);

		$it = 42;
		do {
			if ("wsaprotocol_info_import_ok" == fread($pipes[1], 1024)) {
				socket_wsaprotocol_info_release($info);
				break;
			}
			usleep(300);
			$status = proc_get_status($process);
		} while ($status["running"] && 0 > $it--);

		do {
			echo fread($pipes[1], 1024);
			echo fread($pipes[2], 1024);
			usleep(300);
			$status = proc_get_status($process);
		} while ($status["running"]);

		fclose($pipes[0]);
		fclose($pipes[1]);
		fclose($pipes[2]);

		$status = proc_close($process);
		exit((int)$status);
	}
} else {

	$pid = getmypid();

	$info = fread(STDIN, 1024);
	$sock = socket_wsaprotocol_info_import($info);
	if (!$sock) {
		fprintf(STDERR, "PID: $pid: couldn't import socket");
		exit(3);
	}
	fprintf(STDOUT, "wsaprotocol_info_import_ok");
	fflush(STDOUT);

	do {
		if (($msgsock = socket_accept($sock)) === false) {
			fprintf(STDERR, "socket_accept() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\r\n");
			fflush(STDERR);
			break;
		}
		fprintf(STDOUT, "PID: $pid: incoming connection\r\n");
		fflush(STDOUT);

		/* Send instructions. */
		$msg = "\r\nWelcome to the PHP Test Server. \r\n" .
			"To quit, type 'quit'. To shut down the server type 'shutdown'.\r\n";
		socket_write($msgsock, $msg, strlen($msg));

		do {
			if (false === ($buf = socket_read($msgsock, 2048, PHP_NORMAL_READ))) {
				fprintf(STDERR, "socket_read() failed: reason: " . socket_strerror(socket_last_error($msgsock)) . "\r\n");
				fflush(STDERR);
				break 2;
			}
			if (!$buf = trim($buf)) {
				continue;
			}
			if ($buf == 'quit') {
				fprintf(STDOUT, "PID: $pid: connection quit\r\n");
				fflush(STDOUT);
				break;
			}
			if ($buf == 'shutdown') {
				fprintf(STDOUT, "PID: $pid: shutdown\r\n");
				fflush(STDOUT);
				socket_close($msgsock);
				break 2;
			}
			$talkback = "You said '$buf'.\r\n";
			socket_write($msgsock, $talkback, strlen($talkback));
		
			fprintf(STDOUT, "PID: $pid: $buf\r\n");

			fflush(STDOUT);
			fflush(STDERR);
		} while (true);
		socket_close($msgsock);
	} while (true);

}

socket_close($sock);