detect and handle incorrect stream start. Fixes #4499

src/common/xmpp/dispatcher_nb.py

@@ -141,6 +141,10 @@ class Dispatcher(PlugIn):
 			self.DEBUG('Invalid XML received from server. Forcing disconnect.', 'error')
 			self._owner.Connection.pollend()
 			return 0
+		except ValueError, e:
+			self.DEBUG(str(e), 'error')
+			self._owner.Connection.pollend()
+			return 0
 		if len(self._pendingExceptions) > 0:
 			 _pendingException = self._pendingExceptions.pop()
 			 raise _pendingException[0], _pendingException[1], _pendingException[2]

src/common/xmpp/simplexml.py

@@ -386,7 +386,11 @@ class NodeBuilder:
 				else:
 					self._document_attrs[attr] = val
 			ns = self._document_nsp.get(nsp, 'http://www.gajim.org/xmlns/undeclared-root')
+			try:
 				self.stream_header_received(ns, name, attrs)
+			except ValueError, e:
+				self._document_attrs = None
+				raise ValueError(str(e))
 		if not self.last_is_data and self._ptr.parent: 
 			self._ptr.parent.data.append('')
 		self.last_is_data = 0