PHP SOAP client over IPv4

I have a PHP client that needs to connect to a SOAP server:

$client = new \SoapClient('url_to_wsdl.wsdl', [
                'local_cert' => 'path_to_certificate.pem', 
                'connection_timeout ' => 300,
                'trace' => 1,
            ]);

$params = [];
$response = $client->executeAFunction($params);

But the SOAP client can't connect to the host: SoapFault "Could not connect to host" (it actually can't load the wsdl file either, but I mocked that by using a local copy of the file).

I came to the point where I figured out the Soap client cannot connect to the host because it seemingly uses IPv6 by default (I got to this point because of this answer on SO).

What have I done so far:

I already disabled IPv6 on my server (ubuntu), but that didn't change anything to the SOAP client.

I double-checked the reachability of websites over both IPv4 and IPv6 via the servers terminal

$ curl -6 http://v6.testmyipv6.com/
curl: (6) Could not resolve host: v6.testmyipv6.com

$ curl -4 http://v4.testmyipv6.com/
<html>
<head>
<title>IPv6 Test and Dual-Stack Test For Network Connectivity</title>
...

# the above commands are true for all urls I tested

My actual question is: how can I tell the Soap client to connect to the host using IPv4 instead of using IPv6?

Solution

A SOAP request is a socket connection, so you can use socket_context options. Use stream_context_create() to bind your request to a specified IP.

stream_context_create(['socket' => ['bindto' => '123.123.123.123:0']]);

Set 0 for port number so PHP will set this automatically.