/*
 * call-seq:
 *   from_memory(string, url = nil, encoding = nil, options = 0)
 *
 * Create a new reader that parses +string+
 */
static VALUE from_memory(int argc, VALUE *argv, VALUE klass)
{
  VALUE rb_buffer, rb_url, encoding, rb_options;
  xmlTextReaderPtr reader;
  const char * c_url      = NULL;
  const char * c_encoding = NULL;
  int c_options           = 0;
  VALUE rb_reader, args[3];

  rb_scan_args(argc, argv, "13", &rb_buffer, &rb_url, &encoding, &rb_options);

  if (!RTEST(rb_buffer)) rb_raise(rb_eArgError, "string cannot be nil");
  if (RTEST(rb_url)) c_url = StringValuePtr(rb_url);
  if (RTEST(encoding)) c_encoding = StringValuePtr(encoding);
  if (RTEST(rb_options)) c_options = (int)NUM2INT(rb_options);

  reader = xmlReaderForMemory(
      StringValuePtr(rb_buffer),
      (int)RSTRING_LEN(rb_buffer),
      c_url,
      c_encoding,
      c_options
  );

  if(reader == NULL) {
    xmlFreeTextReader(reader);
    rb_raise(rb_eRuntimeError, "couldn't create a parser");
  }

  rb_reader = Data_Wrap_Struct(klass, NULL, dealloc, reader);
  args[0] = rb_buffer;
  args[1] = rb_url;
  args[2] = encoding;
  rb_obj_call_init(rb_reader, 3, args);

  return rb_reader;
}