timeout when using raw socket ?

[mhow2]

If one doesn't install php curl extension (so it seems to use raw sockets , it hangs for about 1min

  $auth = array('api_key' => 'xx');

  $wrap = new CS_REST_Subscribers('xx', $auth);
  $result = $wrap->get($mail);
// hangs

returns
(...)

User-Agent: CS_REST_Wrapper v5.0.2 PHPv5.5.9-1ubuntu4.20 over Socket with native
Connection: Close
Content-Type: application/json; charset=utf-8
Accept-Encoding: gzip


</pre> down the socket<br />
// hangs here for 1 min

Then:
12:42:30 - CS_REST_SocketTransport: API Call Info for GET https://api.createsend.com/api/v3.1/subscribers/xxx : 368 bytes uploaded. 69 bytes downloaded<br />
12:42:30 - CS_REST_SocketTransport: Received headers <pre>HTTP/1.1 408 REQUEST_TIMEOUT
Content-Length:0
Connection: Close</pre><br />
12:42:30 - CS_REST_SocketTransport: Got HTTP Status Code: 408<br />
12:42:30 - CS_REST_Subscribers: Call result: <pre>array (
  'code' => '408',
  'response' => '',
)</pre><br />

I suspect an SSL error but I have no log to proove or explain that...