XML : How can I use SAX interface of libxml2 to parse streamed xml file?

I have a requirement of parsing big xml files from server. We currently use a stream to read these file which looks like below:

  class stream  {      size_t getSize();      size_t read(void* buf, size_t offset, size_t size);  }    

But I could just find two interfaces:

  XMLPUBFUN int XMLCALL          xmlSAXUserParseFile (xmlSAXHandlerPtr sax,                       void *user_data,                       const char *filename);  XMLPUBFUN int XMLCALL          xmlSAXUserParseMemory   (xmlSAXHandlerPtr sax,                       void *user_data,                       const char *buffer,                       int size);    

How can I solve this problem? Thanks.