Provide a way to specify libxml options

[tehplague]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no

Currently JMS Serializer has some issues when handling large XML datasets. However, SimpleXML or rather libxml2, to be precise, allows to specify parameters to simplexml_load_string and related methods that influence libxml's handling of incoming XML.

Among the available ones LIBXML_COMPACT (trying harder to allocate memory more efficiently) and LIBXML_PARSEHUGE (bypassing some hardcoded limitations inside libxml) are interesting when deserializing large XML bodies. As the invocation of simplexml_load_string is hardcoded in the XmlDeserializationVisitor that class needs to be overridden if one wants to change its parameters.

Thus, I propose to provide a configuration interface that allows to control the configuration of libxml for use in JMS Serializer, i.e. in \JMS\Serializer\XmlDeserializationVisitor::prepare

Steps required to reproduce the problem

1. Deserialize a large XML body with JMS Serializer

Expected Result

• Deserialized object structure

Actual Result

• Exception parser error : internal error: Huge input lookup which goes away if one modifies said invocation of simplexml_load_string into:

        $doc = simplexml_load_string($data, 'SimpleXMLElement', LIBXML_COMPACT | LIBXML_PARSEHUGE);

[goetas]

Make sense. something similar was implemented for the json serializer (here)

[goetas]

PR is welcome